Hubble Space Telescope 2021

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Hubble Status and Imagery in the Period 2021

• December 16, 2021: When you go outside at night in a rural location with dark skies, you can look up and see a band of stars crossing the sky. That band is our Milky Way galaxy, which we see edge-on since we’re inside of it. If we could travel faster than light and climb above the plane of our galaxy, we would see a flat disk with spiral arms wrapping around the core. But what shape, exactly, would those spiral arms have? Stuck here with no bird’s-eye view, we have to apply other methods to measure the galaxy’s shape.

- Moving outward from Earth’s location, astronomers have constructed a model of the neighboring spiral arm, known as the Perseus arm. Previous work suggested that the Perseus arm possesses a narrow and distinct shape. However new research shows that at least a portion of the Perseus arm may be illusory, without any well-defined structure. The illusion is a result of complexities first predicted by W. Burton in 1971.

- Our Milky Way has long been known to be a spiral galaxy, shaped much like a fried egg with a bulbous central bulge and a thin, flat disk of stars. For decades, astronomers have struggled to map the Milky Way’s disk and its associated spiral arms. As the old saying goes, you can’t see the forest for the trees, and if you’re in the middle of the forest, how can you map its groves without a bird’s-eye view? ¹⁾

- Previous work has suggested that the Milky Way is what’s known as a “grand design” spiral, with long, narrow, well-defined spiral arms. However, new research finds that at least one portion of the outer Milky Way (beyond the Sun’s location) is much more clumpy and chaotic.

- “We have long had a picture of the galaxy in our minds, based on a combination of measurements and inference,” said Josh Peek of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “This work calls that picture into question. We don’t see evidence that pieces we’ve been connecting up are actually connected.”

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Distances are Key

- When mapping our galaxy, the biggest challenge is finding the distance to any given star, star cluster, or gas clump. The gold standard is to use parallax measurements of naturally occurring radio sources called masers, some of which are found in high-mass star-forming regions. However, this technique inevitably leaves gaps.

- To fill those gaps, astronomers switch from examining star-forming regions to gas clouds, and more specifically, the motions of those gas clouds. In an ideal situation, the line-of-sight motion we measure for a gas cloud is directly related to its distance due to the overall rotation of the Milky Way. As a result, by measuring gas velocities, we can determine distances and hence the underlying structure of the galaxy.

- The question then becomes, what about a non-ideal situation? While the motion of any given gas cloud might be dominated by its rotation around the galactic center, it undoubtedly has some additional, more random motions as well. Can those extra motions throw off our maps?

Chunky and Lumpy

- To investigate this question, Peek and his colleagues examined not the gas, but the dust. In general within our galaxy, gas and dust are closely associated, so if you can map one, you also map the other.

- 3D dust maps can be created by examining the colors of large collections of stars spread across the sky. The more dust that is between the star and our telescope, the redder the star will appear compared to its natural color.

- Peek and his team examined a region of space known as the Perseus spiral arm, which is beyond our Sun in the Milky Way’s disk. They compared the distances measured via dust reddening to those determined by the velocity relationship. They found that many of the clouds do not, in fact, lie at the distance of the Perseus arm, but instead stretch along a distance of some 10,000 light-years.

- “We don’t have long, skinny spiral arms after all, at least in this section of the galaxy. There are chunks and lumps that don’t look like anything,” explained Peek. “It’s a good possibility that the outer disk of the Milky Way resembles the nearby galaxy Messier 83, with shorter, chopped-up pieces of arms.”

Revising Our Map

- While this latest research focused on the outer Milky Way, Hubble Fellow Catherine Zucker, a member of Peek’s team at STScI, is planning to extend that work to the inner Milky Way. The region interior to the Sun’s orbit is where the spiral arms that are most actively forming stars reside.

- Zucker plans to create 3D dust maps using existing large-scale infrared surveys to measure the reddening of some 1 to 2 billion stars. By linking those new dust maps with existing gas velocity surveys, astronomers can refine our map of the inner Milky Way much as they have already done with the outer galaxy.

- “Previous 3D dust mapping efforts have largely relied on data at wavelengths visible to the human eye. No one has used deep infrared data to create a 3D dust map,” said Zucker. “We may find that this region, like the Perseus arm, is more chaotic and less well defined.”

- Even more insights may come from the upcoming Nancy Grace Roman Space Telescope and Vera Rubin Observatory. The Roman Space Telescope will have the capability to map the entire galactic plane in a few hundred hours. Also, its infrared measurements will cut through the dust.

- “We could see clear to the other side of the galaxy for the first time. If a survey like this is selected for Roman, it would be stunning,” said Peek.

- Rubin, on the other hand, will be able to make deep observations of faint objects at a variety of optical wavelengths. By combining Roman’s infrared view of the sky with Rubin’s deep, multi-wavelength optical data, we may finally map our own cosmic “forest.”

- This work is accepted for publication in The Astrophysical Journal.

- The Space Telescope Science Institute is expanding the frontiers of space astronomy by hosting the science operations center of the Hubble Space Telescope, the science and mission operations centers for the James Webb Space Telescope, and the science operations center for the Nancy Grace Roman Space Telescope. STScI also houses the Barbara A. Mikulski Archive for Space Telescopes (MAST) which is a NASA-funded project to support and provide to the astronomical community a variety of astronomical data archives, and is the data repository for the Hubble, Webb, Roman, Kepler, K2, TESS missions and more. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

• December 14, 2021: Over the last 31 years, NASA’s Hubble Space Telescope has changed the way we view our place in the universe. With more than 1.5 million observations of about 48,000 celestial objects resulting in upwards of 18,000 scientific papers, Hubble has not only revolutionized modern astronomy, but made astronomy relevant, engaging, and accessible for people of all ages. The Space Telescope Science Institute is continuing this legacy with a new exhibit highlighting the range of Hubble’s capabilities and discoveries in the Dulles International Airport. ²⁾

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- A new exhibit, created by the Space Telescope Science Institute (STScI) and detailing the Hubble Space Telescope’s extensive legacy, is now on display at the Washington Dulles International Airport. A “Hubble Hallway” is located between Dulles International’s parking garages and future Metrorail stop, and the airport’s main terminal.

- Images and spectra spanning the breadth of Hubble science, from the local cosmic neighborhood of our solar system, to planets orbiting other stars, to colorful nebulas and distant galaxies in the first eons of the universe, line a section of the walls of the 300-foot-long hallway. Automated walkways allow busy travelers to appreciate the imagery—including the iconic Hubble Ultra Deep Field, a snapshot of auroras on Jupiter, and the stunning Eagle Nebula in both visible and infrared light—as they make their way into the airport.

- “I am really pleased to be able to share some of what we do at the Space Telescope Science Institute and in partnership with NASA with the millions of people who pass this way every year,” said STScI deputy director Nancy Levenson. “The images from Hubble are stunning, showing the beauty of the universe near and far, while also enabling great scientific discoveries.”

- After more than 30 years, Hubble remains among the most durable, powerful, and versatile space telescopes ever built, so the panels located in the “Hubble Hallway” can be modified and updated in the future.

- STScI also recently updated a vitrine located in Dulles International’s baggage claim area, which looks forward to the soon-to-be-launched James Webb Space Telescope.

- Hubble's top accomplishments include measuring the expansion and acceleration rate of the universe; finding that black holes are common among galaxies; characterizing the atmospheres of planets around other stars; monitoring weather changes on planets across our solar system; and looking back in time across 97 percent of the universe to chronicle the birth and evolution of stars and galaxies.

- To learn more about the Dulles International airport exhibit, visit https://www.stsci.edu/communications-and-outreach/public-outreach/exhibit-at-dulles-international-airport

- The Space Telescope Science Institute is expanding the frontiers of space astronomy by hosting the science operations center of the Hubble Space Telescope, the science and operations center for the James Webb Space Telescope, and the science operations center for the future Nancy Grace Roman Space Telescope. STScI also houses the Barbara A. Mikulski Archive for Space Telescopes (MAST) which is a NASA-funded project to support and provide to the astronomical community a variety of astronomical data archives, and is the data repository for the Hubble, Webb, Kepler, K2, TESS missions and more. STScI is operated by the Association of Universities for Research in Astronomy in Washington, D.C.

• December 10, 2021: This stellar whirlpool is a spiral galaxy named NCG 7329, which has been imaged by Hubble’s Wide Field Camera 3 (WFC3). Creating a colorful image such as this one using a telescope such as Hubble is not as straightforward as pointing and clicking a camera. Commercial cameras will typically try to collect as much light of all visible wavelengths as they can, in order to create the most vibrant images possible. In contrast, raw images collected by Hubble are always monochromatic, because astronomers typically want to capture very specific ranges of wavelengths of light at any time, in order to do the best, most accurate science possible. In order to control which wavelengths of light will be collected, Hubble’s cameras are equipped with a wide variety of filters, which only allow certain wavelengths of light to reach the cameras’ CCDs (a CCD is a camera’s light sensor — phone cameras also have CCDs!). ³⁾

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• December 9, 2021: Our Milky Way's central black hole has a leak. This supermassive black hole looks like it still has the vestiges of a blowtorch-like jet dating back several thousand years. NASA's Hubble Space Telescope hasn't photographed the phantom jet but has helped find circumstantial evidence that it is still pushing feebly into a huge hydrogen cloud and then splattering, like the narrow stream from a hose aimed into a pile of sand. ^{4) 5)}

- This is further evidence that the black hole, with a mass of 4.1 million Suns, is not a sleeping monster but periodically hiccups as stars and gas clouds fall into it. Black holes draw some material into a swirling, orbiting accretion disk where some of the infalling material is swept up into outflowing jets that are collimated by the black hole's powerful magnetic fields. The narrow "searchlight beams" are accompanied by a flood of deadly ionizing radiation.

- "The central black hole is dynamically variable and is currently powered down," said Gerald Cecil of the University of North Carolina in Chapel Hill. Cecil pieced together, like a jigsaw puzzle, multiwavelength observations from a variety of telescopes that suggest the black hole burps out mini-jets every time it swallows something hefty, like a gas cloud. His multinational team's research has just been published in the Astrophysical Journal. ⁶⁾

- In 2013 evidence for a stubby southern jet near the black hole came from X-rays detected by NASA's Chandra X-ray Observatory and radio waves detected by the Jansky Very Large Array telescope in Socorro, New Mexico. This jet too appears to be plowing into gas near the black hole.

- Cecil was curious if there was a northern counter-jet as well. He first looked at archival spectra of such molecules as methyl alcohol and carbon monosulfide from the ALMA Observatory in Chile (Atacama Large Millimeter/Submillimeter Array), which uses millimeter wavelengths to peer through the veils of dust between us and the galactic core. ALMA reveals an expanding, narrow linear feature in molecular gas that can be traced back at least 15 light-years to the black hole.

- By connecting the dots, Cecil next found in Hubble infrared-wavelength images a glowing, inflating bubble of hot gas that aligns to the jet at a distance of at least 35 light-years from the black hole. His team suggests that the black hole jet has plowed into it, inflating the bubble. These two residual effects of the fading jet are the only visual evidence of it impacting molecular gas.

- As it blows through the gas the jet hits material and bends along multiple streams. "The streams percolate out of the Milky Way's dense gas disk," said co-author Alex Wagner of Tsukuba University in Japan. "The jet diverges from a pencil beam into tendrils, like that of an octopus." This outflow creates a series of expanding bubbles that extend out to at least 500 light-years. This larger "soap bubble" structure has been mapped at various wavelengths by other telescopes.

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- Wagner and Cecil next ran supercomputer models of jet outflows in a simulated Milky Way disk, which reproduced the observations. "Like in archeology, you dig and dig to find older and older artifacts until you come upon remnants of a grand civilization," said Cecil. Wagner's conclusion: "Our central black hole clearly surged in luminosity at least 1 millionfold in the last million years. That sufficed for a jet to punch into the Galactic halo."

- Previous observations by Hubble and other telescopes found evidence that the Milky Way's black hole had an outburst about 2-4 million years ago. That was energetic enough to create an immense pair of bubbles towering above our galaxy that glow in gamma-rays. They were first discovered by NASA's Fermi Gamma-ray Space Telescope in 2010 and are surrounded by X-ray bubbles that were discovered in 2003 by the ROSAT satellite and mapped fully in 2020 by the eROSITA satellite.

- To get a better idea of what's going on, Cecil looked at Hubble and radio images of another galaxy with a black hole outflow. Located 47 million light-years away, the active spiral galaxy NGC 1068 has a string of bubble features aligned along an outflow from the very active black hole at its center. Cecil found that the scales of the radio and X-ray structures emerging from both NGC 1068 and our Milky Way are very similar. "A bow shock bubble at the top of the NGC 1068 outflow coincides with the scale of the Fermi bubble start in the Milky Way. NGC 1068 may be showing us what the Milky Way was doing during its major power surge several million years ago."

- The residual jet feature is close enough to the Milky Way's black hole that it would become much more prominent only a few decades after the black hole powers up again. Cecil notes that "the black hole need only increase its luminosity by a hundredfold over that time to refill the jet channel with emitting particles. It would be cool to see how far the jet gets in that outburst. To reach into the Fermi gamma-ray bubbles would require that the jet sustain for hundreds of thousands of years because those bubbles are each 50,000 light years across!"

- The anticipated images of the black hole's shadow made with the National Science Foundation's Event Horizon Telescope may reveal where and how the jet is launched.

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• December 7, 2021: NASA’s Hubble Space Telescope team recovered the Space Telescope Imaging Spectrograph on Monday, Dec. 6, and is now operating with all four active instruments collecting science. The team has still not detected any further synchronization message issues since monitoring began Nov. 1. ⁷⁾

- The team will continue work on developing and testing changes to instrument software that would allow them to conduct science operations even if they encounter several lost synchronization messages in the future. The first of these changes is scheduled to be installed on the Cosmic Origins Spectrograph in mid-December. The other instruments will receive similar updates in the coming months.

- Hubble has been operating now for over 31 years, collecting ground-breaking science observations that have changed our fundamental understanding of the universe. With the launch of the Webb Telescope planned for later this month, NASA expects the two observatories will work together well into this decade, expanding our knowledge of the cosmos even further.

• December 3, 2021: In this image the NASA/ESA Hubble Space Telescope peers into the spiral galaxy NGC 1317 in the constellation Fornax, more than 50 million light-years from Earth. This galaxy is one of a pair, but NGC 1317’s rowdy larger neighbor NGC 1316 lies outside Hubble’s field of view. Despite the absence here of its neighboring galaxy, NGC 1317 is accompanied in this image by two objects from very different parts of the Universe. The bright point ringed with a criss-cross pattern is a star from our own galaxy surrounded by diffraction spikes, whereas the redder elongated smudge is a distant galaxy lying far beyond NGC 1317. ⁸⁾

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- Often the most exciting astronomical discoveries require this kind of telescope teamwork, with cutting-edge facilities working together and providing astronomers with information across the electromagnetic spectrum. The same applies to future telescopes, with Hubble’s observations laying the groundwork for future science with the NASA/ESA/CSA James Webb Space Telescope.

• November 29, 2021: The Hubble Space Telescope team recovered the Cosmic Origins Spectrograph (COS) instrument on Sunday, Nov. 28, moving the telescope further toward full science operations. Three of Hubble’s four active instruments are now collecting science data once again. ⁹⁾

- The team also continued work on developing and testing changes to instrument software that would allow them to conduct science operations even if they encounter several lost synchronization messages in the future. Those changes would first be installed on the Cosmic Origins Spectrograph once they’re completed and tested within a few weeks. Hubble’s other instruments would also receive similar changes. The team has not detected further synchronization message issues since monitoring began Nov. 1.

• November 29, 2021: NGC 6891 is a bright, asymmetrical planetary nebula in the constellation Delphinus, the Dolphin. This Hubble image reveals a wealth of structure, including a spherical outer halo that is expanding faster than the inner nebula, and at least two ellipsoidal shells that are orientated differently. The image also reveals filaments and knots in the nebula’s interior, surrounding the central white dwarf star. From their motions, astronomers estimate that one of the shells is 4,800 years old while the outer halo is some 28,000 years old, indicating a series of outbursts from the dying star at different times. ¹⁰⁾

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• November 24, 2021: Mounded, luminous clouds of gas and dust glow in this Hubble image of a Herbig-Haro object known as HH 45. Herbig-Haro objects are a rarely seen type of nebula that occurs when hot gas ejected by a newborn star collides with the gas and dust around it at hundreds of miles per second, creating bright shock waves. In this image, blue indicates ionized oxygen (O II) and purple shows ionized magnesium (Mg II). Researchers were particularly interested in these elements because they can be used to identify shocks and ionization fronts. ¹¹⁾

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• November 22, 2021: NASA continues bringing the Hubble Space Telescope back to normal science operations, most recently recovering the Wide Field Camera 3 instrument Sunday, Nov. 21. This camera will be the second of Hubble’s instruments, after the Advanced Camera for Surveys (ACS), to resume science after suspending the spacecraft’s observations Oct. 25. The Wide Field Camera 3's first science observation since the anomaly will be Nov. 23. ¹²⁾

- The team chose to restore the most heavily used Hubble instrument, the Wide Field Camera 3, which represents more than a third of the spacecraft’s observing time. Engineers also began preparing changes to the instrument parameters, while testing the changes on ground simulators. These changes would allow the instruments to handle several missed synchronization messages while continuing to operate normally if they occur in the future. These changes will first be applied to another instrument, the Cosmic Origins Spectrograph, to further protect its sensitive far-ultraviolet detector. It will take the team several weeks to complete the testing and upload the changes to the spacecraft.

- Although the team has identified no further message losses since monitoring began Nov. 1, NASA is taking extra steps to keep the hardware safe in case the issue reoccurs. Investigation continues into the cause of the missed messages. The remaining Hubble instruments are still in safe mode and the rest of the spacecraft continues to operate as expected.

• November 22, 2021: The Flame Nebula, also called NGC 2024, is a large star-forming region in the constellation Orion that lies about 1,400 light-years from Earth. It’s a portion of the Orion Molecular Cloud Complex, which includes such famous nebulae as the Horsehead Nebula and Orion Nebula. This image focuses on the dark, dusty heart of the nebula, where a star cluster resides, mostly hidden from view. Nearby (but not visible in this image) is the bright star Alnitak, the easternmost star in the Belt of Orion. Radiation from Alnitak ionizes the Flame Nebula’s hydrogen gas. As the gas begins to cool from its higher-energy state to a lower-energy state, it emits energy in the form of light, causing the visible glow behind the swirled wisps of dust. ¹³⁾

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• November 19, 2021: The Prawn Nebula is a massive stellar nursery located in the constellation Scorpius, about 6,000 light years from Earth. Though the nebula stretches 250 light-years and covers a space four times the size of the full moon, it emits light primarily in wavelengths the human eye cannot detect, making it extremely faint to earthbound viewers. Hubble’s gaze, however, shows a small section of the nebula here in both visible and invisible infrared light, capturing dazzling detail of the nebula’s structure, including bright areas of glowing gas. ¹⁴⁾

- The Prawn Nebula, also known as IC 4628, is an emission nebula, which means its gas has been energized, or ionized, by the radiation of nearby stars. The radiation from these massive stars strips electrons from the nebula’s hydrogen atoms. As the energized electrons revert from their higher-energy state to a lower-energy state by recombining with hydrogen nuclei, they emit energy in the form of light, causing the nebula’s gas to glow. In this image, red indicates the presence of ionized iron (Fe II) emission.

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• November 19, 2021: This astronomical portrait from the NASA/ESA Hubble Space Telescope showcases an edge-on view of the majestic spiral galaxy UGC 11537. Hubble’s Wide Field Camera 3 has captured the tightly wound spiral arms swirling around the heart of UGC 11537 at infrared and visible wavelengths, showing both the bright bands of stars and the dark clouds of dust threading throughout the galaxy. ¹⁵⁾

- UGC 11537 is 230 million light-years away in the constellation Aquila, and lies close to the plane of the Milky Way. Being so close to the starry band of the Milky Way means that foreground stars from our own galaxy have crept into the image — the two prominent stars in front of UGC 11537 are interlopers from within the Milky Way. These bright foreground stars are surrounded by diffraction spikes — imaging artifacts caused by starlight interacting with Hubble’s inner structure.

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• November 18, 2021: The NASA/ESA Hubble Space Telescope has completed its annual grand tour of the outer Solar System. This is the realm of the giant planets — Jupiter, Saturn, Uranus, and Neptune — extending as far as 30 times the distance between Earth and the Sun. Unlike the rocky terrestrial planets like Earth and Mars that huddle close to the Sun’s warmth, these far-flung worlds are mostly composed of chilly gaseous soups of hydrogen, helium, ammonia, methane, and other trace gases around a packed, intensely hot, compact core. ^{16) 17)}

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- Though robotic spacecraft have sent back snapshots of their visits to these four monster planets over the past 50 years, their swirling, colorful atmospheres are constantly changing. Fulfilling the role of a weather forecaster, every time Hubble’s sharp cameras revisit these worlds there are new surprises, offering fresh insights into their wild weather, driven by still largely unknown dynamics taking place under the cloudtops.

- Hubble’s snapshots of the outer planets reveal both extreme and subtle changes rapidly taking place in these distant worlds. Hubble’s sharp view gleans insights into the fascinating, dynamic weather patterns and seasons on these gas giants and allows astronomers to investigate the very similar — and very different — variables that contribute to their changing atmospheres.

Jupiter

- This year’s Hubble observations of Jupiter track the ever-changing landscape of its turbulent atmosphere, where several new storms are making their mark and the planet’s equator has changed color yet again.

- Hubble’s 4 September photo puts the giant planet’s tumultuous atmosphere on full display. The planet’s equatorial zone is now a deep orange hue, which researchers are calling unusual. While the equator has departed from its traditional white or beige appearance for a few years now, scientists were surprised to find a deeper orange in Hubble’s recent imaging, when they were expecting the zone to cloud up again.

- Just above the equator, researchers note the appearance of several new storms, nicknamed “barges.” These elongated red cells can be defined as cyclonic vortices, which vary in appearance. Whilst some of the storms are sharply defined and clear, others are fuzzy and hazy. This difference in appearance is caused by the physical properties within the clouds of the vortices.

- Researchers also note that a feature dubbed “Red Spot Jr.” (Oval BA), below the Great Red Spot where Hubble just discovered winds are speeding up, is still a darker beige color, and is joined by several additional white, cyclonic storms to the south.

- Hubble’s crisp views of Jupiter in 2020 was one of the most popular ESA/Hubble photo releases to date.

Saturn

- Hubble’s new look at Saturn on 12 September 2021 shows rapid and extreme color changes in the bands in the planet’s northern hemisphere, where it is now early autumn. The bands have varied throughout Hubble observations in both 2019 and 2020. Hubble’s Saturn image catches the planet following the southern hemisphere’s winter, evident in the lingering blue-ish hue of the south pole.

Uranus

- Hubble’s 25 October view of Uranus puts the planet’s bright northern polar hood in the spotlight. It’s springtime in the northern hemisphere and the increase in ultraviolet radiation from the Sun seems to be causing the polar region to brighten. Researchers aren’t sure why. It could be a change in the opacity of atmospheric methane, or some variation in the aerosol particles. Curiously, even as the atmospheric hood gets brighter, the sharp southernmost boundary remains at the same latitude. This has been constant over the past several years of Hubble observations of the planet. Perhaps some sort of jetstream is setting up a barrier at that latitude of 43 degrees.

Neptune

- In observations taken on 7 September 2021, researchers found that Neptune’s dark spot, which was recently found to have reversed course from moving towards the equator, is still visible in this image, along with a darkened northern hemisphere. There is also a notable dark, elongated circle encompassing Neptune’s south pole. The blue color of both Neptune and Uranus is a result of the absorption of red light by the planets’ methane-rich atmospheres, combined with the same Rayleigh scattering effect that makes Earth's sky blue.

- Notes: These new Hubble images form part of yearly maps of the entire planet taken under the OPAL (Outer Planets Atmospheres Legacy) program. The program provides yearly Hubble global views of the outer planets to look for changes in their storms, winds, and clouds.

• November 17, 2021: Stars are born from clouds of gas and dust that collapse under their own gravitational attraction. As the cloud collapses, a dense, hot core forms and begins gathering dust and gas, creating an object called a “protostar.” ¹⁸⁾

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- This image is part of a Hubble survey targeting 312 protostars within molecular clouds previously identified with the Spitzer and Herschel infrared space observatories. Protostars are visible primarily in infrared light since they emit a lot of heat energy, and their visible light is obscured by the dust around them. Hubble’s advanced infrared capabilities could better resolve the protostars and examine their structure, including the accumulating gas and dust and faint companion objects.

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• November 16, 2021: The Hubble Space Telescope, a project of international cooperation between NASA and ESA (European Space Agency), has fundamentally changed the way we view our universe time and again. Now in its 32nd year in space, Hubble has delivered unprecedented insights about the cosmos, from the most distant galaxy observed so far to familiar planets in our neighborhood, including Jupiter, Saturn, Uranus, and Neptune. ¹⁹⁾

- “Hubble, with its beautiful images and decades-long series of new discoveries about our universe, has captured the imagination of countless individuals and inspired so many,” said Dr. Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at the agency’s Headquarters in Washington.

- With Hubble continuing to make groundbreaking discoveries, the agency has awarded a sole source contract extension to the Association of Universities for Research in Astronomy (AURA) in Washington for continued Hubble science operations support at the Space Telescope Science Institute (STScI) in Baltimore, which AURA operates for NASA. The award extends Hubble’s science mission through June 30, 2026, and increases the value of the existing contract by about $215 million (for a total of about $2.4 billion).

- This contract extension covers the work necessary for STScI to continue to support the Hubble science program. This support includes the products and services required to execute science system engineering; science ground system development; science operations; management of science research awards and public outreach support; and data archive support for mission data in the Mikulski Archive for Space Telescopes.

- Currently, the spacecraft team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, is investigating an issue involving missed synchronization messages that caused Hubble to suspend science observations Oct. 25. One of the instruments, the Advanced Camera for Surveys, resumed science observations Nov. 7, and continues to function as expected. All other instruments remain in safe mode.

- During the week of Nov. 8, the Hubble team identified near-term changes that could be made to how the instruments monitor and respond to missed synchronization messages, as well as to how the payload computer monitors the instruments. This would allow science operations to continue even if several missed messages occur. The team has also continued analyzing the instrument flight software to verify that all possible solutions would be safe for the instruments.

- In the next week, the team will begin to determine the order to recover the remaining instruments. The team expects it will take several weeks to complete the changes for the first instrument.

• November 16, 2021: Stars are born from turbulent clouds of gas and dust that collapse under their own gravitational attraction. As the cloud collapses, a dense, hot core forms and begins gathering dust and gas, creating a protostar. This star-forming nebula in the constellation Aquila, G035.20-0.74, is known for producing a particular kind of massive star known as a B-Type star. These stars are hot, young, blue stars up to five times hotter than our Sun. ²⁰⁾

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- Hubble observed this region because it is home to a massive protostar, specifically as part of a program examining jets of glowing gas blasted into space by massive protostars. These fast-moving jets, which form as gas collects around newly forming stars and last for only about 100,000 years, are known to play a role in star formation. Astronomers were interested to learn whether such jets influence the formation of massive stars similar to the way they affect the formation of lower-mass stars. Massive stars are typically rarer, more distant, and more hidden by dust than lower-mass stars, making studies of their jets more challenging.

• November 15, 2021: This Hubble image captures a portion of a dark nebula in the constellation Cepheus. LDN 1165 is part of a collection called Lynds’ Catalog of Dark Nebulae, originally published in 1962. Dark nebulae – also called absorption nebulae – are clouds of gas and dust that neither emit nor reflect light, instead blocking light coming from behind them. These nebulae tend to contain large amounts of dust, which allows them to absorb visible light from stars or nebulae beyond them. Dark nebulae are so dark that they’ve been referred to as “holes in the sky,” but in reality they may be full of activity, with stars sometimes forming inside their dense clouds. ²¹⁾

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• November 12, 2021: This NASA Hubble Space Telescope image captures a portion of the reflection nebula IC 2631 that contains a protostar, the hot, dense core of a forming star that is accumulating gas and dust. Eventually the protostar may gravitationally gather enough matter to begin nuclear fusion and emit its own energy and starlight. ²²⁾

- Reflection nebulae are clouds of gas and dust that reflect the light from nearby stars. The starlight scatters through the gas and dust like a flashlight beam shining on mist in the dark and illuminates it. Because of the way light scatters when it hits the fine dust of the interstellar medium, these nebulae are often bluish in color.

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• November 12, 2021: This image from the NASA/ESA Hubble Space Telescope features the spiral galaxy Mrk 1337, which is roughly 120 million light-years away from Earth in the constellation Virgo. Hubble’s Wide Field Camera 3 snapped Mrk 1337 at a wide range of ultraviolet, visible and infrared wavelengths, producing this richly detailed image. Mrk 1337 is a weakly barred spiral galaxy, which as the name suggests means that the spiral arms radiate from a central bar of gas and stars. Bars occur in roughly half of spiral galaxies, including our own galaxy the Milky Way. ²³⁾

- Note: Mrk stands for Markarian. Markarian galaxies are a class of galaxies that have nuclei with excessive amounts of ultraviolet emissions compared with other galaxies. Benjamin Markarian drew attention to these types of galaxies starting in 1963.

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• November 10, 2021: The Snowman Nebula is an emission nebula that resides in the constellation Puppis in the southern sky, about 6,000 light-years away from Earth. Emission nebulae are diffuse clouds of gas that have become so charged by the energy of nearby massive stars that they glow with their own light. The radiation from these massive stars strips electrons from the nebula’s hydrogen atoms in a process called ionization. As the energized electrons revert from their higher-energy state to a lower-energy state, they emit energy in the form of light, causing the nebula’s gas to glow. ²⁴⁾

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- From a telescope on Earth, the Snowman looks a bit like a dual-lobed ball of gas, but this Hubble Space Telescope image captures the details of sweeping curves of bright gas and dark knots of dust in a small section of the nebula. The Snowman is also known as Sharpless 2-302, one of the objects in a catalog of mostly emission nebulae that was compiled by astronomer Stewart Sharpless as he sought to identify areas of interstellar ionized hydrogen, or HII regions.

- This image was captured as part of a survey of massive- and intermediate-size “protostars,” or newly forming stars. Astronomers used the infrared sensitivity of Hubble’s Wide Field Camera 3 to look for hydrogen ionized by ultraviolet light from the protostars, jets from the stars, and other features.

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• November 9, 2021: These cosmic ribbons of gas have been left behind by a titanic stellar explosion called a supernova. DEM L249 is thought to be the remnant of a Type 1a supernova, the death of a white dwarf star. White dwarf stars are usually stable, but in a binary system – two stars orbiting each other – a white dwarf can gravitationally pull so much matter from its companion that it reaches critical mass and explodes. ²⁵⁾

- DEM L249, located in the Large Magellanic Cloud, is an unusual supernova remnant. Astronomers using NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton found its gas was hotter and shone brighter in the X-rays than the remnant of a typical Type 1a supernova. Astronomers suspect DEM L249’s white dwarf star was more massive than expected – heavier stars expel more gas – which also means it would have died earlier in its lifecycle.

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• November 8, 2021: The Hubble team successfully recovered the ACS (Advanced Camera for Surveys) instrument Nov. 7. The instrument has started taking science observations once again. Hubble’s other instruments remain in safe mode while NASA continues investigating the lost synchronization messages first detected Oct. 23. The camera was selected as the first instrument to recover as it faces the fewest complications should a lost message occur. ²⁶⁾

- Over the past week, the mission team has continued investigating the root cause of the synchronization issues and has seen no additional problems. The team will continue looking into possible short-term solutions this week and develop estimates for implementation. Once this occurs, the team will discuss returning the other instruments to operational status and resuming their science observations.

• November 5, 2021: This NASA/ESA Hubble Space Telescope Picture of the Week features the galaxy NGC 6984, an elegant spiral galaxy in the constellation Indus roughly 200 million light-years away from Earth. The galaxy is a familiar sight for Hubble, having already been captured in 2013. The sweeping spiral arms are threaded through with a delicate tracery of dark lanes of gas and dust, and studded with bright stars and luminous star-forming regions. ²⁷⁾

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- As well as helping to unravel an astronomical mystery, these new observations added more data to the 2013 observations, and allowed this striking new image to be created. The observations — each of which covers only a narrow range of wavelengths — add new details and a greater range of colors to the image.

• November 4, 2021: NGC 2438 is a planetary nebula, formed after the death of a Sun-like star. The medium-sized star would have expelled its outer layers of gas into space as it died, leaving behind a white-dwarf core. A halo of glowing gas over 4.5 light-years across surrounds the nebula's brighter inner ring. Many round or nearly round planetary nebulae display these halo structures, and astronomers have been investigating how they evolve. NGC 2438 was one of the nebulae studied, and researchers found that the nebula’s halo glows due to the ionizing radiation of the central white dwarf. ²⁸⁾

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• November 4, 2021: NASA is continuing work to resolve an issue that has suspended science operations on the Hubble Space Telescope. The science instruments entered a safe mode configuration on Oct. 25 after detecting a loss of specific data synchronization messages. ²⁹⁾

- The Hubble team is focusing its efforts to isolate the problem on hardware that commands the instruments and is part of the Science Instrument Command and Data Handling Unit. Specifically, the team is analyzing the circuitry of the Control Unit, which generates synchronization messages and passes them onto the instruments.

- The Hubble team is focusing its efforts to isolate the problem on hardware that commands the instruments and is part of the Science Instrument Command and Data Handling Unit. Specifically, the team is analyzing the circuitry of the Control Unit, which generates synchronization messages and passes them onto the instruments.

- While analyzing the Control Unit, the team is working to identify potential workarounds for the issue. These include possible changes to instrument flight software that could check for these lost messages and compensate for them without putting the instruments into safe mode. These workarounds would first be verified using ground simulators to ensure they work as planned.

- Over the weekend of Oct. 30, the team prepared to turn on parts of the Near Infrared Camera and Multi Object Spectrometer (NICMOS) instrument to collect data on this issue, allowing the team to determine how frequently this problem occurs. Installed in 1997, NICMOS has been inactive since 2010, when the Wide Field Camera 3 became operational. NICMOS allowed the team to use an instrument to collect information on these lost messages while keeping the active instruments off as a safety precaution. Since NICMOS was recovered on Nov. 1, no additional synchronization messages have been lost.

- The team is now taking steps to recover Hubble’s Advanced Camera for Surveys (ACS) instrument from safe mode and start collecting science with that instrument at the beginning of next week. The team will make the decision on Sunday after analyzing the latest data. If a lost message is seen before then, the decision to activate ACS will also be revisited. The team is proceeding cautiously to ensure the safety of the instruments and avoid additional stresses on the hardware. Therefore, only ACS will be used in this capacity next week. ACS was selected as the first instrument to recover as it faces the fewest complications should a lost message occur.

- Over the next week, the team will continue analyzing the Control Unit design diagrams and data associated with the lost messages to determine what may have caused this problem. They will also be looking into potential instrument software changes that could help address it. Once the team better understands the frequency of the problem and has determined the time needed to implement possible software changes, they will discuss a plan for returning the other instruments to science operations.

• November 3, 2021: Cleopatra’s Eye, or NGC 1535, is a planetary nebula in the constellation Eridanus. This nebula has an unusual structure that is similar to the better-known NGC 2392, with an outer region and a brighter inner center. ³⁰⁾

- A planetary nebula forms when a star approximately the size of our Sun dies, exhaling its outer layers into space as the core turns into a white dwarf star. Through early telescopes these objects resembled planets – giving them their name – but planetary nebulae are unrelated to actual planets.

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• November 1, 2021: NASA is continuing to investigate why the instruments in the Hubble Space Telescope recently went into safe mode configuration, suspending science operations. The instruments are healthy and will remain in safe mode while the mission team continues its investigation. ³¹⁾

- Hubble’s science instruments issued error codes at 1:46 a.m. EDT Oct. 23, indicating the loss of a specific synchronization message. This message provides timing information the instruments use to correctly respond to data requests and commands. The mission team reset the instruments, resuming science operations the following morning.

- At 2:38 a.m. EDT, Oct. 25, the science instruments again issued error codes indicating multiple losses of synchronization messages. As a result, the science instruments autonomously entered safe mode states as programmed.

- Mission team members are evaluating spacecraft data and system diagrams to better understand the synchronization issue and how to address it. They also are developing and testing procedures to collect additional data from the spacecraft. These activities are expected to take at least one week.

• October 29, 2021: Hubble has a long and fascinating history of crewed service missions, which were performed in order to correct for imperfections in Hubble’s mirror, to update Hubble’s technical systems, and to remove old instruments and install new ones. One of Hubble’s most remarkable features is it’s incredible longevity, and this would not have been possible with the great success of the servicing missions. The juxtaposition of the 2001 and 2021 images of NGC 2903 — both remarkable images for their time — highlights the value of a stable, accessible platform in space that can reliably collect data, not only year after year, but decade after decade.

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• October 28, 2021: A hypnotizing vortex? A peek into a witch's cauldron? A giant space-spider web? — In reality, it's a look at the red giant star CW Leonis as photographed by NASA's Hubble Space Telescope – just in time for celebrating Halloween with creepy celestial sights. ^{32) 33)}

- The orange-red "cobwebs" are dusty clouds of sooty carbon engulfing the dying star. They were created from the outer layers of CW Leonis being thrown out into the inky black void. The carbon, cooked up through nuclear fusion in the star's interior, gives it a carbon-rich atmosphere. Blasting the carbon back into space provides raw material for the formation of future stars and planets. All known life on Earth is built around the carbon atom. Complex biological molecules consist of carbon atoms bonded with other common elements in the universe.

- At a distance of 400 light-years from Earth, CW Leonis is the closest carbon star. This gives astronomers the chance to understand the interplay between the star and its surrounding, turbulent envelope. The complex inner structure of shells and arcs may be shaped by the star’s magnetic field. Detailed Hubble observations of CW Leonis taken over the last two decades also show the expansion of threads of ejected material around the star.

- The bright beams of light radiating outwards from CW Leonis are one of the star's most intriguing features. They've changed in brightness within a 15-year period — an incredibly short timespan in astronomical terms. Astronomers speculate that gaps in the dust shrouding CW Leonis may allow beams of starlight to pierce through and illuminate dust, like searchlight beacons through a cloudy sky. However, the exact cause of the dramatic changes in their brightness is as yet unexplained.

- A star shines when the outward pressure from the fusion furnace at the core balances against the crush of gravity. When the star runs out of hydrogen fuel, the persistent pull of gravity causes the star to start collapsing. As the core shrinks, the shell of plasma surrounding the core becomes hot enough to begin fusing hydrogen, giving the star a second lease on life. It generates enough heat to dramatically expand the star's outer layers and swell up into a bloated red giant.

- CW Leonis has an orange-reddish color due to its relatively low surface temperature of 2,300 degrees Fahrenheit. The green-tinted beams of light emanating from the star, however, glow at invisible mid-infrared wavelengths. In the absence of natural color, green has been added to the infrared image for better analysis through color-contrast.

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• October 22, 2021: This observation from the NASA/ESA Hubble Space Telescope showcases Arp 86, a peculiar pair of interacting galaxies which lies roughly 220 million light-years from Earth in the constellation Pegasus. Arp 86 is composed of the two galaxies NGC 7752 and NGC 7753 — NGC 7753 is the large spiral galaxy dominating this image, and NGC 7752 is its smaller companion. The diminutive companion galaxy almost appears to be attached to NGC 7753, and it is this peculiarity that has earned the designation “Arp 86” — signifying that the galaxy pair appears in the Atlas of Peculiar Galaxies compiled by the astronomer Halton Arp in 1966. The gravitational squabble between the two galaxies is doomed to end catastrophically for NGC 7752. It will eventually either be flung out into intergalactic space or be entirely engulfed by its far larger neighbor. ³⁴⁾

- These observations also helped sow the seeds of future research with an upcoming space telescope, the NASA/ESA James Webb Space Telescope (JWST). This telescope, due to launch later this year, will study star formation in dusty regions such as the galaxies of Arp 86.

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• October 21, 2021: Like a witness to a violent death, NASA's Hubble Space Telescope recently gave astronomers an unprecedented, comprehensive view of the first moments of a star's cataclysmic demise. Hubble's data, combined with other observations of the doomed star from space- and ground-based telescopes, may give astronomers an early warning system for other stars on the verge of blowing up. ³⁵⁾

- "We used to talk about supernova work like we were crime scene investigators, where we would show up after the fact and try to figure out what happened to that star," explained Ryan Foley of the University of California, Santa Cruz, the leader of the team that made this discovery. "This is a different situation, because we really know what's going on and we actually see the death in real time."

Telescope Teamwork

- The supernova, called SN 2020fqv, is in the interacting Butterfly galaxies, which are located about 60 million light-years away in the constellation Virgo. It was discovered in April 2020 by the Zwicky Transient Facility at the Palomar Observatory in San Diego, California. Astronomers realized that the supernova was simultaneously being observed by the Transiting Exoplanet Survey Satellite (TESS), a NASA satellite designed primarily to discover exoplanets, with the ability to detect an assortment of other phenomena. They quickly trained Hubble and a suite of ground-based telescopes on it.

- Together, these observatories gave the first holistic view of a star in the very earliest stage of destruction. Hubble probed the material very close to the star, called circumstellar material, mere hours after the explosion. This material was blown off the star in the last year of its life. These observations allowed astronomers to understand what was happening to the star just before it died.

- "We rarely get to examine this very close-in circumstellar material since it is only visible for a very short time, and we usually don't start observing a supernova until at least a few days after the explosion," explained Samaporn Tinyanont, lead author on the study's paper published in the Monthly Notices of the Royal Astronomical Society (MNRAS). "For this supernova, we were able to make ultra-rapid observations with Hubble, giving unprecedented coverage of the region right next to the star that exploded." ³⁶⁾

Telling the Star's Story

- The team looked at Hubble observations of the star going back to the 1990s. TESS provided an image of the system every 30 minutes starting several days before the explosion, through the explosion itself, and continuing for several weeks. Hubble was used again starting only hours after astronomers first detected the explosion. And from studying the circumstellar material with Hubble, the scientists gained an understanding of what was happening around the star in the previous decade. By combining all of this information, the team was able to create a multi-decade look at the star's final years.

- "Now we have this whole story about what's happening to the star in the years before it died, through the time of death, and then the aftermath of that," said Foley. "This is really the most detailed view of stars like this in their last moments and how they explode."

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The Rosetta Stone of Supernovae

- Tinyanont and Foley called SN 2020fqv "the Rosetta Stone of supernovae." The ancient Rosetta Stone, which has the same text inscribed in three different scripts, helped experts learn to read Egyptian hieroglyphs.

- In the case of this supernova, the science team used three different methods to determine the mass of the exploding star. These included comparing the properties and the evolution of the supernova with theoretical models; using information from a 1997 archival Hubble image of the star to rule out higher-mass stars; and using observations to directly measure the amount of oxygen in the supernova, which probes the mass of the star. The results are all consistent: around 14 to 15 times the mass of the Sun. Accurately determining the mass of the star that explodes in a supernova is crucial to understanding how massive stars live and die.

- "People use the term 'Rosetta Stone' a lot. But this is the first time we've been able to verify the mass with these three different methods for one supernova, and all of them are consistent," said Tinyanont. "Now we can push forward using these different methods and combining them, because there are a lot of other supernovae where we have masses from one method but not another."

An Early Warning System?

- In the years before stars explode, they tend to become more active. Some astronomers point to the red supergiant Betelgeuse, which has recently been belching significant amounts of material, and they wonder if this star will soon go supernova. While Foley doubts Betelgeuse will imminently explode, he does think we should take such stellar outbursts seriously.

- "This could be a warning system," said Foley. "So if you see a star start to shake around a bit, start acting up, then maybe we should pay more attention and really try to understand what's going on there before it explodes. As we find more and more of these supernovae with this sort of excellent data set, we'll be able to understand better what's happening in the last few years of a star's life."

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

• October 15, 2021: NGC 4666’s burst of star formation is driving an unusual form of extreme galactic weather known as a superwind — a gigantic transfer of gas from the bright central heart of the galaxy out into space. This superwind is the result of driving winds from short-lived massive stars formed during NGC 4666’s starburst as well as spectacularly energetic supernova explosions. Two such supernova explosions have been seen in NGC 4666 within the last decade — one in 2014 and the other in 2019. The star which led to the 2019 supernova was recently determined to be 19 times as massive as our Sun! ³⁷⁾

- At peak, supernovae are often the brightest sources of light in their galaxies, shining so bright that they can be seen clear across the Universe. The 2014 supernova in NGC 4666 is still active in this image, but more than 900 days after it peaked, the supernova has faded from its former glory and looks like just one more star in this busy galaxy.

- Though the torrent of superheated gas emanating from NGC 4666 is truly vast in scale — extending for tens of thousands of light-years — it is invisible in this image. The superwind’s extremely high temperature makes it stand out as a luminous plume in x-ray or radio observations, but it doesn’t show up at the visible wavelengths imaged by Hubble’s Wide Field Camera 3.

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• October 14, 2021: NASA's Hubble Space Telescope observations of Jupiter's icy moon Europa have revealed the presence of persistent water vapor – but, mysteriously, only in one hemisphere. ^{38) 39)}

- Europa harbors a vast ocean underneath its icy surface, which might offer conditions hospitable for life. This result advances astronomers' understanding of the atmospheric structure of icy moons, and helps lay the groundwork for planned science missions to the Jovian system to, in part, explore whether an environment half-a-billion miles from the Sun could support life.

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- Previous observations of water vapor on Europa have been associated with plumes erupting through the ice, as photographed by Hubble in 2013. They are analogous to geysers on Earth, but extend more than 60 miles high. They produce transient blobs of water vapor in the moon's atmosphere, which is only one-billionth the surface pressure of Earth's atmosphere.

- The new results, however, show similar amounts of water vapor spread over a larger area of Europa in Hubble observations spanning from 1999 to 2015. This suggests a long-term presence of a water vapor atmosphere only in Europa's trailing hemisphere – that portion of the moon that is always opposite its direction of motion along its orbit. The cause of this asymmetry between the leading and trailing hemisphere is not fully understood.

- This discovery is gleaned from a new analysis of Hubble archival images and spectra, using a technique that recently resulted in the discovery of water vapor in the atmosphere of Jupiter's moon Ganymede, by Lorenz Roth of the KTH Royal Institute of Technology, Space and Plasma Physics, Sweden.

- "The observation of water vapor on Ganymede, and on the trailing side of Europa, advances our understanding of the atmospheres of icy moons," said Roth. "However, the detection of a stable water abundance on Europa is a bit more surprising than on Ganymede because Europa's surface temperatures are lower than Ganymede's."

- Europa reflects more sunlight than Ganymede, keeping the surface 60 ºF cooler than Ganymede. The daytime high on Europa is a frigid -260°F. Yet, even at the lower temperature, the new observations suggest water ice is sublimating – that is, transforming directly from solid to vapor without a liquid phase – off Europa's surface, just like on Ganymede.

- To make this discovery, Roth delved into archival Hubble datasets, selecting ultraviolet observations of Europa from 1999, 2012, 2014 and 2015 while the moon was at various orbital positions. These observations were all taken with Hubble's Space Telescope Imaging Spectrograph (STIS). The ultraviolet STIS observations allowed Roth to determine the abundance of oxygen – one of the constituents of water – in Europa's atmosphere, and by interpreting the strength of emission at different wavelengths he was able to infer the presence of water vapor.

- This detection paves the way for in-depth studies of Europa by future probes including NASA's Europa Clipper and the Jupiter Icy Moons Explorer mission from the European Space Agency (ESA). Understanding the formation and evolution of Jupiter and its moons also helps astronomers gain insights into Jupiter-like planets around other stars.

- These results have been published in the journal Geophysical Research Letters. ⁴⁰⁾

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

- For visuals and more information about the study and Hubble, visit: https://hubblesite.org/contents/news-releases/2021/news-2021-057

• October 8, 2021: Arp 91 provides a particularly vivid example of galactic interaction. NGC 5954 is clearly being tugged towards NGC 5953 — it looks like it is extending one spiral arm downwards. It is the immense gravitational attraction of the two galaxies that is causing them to interact. Such gravitational interactions between galaxies are common, and are an important part of galactic evolution. Most astronomers nowadays believe that collisions between spiral galaxies lead to the formation of another type of galaxy, known as elliptical galaxies. These immensely energetic and massive collisions, however, happen on timescales that dwarf a human lifetime — they take place over hundreds of millions of years. So we should not expect Arp 91 to look any different over the course of our lifetimes! ⁴¹⁾

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• October 7, 2021: Astronomers have seen some pretty weird things scattered across our vast universe, from exploding stars to colliding galaxies. So, you'd think that when they see a strange celestial object, they would be able to identify it. ⁴²⁾

- But NASA's Hubble Space Telescope uncovered what appears to be a pair of identical objects that look so weird it took astronomers several years to determine what they are.

- "We were really stumped," said astronomer Timothy Hamilton of Shawnee State University in Portsmouth, Ohio.

- The oddball objects consist of a pair of galaxy bulges (the central star-filled hub of a galaxy) and at least three nearly parallel split streaks. Hamilton spotted them by accident while using Hubble to survey a collection of quasars, the blazing cores of active galaxies.

- After chasing dead-end theories, soliciting help from colleagues, and doing lots of head-scratching, Hamilton and the growing team, led by Richard Griffiths of the University of Hawaii in Hilo, finally put together all of the clues to solve the mystery.

- The linear objects were the stretched images of a gravitationally lensed distant galaxy, located more than 11 billion light-years away. And, they appeared to be mirror images of each other.

- The team discovered that the immense gravity of an intervening, and uncatalogued, foreground cluster of galaxies was warping space, magnifying, brightening, and stretching the image of a distant galaxy behind it, a phenomenon called gravitational lensing. Though Hubble surveys reveal a lot of these funhouse-mirror distortions caused by gravitational lensing, this object was uniquely perplexing.

- In this case, a precise alignment between a background galaxy and a foreground galaxy cluster produces twin magnified copies of the same image of the remote galaxy. This rare phenomenon occurs because the background galaxy straddles a ripple in the fabric of space. This "ripple" is an area of greatest magnification, caused by the gravity of dense amounts of dark matter, the unseen glue that makes up most of the universe's mass. As light from the faraway galaxy passes through the cluster along this ripple, two mirror images are produced, along with a third image that can be seen off to the side.

- Griffiths compares this effect to the bright wavy patterns seen on the bottom of a swimming pool. "Think of the rippled surface of a swimming pool on a sunny day, showing patterns of bright light on the bottom of the pool," he explained. "These bright patterns on the bottom are caused by a similar kind of effect as gravitational lensing. The ripples on the surface act as partial lenses and focus sunlight into bright squiggly patterns on the bottom."

- In the gravitationally lensed distant galaxy, the ripple is greatly magnifying and distorting the light from the background galaxy that is passing through the cluster. The ripple acts like an imperfect curvy mirror that generates the dual copies.

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Solving the Mystery

- But this rare phenomenon wasn't well-known when Hamilton spotted the strange linear features in 2013.

- As he looked through the quasar images, the snapshot of the mirrored images and parallel streaks stood out. Hamilton had never seen anything like it before, and neither had other team members.

- "My first thought was that maybe they were interacting galaxies with tidally stretched-out arms," Hamilton said. "It didn't really fit well, but I didn't know what else to think."

- So Hamilton and the team began their quest to solve the mystery of these tantalizing straight lines, later dubbed Hamilton's Object for its discoverer. They showed the strange image to colleagues at astronomy conferences, which elicited a variety of responses, from cosmic strings to planetary nebulae.

- But then Griffiths, who was not a member of the original team, offered the most plausible explanation when Hamilton showed him the image at a NASA meeting in 2015. It was a magnified and distorted image caused by a lensing phenomenon similar to those seen in Hubble images of other massive galaxy clusters that are amplifying images of very distant galaxies. Griffiths confirmed this idea when he learned of a similar linear object in one of Hubble's deep-cluster surveys.

- The researchers, however, still had a problem. They couldn't identify the lensing cluster. Normally, astronomers who study galaxy clusters first see the foreground cluster that's causing the lensing, and then find the magnified images of distant galaxies within the cluster. A search of the Sloan Digital Sky Survey images revealed that a galaxy cluster resided in the same area as the magnified images, but it did not show up in any catalogued survey. Nevertheless, the fact that the strange images were at the center of a cluster made it clear to Griffiths that the cluster was producing the lensed images.

- The researchers' next step was in determining whether the three lensed images were at the same distance, and therefore were all the distorted portraits of the same faraway galaxy. Spectroscopic measurements with the Gemini and W. M. Keck observatories in Hawaii helped the researchers make that confirmation, showing that the lensed images were from a galaxy located more than 11 billion light-years away.

- The remote galaxy, based on a reconstruction of the third lensed image, appears to be an edge-on, barred spiral with ongoing, clumpy star formation.

- Around the same time as the spectroscopic observations by Griffiths and undergraduates in Hilo, a separate group of researchers in Chicago identified the cluster and measured its distance using Sloan data. The cluster resides more than 7 billion light-years away.

- But, with very little information about the cluster, Griffiths' team was still struggling with how to interpret these unusual lensing shapes. "This gravitational lens is very different from most of the lenses that were studied before by Hubble, particularly in the Hubble Frontier Fields survey of clusters," Griffiths explained. "You don’t have to stare at those clusters for long to find many lenses. In this object, this is the only lens we have. And we didn't even know about the cluster at first."

Mapping the Invisible

- That's when Griffiths called an expert on gravitational lensing theory, Jenny Wagner of the University of Heidelberg in Germany. Wagner had studied similar objects and, with colleague Nicolas Tessore, now at the University of Manchester in England, developed computer software for interpreting unique lenses like this one. Their software helped the team figure out how all three lensed images came to be. They concluded that the dark matter around the stretched images had to be "smoothly" distributed in space at small scales.

- "It's great that we only need two mirror images in order to get the scale of how clumpy or not dark matter can be at these positions," Wagner said. "Here, we don't use any lens models. We just take the observables of the multiple images and the fact they can be transformed into one another. They can be folded into one another by our method. This already gives us an idea of how smooth the dark matter needs to be at these two positions."

- This result is important, Griffiths said, because astronomers still don't know what dark matter is, nearly a century after its discovery. "We know it's some form of matter, but we have no idea what the constituent particle is. So we don't know how it behaves at all. We just know that it has mass and is subject to gravity. The significance of the limits of size on the clumping or smoothness is that it gives us some clues as to what the particle might be. The smaller the dark matter clumps, the more massive the particles must be."

- The team's paper appears in the September issue of The Monthly Notices of the Royal Astronomical Society. ⁴³⁾

• October 1, 2021: Meet NGC 5728, a spiral galaxy around 130 million light-years from Earth. This image was captured using Hubble’s Wide Field Camera 3 (WFC3), which is extremely sensitive to visible and infrared light. Therefore, this image beautifully captures the regions of NGC 5728 that are emitting visible and infrared light. However, there are many other types of light that galaxies such as NGC 5728 can emit, which WFC3 cannot see. ⁴⁴⁾

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• September 27, 2021: In Jupiter’s Great Red Spot, a storm that has been roiling for centuries, its “outer lane” is moving faster than its “inner lane” — and continues to pick up speed. By analyzing long-term data from this high-speed ring, researchers have found that the wind speed has increased by up to 8 percent between 2009 and 2020. These findings could only be made with the NASA/ESA Hubble Space Telescope, which has amassed more than 10 years of regular observations, acting like a storm watcher for the planets in our Solar System. ⁴⁵⁾

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- The massive storm's colored clouds spin counterclockwise at speeds that exceed 640 km/hr — and the vortex is bigger than Earth itself. The Red Spot is legendary in part because humans have observed it for more than 150 years.

- “When I initially saw the results, I asked 'Does this make sense?' No one has ever seen this before," said Michael Wong of the University of California, Berkeley, who led the analysis. "But this is something only Hubble can do. Hubble's longevity and ongoing observations make this revelation possible."

- Earth-orbiting satellites and aeroplanes track major storms on Earth closely in real time. "Since we don't have a storm chaser plane at Jupiter, we can't continuously measure the winds on site," explained Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who contributed to the research. "Hubble is the only telescope that has the kind of temporal coverage and spatial resolution that can capture Jupiter’s winds in this much detail."

- The change in wind speed they have measured with Hubble amounts to less than 2.5 km/hr/Earth year. "We're talking about such a small change that if we didn’t have eleven years of Hubble data, we wouldn't know it had happened," said Simon. "With Hubble we have the precision we need to spot a trend." Hubble's ongoing monitoring allows researchers to revisit and analyze its data very precisely as they keep adding to it. The smallest features Hubble can reveal in the storm are a mere 170 km across.

- To better analyze Hubble's bounty of data, Wong took a new approach to his data analysis. He used software to track tens to hundreds of thousands of wind vectors (directions and speeds) each time Jupiter was observed by Hubble.

- What does the increase in speed mean? "That's hard to diagnose, since Hubble can't see the bottom of the storm very well. Anything below the cloud tops is invisible in the data," explained Wong. "But it's an interesting piece of the puzzle that can help us understand what's fueling the Great Red Spot and how it's maintaining its energy." There's still a lot of work to do to fully understand it.

- Astronomers have pursued ongoing studies of the "king" of Solar System storms since the 1870s. The Great Red Spot is an upwelling of material from Jupiter's interior. If seen from the side, the storm would have a tiered, wedding-cake structure with high clouds at the center cascading down to its outer layers. Astronomers have noted that it is shrinking in size and becoming more circular than oval in observations spanning more than a century. The current diameter is 16,000 km across, meaning that Earth could still fit inside it.

- In addition to observing this legendary, long-lived storm, researchers have observed storms on other planets, including Neptune, where they tend to travel across the planet’s surface and disappear after only a few years. Research like this helps scientists not only learn about the individual planets, but also draw conclusions about the underlying physics that drives and maintains planets' storms.

- The majority of the data to support this research came from Hubble's Outer Planets Atmospheres Legacy (OPAL) program, which provides annual Hubble global views of the outer planets that allow astronomers to look for changes in the planets' storms, winds, and clouds.

• September 24, 2021: The narrow galaxy elegantly curving around its spherical companion in this image is a fantastic example of a truly strange and very rare phenomenon. This image (Figure 45), taken with the NASA/ESA Hubble Space Telescope, depicts GAL-CLUS-022058s, located in the southern hemisphere constellation of Fornax (The Furnace). GAL-CLUS-022058s is the largest and one of the most complete Einstein rings ever discovered in our Universe. The object has been nicknamed by the Principal Investigator and his team who are studying this Einstein ring as the "Molten Ring", which alludes to its appearance and host constellation. ⁴⁶⁾

- First theorized to exist by Einstein in his general theory of relativity, this object’s unusual shape can be explained by a process called gravitational lensing, which causes light shining from far away to be bent and pulled by the gravity of an object between its source and the observer. In this case, the light from the background galaxy has been distorted into the curve we see by the gravity of the galaxy cluster sitting in front of it. The near exact alignment of the background galaxy with the central elliptical galaxy of the cluster, seen in the middle of this image, has warped and magnified the image of the background galaxy around itself into an almost perfect ring. The gravity from other galaxies in the cluster is soon to cause additional distortions.

- Objects like these are the ideal laboratory in which to research galaxies too faint and distant to otherwise see.

• September 23, 2021: Hubble Space Telescope's glamor shots of the universe are so revealing they nearly always have a discovery behind them. ⁴⁷⁾

- In this particular snapshot, a science discovery followed the release of a Hubble observation of a striking example of a deep-space optical phenomenon dubbed an "Einstein ring." The photo was released in December 2020 as an example of one of the largest, nearly complete Einstein rings ever seen.

- The extremely high rate of star formation in the brightest and very dusty early galaxies saw stars being born at a rate a thousand times faster than occurs within our own galaxy. This could help explain the rapid build-up of present day giant elliptical galaxies.

- This object's unusual partial ring-like appearance can be explained by a phenomenon called gravitational lensing, which causes light shining from a faraway galaxy to be warped by the gravity of an object between its source and the observer. This effect was first theorized by Albert Einstein in 1912, and later worked into his theory of general relativity.

- In this case, the galaxy's light has also been magnified by a factor of 20. This magnification, boosted by mother nature, effectively made Hubble's observing capability equivalent to that of a 48-meter-aperture (157 feet) telescope. The lensing effects also create multiple apparitions around the curved arc of the single background magnified galaxy.

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- In order to derive the physical properties of the galaxy, astronomers had to precisely model the effects of the lensing on the galaxy's image. "Such a model could only be obtained with the Hubble imaging," explained the lead investigator Anastasio Díaz-Sánchez of the Universidad Politécnica de Cartagena in Spain. "In particular, Hubble helped us to identify the four duplicated images and the stellar clumps of the lensed galaxy."

- The initial Hubble observation was first conducted by Saurabh Jha of Rutgers, The State University of New Jersey. His team's science goal was to use Hubble's sharp image to reveal detailed complex structure in the ring arcs.

- The object, GAL-CLUS-022058s, is located in the southern hemisphere constellation of Fornax (the Furnace). The image was nicknamed the "Molten Ring" by Jha, which alludes to its appearance and host constellation.

• September 22, 2021: When the universe was about 3 billion years old, just 20% of its current age, it experienced the most prolific period of star birth in its history. But when NASA's Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile gazed toward cosmic objects in this period, they found something odd: six early, massive, "dead" galaxies that had run out of the cold hydrogen gas needed to make stars. ⁴⁸⁾

- Without more fuel for star formation, these galaxies were literally running on empty. The findings are published in the journal Nature. ⁴⁹⁾

- "At this point in our universe, all galaxies should be forming lots of stars. It's the peak epoch of star formation," explained lead author Kate Whitaker, assistant professor of astronomy at the University of Massachusetts, Amherst. Whitaker is also associate faculty at the Cosmic Dawn Center in Copenhagen, Denmark. "So what happened to all the cold gas in these galaxies so early on?"

- This study is a classic example of the harmony between Hubble and ALMA observations. Hubble pinpointed where in the galaxies the stars exist, showing where they formed in the past. By detecting the cold dust that serves as a proxy for the cold hydrogen gas, ALMA showed astronomers where stars could form in the future if enough fuel were present.

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Using Nature's Own Telescopes

- The study of these early, distant, dead galaxies was part of the appropriately named REQUIEM program, which stands for Resolving QUIEscent Magnified Galaxies At High Redshift. (Redshift happens when light is stretched by the expansion of space and appears shifted toward the red part of the spectrum. The farther away a galaxy is with respect to the observer, the redder it appears.)

- The REQUIEM team uses extremely massive foreground galaxy clusters as natural telescopes. The immense gravity of a galaxy cluster warps space, bending and magnifying light from background objects. When an early, massive and very distant galaxy is positioned behind such a cluster, it appears greatly stretched and magnified, allowing astronomers to study details that would otherwise be impossible to see. This is called "strong gravitational lensing."

- Only by combining the exquisite resolution of Hubble and ALMA with this strong lensing was the REQUIEM team able to able to understand the formation of these six galaxies, which appear as they did only a few billion years after the big bang.

- "By using strong gravitational lensing as a natural telescope, we can find the distant, most massive and first galaxies to shut down their star formation," said Whitaker. "I like to think about it like doing science of the 2030s or 40s—with powerful next-generation space telescopes—but today instead by combining the capabilities of Hubble and ALMA, which are boosted by strong lensing."

- "REQUIEM pulled together the largest sample to date of these rare, strong-lensed, dead galaxies in the early universe, and strong lensing is the key here," said Mohammad Akhshik, principal investigator of the Hubble observing program. "It amplifies the light across all wavelengths so that it's easier to detect, and you also get higher spatial resolution when you have these galaxies stretched across the sky. You can essentially see inside of them at much finer physical scales to figure out what's happening."

Live Fast, Die Young

- These sorts of dead galaxies don't appear to rejuvenate, even through later minor mergers and accretions of nearby, small galaxies and gas. Gobbling up things around them mostly just "puffs up" the galaxies. If star formation does turn back on, Whitaker described it as "a kind of a frosting." About 11 billion years later in the present-day universe, these formerly compact galaxies are thought to have evolved to be larger but are still dead in terms of any new star formation.

- These six galaxies lived fast and furious lives, creating their stars in a remarkably short time. Why they shut down star formation so early is still a puzzle.

- Whitaker proposes several possible explanations: "Did a supermassive black hole in the galaxy's center turn on and heat up all the gas? If so, the gas could still be there, but now it's hot. Or it could have been expelled and now it's being prevented from accreting back onto the galaxy. Or did the galaxy just use it all up, and the supply is cut off? These are some of the open questions that we'll continue to explore with new observations down the road."

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

• September 17, 2021: This comparison view shows puffing dust bubbles and an erupting gas shell — the final acts of a monster star. These Pictures of the Week (Figures 48 and 49) showcase new views of the dual nature of the star AG Carinae, which was the target of the NASA/ESA Hubble Space Telescope’s 31st anniversary image in April 2020. This new perspective was developed thanks to Hubble’s observations of the star in 2020 and 2014, along with others captured by the telescope’s WFPC2 (Wide Field Planetary Camera 2) instrument in 1994. ⁵⁰⁾

- This giant star is waging a tug-of-war between gravity and radiation to avoid self-destruction. The star is surrounded by an expanding shell of gas and dust — a nebula — that is shaped by the powerful winds emanating from the star. The nebula is about five light-years wide, equal to the distance from here to our nearest star, Alpha Centauri.

- AG Carinae is formally classified as a Luminous Blue Variable because it is hot (blue), very luminous, and variable. Such stars are quite rare because there are not many stars that are so massive. Luminous Blue Variable stars continuously lose mass in the final stages of their life, during which a significant amount of stellar material is ejected into the surrounding interstellar space, until enough mass has been lost that the star has reached a stable state.

- AG Carinae is surrounded by a spectacular nebula, formed by material ejected by the star during several of its past outbursts. The nebula is approximately 10,000 years old, and the observed velocity of the gas is approximately 70 km/s. While this nebula looks like a ring, it is in fact a hollow shell rich in gas and dust, the center of which has been cleared by the powerful stellar wind travelling at roughly 200 km/s. The gas (composed mostly of ionized hydrogen and nitrogen) is visible to us in these images as a thick bright red ring, which appears doubled in places — possibly the result of several outbursts colliding into each other. The dust, here visible in blue (Figure 49), has formed in clumps, bubbles and filaments that are shaped by the stellar wind.

- Scientists who observed the star and its surrounding nebula note that the ring is not perfectly spherical; it appears to have a bipolar symmetry, indicating that the mechanism producing the outburst may have been caused by the presence of a disc in the center, or that the star is not alone but might have a companion (known as a binary star). An alternative and simpler theory is that the star rotates very fast (as many massive stars have been found to do).

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• September 13, 2021: It's challenging to make predictions, especially in astronomy. There are however, a few forecasts astronomers can depend on, such as the timing of upcoming lunar and solar eclipses and the clockwork return of some comets. ⁵¹⁾

- Now, looking far beyond the solar system, astronomers have added a solid prediction of an event happening deep in intergalactic space: an image of an exploding star, dubbed Supernova Requiem, which will appear around the year 2037. Although this rebroadcast will not be visible to the naked eye, some future telescopes should be able to spot it.

- It turns out that this future appearance will be the fourth-known view of the same supernova, magnified, brightened, and split into separate images by a massive foreground cluster of galaxies acting like a cosmic zoom lens. Three images of the supernova were first found from archival data taken in 2016 by NASA's Hubble Space Telescope.

- The multiple images are produced by the monster galaxy cluster's powerful gravity, which distorts and magnifies the light from the supernova far behind it, an effect called gravitational lensing. First predicted by Albert Einstein, this effect is similar to a glass lens bending light to magnify the image of a distant object.

- The three lensed supernova images, seen as tiny dots captured in a single Hubble snapshot, represent light from the explosive aftermath. The dots vary in brightness and color, which signify three different phases of the fading blast as it cooled over time.

- "This new discovery is the third example of a multiply imaged supernova for which we can actually measure the delay in arrival times," explained lead researcher Steve Rodney of the University of South Carolina in Columbia. "It is the most distant of the three, and the predicted delay is extraordinarily long. We will be able to come back and see the final arrival, which we predict will be in 2037, plus or minus a couple of years."

- The light that Hubble captured from the cluster, MACS J0138.0-2155, took about 4 billion years to reach Earth. The light from Supernova Requiem needed an estimated 10 billion years for its journey, based on the distance of its host galaxy.

- The team's prediction of the supernova's return appearance is based on computer models of the cluster, which describe the various paths the supernova light is taking through the maze of clumpy dark matter in the galactic grouping. Dark matter is an invisible material that comprises the bulk of the universe's matter and is the scaffolding upon which galaxies and galaxy clusters are built.

- Each magnified image takes a different route through the cluster and arrives at Earth at a different time, due, in part, to differences in the length of the pathways the supernova light followed.

- "Whenever some light passes near a very massive object, like a galaxy or galaxy cluster, the warping of space-time that Einstein's theory of general relativity tells us is present for any mass, delays the travel of light around that mass," Rodney said.

- He compares the supernova's various light paths to several trains that leave a station at the same time, all traveling at the same speed and bound for the same location. Each train, however, takes a different route, and the distance for each route is not the same. Because the trains travel over different track lengths across different terrain, they do not arrive at their destination at the same time.

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- In addition, the lensed supernova image predicted to appear in 2037 lags behind the other images of the same supernova because its light travels directly through the middle of the cluster, where the densest amount of dark matter resides. The immense mass of the cluster bends the light, producing the longer time delay. "This is the last one to arrive because it's like the train that has to go deep down into a valley and climb back out again. That's the slowest kind of trip for light," Rodney explained.

- The lensed supernova images were discovered in 2019 by Gabe Brammer, a study co-author at the Cosmic Dawn Center (DAWN) at the Niels Bohr Institute, University of Copenhagen, in Denmark. Brammer spotted the mirrored supernova images while analyzing distant galaxies magnified by massive foreground galaxy clusters as part of an ongoing Hubble program called REsolved QUIEscent Magnified Galaxies (REQUIEM).

- He was comparing new REQUIEM data from 2019 with archival images taken in 2016 from a different Hubble science program. A tiny red object in the 2016 data caught his eye, which he initially thought was a far-flung galaxy. But it had disappeared in the 2019 images.

- "But then, on further inspection of the 2016 data, I noticed there were actually three magnified objects, two red and a purple," he explained. "Each of the three objects was paired with a lensed image of a distant massive galaxy. Immediately it suggested to me that it was not a distant galaxy but actually a transient source in this system that had faded from view in the 2019 images like a light bulb that had been flicked off."

- Brammer teamed up with Rodney to conduct a further analysis of the system. The lensed supernova images are arranged in an arc around the cluster's core. They appear as small dots near the smeared orange features that are thought to be the magnified snapshots of the supernova's host galaxy.

- Study co-author Johan Richard of the University of Lyon in France produced a map of the amount of dark matter in the cluster, inferred from the lensing it produces. The map shows the predicted locations of lensed objects. This supernova is predicted to appear again in 2042, but it will be so faint that the research team thinks it will not be visible.

- Catching the rerun of the explosive event will help astronomers measure the time delays between all four supernova images, which will offer clues to the type of warped-space terrain the exploded star's light had to cover. Armed with those measurements, researchers can fine-tune the models that map out the cluster's mass. Developing precise dark-matter maps of massive galaxy clusters is another way for astronomers to measure the universe's expansion rate and investigate the nature of dark energy, a mysterious form of energy that works against gravity and causes the cosmos to expand at a faster rate.

- This time-delay method is valuable because it's a more direct way of measuring the universe's expansion rate, Rodney explained. "These long time delays are particularly valuable because you can get a good, precise measurement of that time delay if you are just patient and wait years, in this case more than a decade, for the final image to return," he said. "It is a completely independent path to calculate the universe's expansion rate. The real value in the future will be using a larger sample of these to improve the precision."

- Spotting lensed images of supernovae will become increasingly common in the next 20 years with the launch of NASA's Nancy Grace Roman Space Telescope and the start of operations at the Vera C. Rubin Observatory. Both telescopes will observe large swaths of the sky, which will allow them to spot dozens more multiply imaged supernovae.

- Future telescopes such as NASA's James Webb Space Telescope also could detect light from supernova Requiem at other epochs of the blast.

- The team's results will appear on September 13 in the journal Nature Astronomy. ⁵²⁾

• September 10, 2021: This star-studded image from the NASA/ESA Hubble Space Telescope depicts NGC 6717, which lies more than 20,000 light-years from Earth in the constellation Sagittarius. NGC 6717 is a globular cluster, a roughly spherical collection of stars tightly bound together by gravity. Globular clusters contain more stars in their centers than their outer fringes, as this image aptly demonstrates; the sparsely populated edges of NGC 6717 are in stark contrast to the sparkling collection of stars at its center. ⁵³⁾

- The center of the image also contains some interlopers from closer to home. Bright foreground stars close to Earth are surrounded by criss-cross diffraction spikes formed by starlight interacting with the structures supporting Hubble’s secondary mirror.

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• September 6, 2021: Could dying stars hold the secret to looking younger? New evidence from NASA’s Hubble Space Telescope suggests that white dwarf stars could continue to burn hydrogen in the final stages of their lives, causing them to appear more youthful than they actually are. This discovery could have consequences for how astronomers measure the ages of star clusters, which contain the oldest known stars in the universe. ⁵⁴⁾

- These results challenge the prevalent view of white dwarfs as inert, slowly cooling burned-out stars where nuclear fusion has stopped. Now, an international group of astronomers has discovered the first evidence that white dwarfs can slow down their rate of aging by burning hydrogen on their surfaces.

- “We have found the first observational evidence that white dwarfs can still undergo stable thermonuclear activity,” explained Jianxing Chen of the Alma Mater Studiorum Università di Bologna and the Italian National Institute for Astrophysics, who led this research. “This was quite a surprise, as it is at odds with what is commonly believed.”

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- White dwarfs have cast off their outer layers during the last stages of their lives. They are common objects in the cosmos; roughly 98% of all the stars in the universe will ultimately end up as white dwarfs, including our own Sun. Studying these cooling stages helps astronomers understand not only white dwarfs, but also their earlier stages as well.

- To investigate the physics underpinning white dwarf evolution, astronomers compared cooling white dwarfs in two massive collections of stars: the globular clusters M3 and M13. These two clusters share many physical properties such as age and metallicity (the abundance of heaver elements), but the populations of stars which will eventually give rise to white dwarfs are different. This makes M3 and M13 together a perfect natural laboratory in which to test how different populations of white dwarfs cool.

- “The superb quality of our Hubble observations provided us with a full view of the stellar populations of the two globular clusters,” continued Chen. “This allowed us to really contrast how stars evolve in M3 and M13.”

- Using Hubble’s Wide Field Camera 3 the team observed M3 and M13 at near-ultraviolet wavelengths, which is ideal for finding blue and faint stellar objects in the crowded globular clusters. This allowed the researchers to compare more than 700 white dwarfs in the two clusters. They found that M3 contains standard white dwarfs, which are simply cooling stellar cores. M13, on the other hand, contains two populations of white dwarfs: standard white dwarfs and those which have managed to hold on to an outer envelope of hydrogen, allowing them to burn for longer and hence cool more slowly.

- Comparing their results with computer simulations of stellar evolution in M13, the researchers were able to show that roughly 70% of the white dwarfs in M13 are burning hydrogen on their surfaces, slowing down the rate at which they are cooling. The hydrogen would have been supplied by the star’s outer shells leaking into space.

- This discovery could have consequences for how astronomers measure the ages of stars in the Milky Way galaxy. The evolution of white dwarfs has previously been modeled as a predictable cooling process. This relatively straightforward relationship between age and temperature has led astronomers to use the white dwarf cooling rate as a natural clock to determine the ages of star clusters, particularly globular and open clusters. However, white dwarfs burning hydrogen could cause these age estimates to be inaccurate by as much as one billion years.

- “Our discovery challenges the definition of white dwarfs as we consider a new perspective on the way in which stars get old,” added Francesco Ferraro of the Alma Mater Studiorum Università di Bologna and the Italian National Institute for Astrophysics, who coordinated the study. “We are now investigating other clusters similar to M13 to further constrain the conditions which drive stars to maintain the thin hydrogen envelope which allows them to age slowly.”

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

• August 27, 2021: This Picture of the Week shows an open cluster known as NGC 2164, which was first discovered in 1826 by a Scottish astronomer named James Dunlop. NGC 2164 is located within one of the Milky Way galaxy's closest neighbors — the satellite galaxy known as the Large Magellanic Cloud. The Large Magellanic cloud is a relatively small galaxy that lies about 160 000 light-years from Earth. It is considered a satellite galaxy because it is gravitationally bound to the Milky Way. In fact, the Large Magellanic cloud is on a very slow collision course with the Milky Way — it’s predicted that they will collide 2.4 billion years from now. ⁵⁵⁾

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• August 20, 2021: This jewel-bright image from the NASA/ESA Hubble Space Telescope shows NGC 1385, a spiral galaxy 68 million light-years away from Earth, which lies in the constellation Fornax. The image was taken with Hubble’s Wide Field Camera 3 (WFC3), which is often referred to as Hubble’s workhorse camera, thanks to its reliability and versatility. It was installed in 2009 when astronauts last visited Hubble, and 12 years later it remains remarkably productive. ⁵⁶⁾

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• August 19, 2021: It's suspected that about 5,000 years ago a comet swept within 23 million miles of the Sun, closer than the innermost planet Mercury. The comet might have been a spectacular sight to civilizations across Eurasia and North Africa at the end of the Stone Age. ⁵⁷⁾

- However, this nameless space visitor is not recorded in any known historical account. So how do astronomers know that there was such an interplanetary intruder? — Enter comet ATLAS (C/2019 Y4), which first appeared near the beginning of 2020.

- Comet ATLAS, first detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS), operated by the University of Hawaii, quickly met an untimely death in mid-2020 when it disintegrated into a cascade of small icy pieces.

- In a new study using observations from NASA's Hubble Space Telescope, astronomer Quanzhi Ye of the University of Maryland (UMD) in College Park, reports that ATLAS is a broken-off piece of that ancient visitor from 5,000 years ago. Why? Because ATLAS follows the same orbital "railroad track" as that of a comet seen in 1844. This means the two comets are probably siblings from a parent comet that broke apart many centuries earlier. The link between the two comets was first noted by amateur astronomer Maik Meyer.

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- Such comet families are common. The most dramatic visual example was in 1994 when the doomed comet Shoemaker-Levy 9 (SL9) was pulled into a string of pieces by Jupiter’s gravitational pull. This "comet train" was short-lived. It fell piece by piece into Jupiter in July 1994.

- But comet ATLAS is just "weird," says Ye, who observed it with Hubble about the time of the breakup. Unlike its hypothesized parent comet, ATLAS disintegrated while it was farther from the Sun than Earth, at a distance of over 100 million miles. This was much farther than the distance where its parent passed the Sun. "This emphasizes its strangeness," said Ye.

- "If it broke up this far from the Sun, how did it survive the last passage around the Sun 5,000 years ago? This is the big question," said Ye. "It's very unusual because we wouldn't expect it. This is the first time a long-period comet family member was seen breaking up before passing closer to the Sun."

- Observing the breakup of the fragments offers clues to how the parent comet was put together. The conventional wisdom is that comets are fragile agglomerations of dust and ice. And, they may be lumpy, like raisin pudding.

- In a new paper published in the Astronomical Journal, after one year of analysis Ye and co-investigators report that one fragment of ATLAS disintegrated in a matter of days, while another piece lasted for weeks. "This tells us that part of the nucleus was stronger than the other part," he said. ⁵⁸⁾

- One possibility is that streamers of ejected material may have spun up the comet so fast that centrifugal forces tore it apart. An alternative explanation is that it has so-called super-volatile ices that just blew the piece apart like an exploding aerial firework. "It is complicated because we start to see these hierarchies and evolution of comet fragmentation. Comet ATLAS's behavior is interesting but hard to explain."

- Comet ATLAS's surviving sibling won't return until the 50th century.

• August 13, 2021: Nestled among the vast clouds of star-forming regions like this one lie potential clues about the formation of our own solar system. ⁵⁹⁾

- Stars are born in dusty environments and although this dust makes for spectacular images, it can prevent astronomers from seeing stars embedded in it. Hubble’s Wide Field Camera 3 (WFC3) instrument is designed to capture detailed images in both visible and infrared light, meaning that the young stars hidden in vast star-forming regions like AFGL 5180 can be seen much more clearly.

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• August 13, 2021: Clustered at the center of this image are six luminous spots of light, four of them forming a circle around a central pair. Appearances can be deceiving, however, as this formation is not composed of six individual galaxies, but only three: to be precise, a pair of galaxies and one distant quasar. Hubble data also indicates that there is a seventh spot of light in the very center, which is a rare fifth image of the distant quasar. This rare phenomenon is caused by the presence of two galaxies in the foreground that act as a lens. ⁶⁰⁾

- The central pair of galaxies in this image of Figure 57 are genuinely two separate galaxies. The four bright points circling them, and the fainter one in the very center, are actually five separate images of a single quasar (known as 2M1310-1714), an extremely luminous but distant object. The reason behind this “seeing quintuple” effect is a phenomenon known as gravitational lensing. Gravitational lensing occurs when a celestial object with an enormous amount of mass — such as a pair of galaxies — causes the fabric of space to warp such that the light travelling through that space from a distant object is bent and magnified sufficiently that humans here on Earth can observe multiple magnified images of the far-away source. The quasar in this image actually lies further away from Earth than the pair of galaxies. The light from the quasar has been bent around the galaxy pair because of their enormous mass, giving the incredible appearance that the galaxy pair are surrounded by four quasars — whereas in reality, a single quasar lies far beyond them!

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• August 6, 2021: The spiral galaxy IC 1954 takes centre stage in this image from the NASA/ESA Hubble Space Telescope. The galaxy, which lies approximately 45 million light-years from Earth in the constellation Horologium (The Clock), boasts a bright central bar and lazily winding spiral arms threaded with dark clouds of dust. ⁶¹⁾

- These observations also lay the groundwork for future observations with the upcoming NASA/ESA/CSA James Webb Space Telescope, which will peer into nearby galaxies and observe the earliest phases of star formation.

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• July 30, 2021: A dramatic triplet of galaxies takes center stage in this latest Picture of the Week from the NASA/ESA Hubble Space Telescope, which captures a three-way gravitational tug-of-war between interacting galaxies. This system —known as Arp 195— is featured in the Atlas of Peculiar Galaxies, a list which showcases some of the weirder and more wonderful galaxies in the universe. ⁶²⁾

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• July 26, 2021: Astronomers have used archival datasets from the NASA/ESA Hubble Space Telescope to reveal the first evidence for water vapor in the atmosphere of Jupiter’s moon Ganymede, the result of the thermal escape of water vapor from the moon’s icy surface. ^{63) 64)}

- Jupiter’s moon Ganymede is the largest moon — and the ninth-largest object — in the Solar System. It may hold more water than all of Earth's oceans, but temperatures there are so cold that water on the surface freezes and the ocean lies roughly 160 kilometers below the crust. Nevertheless, where there is water there could be life as we know it. Identifying liquid water on other worlds is crucial in the search for habitable planets beyond Earth. And now, for the first time, evidence has been found for a sublimated water atmosphere on the icy moon Ganymede.

- In 1998, Hubble’s Space Telescope Imaging Spectrograph (STIS) took the first ultraviolet (UV) pictures of Ganymede, which revealed a particular pattern in the observed emissions from the moon’s atmosphere. The moon displays auroral bands that are somewhat similar to the auroral ovals observed on Earth and other planets with magnetic fields. These images were therefore illustrative evidence that Ganymede has a permanent magnetic field. The similarities between the two ultraviolet observations were explained by the presence of molecular oxygen, O₂. The differences were explained at the time by the presence of atomic oxygen, O, which produces a signal that affects one UV color more than the other.

- As part of a large observing programme to support NASA’s Juno mission in 2018, Lorenz Roth, of the KTH Royal Institute of Technology in Stockholm, Sweden, led a team that set out to capture UV spectra of Ganymede with Hubble’s Cosmic Origins Spectrograph (COS) instrument to measure the amount of atomic oxygen. They carried out a combined analysis of new spectra taken in 2018 with the COS and archival images from the STIS instrument from 1998 and 2010. To their surprise, and in contrast to the original interpretations of the data from 1998, they discovered there was hardly any atomic oxygen in Ganymede's atmosphere. This means there must be another explanation for the apparent differences between the UV aurora images.

- The explanation was then uncovered by Roth and his team in the relative distribution of the aurorae in the two images. Ganymede's surface temperature varies strongly throughout the day, and around noon near the equator it may become sufficiently warm that the icy surface releases some small amounts of water molecules. In fact, the perceived differences between the UV images are directly correlated with where water would be expected in the moon’s atmosphere.

- “Initially only the O₂ had been observed,” explained Roth. “This is produced when charged particles erode the ice surface. The water vapor that we have now measured originates from ice sublimation caused by the thermal escape of H₂O vapor from warm icy regions.”

- This finding adds anticipation to ESA’s upcoming JUpiter ICy moons Explorer (JUICE) mission — the first large-class mission in ESA's Cosmic Vision 2015–2025 programme. Planned for launch in 2022 and arrival at Jupiter in 2029, it will spend at least three years making detailed observations of Jupiter and three of its largest moons, with particular emphasis on Ganymede as a planetary body and potential habitable world. Ganymede was identified for detailed investigation because it provides a natural laboratory for the analysis of the nature, evolution and potential habitability of icy worlds in general and the role it plays within the system of Galilean satellites, and its unique magnetic and plasma interactions with Jupiter and its environment (known as the Jovian system).

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- “Our results can provide the JUICE instrument teams with valuable information that may be used to refine their observation plans to optimize the use of the spacecraft,” added Roth.

- Understanding the Jovian system and unravelling its history, from its origin to the possible emergence of habitable environments, will provide us with a better understanding of how gas giant planets and their satellites form and evolve. In addition, new insights will hopefully be found into the potential for the emergence of life in Jupiter-like exoplanetary systems.

- A paper is published in the journal Nature Astronomy. ⁶⁵⁾

• July 23, 2021: The center of this image from the NASA/ESA Hubble Space Telescope is framed by the tell-tale arcs that result from strong gravitational lensing, a striking astronomical phenomenon which can warp, magnify, or even duplicate the appearance of distant galaxies. ⁶⁷⁾

- Gravitational lensing occurs when light from a distant galaxy is subtly distorted by the gravitational pull of an intervening astronomical object. In this case, the relatively nearby galaxy cluster MACSJ0138.0-2155 has lensed a significantly more distant quiescent galaxy — a slumbering giant known as MRG-M0138 which has run out of the gas required to form new stars and is located 10 billion light years away. Astronomers can use gravitational lensing as a natural magnifying glass, allowing them to inspect objects like distant quiescent galaxies which would usually be too difficult for even Hubble to resolve.

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• July 21, 2021: According to the latest cosmological models, large spiral galaxies such as the Milky Way grew by absorbing smaller galaxies, by a sort of galactic cannibalism. Evidence for this is given by very large structures, the tidal stellar streams, which are observed around them, which are the remains of these satellite galaxies. But the full histories of the majority of these cases are hard to study, because these flows of stars are very faint, and only the remains of the most recent mergers have been detected. ⁶⁸⁾

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- A study led by the Instituto de Astrofísica de Andalucía (IAA-CSIC), with the participation of the Instituto de Astrofísica de Canarias (IAC), has made detailed observations of a large tidal flow around the Sombrero galaxy, whose strange morphology has still not been definitively explained. The results are published today in the journal Monthly Notices of the Royal Astronomical Society (MNRAS). ⁶⁹⁾

- The Sombrero galaxy (Messier 104) is a galaxy some thirty million light years away, which is part of the Local Supercluster (a group of galaxies which includes the Virgo cluster and the Local Group containing the Milky Way). It has roughly one third of the diameter of the Milky Way, and shows characteristics of both of the dominant types of galaxies in the Universe, the spirals and the ellipticals. It has spiral arms, and a very large bright central bulge, which makes it look like a hybrid of the two types.

- “Our motive for obtaining these very deep images of the Sombrero galaxy (Messier 104) was to look for the remains of its merger with a very massive galaxy. This possible collision was recently suggested on the basis of studies of the stellar population of its strange halo obtained with the Hubble Space Telescope”, says David Martínez-Delgado, a researcher at the IAA-CSIC and first author of the paper reporting the work.

- The observations with the Hubble, in 2020, showed that the halo, an extensive and faint region surrounding the Sombrero galaxy, shows many stars rich in metals, elements heavier than hydrogen and helium. This is a feature to typical of new generations of stars, which are normally found in the discs of galaxies, and are quite unusual in galactic halos, which are populated by old stars. To explain their presence astronomers suggested what is known as “a wet merger”, a scenario in which a large elliptical galaxy is rejuvenated by large quantities of gas and dust from another massive galaxy, which went into the formation of the disc which we now observe.

- “In our images we have not found any evidence to support this hypothesis, although we cannot rule out that it could have happened several thousand million years ago, and the debris is completely dissipated by now -explains David Martínez-Delgado-. In our search we have in fact been able to trace for the first time the complete tidal stream which surrounds the disc of this galaxy, and our theoretical simulations have let us reconstruct its formation in the last three thousand million years, by cannibalism of a satellite dwarf galaxy”.

- “Observational techniques in present day Astrophysics need advanced image processing. Our modelling of the bright stars around the Sombrero galaxy, and at the same time of the halo light of the galaxy itself has enabled us to unveil the nature of this tidal stream. It is remarkable that thanks to these advanced photometric techniques we have been able to do front line science with a Messier object using only an 18 cm (diameter) telescope”, explains Javier Román, a postdoctoral researcher at the IAC and a co-author of the study.

- The research team rejects the idea that the large stellar tidal stream, known for more than three decades, could be related to the event which produced the strange morphology of the Sombrero galaxy which, if it was caused by a wet merger, would need the interaction of two galaxies with large masses.

- The work has been possible thanks to the collaboration between professional and amateur astronomers. “We have collaborated with the Spanish astrophotographer Manuel Jiménez, who took the images with a robotic telescope of 18 cm diameter, and the well-known Australian astrophotographer David Malin, who discovered this tidal stream on photographic plates taken in the 90’s of the last century. This collaboration shows the potential of amateur telescopes to take deep images of nearby galaxies which give important clues about the process of their assembly which is continuing until the present epoch”, concludes Martínez-Delgado.

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• July 19, 2021: NASA’s Hubble Space Telescope is back in business, exploring the universe near and far. The science instruments have returned to full operation, following recovery from a computer anomaly that suspended the telescope’s observations for more than a month. ⁷⁰⁾

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- “I’m thrilled to see that Hubble has its eye back on the universe, once again capturing the kind of images that have intrigued and inspired us for decades,” said NASA Administrator Bill Nelson. “This is a moment to celebrate the success of a team truly dedicated to the mission. Through their efforts, Hubble will continue its 32nd year of discovery, and we will continue to learn from the observatory’s transformational vision.”

- Hubble’s payload computer, which controls and coordinates the observatory’s onboard science instruments, halted suddenly on June 13. When the main computer failed to receive a signal from the payload computer, it automatically placed Hubble’s science instruments into safe mode. That meant the telescope would no longer be doing science while mission specialists analyzed the situation.

- The Hubble team moved quickly to investigate what ailed the observatory, which orbits about 340 miles (547 kilometers) above Earth. Working from mission control at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, as well as remotely due to COVID-19 restrictions, engineers collaborated to figure out the cause of the problem.

- Complicating matters, Hubble was launched in 1990 and has been observing the universe for over 31 years. To fix a telescope built in the 1980s, the team had to draw on the knowledge of staff from across its lengthy history.

- Hubble alumni returned to support the current team in the recovery effort, lending decades of mission expertise. Retired staff who helped build the telescope, for example, knew the ins and outs of the Science Instrument and Command & Data Handling unit, where the payload computer resides – critical expertise for determining next steps for recovery. Other former team members lent a hand by scouring Hubble’s original paperwork, surfacing 30- to 40-year-old documents that would help the team chart a path forward.

- “That’s one of the benefits of a program that’s been running for over 30 years: the incredible amount of experience and expertise,” said Nzinga Tull, Hubble systems anomaly response manager at Goddard. “It’s been humbling and inspiring to engage with both the current team and those who have moved on to other projects. There’s so much dedication to their fellow Hubble teammates, the observatory, and the science Hubble is famous for.”

- Together, team members new and old worked their way through the list of likely culprits, seeking to isolate the issue to ensure they have a full inventory for the future of which hardware is still working.

- The team then moved on to explore whether other hardware was at fault, including the Command Unit/Science Data Formatter and the Power Control Unit, which is designed to ensure a steady voltage supply to the payload computer’s hardware. However, it would be more complicated to address either of these issues, and riskier for the telescope in general. Switching to these components’ backup units would require switching several other hardware boxes as well.

- “The switch required 15 hours of spacecraft commanding from the ground. The main computer had to be turned off, and a backup safe mode computer temporarily took over the spacecraft. Several boxes also had to be powered on that were never turned on before in space, and other hardware needed their interfaces switched,” said Jim Jeletic, Hubble deputy project manager at Goddard. “There was no reason to believe that all of this wouldn’t work, but it’s the team’s job to be nervous and think of everything that could go wrong and how we might compensate for it. The team meticulously planned and tested every small step on the ground to make sure they got it right.”

- The team proceeded carefully and systematically from there. Over the following two weeks, more than 50 people worked to review, update, and vet the procedures to switch to backup hardware, testing them on a high-fidelity simulator and holding a formal review of the proposed plan.

- Simultaneously, the team analyzed the data from their earlier tests, and their findings pointed to the Power Control Unit as the possible cause of the issue. On July 15, they made the planned switch to the backup side of the Science Instrument and Command & Data Handling unit, which contains the backup Power Control Unit.

- Victory came around 11:30 p.m. EDT July 15, when the team determined the switch was successful. The science instruments were then brought to operational status, and Hubble began taking scientific data once again on July 17. Most observations missed while science operations were suspended will be rescheduled.

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- This is not the first time Hubble has had to rely on backup hardware. The team performed a similar switch in 2008, returning Hubble to normal operations after another part of the Science Instrument and Command & Data Handling (SI C&DH) unit failed. Hubble’s final servicing mission in 2009 – a much-needed tune-up championed by former U.S. Senator Barbara Mikulski – then replaced the entire SI C&DH unit, greatly extending Hubble’s operational lifetime.

- Since that servicing mission, Hubble has taken more than 600,000 observations, bringing its lifetime total to more than 1.5 million. Those observations continue to change our understanding of the universe.

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- “Hubble is in good hands. The Hubble team has once again shown its resiliency and prowess in addressing the inevitable anomalies that arise from operating the world’s most famous telescope in the harshness of space,” said Kenneth Sembach, director of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, which conducts Hubble science operations. “I am impressed by the team’s dedication and common purpose over the past month to return Hubble to service. Now that Hubble is once again providing unprecedented views of the universe, I fully expect it will continue to astound us with many more scientific discoveries ahead.”

- Hubble has contributed to some of the most significant discoveries of our cosmos, including the accelerating expansion of the universe, the evolution of galaxies over time, and the first atmospheric studies of planets beyond our solar system. Its mission was to spend at least 15 years probing the farthest and faintest reaches of the cosmos, and it continues to far exceed this goal.

- “The sheer volume of record-breaking science Hubble has delivered is staggering,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate. “We have so much to learn from this next chapter of Hubble's life – on its own, and together with the capabilities of other NASA observatories. I couldn’t be more excited about what the Hubble team has achieved over the past few weeks. They’ve met the challenges of this process head on, ensuring that Hubble's days of exploration are far from over."

• July 17, 2021: NASA has returned the science instruments on the Hubble Space Telescope to operational status, and the collection of science data will now resume. This will be the first science data collected since the payload computer experienced a problem on June 13, which placed the instruments in a safe configuration and suspended science operations. ⁷¹⁾

- Hubble is an icon, giving us incredible insight into the cosmos over the past three decades,” said NASA Administrator Bill Nelson. “I’m proud of the Hubble team, from current members to Hubble alumni who stepped in to lend their support and expertise. Thanks to their dedication and thoughtful work, Hubble will continue to build on its 31-year legacy, broadening our horizons with its view of the universe.”

- The first observation is scheduled for Saturday afternoon after some instrument calibrations are completed. Most observations missed while science operations were suspended will be rescheduled for a later date.

- The Hubble team has been investigating the cause of the payload computer problem since it first occurred. On July 15, the team switched the spacecraft to backup hardware.

- NASA anticipates that Hubble will last for many more years and will continue making groundbreaking observations, working in tandem with other space observatories including the James Webb Space Telescope to further our knowledge of the cosmos.

- Launched in 1990, Hubble has been observing the universe for over 31 years. It has taken over 1.5 million observations of the universe, and over 18,000 scientific papers have been published with its data. It has contributed to some of the most significant discoveries of our cosmos, including the accelerating expansion of the universe, the evolution of galaxies over time, and the first atmospheric studies of planets beyond our solar system.

• July 16, 2021: NASA has successfully switched to backup hardware on the Hubble Space Telescope, including powering on the backup payload computer, on July 15. The switch was performed to compensate for a problem with the original payload computer that occurred on June 13 when the computer halted, suspending science data collection. ⁷²⁾

- NASA has successfully switched to backup hardware on the Hubble Space Telescope, including powering on the backup payload computer, on July 15. The switch was performed to compensate for a problem with the original payload computer that occurred on June 13 when the computer halted, suspending science data collection.

- The switch included bringing online the backup Power Control Unit (PCU) and the backup Command Unit/Science Data Formatter (CU/SDF) on the other side of the Science Instrument and Command & Data Handling (SI C&DH) unit. The PCU distributes power to the SI C&DH components, and the CU/SDF sends and formats commands and data. In addition, other pieces of hardware onboard Hubble were switched to their alternate interfaces to connect to this backup side of the SI C&DH. Once these steps were completed, the backup payload computer on this same unit was turned on and loaded with flight software and brought up to normal operations mode.

- The Hubble team is now monitoring the hardware to ensure that everything is working properly. The team has also started the process for recovering the science instruments out of their safe mode configuration. This activity is expected to take more than a day as the team runs various procedures and ensures the instruments are at stable temperatures. The team will then conduct some initial calibration of the instruments before resuming normal science operations.

• July 16, 2021: This image shows the globular cluster NGC 6380, which lies around 35,000 light-years from Earth, in the constellation Scorpio (The Scorpion). The very bright star at the top of the image is HD 159073, which is only around 4000 light-years from Earth, making it a much nearer neighbor to Earth than NGC 6380.

- NGC 6380 is not a particularly exciting name, but it indicates that this cluster is catalogued in the New General Catalogue (NGC), which was originally compiled in 1888. This cluster has, however, been known by many other names. It was originally discovered by James Dunlop in 1826, and he rather immodestly named it Dun 538. Eight years later, in 1834, it was independently rediscovered by John Herschel and he (similarly immodestly) went on to name it H 3688. The cluster was re-rediscovered in 1959 in Paris by Pişmiş, who catalogued it as Tonantzintla 1 — and who, to continue the pattern, also referred to it as Pişmiş 25. In addition to its colorful history of rediscovery, up until the 1950s NGC 6380 was thought to be an open cluster. It was A. D. Thackeray who realized that it was in fact a globular cluster. Nowadays, this cluster is reliably recognized in widely available catalogues as a globular cluster, and referred to simply as NGC 6380.

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• July 14, 2021: Dr. Iair Arcavi, a Tel Aviv University researcher at the Raymond and Beverly Sackler Faculty of Exact Sciences, participated in a study that discovered a new type of stellar explosion - an electron-capture supernova. While they have been theorized for 40 years, real-world examples have been elusive. Such supernovas arise from the explosions of stars 8-9 times the mass of the sun. The discovery also sheds new light on the thousand-year mystery of the supernova from A.D. 1054 that was seen by ancient astronomers, before eventually becoming the Crab Nebula, that we know today. ⁷³⁾

- A supernova is the explosion of a star following a sudden imbalance between two opposing forces that shaped the star throughout its life. Gravity tries to contract every star. Our sun, for example, counter balances this force through nuclear fusion in its core, which produces pressure that opposes the gravitational pull. As long as there is enough nuclear fusion, gravity will not be able to collapse the star. However, eventually, nuclear fusion will stop, just like gas runs out in a car, and the star will collapse. For stars like the sun, the collapsed core is called a white dwarf. This material in white dwarfs is so dense that quantum forces between electrons prevent further collapse.

- For stars 10 times more massive than our sun, however, electron quantum forces are not enough to stop the gravitational pull, and the core continues to collapse until it becomes a neutron star or a black hole, accompanied by a giant explosion. In the intermediate mass range, the electrons are squeezed (or more accurately, captured) onto atomic nuclei. This removes the electron quantum forces, and causes the star to collapse and then explode.

- Historically, there have been two main supernova types. One is a thermonuclear supernova — the explosion of a white dwarf star after it gains matter in a binary star system. These white dwarfs are the dense cores of ash that remain after a low-mass star (one up to about 8 times the mass of the sun) reaches the end of its life. Another main supernova type is a core-collapse supernova where a massive star — one more than about 10 times the mass of the sun — runs out of nuclear fuel and has its core collapsed, creating a black hole or a neutron star. Theoretical work suggested that electron-capture supernovae would occur on the borderline between these two types of supernovae.

- That's the theory that was developed in the 1980's by Ken'ichi Nomoto of the University of Tokyo, and others. Over the decades, theorists have formulated predictions of what to look for in an electron-capture supernova. The stars should lose a lot of mass of particular composition before exploding, and the supernova itself should be relatively weak, have little radioactive fallout, and produce neutron-rich elements.

- The new study, published in Nature Astronomy, focuses on the supernova SN2018zd, discovered in 2018 by Japanese amateur astronomer Koihchi Itagaki. Dr. Iair Arcavi, of the astrophysics department at Tel Aviv University, also took part in the study. This supernova, located in the galaxy NGC 2146, has all of the properties expected from an electron-capture supernova, which were not seen in any other supernova. In addition, because the supernova is relatively nearby - only 31 million light years away - the researchers were able to identify the star in pre-explosion archival images taken by the Hubble Space Telescope. Indeed, the star itself also fits the predictions of the type of star that should explode as an electron-capture supernovae, and is unlike stars that were seen to explode as the other types of supernovae. ⁷⁴⁾

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- While some supernovae discovered in the past had a few of the indicators predicted for electron-capture supernovae, only SN2018zd had all six - a progenitor star that fits within the expected mass range, strong pre-supernova mass loss, an unusual chemical composition, a weak explosion, little radioactivity, and neutron-rich material. "We started by asking 'what's this weirdo?'" said Daichi Hiramatsu of the University of California Santa Barbara and Las Cumbres Observatory, who led the study. "Then we examined every aspect of SN 2018zd and realized that all of them can be explained in the electron-capture scenario."

- The new discoveries also illuminate some mysteries of one of the most famous supernovae of the past. In A.D. 1054 a supernova happened in our own Milky Way Galaxy, and according to Chinese and Japanese records, it was so bright that it could be seen in the daytime and cast shadows at night. The resulting remnant, the Crab Nebula, has been studied in great detail, and was found to have an unusual composition. It was previously the best candidate for an electron-capture supernova, but this was uncertain partly because the explosion happened nearly a thousand years ago. The new result increases the confidence that the historic 1054 supernova was an electron-capture supernova.

- "It's amazing that we can shed light on historical events in the Universe with modern instruments," says Dr. Arcavi. "Today, with robotic telescopes that scan the sky in unprecedented efficiency, we can discover more and more rare events which are critical for understanding the laws of nature, without having to wait 1000 years between one event and the next."

• July 9, 2021: Two things capture your attention in this spectacular Picture of the Week, which was taken using Hubble’s Wide Field Camera 3 (WFC3): the two enormous galaxies that flank the left and right sides of the image. The galaxy on the left is a lenticular galaxy, which rejoices in the name of 2MASX J03193743+4137580. The side-on spiral galaxy on the right is more simply named UGC 2665. Both galaxies lie approximately 350 million light-years from Earth, and they both form part of the enormous Perseus galaxy cluster. ⁷⁵⁾

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• July 2, 2021: Pictures of the Week from the NASA/ESA Hubble Space Telescope show us something new about the Universe. This image, however, also contains clues about the inner workings of Hubble itself. The crisscross patterns surrounding the stars in this image — known as diffraction spikes — were created when starlight interacted with the four thin vanes supporting Hubble’s secondary mirror. ⁷⁶⁾

- As star clusters form from a single primordial cloud of gas and dust, all the stars they contain are roughly the same age. This makes them useful natural laboratories for astronomers to learn how stars form and evolve. This image uses observations from Hubble’s Wide Field Camera 3, and incorporates data from two very different astronomical investigations. The first aimed to understand why stars in star clusters appear to evolve differently from stars elsewhere, a peculiarity first observed by the Hubble Space Telescope. The second aimed to determine how large stars can be before they become doomed to end their lives in cataclysmic supernova explosions.

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• June 30, 2021: NASA Preparing for Procedures to Turn On Backup Hardware on the Hubble Space Telescope. ⁷⁷⁾

- NASA is taking additional steps to investigate the Hubble Space Telescope’s payload computer issue that began on June 13, suspending science observations. In parallel with the investigation, NASA is preparing and testing procedures to turn on backup hardware onboard the spacecraft. The telescope itself and science instruments remain healthy and in a safe configuration.

- The source of the computer problem lies in the Science Instrument Command and Data Handling (SI C&DH) unit, where the payload computer resides. A few hardware pieces on the SI C&DH could be the culprit(s).

- The team is currently scrutinizing the Command Unit/Science Data Formatter (CU/SDF), which sends and formats commands and data. They are also looking at a power regulator within the Power Control Unit, which is designed to ensure a steady voltage supply to the payload computer’s hardware. If one of these systems is determined to be the likely cause, the team must complete a more complicated operations procedure to switch to the backup units. This procedure would be more complex and riskier than those the team executed last week, which involved switching to the backup payload computer hardware and memory modules. To switch to the backup CU/SDF or power regulator, several other hardware boxes on the spacecraft must also be switched due to the way they are connected to the SI C&DH unit.

- Over the next week or so, the team will review and update all of the operations procedures, commands and other related items necessary to perform the switch to backup hardware. They will then test their execution against a high-fidelity simulator.

- The team performed a similar switch in 2008, which allowed Hubble to continue normal science operations after a CU/SDF module failed. A servicing mission in 2009 then replaced the entire SI C&DH unit, including the faulty CU/SDF module, with the SI C&DH unit currently in use.

- Since that servicing mission, Hubble has taken over 600,000 additional observations to exceed 1.5 million during its lifetime. Those observations continue to change our understanding of the universe.

- Launched in 1990, Hubble has been observing the universe for over 31 years. It has contributed to some of the most significant discoveries of our cosmos, including the accelerating expansion of the universe, the evolution of galaxies over time, and the first atmospheric studies of planets beyond our solar system. Read more about some of Hubble’s greatest scientific discoveries.

June 25, 2021 - NASA Completes Additional Tests to Diagnose Computer Problem on Hubble Space Telescope

- NASA is continuing to diagnose a problem with the payload computer on the Hubble Space Telescope after completing another set of tests on June 23 and 24. The payload computer halted on June 13 and the spacecraft stopped collecting science data. The telescope itself and its science instruments remain in good health and are currently in a safe configuration.

- The spacecraft has two payload computers, one of which serves as a backup, that are located on the Science Instrument and Command and Data Handling (SI C&DH) unit. There are various pieces of hardware which make up both payload computers, including but not limited to:

a) a Central Processing Module (CPM), which processes the commands that coordinate and control the science instruments

b) a Standard Interface (STINT), which bridges communications between the computer’s CPM and other components

c) a communications bus, which contains lines that pass signals and data between hardware

d) and one active memory module, which stores operational commands to the instruments. There are three additional modules which serve as backups.

- Additional tests performed on June 23 and 24 included turning on the backup computer for the first time in space. The tests showed that numerous combinations of these hardware pieces from both the primary and backup payload computer all experienced the same error - commands to write into or read from memory were not successful.

- Since it is highly unlikely that all individual hardware elements have a problem, the team is now looking at other hardware as the possible culprit, including the Command Unit/Science Data Formatter (CU/SDF), another module on the SI C&DH. The CU formats and sends commands and data to specific destinations, including the science instruments. The SDF formats the science data from the science instruments for transmission to the ground. The team is also looking at the power regulator to see if possibly the voltages being supplied to hardware are not what they should be. A power regulator ensures a steady constant voltage supply. If the voltage is out of limits, it could cause the problems observed.

- Over the next week, the team will continue to assess hardware on the SI C&DH unit to identify if something else may be causing the problem. If the team determines the CU/SDF or the power regulator is the likely cause, they will recommend switching to the backup CU/SDF module and the backup power regulator.

- Launched in 1990, Hubble has been observing the universe for over 31 years. It has contributed to some of the most significant discoveries of our cosmos, including the accelerating expansion of the universe, the evolution of galaxies over time, and the first atmospheric studies of planets beyond our solar system.

June 22, 2021 - Testing Underway to Identify Issue and Restore Payload Computer on NASA’s Hubble Space Telescope

- NASA continues to work to resolve a problem with the Hubble Space Telescope payload computer that halted on June 13. After performing tests on several of the computer’s memory modules, the results indicate that a different piece of computer hardware may have caused the problem, with the memory errors being only a symptom. The operations team is investigating whether the Standard Interface (STINT) hardware, which bridges communications between the computer’s Central Processing Module (CPM) and other components, or the CPM itself is responsible for the issue. The team is currently designing tests that will be run in the next few days to attempt to further isolate the problem and identify a potential solution.

- This step is important for determining what hardware is still working properly for future reference. If the problem with the payload computer can’t be fixed, the operations team will be prepared to switch to the STINT and CPM hardware onboard the backup payload computer. The team has conducted ground tests and operations procedure reviews to verify all the commanding required to perform that switch on the spacecraft.

- If the backup payload computer’s CPM and STINT hardware is turned on, several days will be required to assess the computer performance and restore normal science operations. The backup computer has not been powered on since its installation in 2009; however, it was thoroughly tested on the ground prior to installation on the spacecraft.

- The payload computer is a NASA Standard Spacecraft Computer-1 (NSSC-1) system built in the 1980s that is located on the Science Instrument Command and Data Handling (SI C&DH) unit. After 18 years on orbit, the original SI C&DH experienced a failure in 2008 that delayed the final servicing mission to Hubble while a replacement was prepared for flight. In May 2009, STS-125 was launched and the astronauts installed the existing unit. The replacement contains original hardware from the 1980s with four independent 64K memory modules of Complementary Metal-Oxide Semiconductor (CMOS) memory. Only one memory module is used operationally, with the other three serving as backups. All four modules can be used and accessed from either of the redundant payload computers.

• June 25, 2021: A cataclysmic cosmic collision takes centre stage in this Picture of the Week. The image features the interacting galaxy pair IC 1623, which lies around 275 million light-years away in the constellation Cetus (The Whale). The two galaxies are in the final stages of merging, and astronomers expect a powerful inflow of gas to ignite a frenzied burst of star formation in the resulting compact starburst galaxy. ⁷⁸⁾

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 • June 19, 2021: Spacecraft controllers are continuing to work on a faulty computer memory system on NASA’s Hubble Space Telescope that has stopped telescope operations for nearly a week. ⁷⁹⁾

- A payload computer on Hubble stopped working June 13, the agency said in a June 16 statement. Engineers speculated that the computer, used to manage operations of Hubble’s science instruments, malfunctioned because of a degrading memory module, putting the instruments into a safe mode.

- The agency said at the time that it would switch of a backup memory module that day and, after about a day of testing, restart the instruments and resume science observations.

- However, in a June 18 statement, NASA said those efforts to switch to a backup memory module failed because “the command to initiate the backup module failed to complete.” An attempt to restore the computer with both the original memory module and the backup unit also failed.

- NASA didn’t elaborate on the next steps it will take to correct the problem stating only that the operations team “will be running tests and collecting more information on the system to further isolate the problem.” The instruments themselves, and the rest of the telescope, remain in good health.

- The payload computer is a 1980s-vintage system that can use any one of four memory modules, each containing 64 kilobytes of complementary metal-oxide semiconductor memory. A backup computer is also available.

- This is not the first technical glitch for Hubble, launched 31 years ago and last serviced by the space shuttle 12 years ago. In March, a problem linked to a software “enhancement” recently uploaded to the telescope put the telescope into a safe mode for several days. A faulty gyro took the telescope offline for three weeks in October 2018.

- “We do have anomalies. That happens when you have a decades-old observatory, but we have been able to resolve those anomalies,” Nancy Levenson, deputy director of the Space Telescope Science Institute, said at a town hall session during the 238th Meeting of the American Astronomical Society June 8.

- She emphasized that the telescope, in general, was working well and remained in high demand among astronomers. The institute, which handles science operations of Hubble and, soon, the James Webb Space Telescope, is making plans for extended operations of Hubble.

- “We’re continuing to plan for the very long term,” she said. One example she gave was “COS 2030,” a program to extend the life of the Cosmic Origins Spectrograph, an instrument installed on Hubble on that final servicing mission in 2009, through the end of the decade.

• June 18, 2021: This image shows the spiral galaxy NGC 3254, observed using Hubble's Wide Field Camera 3 (WFC3). WFC3 has the capacity to observe ultraviolet, visible and near-infrared light, and this image is a composite of observations taken in the visible and infrared. In this image, NGC 3254 looks like a typical spiral galaxy, viewed side-on. However, NGC 3254 has a fascinating secret that it is hiding in plain sight — it is a Seyfert galaxy, meaning that it has an extraordinarily active core, known as an active galactic nucleus, which releases as much energy as the rest of the galaxy put together. ⁸⁰⁾

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• June 17, 2021: What if oceanographers found the "tip" of an iceberg and nothing else? Mysteriously missing was the iceberg's immense body, which extends far below the waves. ⁸¹⁾

- Astronomers faced this puzzle when they aimed Hubble at the spheroidal galaxy NGC 1052-DF2, or DF2. It looks like a denizen of intergalactic space that is the closest thing there is to nothing, but is still something. It's physically larger than our Milky Way, but its loose beehive swarm of stars is so thinly scattered that Hubble sees right through it, capturing myriad background galaxies.

- The missing "bottom of the iceberg" for DF2 is the lack of dark matter. Galaxies are partly made up of visible matter—stars and gas. But the bulk of a galaxy's makeup is in dark matter, the invisible glue that keeps a lid on stars, so they don't escape from the galaxy.

- Because this innocuous galaxy challenges conventional theories of how galaxies are put together, astronomers were naturally skeptical when it was first announced that the universe harbored such a rule breaker. After all, the entire cosmos is built on the invisible scaffolding of dark matter.

- To double-check their conclusion, the researchers used a lot more Hubble exposures to better nail down the distance to the stealthy galaxy. If DF2 were closer than they thought, the dark matter mystery goes away.

- They actually found that the galaxy is a little bit farther away than first measured. The researchers say the new milepost helps them confirm that dark matter is really missing in the galactic oddball. They say it's now up to theorists to figure out why.

- When astronomers using NASA's Hubble Space Telescope uncovered an oddball galaxy that looked like it didn't have much dark matter, some thought the finding was hard to believe and looked for a simpler explanation.

- Dark matter, after all, is the invisible glue that makes up the bulk of the universe's matter. All galaxies appear to be dominated by it; in fact, galaxies are thought to form inside immense halos of dark matter.

- So, finding a galaxy lacking the invisible stuff is an extraordinary claim that challenges conventional wisdom. It would have the potential to upset theories of galaxy formation and evolution.

- To bolster their original finding, first reported in 2018 (Dark Matter Goes Missing in Oddball Galaxy (hubblesite.org)), a team of scientists led by Pieter van Dokkum of Yale University in New Haven, Connecticut, followed up their initial study with a more robust Hubble look at the galaxy, named NGC 1052-DF2. Scientists refer to it simply as "DF2."

- "We went out on a limb with our initial Hubble observations of this galaxy in 2018," van Dokkum said. "I think people were right to question it because it's such an unusual result. It would be nice if there were a simple explanation, like a wrong distance. But I think it's more fun and more interesting if it actually is a weird galaxy."

- Determining the amount of the galaxy's dark matter hinges on accurate measurements of how far away it is from Earth.

- If DF2 is as far from Earth as van Dokkum's team asserts, the galaxy's dark-matter content may only be a few percent. The team's conclusion is based on the motions of the stars within the galaxy; their velocities are influenced by the pull of gravity. The researchers found that the observed number of stars accounts for the galaxy's total mass, and there's not much room left for dark matter.

- However, if DF2 were closer to Earth, as some astronomers claim, it would be intrinsically fainter and less massive. The galaxy, therefore, would need dark matter to account for the observed effects of the total mass.

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A Better Yardstick

- Team member Zili Shen, from Yale University, says that the new Hubble observations help them confirm that DF2 is not only farther from Earth than some astronomers suggest, but also slightly more distant than the team's original estimates.

- The new distance estimate is that DF2 is 72 million light-years as opposed to 42 million light-years, as reported by other independent teams. This places the galaxy farther than the original Hubble 2018 estimate of 65 light-years distance.

- The research team based its new result on long exposures with Hubble's Advanced Camera for Surveys, which provide a deeper view of the galaxy for finding a reliable yardstick to nail down the distance. They targeted aging red giant stars on the outskirts of the galaxy that all reach the same peak brightness in their evolution. Astronomers can use the stars' intrinsic brightness to calculate vast intergalactic distances. "Studying the brightest red giants is a well-established distance indicator for nearby galaxies," Shen explained.

- The more accurate Hubble measurements solidify the researchers' initial conclusion of a galaxy deficient in dark matter, team members say. So the mystery of why DF2 is missing most of its dark matter still persists.

- "For almost every galaxy we look at, we say that we can't see most of the mass because it's dark matter," van Dokkum explained. "What you see is only the tip of the iceberg with Hubble. But in this case, what you see is what you get. Hubble really shows the entire thing. That's it. It’s not just the tip of the iceberg, it's the whole iceberg."

- The team's science paper has appeared in the The Astrophysical Journal Letters. ⁸³⁾

A Stealthy Galaxy

- DF2 is a giant cosmic cotton ball that van Dokkum calls a "see-through galaxy," where the stars are spread out. The galactic oddball is almost as wide as the Milky Way, but it contains only 1/200th the number of stars as our galaxy.

- The ghostly galaxy doesn't appear to have a noticeable central region, spiral arms, or a disk. The team estimates that DF2 contains at most 1/400th the amount of dark matter than astronomers had expected. How the galaxy formed remains a complete mystery based on the team's latest measurements.

- DF2 isn't the only galaxy devoid of dark matter. Shany Danieli of the Institute for Advanced Study in Princeton, New Jersey, used Hubble in 2020 to obtain an accurate distance to another ghostly galaxy, called NGC 1052-DF4 (or simply DF4), which apparently lacks dark matter, too. In this case, however, some scientists suggest the dark matter may have been stripped out of the galaxy due to tidal forces from another galaxy.

- The researchers think both DF2 and DF4 were members of a collection of galaxies. However, the new Hubble observations show that the two galaxies are 6.5 million light-years away from each other, farther apart than they first thought. It also appears that DF2 has drifted away from the grouping and is isolated in space.

- Both galaxies were discovered with the Dragonfly Telephoto Array at the New Mexico Skies observatory.

- "Both of them probably were in the same group and formed at the same time," Danieli said. "So maybe there was something special in the environment where they were formed."

- The researchers are hunting for more of these oddball galaxies. Other teams of astronomers are searching, too. In 2020, a group of researchers uncovered 19 unusual dwarf galaxies they say are deficient in dark matter (Off the Baryonic Tully–Fisher Relation: A Population of Baryon-dominated Ultra-diffuse Galaxies – IOPscience). However, it will take uncovering many more dark matter-less galaxies to resolve the mystery.

- Nevertheless, van Dokkum thinks finding a galaxy lacking dark matter tells astronomers something about the invisible substance. "In our 2018 paper, we suggested that if you have a galaxy without dark matter, and other similar galaxies seem to have it, that means that dark matter is actually real and it exists," van Dokkum said. "It's not a mirage."

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

• June 16, 2021: NASA is working to resolve an issue with the payload computer on the Hubble Space Telescope. The computer halted on Sunday, June 13, shortly after 4 p.m. EDT. After analyzing the data, the Hubble operations team is investigating whether a degrading memory module led to the computer halt. The team is preparing to switch to one of several backup modules on Wednesday, June 16. The computer will then be allowed to run for approximately one day to verify that the problem has been solved. The team would then restart all science instruments and return the telescope to normal science operations. ⁸⁴⁾

- The purpose of the payload computer is to control and coordinate the science instruments onboard the spacecraft. After the halt occurred on Sunday, the main computer stopped receiving a “keep-alive” signal, which is a standard handshake between the payload and main spacecraft computers to indicate all is well. The main computer then automatically placed all science instruments in a safe mode configuration. Control center personnel at NASA’s Goddard Space Flight Center in Greenbelt, Maryland restarted the payload computer on Monday, June 14, but it soon experienced the same problem.

- The payload computer is a NASA Standard Spacecraft Computer-1 (NSSC-1) system built in the 1980s. It is part of the Science Instrument Command and Data Handling module, which was replaced during the last astronaut servicing mission in 2009. The module has various levels of redundancy which can be switched on to serve as the primary system when necessary.

• June 11, 2021: The image of Figure 79, taken with Hubble’s Wide Field Camera 3 (WFC3), features the spiral galaxy NGC 4680. At 2 o’clock and 7 o’clock two other galaxies can be seen flanking NGC 4680. NGC 4680 enjoyed a wave of attention in 1997, as it played host to a supernova explosion known as SN 1997bp. Amazingly, the supernova was identified by an Australian amateur astronomer named Robert Evans, who has identified an extraordinary 42 supernova explosions. ⁸⁵⁾

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• June 9, 2021: Brown dwarfs are the cosmic equivalent of tweeners. They're too massive to be planets and too small to sustain nuclear fusion in their cores, which powers stars. Many brown dwarfs are nomadic. They do not orbit stars but drift among them as loners. ⁸⁶⁾

- Astronomers would like to know how these wayward objects are put together. Do they share any kind of kinship with bloated gas-giant planets like Jupiter? Studying brown dwarfs is much more difficult than studying nearby Jupiter for making comparisons. We can send spacecraft to Jupiter. But astronomers need to look across many light-years to peer down into a brown dwarf's atmosphere.

- Researchers used the giant W. M. Keck Observatory in Hawaii to observe a nearby brown dwarf in infrared light. Unlike Jupiter, the young brown dwarf is still so hot it glows from the inside out, and looks like a carved Halloween pumpkin. Because the brown dwarf has scattered clouds, light shining up from deep down in the dwarf's atmosphere fluctuates, which the researchers measured. They found that the dwarf's atmosphere has a layer-cake structure with clouds having different composition at different altitudes.

- Jupiter may be the bully planet of our solar system because it's the most massive planet. But it's actually a runt compared to many of the giant planets found around other stars.

- These alien worlds, called super-Jupiters, weigh up to 13 times Jupiter's mass. Astronomers have analyzed the composition of some of these monsters. But it has been difficult to study their atmospheres in detail because these gas giants get lost in the glare of their parent stars.

- Researchers, however, have a substitute: the atmospheres of brown dwarfs, so-called failed stars that are up to 80 times Jupiter's mass. These hefty objects form out of a collapsing cloud of gas, as stars do, but lack the mass to become hot enough to sustain nuclear fusion in their cores, which powers stars.

- Instead, brown dwarfs share a kinship with super-Jupiters. Both types of objects have similar temperatures and are extremely massive. They also have complex, varied atmospheres. The only difference, astronomers think, is their pedigree. Super-Jupiters form around stars; brown dwarfs often form in isolation.

- A team of astronomers, led by Elena Manjavacas of the Space Telescope Science Institute in Baltimore, Maryland, has tested a new way to peer through the cloud layers of these nomadic objects. The researchers used an instrument at the W. M. Keck Observatory in Hawaii to study in near-infrared light the colors and brightness variations of the layer-cake cloud structure in the nearby, free-floating brown dwarf known as 2MASS J22081363+2921215.

- The Keck Observatory instrument, called the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), also analyzed the spectral fingerprints of various chemical elements contained in the clouds and how they change with time. This is the first time astronomers have used the MOSFIRE instrument in this type of study.

- These measurements offered Manjavacas a holistic view of the brown dwarf's atmospheric clouds, providing more detail than previous observations of this object. Pioneered by Hubble observations, this technique is difficult for ground-based telescopes to do because of contamination from Earth's atmosphere, which absorbs certain infrared wavelengths. This absorption rate changes due to the weather.

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- "The only way to do this from the ground is using the high-resolution MOSFIRE instrument because it allows us to observe multiple stars simultaneously with our brown dwarf," Manjavacas explained. "This allows us to correct for the contamination introduced by the Earth's atmosphere and measure the true signal from the brown dwarf with good precision. So, these observations are a proof-of-concept that MOSFIRE can do these types of studies of brown-dwarf atmospheres."

- Manjavacas will present her results June 9 in a press conference at the virtual meeting of the American Astronomical Society.

- The researcher decided to study this particular brown dwarf because it is very young and therefore extremely bright and has not cooled off yet. Its mass and temperature are similar to those of the nearby giant exoplanet Beta Pictoris b, discovered in 2008 near-infrared images taken by the European Southern Observatory's VLT (Very Large Telescope) in northern Chile.

- "We don't have the ability yet with current technology to analyze in detail the atmosphere of Beta Pictoris b," Manjavacas said. "So, we’re using our study of this brown dwarf's atmosphere as a proxy to get an idea of what the exoplanet's clouds might look like at different heights of its atmosphere."

- Both the brown dwarf and Beta Pictoris b are young, so they radiate heat strongly in the near-infrared. They are both members of a flock of stars and sub-stellar objects called the Beta Pictoris moving group, which shares the same origin and a common motion through space. The group, which is about 33 million years old, is the closest grouping of young stars to Earth. It is located roughly 115 light-years away.

- While they're cooler than bona fide stars, brown dwarfs are still extremely hot. The brown dwarf in Manjavacas' study is a sizzling 2,780º Fahrenheit (1,527º Celsius).

- The giant object is about 12 times heavier than Jupiter. As a young body, it is spinning incredibly fast, completing a rotation every 3.5 hours, compared to Jupiter's 10-hour rotation period. So, clouds are whipping it, creating a dynamic, turbulent atmosphere.

- Keck Observatory's MOSFIRE instrument stared at the brown dwarf for 2.5 hours, watching how the light filtering up through the atmosphere from the dwarf's hot interior brightens and dims over time. Bright spots that appear on the rotating object indicate regions where researchers can see deeper into the atmosphere, where it is hotter. Infrared wavelengths allow astronomers to peer deeper into the atmosphere. The observations suggest the brown dwarf has a mottled atmosphere with scattered clouds. If viewed close-up, it might resemble a carved Halloween pumpkin, with light escaping from its hot interior.

- Its spectrum reveals clouds of hot sand grains and other exotic elements. Potassium iodide traces the object's upper atmosphere, which also includes magnesium silicate clouds. Moving down in the atmosphere is a layer of sodium iodide and magnesium silicate clouds. The final layer consists of aluminum oxide clouds. The atmosphere's total depth is 446 miles (718 km). The elements detected represent a typical part of the composition of brown dwarf atmospheres, Manjavacas said.

- The researcher and her team used computer models of brown dwarf atmospheres to determine the location of the chemical compounds in each cloud layer.

- Manjavacas' plan is to use Keck Observatory's MOSFIRE to study other atmospheres of brown dwarfs and compare them to those of gas giants. Future telescopes such as NASA's James Webb Space Telescope, an infrared observatory scheduled to launch later this year, will provide even more information about a brown dwarf's atmosphere. "JWST will give us the structure of the entire atmosphere, providing more coverage than any other telescope," Manjavacas said.

- The researcher hopes that MOSFIRE can be used in tandem with JWST to sample a wide range of brown dwarfs. The goal is a better understanding of brown dwarfs and giant planets.

• June 4, 2021: Objects such as NGC 691 are observed by Hubble using a range of filters. Each filter only allows certain wavelengths of light to reach Hubble’s WFC3. The images collected using different filters are then colored by specialized visual artists who can make informed choices about which color best corresponds to which filter. By combining the colored images from individual filters, a full-color image of the astronomical object can be recreated. In this way, we can get remarkably good insight into the nature and appearance of these objects. ⁸⁷⁾

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• May 28, 2021: WFC3 (Wide Field Camera 3) is a very versatile camera, as it can collect ultraviolet, visible, and infrared light, thereby providing a wealth of information about the objects it observes. WFC3 was installed on Hubble by astronauts in 2009, during Servicing Mission 4 (SM4). SM4 was Hubble’s final Space Shuttle servicing mission, expected to prolong Hubble’s life for at least another five years. Twelve years later, both Hubble and WFC3 remain very active and scientifically productive. ^{88) 89)}

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• May 27, 2021: The myriad spiral galaxies in our universe almost all look like fried eggs. A central bulge of aging stars is like the egg yolk, surrounded by a disk of stars that are the egg white. The galaxy in this Hubble photo looks like it is sliding off the frying pan. The central bulge is off in one corner relative to the surrounding disk of bright young blue stars. In reality, the stars on the right side of the galaxy are being pulled like taffy by the gravitational tug of a neighboring galaxy, not seen in this close-up view. Galaxies are not solid objects but tenuous agglomerations of tens of billions of stars. When two galaxies come close to each other they feel each other's gravity and are distorted, like pulling on cotton candy. It's the universe's equivalent of the 19th century children's poem about two stuffed animals – the gingham dog and calico cat — who got into a spat and ate each other. It's not so dramatic in this case. The galaxies are only getting a little chewed up because of their close proximity. ^{90) 91)}

What's Going On?

- In reality, a neighboring galaxy to the right of NGC 2276 (NGC 2300, not seen here) is gravitationally tugging on its disk of blue stars, pulling the stars on one side of the galaxy outward to distort the galaxy's normal fried-egg appearance.

- This sort of "tug of war" between galaxies that pass close enough to feel each other's gravitational pull is not uncommon in the universe. But, like snowflakes, no two close encounters look exactly alike.

- In addition, newborn and short-lived massive stars form a bright, blue arm along the upper left edge of NGC 2276. They trace out a lane of intense star formation. This may have been triggered by a prior collision with a dwarf galaxy. It could also be due to NGC 2276 plowing into the superheated gas that lies among galaxies in galaxy clusters. This would compress the gas to precipitate into stars, and trigger a firestorm of starbirth.

- The spiral galaxy lies 120 million light-years away, in the northern constellation Cepheus.

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• May 21, 2021: Hubble image of the week. ⁹²⁾

- The galaxy cluster dominates the center of this image, both visually and physically. The cluster’s huge mass has gravitationally lensed the light from background galaxies, distorting and smearing their shapes. In addition to providing astronomers with a natural magnifying glass with which to study distant galaxies, gravitational lensing has subtly framed the center of this image, producing a visually striking scene.

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• May 20, 2021: Astronomers using NASA's Hubble Space Telescope have traced the locations of five brief, powerful radio blasts to the spiral arms of five distant galaxies. ⁹³⁾

- Called fast radio bursts (FRBs), these extraordinary events generate as much energy in a thousandth of a second as the Sun does in a year. Because these transient radio pulses disappear in much less than the blink of an eye, researchers have had a hard time tracking down where they come from, much less determining what kind of object or objects is causing them. Therefore, most of the time, astronomers don't know exactly where to look.

- Locating where these blasts are coming from, and in particular, what galaxies they originate from, is important in determining what kinds of astronomical events trigger such intense flashes of energy. The new Hubble survey of eight FRBs helps researchers narrow the list of possible FRB sources.

They come from anywhere in the sky: mysterious flashes of radio energy that disappear in the blink of an eye. They're called fast radio bursts (FRBs), and astronomers have spotted roughly 1,000 of them over the past 20 years. But they come and go so quickly that researchers have only been able to trace about 15 of them to their home galaxies, all are massive and far from Earth. After that, their trail runs cold. Astronomers haven't been able to track the bursts to the neighborhoods where the radio waves were beamed. Their location could offer clues to the cause of one of the most enigmatic events in modern astronomy.

Astronomers are now using the Hubble Space Telescope as an intergalactic sleuth on the trail of this cosmic mystery. With Hubble they have tracked five FRBs to the spiral arms of five distant galaxies. But surprisingly, these powerful events don't come from the brightest regions, which blaze with the light from hefty stars. These clues help researchers rule out several possible explanations for the brilliant flares, such as the explosive deaths of the youngest, most massive stars. The researchers' results favor an increasingly popular theory, that the bursts come from magnetars, intensely magnetic remnants of collapsed dead stars.

Flash in the Night

- The first FRB was discovered in archived data recorded by the Parkes radio observatory (New South Wales, Australia) on July 24, 2001. Since then astronomers have uncovered up to 1,000 FRBs, but they have only been able to associate roughly 15 of them to particular galaxies.

- "Our results are new and exciting. This is the first high-resolution view of a population of FRBs, and Hubble reveals that five of them are localized near or on a galaxy's spiral arms," said Alexandra Mannings of the University of California, Santa Cruz, the study's lead author. "Most of the galaxies are massive, relatively young, and still forming stars. The imaging allows us to get a better idea of the overall host-galaxy properties, such as its mass and star-formation rate, as well as probe what's happening right at the FRB position because Hubble has such great resolution."

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- In the Hubble study, astronomers not only pinned all of them to host galaxies, but they also identified the kinds of locations they originated from. Hubble observed one of the FRB locations in 2017 and the other seven in 2019 and 2020.

- "We don't know what causes FRBs, so it's really important to use context when we have it," said team member Wen-fai Fong of Northwestern University in Evanston, Illinois. "This technique has worked very well for identifying the progenitors of other types of transients, such as supernovae and gamma-ray bursts. Hubble played a big role in those studies, too."

- The galaxies in the Hubble study existed billions of years ago. Astronomers, therefore, are seeing the galaxies as they appeared when the universe was about half its current age.

- Many of them are as massive as our Milky Way. The observations were made in ultraviolet and near-infrared light with Hubble's Wide Field Camera 3.

- Ultraviolet light traces the glow of young stars strung along a spiral galaxy's winding arms. The researchers used the near-infrared images to calculate the galaxies' mass and find where older populations of stars reside.

Location, Location, Location

- The images display a diversity of spiral-arm structure, from tightly wound to more diffuse, revealing how the stars are distributed along these prominent features. A galaxy's spiral arms trace the distribution of young, massive stars. However, the Hubble images reveal that the FRBs found near the spiral arms do not come from the very brightest regions, which blaze with the light from hefty stars. The images help support a picture that the FRBs likely do not originate from the youngest, most massive stars.

- These clues helped the researchers rule out some of the possible triggers of types of these brilliant flares, including the explosive deaths of the youngest, most massive stars, which generate gamma-ray bursts and some types of supernovae. Another unlikely source is the merger of neutron stars, the crushed cores of stars that end their lives in supernova explosions. These mergers take billions of years to occur and are usually found far from the spiral arms of older galaxies that are no longer forming stars.

Magnetic Monsters

- The team's Hubble results, however, are consistent with the leading model that FRBs originate from young magnetar outbursts. Magnetars are a type of neutron star with powerful magnetic fields. They’re called the strongest magnets in the universe, possessing a magnetic field that is 10 trillion times more powerful than a refrigerator door magnet. Astronomers last year linked observations of an FRB spotted in our Milky Way galaxy with a region where a known magnetar resides.

- "Owing to their strong magnetic fields, magnetars are quite unpredictable," Fong explained. "In this case, the FRBs are thought to come from flares from a young magnetar. Massive stars go through stellar evolution and becomes neutron stars, some of which can be strongly magnetized, leading to flares and magnetic processes on their surfaces, which can emit radio light. Our study fits in with that picture and rules out either very young or very old progenitors for FRBs."

- The observations also helped the researchers strengthen the association of FRBs with massive, star-forming galaxies. Previous ground-based observations of some possible FRB host galaxies did not as clearly detect underlying structure, such as spiral arms, in many of them. Astronomers, therefore, could not rule out the possibility that FRBs originate from a dwarf galaxy hiding underneath a massive one. In the new Hubble study, careful image processing and analysis of the images allowed researchers to rule out underlying dwarf galaxies, according to co-author Sunil Simha of the University of California, Santa Cruz.

- Although the Hubble results are exciting, the researchers say they need more observations to develop a more definitive picture of these enigmatic flashes and better pinpoint their source. "This is such a new and exciting field," Fong said. "Finding these localized events is a major piece to the puzzle, and a very unique puzzle piece compared to what's been done before. This is a unique contribution of Hubble."

- The team's results will appear in an upcoming issue of The Astrophysical Journal.

• May 14, 2021: The language that astronomers use changes as we become better acquainted with the Universe, and astronomical history is littered with now-obsolete phrases to describe objects in the night sky, such as “spiral nebulae” for spiral galaxies or “inferior planets” for Mercury and Venus. ⁹⁴⁾

- While modern astronomical terminology has become steadily more precise, the nature of objects in astronomical exposures can still occasionally puzzle astronomers. For example, if you look very closely, you can see a faint bluish streak across the center of this image to the bottom right of the blue region. This could be an asteroid, but seems to be travelling far too quickly for such an object — making this one of the remaining mysteries of the night sky.

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• May 7, 2021: Looking at this cluster of hundreds of galaxies, it is amazing to recall that until less than 100 years ago, many astronomers believed that the Milky Way was the only galaxy in the Universe. The possibility of other galaxies had been debated previously, but the matter was not truly settled until Edwin Hubble confirmed that the Great Andromeda Nebula was in fact far too distant to be part of the Milky Way. The Great Andromeda Nebula became the Andromeda Galaxy, and astronomers recognized that our Universe was much, much bigger than humanity had imagined. We can only imagine how Edwin Hubble — after whom the Hubble Space Telescope was named — would have felt if he’d seen this spectacular image of Abell 3827. ⁹⁵⁾

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• April 30, 2021: The Necklace Nebula — which also goes by the less glamorous name of PN G054.2-03.4 — was produced by a pair of tightly orbiting Sun-like stars. Roughly 10,000 years ago, one of the aging stars expanded and engulfed its smaller companion, creating something astronomers call a “common envelope”. The smaller star continued to orbit inside its larger companion, increasing the bloated giant’s rotation rate until large parts of it spun outwards into space. This escaping ring of debris formed the Necklace Nebula, with particularly dense clumps of gas forming the bright “diamonds” around the ring. ⁹⁶⁾

- The pair of stars which created the Necklace Nebula remain so close together — separated by only a few million kilometers — that they appear as a single bright dot in the centre of this image. Despite their close encounter the stars are still furiously whirling around each other, completing an orbit in just over a day.

- The Necklace Nebula was featured in a previously released Hubble image, but now this new image has been created by applying advanced processing techniques, making for a new and improved view of this intriguing object. The composite image includes several exposures from Hubble’s Wide Field Camera 3.

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• April 29, 2021: NASA’s Hubble Space Telescope is giving astronomers a rare look at a Jupiter-sized, still-forming planet that is feeding off material surrounding a young star. ⁹⁷⁾

- “We just don’t know very much about how giant planets grow,” said Brendan Bowler of the University of Texas at Austin. “This planetary system gives us the first opportunity to witness material falling onto a planet. Our results open up a new area for this research.”

- Though over 4,000 exoplanets have been cataloged so far, only about 15 have been directly imaged to date by telescopes. And the planets are so far away and small, they are simply dots in the best photos. The team’s fresh technique for using Hubble to directly image this planet paves a new route for further exoplanet research, especially during a planet’s formative years.

- This huge exoplanet, designated PDS 70b, orbits the orange dwarf star PDS 70, which is already known to have two actively forming planets inside a huge disk of dust and gas encircling the star. The system is located 370 light-years from Earth in the constellation Centaurus.

- “This system is so exciting because we can witness the formation of a planet,” said Yifan Zhou, also of the University of Texas at Austin. “This is the youngest bona fide planet Hubble has ever directly imaged.” At a youthful five million years, the planet is still gathering material and building up mass.

- Hubble’s ultraviolet light (UV) sensitivity offers a unique look at radiation from extremely hot gas falling onto the planet. “Hubble’s observations allowed us to estimate how fast the planet is gaining mass,” added Zhou.

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- The UV observations, which add to the body of research about this planet, allowed the team to directly measure the planet’s mass growth rate for the first time. The remote world has already bulked up to five times the mass of Jupiter over a period of about five million years. The present measured accretion rate has dwindled to the point where, if the rate remained steady for another million years, the planet would only increase by approximately an additional 1/100th of a Jupiter-mass.

- Zhou and Bowler emphasize that these observations are a single snapshot in time – more data are required to determine if the rate at which the planet is adding mass is increasing or decreasing. “Our measurements suggest that the planet is in the tail end of its formation process.”

- The youthful PDS 70 system is filled with a primordial gas-and-dust disk that provides fuel to feed the growth of planets throughout the entire system. The planet PDS 70b is encircled by its own gas-and-dust disk that’s siphoning material from the vastly larger circumstellar disk. The researchers hypothesize that magnetic field lines extend from its circumplanetary disk down to the exoplanet’s atmosphere and are funneling material onto the planet’s surface.

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- “If this material follows columns from the disk onto the planet, it would cause local hot spots,” Zhou explained. “These hot spots could be at least 10 times hotter than the temperature of the planet.” These hot patches were found to glow fiercely in UV light.

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- These observations offer insights into how gas giant planets formed around our Sun 4.6 billion years ago. Jupiter may have bulked up on a surrounding disk of infalling material. Its major moons would have also formed from leftovers in that disk.

- A challenge to the team was overcoming the glare of the parent star. PDS 70b orbits at approximately the same distance as Uranus does from the Sun, but its star is more than 3,000 times brighter than the planet at UV wavelengths. As Zhou processed the images, he very carefully removed the star’s glare to leave behind only light emitted by the planet. In doing so, he improved the limit of how close a planet can be to its star in Hubble observations by a factor of five.

- “Thirty-one years after launch, we’re still finding new ways to use Hubble,” Bowler added. “Yifan’s observing strategy and post-processing technique will open new windows into studying similar systems, or even the same system, repeatedly with Hubble. With future observations, we could potentially discover when the majority of the gas and dust falls onto their planets and if it does so at a constant rate.”

- The researchers' results were published in April 2021 in The Astronomical Journal. ⁹⁸⁾

• April 23, 2021: The giant star featured in this latest Hubble Space Telescope anniversary image is waging a tug-of-war between gravity and radiation to avoid self-destruction. The star, called AG Carinae, is surrounded by an expanding shell of gas and dust — a nebula — that is shaped by the powerful winds of the star. The nebula is about five light-years wide, which equals the distance from here to our nearest star, Alpha Centauri. ⁹⁹⁾

- The huge structure was created from one or more giant eruptions several thousand years ago. The star’s outer layers were blown into space, the expelled material amounting to roughly 10 times the mass of our Sun. These outbursts are typical in the life of a rare breed of star called a Luminous Blue Variable (LBV), a brief unstable phase in the short life of an ultra-bright, glamorous star that lives fast and dies young. These stars are among the most massive and brightest stars known. They live for only a few million years, compared to the roughly 10-billion-year lifetime of our own Sun. AG Carinae is a few million years old and resides 20,000 light-years away inside our Milky Way galaxy. The star’s expected lifetime is between 5 million and 6 million years.

- LBVs have a dual personality. They appear to spend years in semi-quiescent bliss and then they erupt in a petulant outburst, during which their luminosity increases — sometimes by several orders of magnitude. These behemoths are stars in the extreme, far different from normal stars like our Sun. In fact AG Carinae is estimated to be up to 70 times more massive than our Sun and shines with the blinding brilliance of 1 million suns.

- Major outbursts such as the one that produced the nebula featured in this image occur a few times during a LBV’s lifetime. A LBV star only casts off material when it is in danger of self-destruction. Because of their massive forms and super-hot temperatures, luminous blue variable stars like AG Carinae are in a constant battle to maintain stability. It’s an arm-wrestling contest between radiation pressure from within the star pushing outward and gravity pressing inward. This arm-wrestling match results in the star’s expanding and contracting. The outward pressure occasionally wins the battle, and the star expands to such an immense size that it blows off its outer layers, like a volcano erupting. But this outburst only happens when the star is on the verge of coming apart. After the star ejects the material, it contracts to its normal (large) size, settles back down, and becomes stable again.

- LBV stars are rare: fewer than 50 are known among the galaxies in our local group of neighboring galaxies. These stars spend tens of thousands of years in this phase, a blink of an eye in cosmic time. Some are expected to end their lives in titanic supernova blasts, which enrich the Universe with the heavier elements beyond iron.

- Like many other LBVs, AG Carinae remains unstable. It has experienced lesser outbursts that have not been as powerful as the one that created the present nebula. Although AG Carinae is semi-quiescent now, its searing radiation and powerful stellar wind (streams of charged particles) have been shaping the ancient nebula, sculpting intricate structures as outflowing gas slams into the slower-moving outer nebula. The wind is travelling at up to 1 million kilometers per hour, about 10 times faster than the expanding nebula. Over time, the hot wind catches up with the cooler expelled material, ploughs into it, and pushes it farther away from the star. This “snowplough” effect has cleared a cavity around the star.

- The red material is glowing hydrogen gas laced with nitrogen gas. The diffuse red material at upper left pinpoints where the wind has broken through a tenuous region of material and swept it into space. The most prominent features, highlighted in blue, are filamentary structures shaped like tadpoles and lopsided bubbles. These structures are dust clumps illuminated by the star’s light. The tadpole-shaped features, most prominent at left and bottom, are denser dust clumps that have been sculpted by the stellar wind. Hubble’s sharp vision reveals these delicate-looking structures in great detail.

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• April 23, 2021: This image shows a close-up portrait of the magnificent spiral galaxy NGC 4603, which lies over 100 million light-years away in the constellation of Centaurus (The Centaur). Bright bands of blue young stars make up the arms of this galaxy, which wind lazily outwards from the luminous core. The intricate red-brown filaments threading through the spiral arms are known as dust lanes, and consist of dense clouds of dust which obscure the diffuse starlight from the galaxy. ¹⁰⁰⁾

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• April 16, 2021: This extraordinary image from the NASA/ESA Hubble Space Telescope of the galaxy cluster Abell 2813 (also known as ACO 2813) has an almost delicate beauty, which also illustrates the remarkable physics at work within it. The image spectacularly demonstrates the concept of gravitational lensing. ¹⁰¹⁾

- In amongst the tiny dots, spirals and ovals that are the galaxies that belong to the cluster, there are several distinct crescent shapes. These curved arcs of light are strong examples of a phenomenon known as gravitational lensing. The image was compiled using observations taken with the Hubble Space Telescope’s Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3).

- This very visual evidence that mass causes light to bend has been famously used as a proof of one of the most famous scientific theories: Einstein’s theory of general relativity.

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• April 9, 2021: M61 appears almost face-on, making it a popular subject for astronomical images, even though the galaxy lies more than 52 million light-years from Earth. This particular astronomical image incorporates data from not only Hubble, but also the FORS camera at the European Southern Observatory’s VLT (Very Large Telescope), together revealing M61 in unprecedented detail. This striking image is one of many examples of telescope teamwork — astronomers frequently combine data from ground-based and space-based telescopes to learn more about the Universe. ¹⁰²⁾

- Though the gleaming spiral of this galaxy makes for a spectacular sight, one of the most interesting features of M61 lurks unseen at the center of this image. As well as widespread pockets of star formation, M61 hosts a supermassive black hole more than 5 million times as massive as the Sun.

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• April 8, 2021: Forty years ago in 1981, the first space shuttle launched, the Voyager 2 space probe encountered Saturn, and in Baltimore, Maryland, the Space Telescope Science Institute (STScI) was founded. In that year, NASA selected a proposal by the Association of Universities for Research in Astronomy to establish STScI on the Johns Hopkins University Homewood campus. ¹⁰³⁾

- STScI would serve as the science operations center for NASA’s Hubble Space Telescope (then known as the Large Space Telescope). Nine years later in 1990 Hubble launched, and for the past 31 years STScI has provided Hubble data to the astronomical community, and publicized Hubble's revolutionary discoveries and inspirational images to the world. As it celebrates its 40th anniversary STScI is looking forward to the future, including the October 2021 launch of NASA's next flagship mission, the James Webb Space Telescope, as well as other endeavors.

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- “For the past 40 years, STScI has partnered with NASA and the astronomical community to advance scientific discovery,” said STScI director Kenneth Sembach. “Much has changed in the field of astronomy over that time as Hubble has revolutionized our understanding of astrophysical phenomena. We’ve grown and changed as well to meet the needs of the astronomical community, create new avenues for exploration, and engage the public in the wonders of the universe. I can hardly wait to see what the future holds as we look ahead to many more years of Hubble operations, the launch of Webb, and the upcoming Nancy Grace Roman Space Telescope.”

- STScI is best known for its role in the Hubble mission. As science operations center, the institute enables scientists around the world to make maximum use of Hubble’s unique capabilities to conduct cutting-edge science. STScI personnel strive not only to maintain but also continuously improve Hubble operations, ensuring that the telescope will provide quality data for years into the future. Members of the institute's scientific staff also conduct their own research, producing hundreds of peer-reviewed articles each year, and help lead initiatives guiding the future of astrophysics research.

- "In 1976, a committee of the National Academy of Sciences proposed a radical idea that STScI should run Hubble. Working in partnership with the scientific community and NASA, the new organization’s sole job was to advocate for the science," commented Matt Mountain, President of the Association of Universities for Research in Astronomy (AURA), which runs STScI. "Today, no one doubts the value of that prescient decision by NASA to create STScI to run the science program for the Hubble Space Telescope. Driven by the science of the astronomical community, Hubble has become the scientific ‘gold standard’ and a global brand, precisely because STScI has retained the scientific independence and integrity entrusted to AURA and its partner Johns Hopkins University."

- In planning for Hubble’s launch and science operations, STScI was instrumental in making a transformative change to how astronomy is conducted. Unlike previous space missions, Hubble was opened to observers around the world. Accordingly, the institute fostered the growth of astronomer teams, which provided opportunities to more researchers. Under the guidance of its first director, Riccardo Giacconi, STScI made a pioneering effort by taking a novel approach to opening up astronomy to general users. The world’s first digitized sky catalog was created for aiming the telescope, and complex automation was developed for planning, scheduling, and archiving observations. This became the guide for future NASA space astrophysics missions.

- In 2001 STScI was selected to oversee the science and mission operations of NASA’s James Webb Space Telescope, planned to launch later this year. Webb will be the largest, most powerful and complex space telescope ever built and launched into space. It will complement and extend the discoveries of Hubble, with infrared detectors that will allow it to observe the first galaxies, as well as look inside dust clouds where stars and planetary systems are forming today.

- STScI will also play a key role in the science operations for NASA’s Nancy Grace Roman Space Telescope, which is planned to launch in the mid-2020s. The Roman Space Telescope will provide a panoramic field of view that is 100 times greater than Hubble's, leading to the first wide-field maps of the universe at space-based resolution.

- A key element of the institute's work is the Barbara A. Mikulski Archive for Space Telescopes (MAST). Established at the outset of the Hubble mission in 1990, it was expanded in 1997 to include data from other ultraviolet and optical space astronomy missions. Today, MAST provides astronomers access to data from more than 20 space missions and ground-based observatories.

- STScI also plays a vital role in the development of technologies for future observatories. The institute’s Russell B. Makidon Optics Laboratory, created in 2013, conducts research focused on enabling direct images of exoplanets using large segmented telescopes in space, including high-contrast coronagraphy, optical mirror alignments, applications of deformable mirrors for wavefront sensing and control, and digital micromirror devices for multi-object spectroscopy.

- In addition to its scientific leadership, STScI strives to be a leader in diversity, equity and inclusion (DE&I). The Institute pioneered the use of a dual-anonymous review process, in which scientists reviewing requests for Hubble observing time do not know the names or locations of the proposers. The process proved so successful in achieving gender parity that NASA is mandating it for all its astrophysics missions in the future. The review process is only one element of a broad commitment to DE&I as STScI strives to model the workplace of the future, while also broadening participation in the exploration of the universe.

- STScI is a leader in the field of astronomy communications and outreach. The institute’s public outreach team leverages unique access to scientific discoveries, data, and mission experts to produce a broad variety of materials ranging from awe-inspiring images and press releases to videos and in-depth articles. Additional products and learning experiences, grounded in evidence-based learning strategies and externally evaluated, are used by museums, libraries, and other organizations nationwide, as well as the general public. STScI’s outreach team maintains a web presence for core science missions, provides support for the Space Astronomy Summer Program (SASP) for undergraduates, and leverages new technologies to create virtual reality (VR) and other interactive experiences. STScI also leads the multi-institutional NASA’s Universe of Learning project.

• April 6, 2021: NASA's Hubble Space Telescope is "seeing double." Peering back 10 billion years into the universe's past, Hubble astronomers found a pair of quasars that are so close to each other they look like a single object in ground-based telescopic photos, but not in Hubble’s crisp view. ¹⁰⁴⁾

- The researchers believe the quasars are very close to each other because they reside in the cores of two merging galaxies. The team went on to win the "daily double" by finding yet another quasar pair in another colliding galaxy duo.

- A quasar is a brilliant beacon of intense light from the center of a distant galaxy that can outshine the entire galaxy. It is powered by a supermassive black hole voraciously feeding on inflating matter, unleashing a torrent of radiation.

- "We estimate that in the distant universe, for every 1,000 quasars, there is one double quasar. So finding these double quasars is like finding a needle in a haystack," said lead researcher Yue Shen of the University of Illinois at Urbana-Champaign.

- The discovery of these four quasars offers a new way to probe collisions among galaxies and the merging of supermassive black holes in the early universe, researchers say.

- Quasars are scattered all across the sky and were most abundant 10 billion years ago. There were a lot of galaxy mergers back then feeding the black holes. Therefore, astronomers theorize there should have been many dual quasars during that time.

- "This truly is the first sample of dual quasars at the peak epoch of galaxy formation with which we can use to probe ideas about how supermassive black holes come together to eventually form a binary," said research team member Nadia Zakamska of Johns Hopkins University in Baltimore, Maryland.

- The team's results appeared in the April 1 online issue of the journal Nature Astronomy. ¹⁰⁵⁾

- Shen and Zakamska are members of a team that is using Hubble, the European Space Agency's Gaia space observatory, and the Sloan Digital Sky Survey, as well as several ground-based telescopes, to compile a robust census of quasar pairs in the early universe.

- The observations are important because a quasar's role in galactic encounters plays a critical part in galaxy formation, the researchers say. As two close galaxies begin to distort each other gravitationally, their interaction funnels material into their respective black holes, igniting their quasars.

- Over time, radiation from these high-intensity "light bulbs" launch powerful galactic winds, which sweep out most of the gas from the merging galaxies. Deprived of gas, star formation ceases, and the galaxies evolve into elliptical galaxies.

- "Quasars make a profound impact on galaxy formation in the universe," Zakamska said. "Finding dual quasars at this early epoch is important because we can now test our long-standing ideas of how black holes and their host galaxies evolve together."

- Astronomers have discovered more than 100 double quasars in merging galaxies so far. However, none of them is as old as the two double quasars in this study.

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- The Hubble images show that quasars within each pair are only about 10,000 light-years apart. By comparison, our Sun is 26,000 light-years from the supermassive black hole in the center of our galaxy.

- The pairs of host galaxies will eventually merge, and then the quasars also will coalesce, resulting in an even more massive, single solitary black hole.

- Finding them wasn't easy. Hubble is the only telescope with vision sharp enough to peer back to the early universe and distinguish two close quasars that are so far away from Earth. However, Hubble's sharp resolution alone isn't good enough to find these dual light beacons.

- Astronomers first needed to figure out where to point Hubble to study them. The challenge is that the sky is blanketed with a tapestry of ancient quasars that flared to life 10 billion years ago, only a tiny fraction of which are dual. It took an imaginative and innovative technique that required the help of the European Space Agency's Gaia satellite and the ground-based Sloan Digital Sky Survey to compile a group of potential candidates for Hubble to observe.

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- Located at Apache Point Observatory in New Mexico, the Sloan telescope produces three-dimensional maps of objects throughout the sky. The team poured through the Sloan survey to identify the quasars to study more closely.

- The researchers then enlisted the Gaia observatory to help pinpoint potential double-quasar candidates. Gaia measures the positions, distances, and motions of nearby celestial objects very precisely. But the team devised a new, innovative application for Gaia that could be used for exploring the distant universe. They used the observatory's database to search for quasars that mimic the apparent motion of nearby stars. The quasars appear as single objects in the Gaia data. However, Gaia can pick up a subtle, unexpected "jiggle" in the apparent position of some of the quasars it observes.

- The quasars aren't moving through space in any measurable way, but instead their jiggle could be evidence of random fluctuations of light as each member of the quasar pair varies in brightness. Quasars flicker in brightness on timescales of days to months, depending on their black hole's feeding schedule.

- This alternating brightness between the quasar pair is similar to seeing a railroad crossing signal from a distance. As the lights on both sides of the stationary signal alternately flash, the sign gives the illusion of "jiggling."

- When the first four targets were observed with Hubble, its crisp vision revealed that two of the targets are two close pairs of quasars. The researchers said it was a "light bulb moment" that verified their plan of using Sloan, Gaia, and Hubble to hunt for the ancient, elusive double powerhouses.

- Team member Xin Liu of the University of Illinois at Urbana-Champaign called the Hubble confirmation a "happy surprise." She has long hunted for double quasars closer to Earth using different techniques with ground-based telescopes. "The new technique can not only discover dual quasars much further away, but it is much more efficient than the methods we’ve used before," she said.

- Their Nature Astronomy article is a "proof of concept that really demonstrates that our targeted search for dual quasars is very efficient," said team member Hsiang-Chih Hwang, a graduate student at Johns Hopkins University and the principal investigator of the Hubble program. "It opens a new direction where we can accumulate a lot more interesting systems to follow up, which astronomers weren’t able to do with previous techniques or datasets."

- The team also obtained follow-up observations with the National Science Foundation NOIRLab's Gemini telescopes. "Gemini’s spatially-resolved spectroscopy can unambiguously reject interlopers due to chance superpositions from unassociated star-quasar systems, where the foreground star is coincidentally aligned with the background quasar," said team member Yu-Ching Chen, a graduate student at the University of Illinois at Urbana-Champaign.

- Although the team is convinced of their result, they say there is a slight chance that the Hubble snapshots captured double images of the same quasar, an illusion caused by gravitational lensing. This phenomenon occurs when the gravity of a massive foreground galaxy splits and amplifies the light from the background quasar into two mirror images. However, the researchers think this scenario is highly unlikely because Hubble did not detect any foreground galaxies near the two quasar pairs.

- Galactic mergers were more plentiful billions of years ago, but a few are still happening today. One example is NGC 6240, a nearby system of merging galaxies that has two and possibly even three supermassive black holes. An even closer galactic merger will occur in a few billion years when our Milky Way galaxy collides with neighboring Andromeda galaxy. The galactic tussle would likely feed the supermassive black holes in the core of each galaxy, igniting them as quasars.

- Future telescopes may offer more insight into these merging systems. NASA's James Webb Space Telescope, an infrared observatory scheduled to launch later this year, will probe the quasars' host galaxies. Webb will show the signatures of galactic mergers, such as the distribution of starlight and the long streamers of gas pulled from the interacting galaxies.

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

• April 2, 2021: The Veil Nebula lies around 2,100 light-years from Earth in the constellation of Cygnus (the Swan), making it a relatively close neighbor in astronomical terms. Only a small portion of the nebula was captured in this image. ¹⁰⁶⁾

- The Veil Nebula is the visible portion of the nearby Cygnus Loop, a supernova remnant formed roughly 10,000 years ago by the death of a massive star. That star – which was 20 times the mass of the Sun – lived fast and died young, ending its life in a cataclysmic release of energy. Despite this stellar violence, the shockwaves and debris from the supernova sculpted the Veil Nebula’s delicate tracery of ionized gas – creating a scene of surprising astronomical beauty.

- To create this colorful image, observations were taken by Hubble's Wide Field Camera 3 instrument using five different filters. The new post-processing methods have further enhanced details of emissions from doubly ionized oxygen (seen here in blues), ionized hydrogen, and ionized nitrogen (seen here in reds).

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• March 31, 2021: The NHFP (NASA Hubble Fellowship Program) is one of the highlights of NASA's pursuit of excellence in astrophysics. The program enables outstanding postdoctoral scientists to pursue independent research in any area of NASA Astrophysics, using theory, observation, experimentation, or instrument development. Over 400 applicants vied for the fellowships. Each fellowship provides the awardee up to three years of support. ¹⁰⁷⁾

- NASA has selected 24 new Fellows for its prestigious NASA Hubble Fellowship Program (NHFP). The NHFP is one of the highlights of NASA's pursuit of excellence in astrophysics. The program enables outstanding postdoctoral scientists to pursue independent research in any area of NASA Astrophysics, using theory, observation, experimentation, or instrument development. Over 400 applicants vied for the fellowships. Each fellowship provides the awardee up to three years of support.

- Once selected, Fellows are named to one of three sub-categories corresponding to three broad scientific questions NASA seeks to answer about the universe:

a) How does the universe work? – Einstein Fellows

b) How did we get here? – Hubble Fellows

c) Are we alone? – Sagan Fellows

- “The annual selection of NASA Hubble Fellows always fills me with hope,” said Paul Hertz, Director of Astrophysics at NASA Headquarters in Washington. “These outstanding young scientists are the future of astrophysics, and their impact on our understanding of the cosmos will be felt for decades to come.”

- The newly selected NHFP Fellows will begin their programs in the fall of 2021 at a university or research center of their choosing in the United States. The list below provides the names of the 2021 awardees, their fellowship host institutions, and their proposed research topics.

An important part of the NHFP are the Symposia, which allow Fellows the opportunity to present results of their research, and to meet each other and the scientific and administrative staff who manage the program. A lively and very successful virtual symposium was held in the fall of 2020, and organizers are waiting to make a decision on whether the 2021 symposium will be virtual or in-person.

The Space Telescope Science Institute administers the NHFP on behalf of NASA, in collaboration with the Chandra X-ray Center at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and the NASA Exoplanet Science Institute at Caltech/IPAC in Pasadena, California.

How does the universe work? – Einstein Fellows:

• Kishalay De, Massachusetts Institute of Technology, Unveiling the Local Stellar Graveyard

• Sara Issaoun, Smithsonian Astrophysical Observatory, Connecting Black Hole Shadows to Multi-Wavelength Accretion and Outflow Physics

• Mikhail Ivanov, Institute for Advanced Study, Fundamental Cosmology from Galaxy Clustering

• Lea Marcotulli, Yale University, Unveiling the Hidden Connection Between Supermassive Black Holes and Jet Triggering Mechanisms

• Ariadna Murguia-Berthier, Northwestern University, The Study of Hyper-Accreting Black Holes and the Origin of Gold in the Universe

• Antonella Palmese, University of California, Berkeley, Gravitational Wave Cosmology Through the Eyes of Dark Energy Experiments

• Anowar Shajib, University of Chicago, Internal Structure of Massive Elliptical Galaxies: The Missing Piece at the Intersection of Astrophysics and Cosmology

• Alexandra Tetarenko, Texas Tech University, Unraveling the Complex Nature of Black Holes and How They Power Explosive Outflows with Time-Domain Observations

How did we get here? – Hubble Fellows:

• Kirk Barrow, Harvard University, High-Cadence Radiative Transfer Modeling on Galactic Scales

• Pradip Gatkine, California Institute of Technology, Probing the CGM-Galaxy Connection Using Multi-Object Spectroscopy and Astrophotonics

• Michael Grudic, Carnegie Observatories, Star Formation Physics from Cosmos to Cores

• Thales Gutcke, Princeton University, Linking ISM Physics and Galaxy Formation

• Erika Holmbeck, Carnegie Observatories, The R-Process Refinery: Distilling Stellar Signatures to Characterize the Astrophysical Production Site of the Heavy Elements

• Sinclaire Manning, University of Massachusetts, Amherst, Revealing Optically Invisible Dusty Star-Forming Galaxies in the Early Universe

• Viraj Pandya, Columbia University, Towards a Fully Predictive Standard Model of Galaxy Formation

• Melinda Soares, University of Wisconsin, Madison, Devoured Worlds—The Signatures of Substellar Ingestion

• Catherine Zucker, Space Telescope Science Institute, Knitting Together the Milky Way: Tracing Gas Flows in the Era of Big Data

Are we alone? – Sagan Fellows:

• Marta Bryan, University of California, Berkeley, The Celestial Movers and Shakers: Gas Giant Planets Provide Key Insights into the Formation Histories of Exoplanet Systems

• Megan Mansfield, University of Arizona, Steward Observatory, Atmospheres as Windows to the Diversity of Extrasolar Planets

• Diana Powell, Smithsonian Astrophysical Observatory, Origins: Relating Protoplanetary Disks to Planetary Atmospheres

• Raluca Rufu, Southwest Research Institute, A New Paradigm for Compact Exoplanetary System Origin

• Jake Turner, Cornell University, Studying Exoplanetary Magnetic Fields Using Radio and High-Resolution Spectropolarimetry Observations

• Luis Welbanks, Arizona State University, High-Definition Exo-Atmospheric Characterization with Transit Spectroscopy

• Jon Zink, California Institute of Technology, Expanding Exoplanet Demographics to Identify Key Components of Planet Formation

• March 26, 2021: This week’s Hubble/ESA Picture of the Week features NGC 7678 — a galaxy located approximately 164 million light-years away in the constellation of Pegasus (The Winged Horse). With a diameter of around 115,000 light-years, this bright spiral galaxy is a similar size to our own galaxy (the Milky Way), and was discovered in 1784 by the German-British astronomer William Herschel. ¹⁰⁸⁾

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This week’s Hubble/ESA Picture of the Week features NGC 7678 — a galaxy located approximately 164 million light-years away in the constellation of Pegasus (The Winged Horse). With a diameter of around 115 000 light-years, this bright spiral galaxy is a similar size to our own galaxy (the Milky Way), and was discovered in 1784 by the German-British astronomer William Herschel

• March 19, 2021: Located around 5000 light-years away in the constellation of Cygnus (The Swan), Abell 78 is an unusual type of planetary nebula. ¹⁰⁹⁾

- After exhausting the nuclear fuel in their cores, stars with a mass of around 0.8 to 8 times the mass of our Sun collapse to form dense and hot white dwarf stars. As this process occurs, the dying star will throw off its outer layers of material, forming an elaborate cloud of gas and dust known as a planetary nebula. This phenomenon is not uncommon, and planetary nebulae are a popular focus for astrophotographers because of their often beautiful and complex shapes. However, a few like Abell 78 are the result of a so-called “born again” star.

- Although the core of the star has stopped burning hydrogen and helium, a thermonuclear runaway at its surface ejects material at high speeds. This ejecta shocks and sweeps up the material of the old nebula, producing the filaments and irregular shell around the central star seen in this Picture of the Week, which features data from Hubble’s Wide Field Camera 3 and Pan-STARSS.

• March 18, 2021: NASA's Hubble Space Telescope is giving astronomers a view of changes in Saturn's vast and turbulent atmosphere as the planet's northern hemisphere summer transitions to fall as shown in this series of images taken in 2018, 2019, and 2020 (left to right). ¹¹⁰⁾

- "These small year-to-year changes in Saturn's color bands are fascinating," said Amy Simon, planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "As Saturn moves towards fall in its northern hemisphere, we see the polar and equatorial regions changing, but we are also seeing that the atmosphere varies on much shorter timescales." Simon is lead author of a paper on these observations published March 11 in Planetary Science Journal.

- The Hubble data show that from 2018 to 2020 the equator got 5 to 10 percent brighter, and the winds changed slightly. In 2018, winds measured near the equator were about 1,000 miles per hour (roughly 1,600 kilometers per hour), higher than those measured by NASA's Cassini spacecraft during 2004-2009, when they were about 800 miles per hour (roughly 1,300 kilometers per hour). In 2019 and 2020 they decreased back to the Cassini speeds. Saturn's winds also vary with altitude, so the change in measured speeds could possibly mean the clouds in 2018 were around 37 miles (~ 60 km) deeper than those measured during the Cassini mission. Further observations are needed to tell which is happening.

- Saturn is the sixth planet from our Sun and orbits at a distance of about 886 million miles (1.4 billion kilometers) from the Sun. It takes around 29 Earth years to orbit the Sun, making each season on Saturn more than seven Earth years long. Earth is tilted with respect to the Sun, which alters the amount of sunlight each hemisphere receives as our planet moves in its orbit. This variation in solar energy is what drives our seasonal changes. Saturn is tilted also, so as the seasons change on that distant world, the change in sunlight could be causing some of the observed atmospheric changes.

- Like Jupiter, the solar system's largest planet, Saturn is a "gas giant" made mostly of hydrogen and helium, although there may be a rocky core deep inside. Enormous storms, some almost as large as Earth, occasionally erupt from deep within the atmosphere. Since many of the planets discovered around other stars are gas giants as well, astronomers are eager to learn more about how gas giant atmospheres work.

- Saturn is the second largest planet in the solar system, over 9 times wider than Earth, with more than 50 moons and a spectacular system of rings made primarily of water ice. Two of these moons, Titan and Enceladus, appear to have oceans beneath their icy crusts that might support life. Titan, Saturn's largest moon, is the only moon in our solar system with a thick atmosphere, including clouds that rain liquid methane and other hydrocarbons on to the surface, forming rivers, lakes, and seas. This mix of chemicals is thought to be similar to that on Earth billions of years ago when life first emerged. NASA's Dragonfly mission will fly over the surface of Titan, touching down in various locations to search for the primal building blocks of life.

- The Saturn observations are part of Hubble's Outer Planets Atmospheres Legacy (OPAL) program. "The OPAL program allows us to observe each of the outer planets with Hubble every year, enabling new discoveries and watching how each planet is changing over time," said Simon, principal investigator for OPAL.

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

• March 18, 2021: Though our galaxy is an immense city of at least 200 billion stars, the details of how they formed remain largely cloaked in mystery. ¹¹¹⁾

- Scientists know that stars form from the collapse of huge hydrogen clouds that are squeezed under gravity to the point where nuclear fusion ignites. But only about 30 percent of the cloud's initial mass winds up as a newborn star. Where does the rest of the hydrogen go during such a terribly inefficient process?

- It has been assumed that a newly forming star blows off a lot of hot gas through lightsaber-shaped outflowing jets and hurricane-like winds launched from the encircling disk by powerful magnetic fields. These fireworks should squelch further growth of the central star. But a new, comprehensive Hubble survey shows that this most common explanation doesn't seem to work, leaving astronomers puzzled.

- Researchers used data previously collected from NASA's Hubble and Spitzer space telescopes and the European Space Agency's Herschel Space Telescope to analyze 304 developing stars, called protostars, in the Orion Complex, the nearest major star-forming region to Earth. (Spitzer and Herschel are no longer operational).

- In this largest-ever survey of nascent stars to date, researchers are finding that gas-clearing by a star's outflow may not be as important in determining its final mass as conventional theories suggest. The researchers' goal was to determine whether stellar outflows halt the infall of gas onto a star and stop it from growing.

- Instead, they found that the cavities in the surrounding gas cloud sculpted by a forming star's outflow did not grow regularly as they matured, as theories propose.

- "In one stellar formation model, if you start out with a small cavity, as the protostar rapidly becomes more evolved, its outflow creates an ever-larger cavity until the surrounding gas is eventually blown away, leaving an isolated star," explained lead researcher Nolan Habel of the University of Toledo in Ohio, USA.

- "Our observations indicate there is no progressive growth that we can find, so the cavities are not growing until they push out all of the mass in the cloud. So, there must be some other process going on that gets rid of the gas that doesn't end up in the star."

- The team's results will appear in an upcoming issue of The Astrophysical Journal. ¹¹²⁾

A Star is Born

- During a star's relatively brief birthing stage, lasting only about 500,000 years, the star quickly bulks up on mass. What gets messy is that, as the star grows, it launches a wind, as well as a pair of spinning, lawn-sprinkler-style jets shooting off in opposite directions. These outflows begin to eat away at the surrounding cloud, creating cavities in the gas.

- Popular theories predict that as the young star evolves and the outflows continue, the cavities grow wider until the entire gas cloud around the star is completely pushed away. With its gas tank empty, the star stops accreting mass – in other words, it stops growing.

- To look for cavity growth, the researchers first sorted the protostars by age by analyzing Herschel and Spitzer data of each star's light output. The protostars in the Hubble observations were also observed as part of the Herschel telescope's Herschel Orion Protostar Survey.

- Then the astronomers observed the cavities in near-infrared light with Hubble's Near-infrared Camera and Multi-object Spectrometer and Wide Field Camera 3. The observations were taken between 2008 and 2017. Although the stars themselves are shrouded in dust, they emit powerful radiation which strikes the cavity walls and scatters off dust grains, illuminating the gaps in the gaseous envelopes in infrared light.

- The Hubble images reveal the details of the cavities produced by protostars at various stages of evolution. Habel's team used the images to measure the structures' shapes and estimate the volumes of gas cleared out to form the cavities. From this analysis, they could estimate the amount of mass that had been cleared out by the stars' outbursts.

Figure 107: Though our galaxy is an immense city of at least 200 billion stars, the details of how they formed remain largely cloaked in mystery. Scientists know that stars form from the collapse of huge hydrogen clouds that are squeezed under gravity to the point where nuclear fusion ignites. But only about 30 percent of the cloud's initial mass winds up as a newborn star. Where does the rest of the hydrogen go during such a terribly inefficient process? (video credit: NASA Goddard Space Flight Center)

- "We find that at the end of the protostellar phase, where most of the gas has fallen from the surrounding cloud onto the star, a number of young stars still have fairly narrow cavities," said team member Tom Megeath of the University of Toledo. "So, this picture that is still commonly held of what determines the mass of a star and what halts the infall of gas is that this growing outflow cavity scoops up all of the gas. This has been pretty fundamental to our idea of how star formation proceeds, but it just doesn't seem to fit the data here."

- Future telescopes such as NASA's upcoming James Webb Space Telescope will probe deeper into a protostar's formation process. Webb spectroscopic observations will observe the inner regions of disks surrounding protostars in infrared light, looking for jets in the youngest sources. Webb also will help astronomers measure the accretion rate of material from the disk onto the star, and study how the inner disk is interacting with the outflow.

• March 12, 2021: NASA's Hubble Space Telescope resumed observations March 11 after a software error placed it in a protective safe mode several days earlier, but the incident is a reminder of the telescope's mortality. ¹¹³⁾

- NASA said Hubble resumed observations at 8 p.m. Eastern March 11, more than four and a half days after a software error caused the spacecraft to go into a safe mode, suspending normal operations of the nearly 31-year-old space telescope. ¹¹⁴⁾

- The software error was traced to what an agency statement called an "enhancement" recently uploaded to the spacecraft. That enhancement was intended to compensate for fluctuations from one of the telescope's gyroscopes, but a glitch in the software caused a broader problem with Hubble's main computer, triggering the safe mode early March 7.

- Controllers resolved the problem for now by disabling that software enhancement, and plan to correct the flaw and test the new software further before uploading it again.

- That safe mode, though, caused two other problems with Hubble. The telescope's aperture door, a cover on top of the telescope, is designed to automatically close when the spacecraft enters safe mode to prevent stray sunlight from entering, which could damage instruments and optics. During this safe mode, though, the door did not swing shut, a problem never before seen with Hubble.

- Engineers troubleshooting the problem found that the door did close once they switched to a backup motor. They have now set that motor as the primary one as they continue to study the problem with the other motor.

- One of Hubble's instruments, the Wide Field Camera 3, "experienced an unexpected error" during the recovery from safe mode. NASA did not elaborate on the error but said that observations using that instrument will remain on hold as engineers study the problem. The spacecraft's other instruments, including a camera and two spectrographs, are functioning.

- The safe mode, and related issues, is a reminder of Hubble's age. The spacecraft was launched in April 1990 and serviced by the space shuttle five times, most recently in May 2009. With the shuttle long since retired, astronomers know that, at some point, Hubble will suffer an unrecoverable failure that will end its historic mission.

- "Right now we're in the middle of what I think is a very good news story about Hubble," Jennifer Wiseman, an astronomer at NASA's Goddard Space Flight Center, said at a conference last year about the space telescope. She and others believe that the telescope can remain operational through much of this decade, based on trends in the performance of key components, such as its gyroscopes and batteries.

- Some have argued for a new servicing mission to Hubble using either a robotic or crewed spacecraft. John Grunsfeld, a former NASA astronaut who flew on three Hubble servicing missions and later served as the agency's associate administrator for science, presented a concept last year for a crewed servicing mission using an Orion spacecraft and a module equipped with a robotic arm and airlock. That spacecraft would dock with Hubble, with astronauts then performing repairs much as they did on past servicing missions.

- "We have the technology to go back to Hubble," he said in a presentation last June to the Space Transportation Association, noting that a commercial crew vehicle, like Crew Dragon, could be used in place of Orion. "We could keep Hubble going for another few decades."

- NASA, though, has shown no public interest in such a servicing mission, whose expense would run in the hundreds of millions to billions of dollars. "It's not currently on the books. Nobody is really talking about it a lot, at least publicly," Grunsfeld acknowledged.

- Without a servicing mission, Hubble could last for many years, or fail tomorrow, astronomers like Wiseman acknowledge. "We don't know how long Hubble's going to last," she said.

• March 11, 2021: For the first time, scientists using the NASA/ESA Hubble Space Telescope have found evidence of volcanic activity reforming the atmosphere on a rocky planet around a distant star. The planet, GJ 1132 b, has a similar density, size, and age to those of Earth. ^{115) 116)}

- The planet GJ 1132 b appears to have begun life as a gaseous world with a thick blanket of atmosphere. Starting out at several times the radius of Earth, this so-called "sub-Neptune" quickly lost its primordial hydrogen and helium atmosphere, which was stripped away by the intense radiation from its hot, young star. In a short period of time, it was reduced to a bare core about the size of Earth.

- To the surprise of astronomers, new observations from Hubble have uncovered a secondary atmosphere that has replaced the planet's first atmosphere. It is rich in hydrogen, hydrogen cyanide, methane and ammonia, and also has a hydrocarbon haze. Astronomers theorize that hydrogen from the original atmosphere was absorbed into the planet's molten magma mantle and is now being slowly released by volcanism to form a new atmosphere. This second atmosphere, which continues to leak away into space, is continually being replenished from the reservoir of hydrogen in the mantle's magma.

- "This second atmosphere comes from the surface and interior of the planet, and so it is a window onto the geology of another world," explained team member Paul Rimmer of the University of Cambridge, UK. "A lot more work needs to be done to properly look through it, but the discovery of this window is of great importance."

- "We first thought that these highly radiated planets would be pretty boring because we believed that they lost their atmospheres," said team member Raissa Estrela of the Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California, USA. But we looked at existing observations of this planet with Hubble and realized that there is an atmosphere there."

- "How many terrestrial planets don't begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism whereby light evaporates the primordial atmosphere. This process works early in a planet's life, when the star is hotter," said team leader Mark Swain of the Jet Propulsion Laboratory. "Then the star cools down and the planet's just sitting there. So you've got this mechanism that can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it."

- In some ways, GJ 1132 b has various parallels to Earth, but in some ways it is also very different. Both have similar densities, similar sizes, and similar ages, being about 4.5 billion years old. Both started with a hydrogen-dominated atmosphere, and both were hot before they cooled down. The team's work even suggests that GJ 1132 b and Earth have similar atmospheric pressure at the surface.

- However, the planets' formation histories are profoundly different. Earth is not believed to be the surviving core of a sub-Neptune. And Earth orbits at a comfortable distance from our yellow dwarf Sun. GJ 1132 b is so close to its host red dwarf star that it completes an orbit the star once every day and a half. This extremely close proximity keeps GJ 1132 b tidally locked, showing the same face to its star at all times — just as our moon keeps one hemisphere permanently facing Earth.

- "The question is, what is keeping the mantle hot enough to remain liquid and power volcanism?" asked Swain. "This system is special because it has the opportunity for quite a lot of tidal heating."

- The phenomenon of tidal heating occurs through friction, when energy from a planet's orbit and rotation is dispersed as heat inside the planet. GJ 1132 b is in an elliptical orbit, and the tidal forces acting on it are strongest when it is closest to or farthest from its host star. At least one other planet in the host star's system also exerts a gravitational pull on the planet. The consequences are that the planet is squeezed or stretched by this gravitational "pumping." That tidal heating keeps the mantle liquid for a long time. A nearby example in our own Solar System is the Jovian moon, Io, which has continuous volcanism as a result of a tidal tug-of-war between Jupiter and the neighboring Jovian moons.

- The team believes the crust of GJ 1132 b is extremely thin, perhaps only hundreds of feet thick. That's much too feeble to support anything resembling volcanic mountains. Its flat terrain may also be cracked like an eggshell by tidal flexing. Hydrogen and other gases could be released through such cracks.

- "This atmosphere, if it's thin — meaning if it has a surface pressure similar to Earth — probably means you can see right down to the ground at infrared wavelengths. That means that if astronomers use the James Webb Space Telescope to observe this planet, there's a possibility that they will see not the spectrum of the atmosphere, but rather the spectrum of the surface," explained Swain. "And if there are magma pools or volcanism going on, those areas will be hotter. That will generate more emission, and so they'll potentially be looking at the actual geological activity — which is exciting!"

• March 5, 2021: Hubble Space Telescope image of the week of the NGC2336 galaxy. Its spiral arms are glittered with young stars, visible in their bright blue light. In contrast, the redder central part of the galaxy is dominated by older stars. ^{117) 118)}

- NGC 2336 was discovered in 1876 by German astronomer Wilhelm Tempel, using a 28-centimeter telescope. This Hubble image is so much better than the view Tempel would have had — Hubble's main mirror is 2.4 meters across, nearly ten times the size of the telescope Tempel used. In 1987, NGC 2336 experienced a Type-Ia supernova, the only observed supernova in the galaxy since its discovery 111 years earlier.

• March 4, 2021: The red hypergiant VY Canis Majoris is enshrouded in huge clouds of dust. Stars come in an extraordinary range of sizes. One of the most colossal is VY Canis Majoris. If placed in the middle of our solar system it would engulf all the planets out to Saturn's orbit. This monster, appropriately called a red hypergiant, is as bright as 300,000 Suns. Yet it is so far away that, 200 years ago, it could be seen only as a faint star in the winter constellation of the Great Dog. Since then, it has faded and is no longer visible to the naked eye. Astronomers used Hubble to get a close-up look at the star and discovered the reason for the dimming. The star is expelling huge clouds of dust in the final stages of its life. Eventually, the bloated star may explode as a supernova, or may simply collapse and form a black hole. ¹¹⁹⁾

- Last year, astronomers were puzzled when Betelgeuse, the bright red supergiant star in the constellation Orion, dramatically faded, but then recovered. The dimming lasted for weeks. Now, astronomers have turned their sights toward a monster star in the adjoining constellation Canis Major, the Great Dog.

- The red hypergiant VY Canis Majoris—which is far larger, more massive, and more violent than Betelgeuse—experiences much longer, dimmer periods that last for years. New findings from NASA's Hubble Space Telescope suggest the same processes that occurred on Betelgeuse are happening in this hypergiant, but on a much grander scale.

- "VY Canis Majoris is behaving a lot like Betelgeuse on steroids," explained the study's leader, astrophysicist Roberta Humphreys of the University of Minnesota, Minneapolis.

- As with Betelgeuse, Hubble data suggest the answer for why this bigger star is dimming. For Betelgeuse, the dimming corresponded to a gaseous outflow that may have formed dust, which briefly obstructed some of Betelgeuse's light from our view, creating the dimming effect.

- "In VY Canis Majoris we see something similar, but on a much larger scale. Massive ejections of material which correspond to its very deep fading, which is probably due to dust that temporarily blocks light from the star," said Humphreys.

- The enormous red hypergiant is 300,000 times brighter than our Sun. If it replaced the Sun in our own solar system, the bloated monster would extend out for hundreds of millions of miles, between the orbits of Jupiter and Saturn.

- "This star is absolutely amazing. It's one of the largest stars that we know of—a very evolved, red supergiant. It has had multiple, giant eruptions," explained Humphreys.

- Giant arcs of plasma surround the star at distances from it that are thousands of times farther away than the Earth is from the Sun. These arcs look like the solar prominences from our own Sun, only on a much grander scale. Also, they're not physically connected to the star, but rather, appear to have been thrown out and are moving away. Some of the other structures close to the star are still relatively compact, looking like little knots and nebulous features.

- In previous Hubble work, Humphreys and her team were able to determine when these large structures were ejected from the star. They found dates ranging over the past several hundred years, some as recently as the past 100 to 200 years.

- Now, in new work with Hubble, researchers resolved features much closer to the star that may be less than a century old. By using Hubble to determine the velocities and motions of the close-in knots of hot gas and other features, Humphreys and her team were able to date these eruptions more accurately. What they found was remarkable: many of these knots link to multiple episodes in the 19th and 20th centuries when VY Canis Majoris faded to one-sixth its usual brightness.

- Unlike Betelgeuse, VY Canis Majoris is now too faint to be seen by the naked eye. The star was once visible but has dimmed so much that it can now only be seen with telescopes.

- The hypergiant sheds 100 times as much mass as Betelgeuse. The mass in some of the knots is more than twice the mass of Jupiter. "It's amazing the star can do it," Humphreys said. "The origin of these high mass-loss episodes in both VY Canis Majoris and Betelgeuse is probably caused by large-scale surface activity, large convective cells like on the Sun. But on VY Canis Majoris, the cells may be as large as the whole Sun or larger."

- "This is probably more common in red supergiants than scientists thought and VY Canis Majoris is an extreme example," Humphreys continued. "It may even be the main mechanism that's driving the mass loss, which has always been a bit of a mystery for red supergiants."

- Though other red supergiants are comparably bright and eject a lot of dust, none of them is as complex as VY Canis Majoris. "So what's special about it? VY Canis Majoris may be in a unique evolutionary state that separates it from the other stars. It's probably this active over a very short period, maybe only a few thousand years. We're not going to see many of those around," said Humphreys.

- The star began life as a super-hot, brilliant, blue supergiant star perhaps as much as 35 to 40 times our Sun's mass. After a few million years, as the hydrogen fusion burning rate in its core changed, the star swelled up to a red supergiant. Humphreys suspects that the star may have briefly returned to a hotter state and then swelled back up to a red supergiant stage.

- "Maybe what makes VY Canis Majoris so special, so extreme, with this very complex ejecta, might be that it's a second-stage red supergiant," explained Humphreys. VY Canis Majoris may have already shed half of its mass. Rather than exploding as a supernova, it might simply collapse directly to a black hole.

- The team's findings appear in the February 4, 2021 edition of The Astronomical Journal. ¹²⁰⁾

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

• February 26, 2021: This NASA/ESA Hubble Space Telescope Picture of the Week features NGC4826 — a spiral galaxy located 17 million light-years away in the constellation of Coma Berenices (Berenice's Hair). This galaxy is often referred to as the "Black Eye", or "Evil Eye", galaxy because of the dark band of dust that sweeps across one side of its bright nucleus. ^{121) 122)}

- NGC4826 is known by astronomers for its strange internal motion. The gas in the outer regions of this galaxy and the gas in its inner regions are rotating in opposite directions, which might be related to a recent merger. New stars are forming in the region where the counter rotating gases collide.

- This galaxy was first discovered in 1779 by the English astronomer Edward Pigott.

• February 25, 2021: For the first time, a wayward comet-like object has been spotted near the family of ancient asteroids. ¹²³⁾

- After traveling several billion miles toward the Sun, a wayward young comet-like object orbiting among the giant planets has found a temporary parking place along the way. The object has settled near a family of captured ancient asteroids, called Trojans, that are orbiting the Sun alongside Jupiter. This is the first time a comet-like object has been spotted near the Trojan population.

- The unexpected visitor belongs to a class of icy bodies found in space between Jupiter and Neptune. Called Centaurs, they become active for the first time when heated as they approach the Sun, and dynamically transition into becoming more comet-like.

- Visible-light snapshots by NASA's Hubble Space Telescope reveal that the vagabond object shows signs of comet activity, such as a tail, outgassing in the form of jets, and an enshrouding coma of dust and gas. Earlier observations by NASA's Spitzer Space Telescope gave clues to the composition of the comet-like object and the gasses driving its activity.

- "Only Hubble could detect active comet-like features this far away at such high detail, and the images clearly show these features, such as a roughly 400,000-mile-long broad tail and high-resolution features near the nucleus due to a coma and jets," said lead Hubble researcher Bryce Bolin of Caltech in Pasadena, California.

- Describing the Centaur's capture as a rare event, Bolin added, "The visitor had to have come into the orbit of Jupiter at just the right trajectory to have this kind of configuration that gives it the appearance of sharing its orbit with the planet. We're investigating how it was captured by Jupiter and landed among the Trojans. But we think it could be related to the fact that it had a somewhat close encounter with Jupiter."

- The team's paper appears in Feb. 11 issue of The Astronomical Journal. ¹²⁴⁾

- The research team's computer simulations show that the icy object, called P/2019 LD2 (LD2), probably swung close to Jupiter about two years ago. The planet then gravitationally punted the wayward visitor to the Trojan asteroid group's co-orbital location, leading Jupiter by about 437 million miles.

Bucket Brigade

- The nomadic object was discovered in early June 2019 by the University of Hawaii's Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes located on the extinct volcanoes, one on Mauna Kea and one on Haleakala. Japanese amateur astronomer Seiichi Yoshida tipped off the Hubble team to possible comet activity. The astronomers then scanned archival data from the Zwicky Transient Facility, a wide-field survey conducted at Palomar Observatory in California, and realized that the object was clearly active in images from April 2019.

- They followed up with observations from the Apache Point Observatory in New Mexico, which also hinted at the activity. The team observed the comet using Spitzer just days before the observatory's retirement in January 2020, and identified gas and dust around the comet nucleus. These observations convinced the team to use Hubble to take a closer look. Aided by Hubble's sharp vision, the researchers identified the tail, coma structure, the size of the dust particles, and their ejection velocity. These images helped them confirm that the features are due to relatively new comet-like activity.

- Although LD2's location is surprising, Bolin wonders whether this pit stop could be a common pull-off for some sunward-bound comets. "This could be part of the pathway from our solar system through the Jupiter Trojans to the inner solar system," he said.

- The unexpected guest probably will not stay among the asteroids for very long. Computer simulations show that it will have another close encounter with Jupiter in about another two years. The hefty planet will boot the comet from the system, and it will continue its journey to the inner solar system.

- "The cool thing is that you're actually catching Jupiter flinging this object around and changing its orbital behavior and bringing it into the inner system," said team member Carey Lisse of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. "Jupiter controls what's going on with comets once they get into the inner system by altering their orbits."

- The icy interloper is most likely one of the latest members of the so-called "bucket brigade" of comets to get kicked out of its frigid home in the Kuiper Belt and into the giant planet region through interactions with another Kuiper Belt object. Located beyond Neptune's orbit, the Kuiper Belt is a haven of icy, leftover debris from our planets' construction 4.6 billion years ago, containing millions of objects, and occasionally these objects have near misses or collisions that drastically alter their orbits from the Kuiper Belt inward into the giant planet region.

- The bucket brigade of icy relics endure a bumpy ride during their journey sunward. They bounce gravitationally from one outer planet to the next in a game of celestial pinball before reaching the inner solar system, warming up as they come closer to the Sun. The researchers say the objects spend as much or even more time around the giant planets, which are gravitationally pulling on them – about 5 million years – than they do crossing into the inner system where we live.

- "Inner-system, ‘short-period' comets break up about once a century," Lisse explained. "So, in order to maintain the number of local comets we see today, we think the bucket brigade has to deliver a new short-period comet about once every 100 years."

An Early Bloomer

- Seeing outgassing activity on a comet 465 million miles away from the Sun (where the intensity of sunlight is 1/25th as strong as on Earth) surprised the researchers. "We were intrigued to see that the comet had just started to become active for the first time so far away from the Sun at distances where water ice is barely starting to sublimate," said Bolin.

- Water remains frozen on a comet until it reaches about 200 million miles from the Sun, where heat from sunlight converts water ice to gas that escapes from the nucleus in the form of jets. So the activity signals that the tail might not be made of water. In fact, observations by Spitzer indicated the presence of carbon monoxide and carbon dioxide gas, which could be driving the creation of the tail and jets seen on the Jupiter-orbiting comet. These volatiles do not need much sunlight to heat their frozen form and convert them to gas.

- Once the comet gets kicked out of Jupiter's orbit and continues its journey, it may meet up with the giant planet again. "Short-period comets like LD2 meet their fate by being thrown into the Sun and totally disintegrating, hitting a planet, or venturing too close to Jupiter once again and getting thrown out of the solar system, which is the usual fate," Lisse said. "Simulations show that in about 500,000 years, there's a 90% probability that this object will be ejected from the solar system and become an interstellar comet."

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, managed the Spitzer mission for NASA's Science Mission Directorate in Washington, D.C. Science operations were conducted at the Spitzer Science Center at IPAC at Caltech. Spitzer's entire science catalogue is available via the Spitzer data archive, housed at the Infrared Science Archive at IPAC. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado.

• February 19, 2021: Tantrums of a baby star - a Milky War star with circumstellar material outflow at a distance of 1400 light years.. Week in images. ¹²⁵⁾

- Before 1997 it was theorized by Schwartz and others that the objects could be a type of reflection nebula, or a type of shock wave formed from the gas emitted from a star interacting with the surrounding matter. The mystery was finally solved when a protostar, unseen in this image, was discovered at the centre of the long jets of matter. The outflows of matter, some 10 light-years across, were ejected from the newly born star and violently propelled outwards at speeds of over 150 kilometers per second. Upon reaching the surrounding gas, the collision created the bright shock waves seen here.

• February 12, 2021: This week's NASA/ESA Hubble Space Telescope Picture of the Week features an impressive portrait of M1-63, a beautifully captured example of a bipolar planetary nebula located in the constellation of Scutum (the Shield). A nebula like this one is formed when the star at its center sheds huge quantities of material from its outer layers, leaving behind a spectacular cloud of gas and dust. ¹²⁶⁾

- It is believed that a binary system of stars at the center of the bipolar nebula is capable of creating hourglass or butterfly-like shapes like the one in this image. This is because the material from the shedding star is funneled towards its poles, with the help of the companion, creating the distinctive double-lobed structure seen in nebulae such as M1-63.

• February 11, 2021: Scientists were expecting to find an intermediate-mass black hole at the heart of the globular cluster NGC 6397, but instead they found evidence of a concentration of smaller black holes lurking there. New data from the NASA/ESA Hubble Space Telescope have led to the first measurement of the extent of a collection of black holes in a core-collapsed globular cluster. ^{127) 128)}

- Globular clusters are extremely dense stellar systems, in which stars are packed closely together. They are also typically very old — the globular cluster that is the focus of this study, NGC 6397, is almost as old as the Universe itself. It resides 7800 light-years away, making it one of the closest globular clusters to Earth. Because of its very dense nucleus, it is known as a core-collapsed cluster.

- When Eduardo Vitral and Gary A. Mamon of the Institut d'Astrophysique de Paris set out to study the core of NGC 6397, they expected to find evidence for an "intermediate-mass" black hole (IMBH). These are smaller than the supermassive black holes that lie at the cores of large galaxies, but larger than stellar-mass black holes formed by the collapse of massive stars. IMBH are the long-sought "missing link" in black hole evolution and their mere existence is hotly debated, although a few candidates have been found (see Notes [1]).

- To look for the IMBH, Vitral and Mamon analyzed the positions and velocities of the cluster's stars. They did this using previous estimates of the stars' proper motions [2] from Hubble images of the cluster spanning several years [3], in addition to proper motions provided by ESA's Gaia space observatory, which precisely measures the positions, distances and motions of stars. Knowing the distance to the cluster allowed the astronomers to translate the proper motions of these stars into velocities.

- "Our analysis indicated that the orbits of the stars are close to random throughout the globular cluster, rather than systematically circular or very elongated," explained Mamon.

- "We found very strong evidence for invisible mass in the dense central regions of the cluster, but we were surprised to find that this extra mass is not point-like but extended to a few percent of the size of the cluster," added Vitral.

- This invisible component could only be made up of the remnants (white dwarfs, neutron stars, and black holes) of massive stars whose inner regions collapsed under their own gravity once their nuclear fuel was exhausted. The stars progressively sank to the cluster's centre after gravitational interactions with nearby less massive stars, leading to the small extent of the invisible mass concentration. Using the theory of stellar evolution, the scientists concluded that the bulk of the unseen concentration is made of stellar-mass black holes, rather than white dwarfs or neutron stars that are too faint to observe.

- Two recent studies had also proposed that stellar remnants and in particular, stellar-mass black holes, could populate the inner regions of globular clusters.

- "Our study is the first finding to provide both the mass and the extent of what appears to be a collection of mostly black holes in a core-collapsed globular cluster," said Vitral.

- "Our analysis would not have been possible without having both the Hubble data to constrain the inner regions of the cluster and the Gaia data to constrain the orbital shapes of the outer stars, which in turn indirectly constrain the velocities of foreground and background stars in the inner regions," added Mamon, attesting to an exemplary international collaboration.

- The astronomers also note that this discovery raises the question of whether mergers of these tightly packed black holes in core-collapsed globular clusters may be an important source of gravitational waves recently detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) experiment.

Notes:

[1] In 2020, new data from the NASA/ESA Hubble Space Telescope provided the strongest evidence to date for a mid-sized black hole. Read the full press release on this result here.

[2] Proper motion describes how fast objects move in the sky.

[3] The Hubble data for this study were provided by A. Bellini, who measured the proper motions for over 1.3 million stars in 22 globular clusters, including NGC 6397.

• February 5, 2021: Picture of the Week: The Modest Galaxy (Astronomy). ¹²⁹⁾

- Many young blue stars are sprinkled throughout the circular patterns of UGC 3885's arms, contrasted and complemented by dark lanes of dust also following the spiral structure. A glancing look at UGC 3885 (Uppsala General Catalogue) of Galaxies may only leave you with an impression of the galaxy, but spare a moment longer and the intricacies of the galaxy begin to emerge. Located in the constellation of Lynx, a spiral galaxy some 180 million light-years away. UGC 3885 is a cosmic beauty to behold.

• January 29, 2021: The lives of planetary nebulae are often chaotic, from the death of their parent star to the scattering of its contents far out into space. Captured here by the NASA/ESA Hubble Space Telescope, ESO 455-10 is one such planetary nebula, located in the constellation of Scorpius (The Scorpion). ¹³⁰⁾

- The oblate shells of ESO 455-10, previously held tightly together as layers of its central star, not only give this planetary nebula its unique appearance, but also offer information about the nebula. Seen in a field of stars, the distinct asymmetrical arc of material over the north side of the nebula is a clear sign of interactions between ESO 455-10 and the interstellar medium.

• January 22, 2021: Located in the constellation of Virgo (The Virgin), around 50 million light-years from Earth, NGC 4535 is truly a stunning sight to behold. Despite the incredible quality of this image, taken from the NASA/ESA Hubble Space Telescope, NGC 4535 has a hazy, somewhat ghostly, appearance when viewed from a smaller telescope. This led amateur astronomer Leland S. Copeland to nickname NGC 4535 the "Lost Galaxy" in the 1950s. ^{131) 132)}

- This galaxy was studied as part of the PHANGS (Physics at High Angular resolution in Nearby GalaxieS) survey, which aims to clarify many of the links between cold gas clouds, star formation, and the overall shape and other properties of galaxies. On 11 January 2021 the first release of the PHANGS-HST Collection was made publicly available. ¹³³⁾

• January 15, 2021: Images of two iconic planetary nebulae taken by the Hubble Space Telescope are revealing new information about how they develop their dramatic features. Researchers from Rochester Institute of Technology (RIT) and Green Bank Observatory presented new findings about the Butterfly Nebula (NGC 6302) and the Jewel Bug Nebula (NGC 7027) at the 237th meeting of the American Astronomical Society on Friday, Jan. 15. ¹³⁴⁾

- Hubble's Wide Field Camera 3 observed the nebulae in 2019 and early 2020 using its full, panchromatic capabilities, and the astronomers involved in the project have been using emission line images from near-ultraviolet to near-infrared light to learn more about their properties. The studies were first-of-their-kind panchromatic imaging surveys designed to understand the formation process and test models of binary-star-driven planetary nebula shaping.

- "We're dissecting them," said Joel Kastner, a professor in RIT's Chester F. Carlson Center for Imaging Science and School of Physics and Astronomy. "We're able to see the effect of the dying central star in how it's shedding and shredding its ejected material. We're now seeing where material that the central star has tossed away is being dominated by ionized gas, where it's dominated by cooler dust, and even how the hot gas is being ionized, whether by the star's UV or by collisions caused by its present, fast winds."

- Kastner said analysis of the new HST images of the Butterfly Nebula is confirming that the nebula was ejected only about 2,000 years ago—an eyeblink by the standards of astronomy – and established that the S-shaped iron emission that helps give it the "wings" of gas is even younger. Surprisingly, they found that while astronomers previously believed they had located the nebula's central star, that previously-identified star is actually not associated with the nebula and is instead much closer to Earth than the Butterfly Nebula. Kastner said he hopes that future studies with the James Webb Space Telescope could help locate the real dying star at the heart of the nebula.

• January 15, 2021: First discovered in 1798 by German-English astronomer William Hershel, NGC 613 is a galaxy which lies in the southern constellation of Sculptor 67 million light-years away. ¹³⁵⁾

- Recent studies have shown that bars are more common in galaxies now than they were in the past, which gives us important clues about galaxy formation and evolution.

• January 14, 2021: Astronomers are winding back the clock on the expanding remains of a nearby, exploded star. By using NASA's Hubble Space Telescope, they retraced the speedy shrapnel from the blast to calculate a more accurate estimate of the location and time of the stellar detonation. ^{136) 137)}

- The victim is a star that exploded long ago in the Small Magellanic Cloud, a satellite galaxy to our Milky Way. The doomed star left behind an expanding, gaseous corpse, a supernova remnant named 1E 0102.2-7219, which NASA's Einstein Observatory first discovered in X-rays. Like detectives, researchers sifted through archival images taken by Hubble, analyzing visible-light observations made 10 years apart.

- The research team, led by John Banovetz and Danny Milisavljevic of Purdue University in West Lafayette, Indiana, measured the velocities of 45 tadpole-shaped, oxygen-rich clumps of ejecta flung by the supernova blast. Ionized oxygen is an excellent tracer because it glows brightest in visible light.

- To calculate an accurate explosion age, the astronomers picked the 22 fastest moving ejecta clumps, or knots. The researchers determined that these targets were the least likely to have been slowed down by passage through interstellar material. They then traced the knots' motion backward until the ejecta coalesced at one point, identifying the explosion site. Once that was known, they could calculate how long it took the speedy knots to travel from the explosion center to their current location.

- According to their estimate, light from the blast arrived at Earth 1,700 years ago, during the decline of the Roman Empire. However, the supernova would only have been visible to inhabitants of Earth's southern hemisphere. Unfortunately, there are no known records of this titanic event.

- The researchers' results differ from previous observations of the supernova's blast site and age. Earlier studies, for example, arrived at explosion ages of 2,000 and 1,000 years ago. However, Banovetz and Milisavljevic say their analysis is more robust.

- "A prior study compared images taken years apart with two different cameras on Hubble, the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys (ACS)," Milisavljevic said. "But our study compares data taken with the same camera, the ACS, making the comparison much more robust; the knots were much easier to track using the same instrument. It's a testament to the longevity of Hubble that we could do such a clean comparison of images taken 10 years apart."

- The astronomers also took advantage of the sharp ACS images in selecting which ejecta clumps to analyze. In prior studies, researchers averaged the speed of all of the gaseous debris to calculate an explosion age. However, the ACS data revealed regions where the ejecta slowed down because it was slamming into denser material shed by the star before it exploded as a supernova. Researchers didn't include those knots in the sample. They needed the ejecta that best reflected their original velocities from the explosion, using them to determine an accurate age estimate of the supernova blast.

- Hubble also clocked the speed of a suspected neutron star—the crushed core of the doomed star—that was ejected from the blast. Based on their estimates, the neutron star must be moving at more than 2 million miles per hour from the center of the explosion to have arrived at its current position. The suspected neutron star was identified in observations with the European Southern Observatory's VLT (Very Large Telescope) in Chile, in combination with data from NASA's Chandra X-ray Observatory.

- "That is pretty fast and at the extreme end of how fast we think a neutron star can be moving, even if it got a kick from the supernova explosion," Banovetz said. "More recent investigations call into question whether the object is actually the surviving neutron star of the supernova explosion. It is potentially just a compact clump of supernova ejecta that has been lit up, and our results generally support this conclusion."

- So the hunt may still be on for the neutron star. "Our study doesn't solve the mystery, but it gives an estimate of the velocity for the candidate neutron star," Banovetz said.

• January 8, 2021: The galaxy NGC 6946 is nothing short of spectacular. In the last century alone, NGC 6946 has experienced 10 observed supernovae, earning its nickname as the Fireworks Galaxy. In comparison, our Milky Way averages just one to two supernova events per century. This NASA/ESA Hubble Space Telescope image shows the stars, spiral arms, and various stellar environments of NGC 6946 in phenomenal detail. ¹³⁸⁾

- We are able to marvel at NGC 6946 as it is a face-on galaxy, which means that we see the galaxy "facing" us, rather than seeing it from the side (known as edge-on). The Fireworks Galaxy is further classified as an intermediate spiral galaxy and as a starburst galaxy. The former means the structure of NGC 6946 sits between a full spiral and a barred spiral galaxy, with only a slight bar in its center, and the latter means it has an exceptionally high rate of star formation.

• January 7, 2021: It is during rare merging events that galaxies undergo dramatic changes in their appearance and in their stellar content. These systems are excellent laboratories to trace the formation of star clusters under extreme physical conditions. ^{139) 140)}

- The Milky Way typically forms star clusters with masses that are 10 thousand times the mass of our Sun. This doesn't compare to the masses of the star clusters forming in colliding galaxies, which can reach millions of times the mass of our Sun.

- These dense stellar systems are also very luminous. Even after the collision, when the resulting galactic system begins to fade into a more quiescent phase, these very massive star clusters will shine throughout their host galaxy, as long-lasting witnesses of past merging events.

- By studying the six galaxy mergers shown here, the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey has investigated how star clusters are affected during collisions by the rapid changes that drastically increase the rate at which new stars are formed in these galaxies. Hubble's capabilities have made it possible to resolve large star-forming "knots" into numerous compact young star clusters. Hubble's ultraviolet and near-infrared observations of these systems have been used to derive star cluster ages, masses, and extinctions and to analyze the star formation rate within these six merging galaxies. The HiPEEC study reveals that the star cluster populations undergo large and rapid variations in their properties, with the most massive clusters formed towards the end of the merger phase.

- Each of the merging systems shown here has been previously published by Hubble, as early as 2008 and as recently as October 2020. To celebrate it's 18th anniversary in 2008, the Hubble Space Telescope released a collection of 59 images of merging galaxies, which can be explored here.

1) "Our Milky Way May Be More Fluffy, Less Wiry," NASA Hubblesite, 16 December 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-061.html

2) "New Exhibit Displaying Hubble Science ‘Brings the Universe Home'," NASA Hubblesite, 14 December 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-067.html

3) "Four filter fusion," ESA Science & Exploration, 10 December 2021 Release ID: 2021-067 , URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_6_-_10_December_2021

4) Claire Andreoli, Ray Willard, "Mini-Jet Found Near Milky Way's Supermassive Black Hole," NASA Feature, 9 December 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-mini-jet-found-near-milky-ways-supermassive-black-hole

5) "Mini-Jet Found Near Milky Way's Supermassive Black Hole," NASA Hubblesite, 9 December 2021, Release ID: 2021-062, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-062.html

6) Gerald Cecil, Alexander Y. Wagner, Joss Bland-Hawthorn, Geoffrey V. Bicknell, and Dipanjan Mukherjee, "Tracing the Milky Way's Vestigial Nuclear Jet," The Astrophysical Journal, Volume 922, Number 2, Published: 6 December 2021, https://doi.org/10.3847/1538-4357/ac224f

7) "NASA Returns Hubble to Full Science Operations," NASA Feature, 7 December 2021, URL: https://www.nasa.gov/feature/goddard/2021/nasa-returns-hubble-to-full-science-operations

8) "One of a pair," ESA Science & Exploration, 03 December 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_29_November_-_3_December_2021

9) "NASA Takes Another Step Toward Full Hubble Ops: Spectrograph Returns," NASA Feature, 29 November 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-instruments-remain-in-safe-mode-nasa-team-investigating

10) Clair Andreoli, "Hubble's View of Planetary Nebula Reveals Complex Structure," NASA Feature, 29 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-s-view-of-planetary-nebula-reveals-complex-structure

11) Claire Andreoli, Andrea Gianopoulos, "Hubble Witnesses Shock Wave of Colliding Gases in Running Man Nebula," NASA Feature, 24 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-witnesses-shock-wave-of-colliding-gases-in-running-man-nebula

12) Claire Andreoli, Elizabeth Landau, "NASA Closer to Full Hubble Operations as Another Instrument Resumes Science," NASA Feature, 22 November 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-instruments-remain-in-safe-mode-nasa-team-investigating

13) Claire Andreoli, "Hubble Spots Swirls of Dust in the Flame Nebula," NASA Feature, 22 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-spots-swirls-of-dust-in-the-flame-nebula

14) Claire Andreoli, "Hubble Catches Celestial Prawn Drifting Through the Cosmic Deep," NASA Feature, 19 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-catches-celestial-prawn-drifting-through-the-cosmic-deep

15) "A spectacular side-on spiral," ESA Science & Exploration, 10 November 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_15_-_19_November_2021

16) "Hubble Takes a Grand Tour of the Solar System," ESA, heic2113 — Photo Release, 18 November 2021, URL: https://esahubble.org/news/heic2113/?lang

17) "Hubble's Grand Tour of the Outer Solar System," Hubblesite Release ID: 2021-047, 18 November 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-047.html

18) Claire Andreoli, "Hubble Spies Newly Forming Star Incubating in IC 2631," NASA Feature, 17 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-spies-newly-forming-star-incubates-in-ic-2631

19) Claire Andreoli, Cynthia M. O'Carroll, Elizabeth Landau, "NASA Extends Hubble Operations Contract, Provides Mission Update," NASA Feature, 16 November 2021, URL: https://www.nasa.gov/feature/nasa-extends-hubble-operations-contract-provides-mission-update

20) Claire Andreoli, "Nebula Churns Out Massive Stars in New Hubble Image," NASA Feature, 16 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/nebula-churns-out-massive-stars-in-new-hubble-image

21) Claire Andreoli, "Hubble Images Dark Nebula Cloaking Stars Within Dusty Depths," NASA Feature, 15 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-images-dark-nebula-cloaking-stars-within-dusty-depths

22) Claire Andreoli, "Reflected Starlight Bathes Forming Star in New Hubble Image," NASA Feature, 12 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/reflected-starlight-bathes-forming-star-in-new-hubble-image

23) "Cosmological curiosity," ESA Science & Exploration, 12 November 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_08_-_12_November_2021

24) Claire Andreoli, "Hubble Surveys A Snowman Sculpted from Gas and Dust," NASA Feature, 10 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-surveys-a-snowman-sculpted-from-gas-and-dust

25) Claire Andreoli, "Hubble Captures the Shredded Remains of a Cosmic Explosion," NASA Feature, 9 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-captures-the-shredded-remains-of-a-cosmic-explosion

26) Claire Andreoli, Elizabeth Landau, "Hubble's Advanced Camera for Surveys Instrument Resumes Science, Investigation Continues," NASA Feature, 8 November 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-instruments-remain-in-safe-mode-nasa-team-investigating

27) "Cosmic fireworks," ESA Science & Exploration, 05 November 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_01_-_05_November_2021

28) "Hubble Images Colorful Planetary Nebula Ringed by Hazy Halo," NASA, 4 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-images-colorful-planetary-nebula-ringed-by-hazy-halo

29) Claire Andreoli, Elizabeth Landau, "NASA Takes Additional Steps to Investigate Hubble Instruments in Safe Mode," NASA Feature, 4 November 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-instruments-remain-in-safe-mode-nasa-team-investigating

30) "Hubble Spies Eye in the Sky," NASA, 3 November 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-spies-eye-in-the-sky

31) Claire Andreoli, "Hubble Remains in Safe Mode, NASA Team Investigating," NASA, 1 November 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-remains-in-safe-mode-nasa-team-investigating

32) Claire Andreoli, Ray Villard, "Hubble Celebrates Halloween with a Glowering, Dying Star," NASA Feature, 28 October 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-celebrates-halloween-with-a-glowering-dying-star

33) "Hubble Celebrates Halloween With A Glowering Carbon Star," ESA heic2112 — Photo Release, 28 October 2021, URL: https://esahubble.org/news/heic2112/?lang

34) "Hubble spies a pair of squabbling galaxies," ESA Science & Exploration, 22 October 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_18_-_22_October_2021

35) "Hubble Gives Unprecedented, Early View of a Doomed Star's Destruction," NASA, 21 October 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-gives-unprecedented-early-view-of-a-doomed-stars-destruction

36) Samaporn Tinyanont, et al., "Progenitor and Close-In Circumstellar Medium of Type II Supernova 2020fqv from High-Cadence Photometry and Ultra-Rapid UV Spectroscopy," MNRAS 000, 1–17 (2020), URL: https://stsci-opo.org/STScI-01FH8PXT7J03QWHH2JAZYN79DK.pdf

37) "Invisible galactic gale," ESA Science & Exploration, 15 October 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_11_-_15_October_2021

38) "Hubble Finds Evidence of Persistent Water Vapor in One Hemisphere of Europa," NASA Feature, 14 October 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-finds-evidence-of-persistent-water-vapor-in-one-hemisphere-of-europa

39) "Hubble Finds Evidence of Persistent Water Vapor Atmosphere on Europa," heic2111 — Science Release, 14 October 2021, URL: https://esahubble.org/news/heic2111/?lang

40) Lorenz Roth, "A Stable H₂O Atmosphere on Europa's Trailing Hemisphere From HST Images," Geophysical Research Letters, Volume48, Issue20, 28 October 2021, e2021GL094289, First published: 13 September 2021, https://doi.org/10.1029/2021GL094289, URL: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2021GL094289

41) "A dangerous dance," ESA Space Science, 8 October 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_4_-_8_October_2021

42) Donna Weaver, Lynn Jenner, "'Double' Galaxy Mystifies Hubble Astronomers," NASA Feature, 7 October 2021, URL: https://www.nasa.gov/feature/goddard/2021/double-galaxy-mystifies-hubble-astronomers

43) Richard E Griffiths, Mitchell Rudisel, Jenny Wagner, Timothy Hamilton, Po-Chieh Huang, Carolin Villforth, "Hamilton's Object – a clumpy galaxy straddling the gravitational caustic of a galaxy cluster: constraints on dark matter clumping," Monthly Notices of the Royal Astronomical Society, Volume 506, Issue 2, September 2021, Pages 1595–1608, Published: 17 May 2021, https://doi.org/10.1093/mnras/stab1375

44) "More than Meets the Eye," ESA Science & Exploration, 01 October 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_27_September_-_1_October_2021

45) "Hubble Shows Winds in Jupiter's Great Red Spot Are Speeding Up," ESA heic2110 — Science Release, 27 September 2021, URL: https://esahubble.org/news/heic2110/?lang

46) "Rings of Relativity," ESA Science & Exploration, 24 September 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_20_-_24_September_2021

47) "Hubble Snapshot of "Molten Ring" Galaxy Prompts New Research," NASA Feature, 23 September 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-snapshot-of-molten-ring-galaxy-prompts-new-research

48) "Hubble Finds Early, Massive Galaxies Running on Empty," NASA Hubblesite news release, 22 September 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-039.html

49) Katherine E. Whitaker, Christina C. Williams, Lamiya Mowla, Justin S. Spilker, Sune Toft, Desika Narayanan, Alexandra Pope, Georgios E. Magdis, Pieter G. van Dokkum, Mohammad Akhshik, Rachel Bezanson, Gabriel B. Brammer, Joel Leja, Allison Man, Erica J. Nelson, Johan Richard, Camilla Pacifici, Keren Sharon & Francesco Valentino, "Quenching of star formation from a lack of inflowing gas to galaxies," Nature, Volume 597, pp: 485-488, Published: 22 September 2021, https://doi.org/10.1038/s41586-021-03806-7

50) "A closer look at Hubble's 31st anniversary snapshot," ESA Science & Exploration, 17 September 2021, URL: https://www.esa.int/ESA_Multimedia/Images/2021/09/A_closer_look_at_Hubble_s_31st_anniversary_snapshot

51) "Rerun of Supernova Blast Is Expected to Appear in 2037," NASA Hubblesite, 13 September 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-030.html

52) Steven A. Rodney, Gabriel B. Brammer, Justin D. R. Pierel, Johan Richard, Sune Toft, Kyle F. O'Connor, Mohammad Akhshik & Katherine E. Whitaker, "A gravitationally lensed supernova with an observable two-decade time delay," Nature Astronomy Letter, Published: 13 September 2021, https://doi.org/10.1038/s41550-021-01450-9

53) "A glittering globular cluster," ESA Science & Exploration, 10 September 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_6_-_10_September_2021

54) Claire Andreoli, Ray Willard, Bethany Downer, "Hubble Discovers Hydrogen-Burning White Dwarfs Enjoying Slow Aging," NASA Feature, 6 September 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-discovers-hydrogen-burning-white-dwarfs-enjoying-slow-aging

55) "Cluster in the cloud," ESA Science & Exploration, 27 August 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_23_-_27_August_2021

56) "In the heart of the furnace," ESA Science & Exploration, 20 August 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_16_-_20_August_2021

57) "Comet ATLAS May Have Been a Blast from the Past," NASA Hubblesite, 19 August 2021 Release ID: 2021-031, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-031

58) Quanzhi Ye, David Jewitt, Man-To Hui, Qicheng Zhang, Jessica Agarwal, Michael S. P. Kelley, Yoonyoung Kim, Jing Li, Tim Lister, Max Mutchler, and Harold A. Weaver, "Disintegration of Long-period Comet C/2019 Y4 (ATLAS). I. Hubble Space Telescope Observations, The Astronomical Journal, Volume 162, No 2, Published: 21 July 2021, https://doi.org/10.3847/1538-3881/abfec3

59) Claire Andreoli, Rob Gutro, "Hubble Peers into a Dusty Stellar Nursery," NASA Feature, 13 August 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-peers-into-a-dusty-stellar-nursery

60) "Seeing quintuple," ESA Science & Exploration, 13 August 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_09_-_13_August_2021

61) "Portrait of a swirling galaxy," ESA Science & Exploration, 6 August 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_02_-_06_August_2021

62) "Squabbling galactic siblings," ESA Science & Exploration, 30 July 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_26_-_30_July_2021

63) "Hubble Finds First Evidence of Water Vapor at Jupiter's Moon Ganymede," ESA, heic2107 — Science Release, 26 July 2021, URL: https://esahubble.org/news/heic2107/?lang

64) "Hubble Finds First Evidence of Water Vapor at Jupiter's Moon Ganymede," NASA HubbleSite, 26 July 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-033

65) Lorenz Roth, Nickolay Ivchenko, G. Randall Gladstone, Joachim Saur, Denis Grodent, Bertrand Bonfond, Philippa M. Molyneux & Kurt D. Retherford, "A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations," Nature Astronomy, Published: 26 July 2021, https://doi.org/10.1038/s41550-021-01426-9

66) Claire Andreoli, Ray Villard, Bethany Downer, "Hubble Finds First Evidence of Water Vapor at Jupiter's Moon Ganymede," NASA Feature, 26 July 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-finds-first-evidence-of-water-vapor-at-jupiter-s-moon-ganymede

67) "Cosmic lens flare," ESA Science & Exploration, 23 July 2021, URL: https://www.esa.int/ESA_Multimedia/Images/2021/07/Cosmic_lens_flare

68) "A large tidal stream observed in the Sombrero galaxy," IAC (Instituto de Astrofísica de Canarias) Press Release, 21 July 2021, URL:https://www.iac.es/en/outreach/news/large-tidal-stream-observed-sombrero-galaxy

69) David Martínez-Delgado, Javier Román, Denis Erkal, Mischa Schirmer, Santi Roca-Fábrega, Seppo Laine, Giuseppe Donatiello, Manuel Jimenez, David Malin, Julio A Carballo-Bello, "A feather on the hat: Tracing the giant stellar stream around the Sombrero galaxy," MNRAS, stab1874, Published: 20 July 2021, https://doi.org/10.1093/mnras/stab1874

70) "Hubble Returns to Full Science Observations and Releases New Images," NASA Feature, 19 July 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-returns-to-full-science-observations-and-releases-new-images

71) Claire Andreoli, Alise Fisher, Elizabeth Landau, Rob Gutro, "NASA Returns Hubble Space Telescope to Science Operations," NASA Feature, 17 July 2021, URL: https://www.nasa.gov/feature/goddard/2021/operations-underway-to-restore-payload-computer-on-nasas-hubble-space-telescope

72) "NASA Successfully Switches to Backup Hardware on Hubble Space Telescope," NASA Feature, 16 July 2021, URL: https://www.nasa.gov/feature/goddard/2021/operations-underway-to-restore-payload-computer-on-nasas-hubble-space-telescope

73) "A star in a distant galaxy blew up in a powerful explosion, solving an astronomical mystery," Tel-Aviv University News Release, 14 July 2021, URL: https://www.eurekalert.org/pub_releases/2021-07/tu-asi071421.php

74) Daichi Hiramatsu, D. Andrew Howell, Schuyler D. Van Dyk, Jared A. Goldberg, Keiichi Maeda, Takashi J. Moriya, Nozomu Tominaga, Ken'ichi Nomoto, Griffin Hosseinzadeh, Iair Arcavi, Curtis McCully, Jamison Burke, K. Azalee Bostroem, Stefano Valenti, Yize Dong, Peter J. Brown, Jennifer E. Andrews, Christopher Bilinski, G. Grant Williams, Paul S. Smith, Nathan Smith, David J. Sand, Gagandeep S. Anand, Chengyuan Xu, Alexei V. Filippenko, Melina C. Bersten, Gastón Folatelli, Patrick L. Kelly, Toshihide Noguchi, Koichi Itagaki, "The electron-capture origin of supernova 2018zd," Nature Astronomy Letters, Published: 28 June 2021, https://doi.org/10.1038/s41550-021-01384-2, URL: https://is.gd/ADVWx3

75) "One of the greats," ESA Science & Exploration, 09 July 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_05_-_09_July_2021

76) "A scattering of stars," ESA Science & Exploration, 02 July 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_28_June_-_02_July_2021

77) Rob Gutro, "Operations Underway to Restore Payload Computer on NASA's Hubble Space Telescope," NASA Feature, 30 June 2021, URL: https://www.nasa.gov/feature/goddard/2021/operations-underway-to-restore-payload-computer-on-nasas-hubble-space-telescope

78) "Clash of the Titans," ESA Science & Exploration, 26 June 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_21_-_25_June_2021

79) Jeff Foust, "Computer problem takes Hubble offline," SpaceNews, 19 June 2021, URL: https://spacenews.com/computer-problem-takes-hubble-offline/

80) "A galactic powerhouse," ESA Science & Exploration, 18 June 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_14_-_18_June_2021

81) "Precise Distance to Galaxy Bolsters Missing Dark Matter Claim," NASA HubbleSite, 17 June 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-025.html

82) Claire Andreoli, Donna Weaver, Ray Villard, "Mystery of Galaxy's Missing Dark Matter Deepens," NASA Feature, 17 June 2021, URL: https://www.nasa.gov/feature/goddard/2021/mystery-of-the-galaxys-missing-dark-matter-deepens

83) Zili Shen, Shany Danieli, Pieter van Dokkum, Roberto Abraham, Jean P. Brodie, Charlie Conroy, Andrew E. Dolphin, Aaron J. Romanowsky, J. M. Diederik Kruijssen, and Dhruba Dutta Chowdhury, "A Tip of the Red Giant Branch Distance of 22.1 ± 1.2 Mpc to the Dark Matter Deficient Galaxy NGC 1052–DF2 from 40 Orbits of Hubble Space Telescope Imaging," The Astrophysical Journal Letters, Volume 914, Number 1, Published: 9 June 2021, https://doi.org/10.3847/2041-8213/ac0335

84) "Operations Underway to Restore Payload Computer on NASA's Hubble Space Telescope," NASA Feature, 16 June 2021, URL: https://www.nasa.gov/feature/goddard/2021/operations-underway-to-restore-payload-computer-on-nasas-hubble-space-telescope

85) "A Spiral Amongst Friends," ESA Science & Exploration, 11 June 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_07_-_11_June_2021

86) "Astronomers Probe Layer-Cake Structure of Brown Dwarf's Atmosphere," NASA HubbleSite, 09 June 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-028#section-id-2

87) "The eponymous NGC 691," ESA Science & Exploration, 4 June 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_31_May_-_04_June_2021

88) "Hubble Captures a Captivating Spiral," NASA Feature, 28 May 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-captures-a-captivating-spiral

89) "A distant spiral in Virgo," ESA Science & Exploration, 28 May 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_24_-_28_May_2021

90) "Lopsided galaxy 2276," NASA HubbleSite News, 27 May 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-029?news=true

91) "Hubble Inspects a Contorted Spiral Galaxy," heic2106 — Photo Release, 27 May 2021, URL: https://esahubble.org/news/heic2106/?lang

92) "A menagerie of galaxies," ESA Science & Exploration, 21 May 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_17_-_21_May_2021

93) "Hubble tracks down fast radio bursts to galaxies' spiral arms," NASA HubbleSite, 20 May 2021, Release ID: 2021-010, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-010.html#section-id-2

94) "Cosmic silver lining," ESA Science & Exploration, 14 May 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_10_-_14_May_2021

95) "Our giant universe," ESA Science & Exploration, 7 May 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_03_-_07_April_2021

96) "In the sky with diamonds," ESA Science & Exploration, 30 April 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_26_-_30_April_2021

97) Claire Andreoli, Claire Blome, Ray Villard, Lynn Jenner, "Hubble Watches How a Giant Planet Grows," NASA Feature, 29 April 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-watches-how-a-giant-planet-grows

98) Yifan Zhou, Brendan P. Bowler, Kevin R. Wagner, Glenn Schneider, Dániel Apai, Adam L. Kraus, Laird M. Close, Gregory J. Herczeg, and Min Fang, "Hubble Space Telescope UV and Hα Measurements of the Accretion Excess Emission from the Young Giant Planet PDS 70 b," The Astronomical Journal, Volume 161, Number 5, Published 29 April 2021, https://doi.org/10.3847/1538-3881/abeb7a

99) "Hubble Celebrates 31st Birthday with Giant Star on the Edge of Destruction," ESA/Hubble photo release heic2105, 23 April 2021, URL: https://esahubble.org/news/heic2105/?lang

100) "Galactic close-up," ESA science & Exploration, 23 April 2021, URL: https://esahubble.org/images/potw2116a/

101) "Light bends from the beyond," ESA Science & Exploration, 16 April 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_12_-_16_April_2021

102) "Spiral snapshot," ESA Science & Exploration, 9 April 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_05_-_09_April_2021

103) "Space Telescope Science Institute Celebrates Its 40th Anniversary," NASA HubbleSite, 08 April 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-11

104) "Hubble Spots Double Quasars in Merging Galaxies," NASA HubbleSite, 06 April 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-14

105) Yue Shen, Yu-Ching Chen, Hsiang-Chih Hwang, Xin Liu, Nadia Zakamska, Masamune Oguri, Jennifer I-Hsiu Li, Joseph Lazio & Peter Breiding , "A hidden population of high-redshift double quasars unveiled by astrometry," Nature Astronomy Letter, Published: 01 April 2021, https://doi.org/10.1038/s41550-021-01323-1

106) "Hubble Revisits the Veil Nebula," NASA, 2 April 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-revisits-the-veil-nebula

107) "NASA has selected 24 new Fellows for its prestigious NASA Hubble Fellowship Program (NHFP)," NASA HubbleSite, 31 March 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-16

108) "A peculiar sight," ESA Science & Exploration, 26 March 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_22_-_26_March_2021

109) "A flash of life," ESA Science & Exploration, 19 March 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_15_-_19_March_2021

110) "Hubble Sees Changing Seasons on Saturn," NASA Feature, 18 March 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/saturn-season-change

111) "Hubble Shows Torrential Outflows from Infant Stars May Not Stop Them from Growing," NASA Feature, 18 March 2021, URL: https://www.nasa.gov/feature/goddard/2021/hubble-shows-torrential-outflows-from-infant-stars-may-not-stop-them-from-growing

112) Nolan M. Habel, S. Thomas Megeath, Joseph Jon Booker, William J. Fischer, Marina Kounkel, Charles Poteet, Elise Furlan, Amelia Stutz, P. Manoj, John J. Tobin, Zsofia Nagy, Riwaj Pokhrel, Dan Watson, "An HST Survey of Protostellar Outflow Cavities: Does Feedback Clear Envelopes?," The Astrophysical Journal, Draft version February 16, 2021, URL: https://arxiv.org/pdf/2102.06717.pdf

113) Jeff Foust, "Aging Hubble returns to operations after software glitch," Space News, 12 March 2021, URL: https://spacenews.com/aging-hubble-returns-to-operations-after-software-glitch/

114) "NASA's Hubble Space Telescope Resumes Science Operations," NASA, 12 March 2021, URL: https://www.nasa.gov/feature/goddard/2021/nasa-s-hubble-space-telescope-set-to-resume-science-operations

115) "Hubble Sees New Atmosphere Forming on a Rocky Exoplanet," heic2104 — Science Release, 11 March 2021, URL: https://esahubble.org/news/heic2104/?lang

116) "Distant Planet May Be on Its Second Atmosphere, NASA's Hubble Finds," NASA/JPL, 11 March 2021, URL: https://www.jpl.nasa.gov/news/distant-planet-may-be-on-its-second-atmosphere-nasas-hubble-finds?utm_source=iContact&utm_medium=email&utm_campaign=nasajpl&utm_content=Exoplanet20210311-1

117) "Big, beautiful and blue," ESA Science & Exploration, 05 March 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_01_-_05_March_2021

118) Claire Andreoli, Lynn Jenner, "Hubble Beholds a Big, Beautiful Blue Galaxy," NASA, 5 March 2021, URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-beholds-a-big-beautiful-blue-galaxy

119) "Hubble Solves Mystery of Monster Star's Dimming," HubbleSite News, 04 March 2021, URL: https://hubblesite.org/contents/news-releases/2021/news-2021-09

120) Roberta M. Humphreys, Kris Davidson, A. M. S. Richards, L. M. Ziurys, Terry J. Jones, and Kazunori Ishibashi, "The Mass-loss History of the Red Hypergiant VY CMa*," The Astronomical Journal, Volume 161, Number 3, Published: 4 February 2021, https://doi.org/10.3847/1538-3881/abd316

121) Eye in the sky," ESA Science & Exploration, 26 February 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_22_-_26_February_2021

122) "Hubble Captures an Eye in the Sky – "Evil Eye" Galaxy With Strange Internal Motion," SciTech Daily, 21 February, 2021, URL: https://scitechdaily.com/hubble-captures-an-eye-in-the-sky-evil-eye-galaxy-with-strange-internal-motion/

123) "Comet Makes a Pit Stop Near Jupiter's Asteroids," NASA/JPL News, 25 February 2021, URL: https://www.jpl.nasa.gov/news/comet-makes-a-pit-stop-near-jupiters-asteroids?utm_source=iContact&utm_medium=email&utm_campaign=nasajpl&utm_content=hubble20210225-1

124) Bryce T. Bolin, Yanga R. Fernandez, Carey M. Lisse, Timothy R. Holt, Zhong-Yi Lin, Josiah N. Purdum, Kunal P. Deshmukh, James M. Bauer, Eric C. Bellm, Dennis Bodewits, Kevin B. Burdge, Sean J. Carey, Chris M. Copperwheat, George Helou, Anna Y. Q. Ho, Jonathan Horner, Jan van Roestel, Varun Bhalerao, Chan-Kao Chang, Christine Chen, Chen-Yen Hsu, Wing-Huen Ip, Mansi M. Kasliwal, Frank J. Masci, Chow-Choong Ngeow, Robert Quimby, Rick Burruss, Michael Coughlin, Richard Dekany, Alexandre Delacroix, Andrew Drake, Dmitry A. Duev, Matthew Graham, David Hale, Thomas Kupfer, Russ R. Laher, Ashish Mahabal, Przemyslaw J. Mróz, James D. Neill, Reed Riddle, Hector Rodriguez, Roger M. Smith, Maayane T. Soumagnac, Richard Walters, Lin Yan, and Jeffry Zolkower, "Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS), Using Hubble, Spitzer, ZTF, Keck, Apache Point Observatory, and GROWTH Visible and Infrared Imaging and Spectroscopy," The Astronomical Journal, Volume 161, No 3, Published: 11 February 2021, https://doi.org/10.3847/1538-3881/abd94b

125) "Tantrums of a baby star," ESA Science & Exploration, 19 February 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_15_-_19_February_2021

126) A cosmic hourglass," ESA Science & Exploration, 12 February 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_08_-_12_February_2021

127) "Hubble Uncovers Concentration of Small Black Holes," heic2103 — Science Release, 11 February 2021, URL: https://esahubble.org/news/heic2103/?lang

128) Eduardo Vitral and Gary A. Mamon, "Does NGC 6397 contain an intermediate-mass black hole or a more diffuse inner subcluster?," Astronomy & Astrophysics, Volume 646, Published: 11 February 2021, Article No: A63, https://doi.org/10.1051/0004-6361/202039650

129) "The modest galaxy," ESA Science & Exploration, 5 February 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_01_-_05_February_2021

130) "An interstellar distributor," ESA Science & Exploration, 29 January 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_25_-_29_January_2021

131) "Colors of the lost galaxy," ESA Science & Exploration, 22 January 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_18_-_22_January_2021

132) "Hubble Takes Portrait of the ‘Lost Galaxy'," NASA, 21 January 2021: URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-takes-portrait-of-the-lost-galaxy

133) Janice C. Lee,Bradley C. Whitmore,David A. Thilker, Sinan Deger, Kirsten L. Larson, Leonardo Ubeda,Gagandeep S. Anand, Mederic Boquien, Rupali Chandar,Daniel A. Dale,Eric Emsellem, Adam K. Leroy, Erik Rosolowsky, Eva Schinnerer, Judy Schmidt, Jordan Turner, Schuyler Van Dyk, Richard L. White, Ashley T. Barnes, Francesco Belfiore, Frank Bigiel, Guillermo A. Blanc, Yixian Cao, Melanie Chevance, Enrico Congiu, Oleg V. Egorov, Simon C. O. Glover, Kathryn Grasha, Brent Groves, Jonathan Henshaw, Annie Hughes, Ralf S. Klessen, Eric Koch, Kathryn Kreckel, J. M. Diederik Kruijssen, Daizhong Liu, Laura A. Lopez, Ness Mayker, Sharon E. Meidt, Eric J. Murphy, Hsi-An Pan, J éróme Pety, Miguel Querejeta, Alessandro Razza, Toshiki Saito, Patricia S ánchez-Bl ázquez, Francesco Santoro, Amy Sardone, Fabian Scheuermann, Andreas Schruba, Jiayi Sun, Antonio Usero, E. Watkins, and Thomas G. Williams, "The PHANGS-HST Survey:Physics at High Angular resolution in Nearby GalaxieS with the Hubble Space Telescope," Astrophysics of Galaxies, Draft version January 11, 2021, https://arxiv.org/pdf/2101.02855.pdf

134) "Astronomers dissect the anatomy of planetary nebulae using Hubble Space Telescope images, Researchers from RIT and Green Bank Observatory shed new light on nebula formation processes," RIT News, 15 January 2021, URL: https://www.rit.edu/news/astronomers-dissect-anatomy-planetary-nebulae-using-hubble-space-telescope-images

135) "Sculpted in sculptor," ESA Science & Exploration, 15 January 2021, URL: https://www.esa.int/About_Us/Week_in_images/Week_in_images_11_-_15_January_2021

136) Claire Andreoli, Donna Weaver, Ray Villard, John Banovetz, Danny Milisavljevic, "Researchers Rewind the Clock to Calculate Age and Site of Supernova Blast," NASA Feature, 14 January 2021, URL: https://www.nasa.gov/feature/goddard/2021/researchers-rewind-the-clock-to-calculate-age-and-site-of-supernova-blast

137) "Hubble Pinpoints Supernona Blast," ESA Hubble heic2102 — Photo Release, 15 January 2021, URL: https://esahubble.org/news/heic2102/?lang

138) Lynn Jenner, "Hubble Views a Dazzling ‘Fireworks Galaxy'," NASA Feature, 8 January 2021: URL: https://www.nasa.gov/image-feature/goddard/2021/hubble-views-a-dazzling-fireworks-galaxy/

139) "When Galaxies Collide: Hubble Showcases 6 Beautiful Galaxy Mergers," Hubble, heic2101 — Photo Release, 7 January 2021, URL: https://esahubble.org/news/heic2101/

140) A. Adamo, K. Hollyhead, M. Messa, J. E. Ryon, V. Bajaj, A. Runnholm, S. Aalto, D. Calzetti, J. S. Gallagher, M. J. Hayes, J. M. D. Kruijssen, S. König, S. S. Larsen, J. Melinder, E. Sabbi, L. J. Smith, G. Östlin, "Star cluster formation in the most extreme environments: insights from the HiPEEC survey," MNRAS, Volume 499, Issue 3, December 2020, Pages 3267–3294, https://doi.org/10.1093/mnras/staa2380
 

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (eoportal@symbios.space).