In the decades following the launch of NASA’s , astronomers have tallied over 1 trillion galaxies in the universe. But only one galaxy stands out as the most important nearby stellar island to our Milky Way — the Andromeda galaxy. It can be seen with the naked eye on clear autumn nights as a faint oval object roughly the size of the moon.

A century ago, astronomer Edwin Hubble first established that this so-called “spiral nebula” was approximately 2.5 million light years away from our own Milky Way galaxy.

Now, the space telescope named after Hubble has accomplished the most comprehensive survey of this galaxy. The work yields new clues to the evolutionary history of Andromeda — and it looks markedly different from the Milky Way’s history.

91̽�� astronomers presented the findings Jan. 16 in Maryland at a meeting of the , and in an accompanying published the same date in The Astrophysical Journal.

Without Andromeda as an example of a spiral galaxy, astronomers would know much less about the structure and evolution of our own Milky Way. That’s because Earth is embedded inside the Milky Way. This is like trying to understand the layout of New York City by standing in the middle of Central Park.��

“With Hubble we can get into enormous detail about what’s happening on a holistic scale across the entire disk of the galaxy. You can’t do that with any other large galaxy,” said principal investigator , a 91̽��research associate professor of astronomy.����

Hubble’s sharp imaging capabilities can resolve more than 200 million stars in the Andromeda galaxy, detecting only stars brighter than our sun. They look like grains of sand across the beach. But the telescope can’t capture everything. Andromeda’s total population is estimated to be 1 trillion stars, with many less massive stars falling below Hubble’s sensitivity limit.��

Photographing Andromeda was a Herculean task because the galaxy is a much bigger target in the sky than the galaxies Hubble routinely observes, which are often billions of light years away. The full mosaic was carried out under two Hubble programs. In total it required over 1,000 Hubble orbits, spanning more than a decade.��

This panorama started about a decade ago with the . Images were obtained at near-ultraviolet, visible and near-infrared wavelengths using instruments aboard Hubble to photograph the northern half of Andromeda.��

This has now been followed by the newly published . This phase added images of approximately 100 million stars in the southern half of Andromeda. This southern region is structurally unique and more sensitive to the galaxy’s merger history than the northern disk mapped earlier.��

Combined, the two programs collectively cover the entire disk of Andromeda, which is seen almost edge on — tilted by 77 degrees relative to the view we see from Earth. The galaxy is so large that the mosaic is assembled from approximately 600 separate fields of view. The mosaic image is made up of at least 2.5 billion pixels.��

“The asymmetry between the two halves — now visually evident in this image — is incredibly intriguing,” said , a 91̽��postdoctoral researcher in astronomy and lead author of the accompanying . “It’s fascinating to see the detailed structures of an external spiral galaxy mapped over such a large, contiguous area.”��

The complementary Hubble survey programs provide information about the age, heavy-element abundance and stellar masses inside Andromeda. This will allow astronomers to distinguish between competing scenarios where Andromeda merged with one or more galaxies. Hubble’s detailed measurements constrain models of Andromeda’s merger history and disk evolution.��

“This ambitious photography of the Andromeda galaxy sets a new benchmark for precision studies of large spiral galaxies,” Chen said.��

Though the Milky Way and Andromeda galaxies formed presumably around the same time many billions of years ago, observational evidence shows that they have very different evolutionary histories, despite growing up in the same cosmological neighborhood. Andromeda seems to be more highly populated with younger stars and unusual features like coherent streams of stars, researchers say. This implies it has a more active recent star formation and interaction history than the Milky Way.��

“This detailed look at the resolved stars will help us to piece together the galaxy’s past merger and interaction history,” Williams said.��

This research was funded by NASA and the Simons Foundation. A full list of co-authors is listed with the .

For more information, contact Williams at benw1@uw.edu or Chen at zczhuo@uw.edu.��

This article was adapted from a by the Space Telescope Science Institute. See related posts from and the .

A team of scientists based in the U.S. and Canada recently confirmed that carbon and other star-formed atoms don’t just drift idly through space until they are dragooned for new uses. For galaxies like ours, which are still actively forming new stars, these atoms take a circuitous journey. They circle their galaxy of origin on giant currents that extend into intergalactic space. These currents — known as the circumgalactic medium — resemble giant conveyor belts that push material out and draw it back into the galactic interior, where gravity and other forces can assemble these raw materials into planets, moons, asteroids, comets and even new stars.

“Think of the circumgalactic medium as a giant train station: It is constantly pushing material out and pulling it back in,” said team member , a 91̽�� doctoral candidate. “The heavy elements that stars make get pushed out of their host galaxy and into the circumgalactic medium through their explosive supernovae deaths, where they can eventually get pulled back in and continue the cycle of star and planet formation.”

Garza is lead author on a describing these findings that was published Dec. 27 in the Astrophysical Journal Letters.

“The implications for galaxy evolution, and for the nature of the reservoir of carbon available to galaxies for forming new stars, are exciting,” said co-author , 91̽��professor and chair of the Department of Astronomy. “The same carbon in our bodies most likely spent a significant amount of time outside of the galaxy!”

In 2011, a team of scientists for the first time confirmed the long-held theory that — and that this large, circulating cloud of material includes hot gases enriched in oxygen. Garza, Werk and their colleagues have discovered that the circumgalactic medium of star-forming galaxies also circulates lower-temperature material like carbon.

“We can now confirm that the circumgalactic medium acts like a giant reservoir for both carbon and oxygen,” said Garza. “And, at least in star-forming galaxies, we suggest that this material then falls back onto the galaxy to continue the recycling process.”

Studying the circumgalactic medium could help scientists understand how this recycling process subsides, which will happen eventually for all galaxies — even ours. One theory is that a slowing or breakdown of the circumgalactic medium’s contribution to�������� ��the recycling process may explain why a galaxy’s stellar populations decline over long periods of time.

“If you can keep the cycle going — pushing material out and pulling it back in — then theoretically you have enough fuel to keep star formation going,” said Garza.

For this study, the researchers used the Cosmic Origins Spectrograph on the Hubble Space Telescope. The spectrograph measured how light from nine distant quasars — ultra-bright sources of light in the cosmos — is affected by the circumgalactic medium of 11 star-forming galaxies. The Hubble readings indicated that some of the light from the quasars was being absorbed by a specific component in the circumgalactic medium: carbon, and lots of it. In some cases, they detected carbon extending out almost 400,000 light years — or four times the diameter of our own galaxy — into intergalactic space.

Future research is needed to quantify the full extent of the other elements that make up the circumgalactic medium and to further compare how their compositions differ between galaxies that are still making large amounts of stars and galaxies that have largely ceased star formation. Those answers could illuminate not just when galaxies like ours transition into stellar deserts, but why.

Co-authors on the paper are , research fellow at the Herzberg Astronomy and Astrophysics Research Centre in British Columbia; , a 91̽��postdoctoral researcher in astronomy; , a research fellow at the University of Colorado Boulder; , assistant professor of physics at North Carolina State University; and , professor of physics and astronomy at the University of Victoria. The research was funded by NASA and the National Science Foundation.

For more information, contact Garza at samgarza@uw.edu and Werk at jwerk@uw.edu.

Since 2018 the��, an international astronomical collaboration based at the Palomar Observatory in California, has scanned the entire sky every two to three nights. As part of this mission, the ZTF’s has been counting and cataloguing supernovae — flashes of light in the sky that are the telltale signs of stars dying in spectacular explosions.

On Dec. 4, ZTF researchers — including astronomers at the 91̽�� — announced that that they have identified more than 10,000 of these stellar events, the largest number ever identified by an astronomical survey.

“There are trillions of stars in the universe, and about every second, one of them explodes,” said Christoffer Fremling, an astronomer at Caltech who leads the Bright Transient Survey. “ZTF detects hundreds of these explosions per night and a handful are then confirmed as supernovae. Systematically doing this for seven years has led to the most complete record of confirmed supernovae to date.”

The Bright Transient Survey is currently the primary discovery pipeline for cosmic flashes — also known as astronomical transients — in the world. To determine which transients are supernovae, ZTF shares a stream of nightly transient detections with the wider astronomical community so that other telescopes around the world can conduct follow-up observations of candidate transients. This includes conducting a spectral analysis, in which instruments on observatory telescopes split the light from a transient object into its individual colors to reveal its distance from Earth and other properties.

“Classifying 10,000 supernovae is a tremendous achievement and will enable unprecedented scientific studies of explosive transients,” said ZTF team member , a 91̽��research associate professor of astronomy and scientist with the UW’s . “Reaching this milestone required careful technical work on scheduling and processing the ZTF discovery images, human and machine vetting of the alerts and obtaining timely follow-up spectra.”

For the Bright Transient Survey, a 60-megapixel wide-field camera mounted on Palomar’s Samuel Oschin telescope scanned the entire visible sky every two nights. To detect new astronomical events, astronomers subtracted images of the same portion of the sky from subsequent scans. Next, members of the ZTF team studied the subtracted images and triggered follow-up spectral observations by a second telescope at Palomar or other observatories.

Bellm, 91̽��research scientist and , 91̽��professor of astronomy and director of the DiRAC Institute, all contributed to the Bright Transient Survey. Bellm managed alerts of new transients and scheduled imaging for the survey. Jurić helped set up the ZTF’s automated system to alert team members around the world of new transients.

Developing automated analysis pipelines and alert systems are critical for the field as more powerful imaging technologies and new generations of observatories continue to transform astronomy into a “big data” endeavor. , a 20th century astronomer who first coined the term “supernova,” identified 120 supernovae in 52 years. The Bright Transient Survey by the ZTF — named for Zwicky — found 10,000 in a fraction of that time.

“The Bright Transient Survey program serves as an exemplar for the kinds of science we hope to do with the in the near future,” said Bellm.

Under construction in Chile, the Vera C. Rubin Observatory is the future home of the Legacy Survey of Space and Time, or LSST, a mission that will take deep images of the sky nightly and detect even more cosmic transients than ZTF. 91̽��scientists with the DiRAC Institute have been heavily involved in planning for the launch of the LSST. Collaborations like the ZTF have been a proving ground for developing and testing methods for use in the LSST.

For the Bright Transient Survey, Graham conducted follow-up spectral analyses of transients at in New Mexico. These efforts were especially valuable in catching some of the fainter, fading supernovae that would have been missed at Palomar.

“As 91̽��astronomers, we are so fortunate to have access to the Apache Point Observatory for our research,” said Graham. “One of the most impactful — and fun — parts of obtaining optical spectra is being surprised by rare transients with peculiar characteristics, which often reveal more about supernova physics than hundreds of ordinary objects. Figuring out how to do this work with the even larger number of LSST supernovae is the next big challenge.”

Most of the transients in the Bright Transient Survey are classified as one of two common types of supernovae: Type Ia, when a white dwarf steals so much material from another nearby star that it explodes, or Type II, when massive stars collapse and die under their own gravity. Thanks to the treasure trove of data from the Bright Transient Survey, astronomers are now better equipped to answer questions about how stars grow and die, as well as how dark energy drives the expansion of the universe.

After its expected 2025 commissioning, the Vera Rubin C. Observatory could discover millions more supernovae.

“The machine learning and AI tools we have developed for ZTF will become essential when the Vera Rubin Observatory begins operations,” said ZTF team member Daniel Perley, an astronomer at Liverpool John Moores University. “We have already planned to work closely with Rubin to transfer our machine learning knowledge and technology.”

With an additional $1.6 million of funding from the National Science Foundation, ZTF will continue to scan the night sky for the next two years.

“The period in 2025 and 2026 when ZTF and Vera Rubin can both operate in tandem is fantastic news for time-domain astronomers,” said Mansi Kasliwal, an astronomy professor at Caltech who will lead ZTF in the next two years. “Combining data from both observatories, astronomers can directly address the physics of why supernovae explode and discover fast and young transients that are inaccessible to ZTF or Rubin alone. I am excited about the future.”

For more information, contact Bellm at ecbellm@uw.edu and Graham at mlg3k@uw.edu.

Adapted from a by Caltech.

The universe is a dynamic place where galaxies are dancing, merging and shifting appearance. Unfortunately, because these changes take millions or billions of years, telescopes can only provide snapshots, squeezed into a human lifetime.

Luckily, galaxies leave behind clues to their histories and origins. NASA’s upcoming will have the capacity to look for these “fossils” of galaxy formation by conducting high-resolution imaging of galaxies in the nearby universe.

Through a grant from NASA, astronomers are designing a set of possible observations called RINGS — the Roman Infrared Nearby Galaxies Survey — that would collect these images, and the team is producing publicly available tools that the astronomy community can use once Roman launches and starts collecting data.

“Roman is the next flagship NASA mission, and it will provide a treasure trove of new data for unraveling the evolutionary histories of galaxies,” said RINGS principal investigator , a 91̽�� research associate professor of astronomy.

Roman is uniquely prepared for RINGS due to its resolution, which is akin to NASA’s Hubble Space Telescope, as well as its wide field of view — 200 times that of Hubble in the infrared — making it a sky survey telescope that complements Hubble’s narrow-field capabilities.

Galaxies leave behind “hints” about how they evolved, embedded in their stellar structures — similar to how living organisms on Earth can leave behind imprints in rock. These “galactic fossils” are groups of ancient stars that hold the history of the galaxy’s formation and evolution, including the complex chemical makeup of the galaxy when those stars formed.

Such cosmic fossils are of particular interest to , the deputy principal investigator of RINGS and an assistant professor at the University of Pennsylvania. She describes the process of analyzing stellar structures in galaxies as “like going through an excavation and trying to sort out bones and put them back together.”

Roman’s high resolution will allow scientists to pick out these galactic fossils, using structures ranging from long tidal tails on a galaxy’s outskirts to stellar streams within it. These large-scale structures, which Roman is uniquely capable of capturing, can give clues to a galaxy’s merger history. The goal is to “reassemble these fossils in order to look back in time and understand how these galaxies came to be,” said Sanderson.

RINGS will also enable further investigations of one of the most mysterious substances in the universe: dark matter, an invisible form of matter that makes up most of a galaxy’s mass. Scientist cannot currently directly detect dark matter and do not know what it consists of. Yet there exists a particularly useful class of objects for testing dark matter theories: ultra-faint dwarf galaxies.

“Ultra faint dwarf galaxies are so dark matter-dominated that they have very little normal matter for star formation,” said , professor at the University of California, Santa Cruz. “With so few stars being created, ultra-faint galaxies can essentially be seen as pure blobs of dark matter to study.”

Roman, thanks to its large field of view and high resolution, will observe these ultra-faint galaxies to help test multiple theories of dark matter. With these new data, the astronomical community will come closer to finding the truth about this unobservable dark matter that vastly outweighs visible matter: Dark matter makes up about 80% of the universe’s matter while normal matter comprises the remaining 20%.

Ultra-faint galaxies are far from the only test of dark matter. Often, just looking in an average-sized galaxy’s backyard is enough. Structures in the halo of stars surrounding a galaxy often give hints to the amount of dark matter present. But, due to the sheer size of galactic halos — they are often 15-20 times as big as the galaxy itself — current telescopes are deeply inefficient at observing them.

At the moment, the only fully resolved galactic halos scientists have to go on are our own Milky Way and Andromeda, our neighbor galaxy.

“We only have reliable measurements of the Milky Way and Andromeda, because those are close enough that we can get measurements of a large number of stars distributed across their stellar halos,” said Williams. “So, with Roman, all of a sudden we’ll have 100 or more of these fully resolved galaxies.”

When Roman launches by May 2027, it is expected to fundamentally alter how scientists understand galaxies. In the process, it will shed some light on our own home galaxy. The Milky Way is easy to study up close, but we do not have a large enough selfie stick to take a photo of our entire galaxy and its surrounding halo. RINGS shows what Roman is capable of should such a survey be approved. By studying the nearby universe, RINGS can examine galaxies similar in size and age to the Milky Way, and shed light on how we came to be here.

For more information, contact Williams at benw1@uw.edu.

Adapted from a by NASA’s Space Telescope Science Institute.

For decades, scientists have known that some galaxies reside in dense environments with lots of other galaxies nearby. Others drift through the cosmos essentially alone, with few or no other galaxies in their corner of the universe.

A new study has found a major difference between galaxies in these divergent settings: Galaxies with more neighbors tend to be larger than their counterparts, which have a similar shape and mass, but reside in less dense environments. In a published Aug. 14 in the Astrophysical Journal, researchers at the 91̽��, Yale University, the Leibniz Institute for Astrophysics Potsdam in Germany and Waseda University in Japan report that galaxies found in denser regions of the universe are as much as 25% larger than isolated galaxies.

The research, which used a new machine-learning tool to analyze millions of galaxies, helps resolve a long-standing debate among astrophysicists over the relationship between a galaxy’s size and its environment. The findings also raise new questions about how galaxies form and evolve over billions of years.

“Current theories of galaxy formation and evolution cannot adequately explain the finding that clustered galaxies are larger than their identical counterparts in less dense regions of the universe,” said lead author , a 91̽��postdoctoral researcher in astronomy and with the UW’s . “That’s one of the most interesting things about astrophysics. Sometimes what the theories predict we should find and what a survey actually finds are not in agreement, and so we go back and try to modify existing theories to better explain the observations.”

Past studies that looked into the relationship between galaxy size and environment came up with contradictory results. Some determined that galaxies in clusters were smaller than isolated galaxies. Others came to the opposite conclusion. The studies were generally much smaller in scope, based on observations of hundreds or thousands of galaxies.

In this new study, Ghosh and his colleagues utilized a survey of millions of galaxies conducted using the in Hawaii. This endeavor, known as the , took high-quality images of each galaxy. The team selected approximately 3 million galaxies with the highest-quality data and used a machine learning algorithm to determine the size of each one. Next, the researchers essentially placed a circle — one with a radius of 30 million light years — around each galaxy. The circle represents the galaxy’s immediate vicinity. They then asked a simple question: How many neighboring galaxies lie within that circle?

The answer showed a clear general trend: Galaxies with more neighbors were also on average larger.

There could be many reasons why. Perhaps densely clustered galaxies are simply larger when they first form, or are more likely to undergo efficient mergers with close neighbors. Perhaps dark matter — that mysterious substance that makes up most of the matter in the universe, yet cannot be detected directly by any current means – plays a role. After all, galaxies form within individual “halos” of dark matter and the gravitational pull from those halos plays a critical role in how galaxies evolve.

“Theoretical astrophysicists will have to perform more comprehensive studies using simulations to conclusively establish why galaxies with more neighbors tend to be larger,” said Ghosh. “For now, the best we can say is that we’re confident that this relationship between galaxy environment and galaxy size exists.”

Utilizing an incredibly large dataset like the Hyper Suprime-Cam Subaru Strategic Program helped the team reach a clear conclusion. But that’s only part of the story. The novel machine learning tool they used to help determine the size of each individual galaxy also accounted for inherent uncertainties in the measurements of galaxy size.

“One important lesson we had learned prior to this study is that settling this question doesn’t just require surveying large numbers of galaxies,” said Ghosh. “You also need careful statistical analysis. A part of that comes from machine learning tools that can accurately quantify the degree of uncertainty in our measurements of galaxy properties.”

The machine learning tool that they used is called GaMPEN — or Galaxy Morphology Posterior Estimation Network. As a doctoral student at Yale, Ghosh led development of GaMPEN, which was unveiled in papers published in and in the Astrophysical Journal. The tool is freely available online and could be adapted to analyze other large surveys, said Ghosh.

Though this new study focuses on galaxies, it also forecasts the types of research — centered on complex analyses of incredibly large datasets — that will soon take astronomy by storm. When a generation of new telescopes with powerful cameras, including the in Chile, come online, they will collect massive amounts of data on the cosmos every night. In anticipation, scientists have been developing new tools like GaMPEN that can utilize these large datasets to answer pressing questions in astrophysics.

“Very soon, large datasets will be the norm in astronomy,” said Ghosh. “This study is a perfect demonstration of what you can do with them — when you have the right tools.”

Co-authors on the study are , professor of physics and of astronomy at Yale; , a research fellow with the Leibniz Institute; , associate professor at Waseda University; , a Yale professor of astronomy; , professor of physics and of astronomy at Yale; , a doctoral student at Yale; and , professor of astronomy at the 91̽��and faculty member in the DiRAC Institute and the . The research was funded by NASA, the Yale Graduate School of Arts & Sciences, the John Templeton Foundation, the Charles and Lisa Simonyi Fund for Arts and Sciences, the Washington Research Foundation and the 91̽��eScience Institute.

For more information, contact Ghosh at aritrag@uw.edu.

On Monday, large parts of the United States will experience a . This eclipse is expected to be a more significant event than the one in 2017, and the next one visible from the U.S. won’t happen until 2044. The sky will darken in Uvalde, Texas, just seconds before 2:30 p.m. Eastern Time (1:30 p.m. local time in Texas) on April 8. The will then arc up through Arkansas, Missouri, Illinois, Ohio and New York state before exiting the U.S. over Maine at 3:30 p.m. Eastern Time. Seattle is on the outer edge of the eclipse’s effects, with skies expected to darken here just 20% below regular levels.��

Among the many people travelling to witness the total eclipse firsthand will be , a 91̽�� research assistant professor of Earth and space sciences, along with four 91̽��graduate students. This effort is funded in part by the .

Journaux’s research combines results from experiments and space missions to understand Earth as well as other planets and moons within our solar system. For this trip he will bring a special telescope to capture the unique view of the sun and surrounding skies that becomes possible during a solar eclipse. ��

91̽��News asked Baptiste about the upcoming trip as part of an occasional series, “In the Field,” highlighting 91̽��field efforts.��

Where are you going, and when?����

Baptiste Journaux: We are currently aiming for somewhere along the border between Arkansas and Oklahoma. We will be there Sunday and Monday. The final location on Monday will depend on last-minute weather assessments to make sure we have the best chances of low cloud coverage. The choice of that general area is guided by flight prices and low population density to avoid traffic.����

Have you visited this site before?��

BP: No — it will be quite exploratory! ��

What do you and your students hope to see?��

BP: First, we are hoping to be able to observe the eclipse in the totality zone without too much cloud cover for near the longest eclipse time possible (more than 4 minutes). This will be significantly longer than the 2017 eclipse. During the totality, we will be able to see the sun’s corona with the naked eye. This is the farthest-extending feature of the sun’s atmosphere and is only visible during total eclipses.����

As the sun is currently approaching its — or the peak in the roughly 11-year cycle of solar activity — we are expecting to see quite a few more solar features than in 2017. One feature we hope to see is large plasma bridges, called , that are suspended over the surface of the sun by its strong magnetic field.����

During totality, the sky will get dark, and we should be able to see Mercury, Venus, Mars, Jupiter and Saturn appear on both sides of the sun. There is also a comet, , that should be visible just next to Jupiter. Overall, it promises to be quite an incredible and unique spectacle.��

Who will be participating in this field effort?��

BP: We will be going with four Earth and space sciences graduate students — , , and — as well as Sarah Smith with the College of the Environment, who will help to document the effort.��

What is the telescope that you will be bringing? What do you hope to learn?��

BP: We are bringing a special telescope that allows us to observe the sun in a single wavelength of hydrogen, the main constituent of the sun, to capture images of the sun’s surface features during the progression of the eclipse. We have been taking images of the sun from the 91̽��campus to practice the use of this type of telescope, known as an H-alpha telescope.��

What’s something you enjoy about going into the field?��

BP: The main thing is experiencing a unique cosmic event that really gives perspective on the size and force of the universe. This is, honestly, one of the most incredible things that one can experience. Sharing that with our students will be a privilege. ��

Can people follow your efforts?��

BP: I will post on my X account, , and we will have full coverage through the 91̽��Environment channels on and .��

Anything you’d like to add?��

BP: Wish us luck with the weather! ��

����

For more information, contact Journaux at bjournau@uw.edu.��

Not all asteroids are alike. Some of them, known as “active” asteroids, sport comet-like tails of gas and dust. Studying active asteroids could reveal clues to how the solar system formed and how Earth became a water-bearing oasis for life. They may also aid future space missions.

Active asteroids are also rare. But now scientists have 15 new ones to study. They were spotted by , a partnership between NASA, the citizen science platform Zooniverse, astronomers and thousands of citizen scientist volunteers. The team announced its discoveries — among the first since the initiative was formed in 2021 — in a published March 15 in The Astronomical Journal.

“The collective effort of our volunteers has expanded our understanding of the solar system,” said project founder and lead author Colin Orion Chandler, a project scientist at the 91̽��’s . “The discoveries made by this diverse group of individuals highlight the importance of engaging the public in scientific endeavors.”

Around 8,300 volunteers combed through 430,000 images of known asteroids, looking for comet tails or other signatures of active asteroids. The images had been taken by the Victor M. Blanco Telescope at the in Chile. After searching for additional archival images of each candidate from the Active Asteroids project, the team discovered evidence of tails on more than a dozen objects. Some are in the Asteroid Belt, but others reside closer to Jupiter or wander the outer solar system.

“For an amateur astronomer like me it’s a dream come true,” said co-author Virgilio Gonano, an Active Asteroids volunteer in Udine, Italy. “Congratulations to all the staff and the friends that also check the images!”

Asteroids can become active due to impacts from other asteroids or by spinning so fast that they eject material off into space. Studying these objects is crucial for scientists to answer pressing questions about the formation and evolution of the solar system, including the origins of water here on Earth. Additionally, active asteroids may be valuable resources for future space exploration missions, because the same ices that are responsible for the comet-like tails could also be critical resources, such as the basis of rocket fuel or even breathable air.

Identifying active asteroids also helps scientists learn more about how often tail-generating events occur and help them understand asteroid behavior — insights that in turn can inform the design of future asteroid deflection endeavors like NASA’s recent .

“I have been a member of the Active Asteroids team since its first batch of data. And to say that this project has become a significant part of my life is an understatement,” said co-author Tiffany Shaw-Diaz, an Active Asteroids volunteer who lives in Dayton, Ohio. “I look forward to classifying subjects each day, as long as time or health permits, and I am beyond honored to work with such esteemed scientists on a regular basis.”

These efforts complement upcoming missions to rapidly identify solar system objects, such as the Legacy Survey of Space and Time based at the in Chile, which many 91̽��scientists are part of. And with its recent successes the Active Asteroids Citizen Science team will keep up the search for tails on asteroids near and far, including in the upcoming Rubin data, according to Chandler.

“This project not only furthers our knowledge of celestial bodies but also demonstrates the potential of citizen science in advancing cutting-edge research. Nine of the authors on this paper are citizen scientists,” said Chandler. “The success of this initiative reaffirms the importance of collaborative efforts in exploring the mysteries of the cosmos.”

Active Asteroids is accepting volunteers for its ongoing work:

The research was funded by NASA and the National Science Foundation.

For more information, contact Chandler at coc123@uw.edu.

Adapted from press releases by and .

A team of scientists has been tracking a bright object in the sky. But it’s not a star. It’s a new type of commercial satellite. Astronomers are trying to understand how its brightness and transmissions will interfere with Earth-based observations of the universe — and what can be done to minimize these effects as more of these satellites are launched.

In a published Oct. 2 in Nature, the team reports its first detailed assessment on how the satellite — — could impact astronomy.

“While there is only one BlueWalker 3 satellite, it is one of the brightest objects in the sky, and a harbinger of where low-Earth orbit is heading for sky observers,” said co-author , a research scientist with the 91̽��’s and the Vera C. Rubin Observatory in Chile.

Building on initial observations made shortly after its launch, these new results complement��of this unusual satellite. The paper includes details of how the satellite’s brightness changes over time, as well as the visibility of jettisoned hardware. With companies intending to deploy more commercial satellites in the coming years, this paper highlights the need for pre-launch impact assessments.

“The interference of satellites in astronomy has become an increasingly pressing issue over the last few years,”��said first author Sangeetha Nandakumar of the University of Atacama in Chile.

BlueWalker 3 was launched into low-Earth orbit on Sept. 10, 2022, by��. The craft is a prototype for a planned constellation of more than a hundred satellites for use in mobile communications. Observations made shortly after launch showed that the satellite was among the brightest objects in the sky.

To better understand its impact on astronomy, the International Astronomical Union’s , or CPS, initiated an international observing campaign. As part of this initiative, both professional and amateur observations were contributed from across the world from sites in Chile, the United States, Mexico, New Zealand, the Netherlands and Morocco.

“It is exciting that we could incorporate images from many different telescopes and visual observations from highly skilled amateur observers in this analysis,” said Rawls. “It’s an example of the kind of thing that is possible only when folks from many institutions and with many backgrounds work together with a common purpose.”

The CPS is co-hosted by NSF’s and the , an international partnership. The CPS facilitates global coordination of efforts by the astronomical community — in concert with observatories, space agencies, industry, regulators and other sectors — to help mitigate the negative consequences of satellite constellations on astronomy. Its four working groups — or hubs — pursue different projects analyzing different types of interference from satellites and other sources.

“This paper brings together observers from across the globe under the umbrella of the CPS SatHub to better understand the ramifications,” said Rawls, who co-leads SatHub. “This is the first peer-reviewed research to quantitatively measure the high brightness of BlueWalker 3 and discuss the impacts on astronomy.”

The newly released data show an abrupt increase in the brightness of BlueWalker 3 over a period of 130 days — coinciding with the complete unfolding of its antenna array — followed by fluctuations over the subsequent weeks. Data also showed a relationship between the varying brightness and other factors after unfolding, such as the satellite’s height above the horizon and the angle between the observer, the satellite and the sun. The team also used a subset of the observations to calculate the satellite’s trajectory over time. Comparing the predicted path with the observations collected, they could evaluate the accuracy of these predictions and observe how its elevation declined over time due to atmospheric drag and other factors.

In addition, they observed the launch vehicle adapter attached to BlueWalker 3 decoupling from the satellite. This component reached magnitude 5.5 in brightness, exceeding maximum recommendations set out by the IAU to avoid the worst impacts of satellites on optical astronomy.

“These results demonstrate a continuing trend towards larger, brighter commercial satellites, which is of particular concern given the plans to launch many more in the coming years,”��said co-author and CPS scientist Siegfried Eggl of the University of Illinois at Urbana-Champaign. “While these satellites can play a role in improving communications, it is imperative that their disruptions of scientific observations are minimized. This could preferably be achieved through continuing cooperation on mitigation efforts, or, if that is not successful, through a requirement for pre-launch impact assessments as part of future launching authorization processes.”

“Besides the effect on visible observations, BlueWalker 3 could also interfere with radio astronomy, since it transmits in radio frequencies close to those that radio telescopes observe in,”��said Federico Di Vruno, co-director of the CPS.��“The novel aspect of BlueWalker 3 is that it uses frequencies that are normally used by terrestrial transmitters.”

Observations of BlueWalker 3 will continue, with plans by astronomers to observe its thermal emission later this year. Astronomers will continue to discuss this topic at this month.

“This is a global issue, since satellites approved by any country are visible in the night sky across the world, highlighting the importance of international coordination,”��said co-author Jeremy Tregloan-Reed of the University of Atacama and the CPS.

For more information, contact Rawls at mrawls@uw.edu.

Adapted from a by the IAU.

An asteroid discovery algorithm — designed to uncover near-Earth asteroids for the ’s upcoming 10-year survey of the night sky — has identified its first “potentially hazardous” asteroid, a term for space rocks in Earth’s vicinity that scientists like to keep an eye on. The roughly 600-foot-long asteroid, designated , was discovered during a test drive of the algorithm with the survey in Hawaii. Finding 2022 SF289, which poses no risk to Earth for the foreseeable future, confirms that the next-generation algorithm, known as HelioLinc3D, can identify near-Earth asteroids with fewer and more dispersed observations than required by today’s methods.

“By demonstrating the real-world effectiveness of the software that Rubin will use to look for thousands of yet-unknown potentially hazardous asteroids, the discovery of 2022 SF289 makes us all safer,” said Rubin scientist , the principal developer of HelioLinc3D and a researcher at the 91̽��.

The solar system is home to tens of millions of rocky bodies ranging from small asteroids not larger than a few feet, to dwarf planets the size of our moon. These objects remain from an era over four billion years ago, when the planets in our system formed and took their present-day positions.

Most of these bodies are distant, but a number orbit close to the Earth, and are known as near-Earth objects, or NEOs. The closest of these — those with a trajectory that takes them within about 5 million miles of Earth’s orbit, or about 20 times the distance from Earth to the moon — warrant special attention. Such “potentially hazardous asteroids,” or PHAs, are systematically searched for and monitored to ensure they won’t collide with Earth, a potentially devastating event.

Scientists search for PHAs using specialized telescope systems like the NASA-funded ATLAS survey, run by a team at the University of Hawaii’s . They do so by taking images of parts of the sky at least four times every night. A discovery is made when they notice a point of light moving unambiguously in a straight line over the image series. Scientists have discovered about 2,350 PHAs using this method, but estimate that at least as many more await discovery.

From its peak in the Chilean Andes, the Vera C. Rubin Observatory is set to join the hunt for these objects in early 2025. Funded primarily by the U.S. National Science Foundation and the U.S. Department of Energy, Rubin’s observations will dramatically increase the discovery rate of PHAs. Rubin will scan the sky unprecedentedly quickly with its 8.4-meter mirror and massive 3,200-megapixel camera, visiting spots on the sky twice per night rather than the four times needed by present telescopes. But with this novel observing “cadence,” researchers need a new type of discovery algorithm to reliably spot space rocks.

Rubin’s solar system software team at the 91̽��’s has been working to just develop such codes. Working with Smithsonian senior astrophysicist and Harvard University lecturer , who in 2018 pioneered a new class of heliocentric asteroid search algorithms, Heinze and , a former 91̽�� researcher who is now an assistant professor at the University of Illinois at Urbana-Champaign, developed HelioLinc3D: a code that could find asteroids in Rubin’s dataset. With Rubin still under construction, Heinze and Eggl wanted to test HelioLinc3D to see if it could discover a new asteroid in existing data, one with too few observations to be discovered by today’s conventional algorithms.

and , lead ATLAS astronomers, offered their data for a test. The Rubin team set HelioLinc3D to search through this data and on July 18, 2023 it spotted its first PHA: 2022 SF289, initially imaged by ATLAS on September 19, 2022 at a distance of 13 million miles from Earth.

In retrospect, ATLAS had observed 2022 SF289 three times on four separate nights, but never the requisite four times on one night to be identified as a new NEO. But these are just the occasions where HelioLinc3D excels: It successfully combined fragments of data from all four nights and made the discovery.

“Any survey will have difficulty discovering objects like 2022 SF289 that are near its sensitivity limit, but HelioLinc3D shows that it is possible to recover these faint objects as long as they are visible over several nights,” said Denneau. “This in effect gives us a ‘bigger, better’ telescope.”

Other surveys had also missed 2022 SF289, because it was passing in front of the rich starfields of the Milky Way. But by now knowing where to look, additional observations from Pan-STARRS and Catalina Sky Survey quickly confirmed the discovery. The team used B612 Asteroid Institute’s to recover further unrecognized observations by the NSF-supported Zwicky Transient Facility telescope.

2022 SF289 is classified as an -type NEO. Its closest approach brings it within 140,000 miles of Earth’s orbit, closer than the moon. Its diameter of 600ft is large enough to be classified as “potentially hazardous.” But despite its proximity, projections indicate that it poses no danger of hitting Earth for the foreseeable future. Its discovery has been announced in the International Astronomical Union’s Minor Planet Electronic Circular .

Currently, scientists know of 2,350 PHAs but expect there are more than 3,000 yet to be found.

“This is just a small taste of what to expect with the Rubin Observatory in less than two years, when HelioLinc3D will be discovering an object like this every night,” said Rubin scientist Mario Jurić, director of the DiRAC Institute, professor of astronomy at the 91̽�� and leader of the team behind HelioLinc3D.�� “But more broadly, it’s a preview of the coming era of data-intensive astronomy. From HelioLinc3D to AI-assisted codes, the next decade of discovery will be a story of advancement in algorithms as much as in new, large, telescopes.”

Financial support for Rubin Observatory comes from the U.S. National Science Foundation, the U.S. Department of Energy and private funding raised by the LSST Corporation.

For more information, contact Heinze at aheinze@uw.edu and Jurić at mjuric@uw.edu.

Planetary nebulae form when red giant stars expel their outermost layers as they run out of helium fuel — becoming hot, dense white dwarf stars that are roughly the size of Earth. The material that was shed, enriched in carbon, forms dazzling patterns as it is blown gently into the interstellar medium.

Most planetary nebulae are roughly circular, but a few have an hourglass or wing-like shape, like the aptly named “Butterfly Nebula.” These shapes are likely formed by the gravitational tug of a second star orbiting the nebula’s “parent” star, causing the material to expand into a pair of nebular lobes, or “wings.” Like an expanding balloon, the wings grow over time without changing their original shape.

Yet new research shows that something is amiss in the Butterfly Nebula. When a team led by astronomers at the 91̽�� compared two exposures of the Butterfly Nebula taken by the Hubble Space Telescope in 2009 and 2020, they saw dramatic changes in the material within the wings. As they reported on Jan. 12 at the in Seattle, powerful winds are driving complex alterations of material within the nebula’s wings. They want to understand how such activity is possible from what should be a “sputtering, largely moribund star with no remaining fuel.”

“The Butterfly Nebula is extreme for the mass, speed and complexity of its ejections from its central star, whose temperature is more than 200 times hotter than the sun yet is just slightly larger than the Earth,” said team leader Bruce Balick, a 91̽��professor emeritus of astronomy. “I’ve been comparing Hubble images for years and I’ve never seen anything quite like it.”

The team compared high-quality Hubble images taken 11 years apart to chart the speeds and growth patterns of features within the nebula’s wings. The bulk of the analysis was performed by Lars Borchert, a graduate student at Aarhus University in Denmark who participated in this study as a 91̽��undergraduate student.

Borchert discovered roughly half a dozen “jets” — beginning about 2,300 years ago and ending 900 years ago — pushing material out in a series of asymmetrical outflows. Material in the outer portions of the nebula is moving rapidly, at about 500 miles per second, while material closer to the hidden central star is expanding much more slowly, at about a tenth of that speed. Paths of the jets cross one another, forming “messy” structures and growth patterns within the wings.

The nebula’s multi-polar and swiftly changing interior structure is not easy to explain using existing models of how planetary nebulae form and evolve, according to Balick. The star at the center of the nebula, which is hidden by dust and debris, could have merged with a companion star or drew off material from a nearby star, creating complex magnetic fields and generating the jets.

“At this point, these are all just hypotheses,” said Balick. “What this shows us is that we don’t fully understand the full range of shaping processes at work when planetary nebulae form. The next step is to image the nebular center using the James Webb Space Telescope, since infrared light from the star can penetrate through the dust.”

Stars like our sun will swell into a red giant and form planetary nebulae someday, expelling carbon and other relatively heavy elements into the interstellar medium to form star systems and planets in the far future. This new research, and other “time-lapse” analyses of planetary nebulae, can help illustrate not just how the materials for the star systems of tomorrow will take shape, but also how the building blocks of our own oasis were produced and gathered billions of years ago.

“It’s a creation story that is happening over and over again in our universe,” said Balick. “The shaping processes provide key insight into the history and impacts of the stellar activity.”

Other team members are Joel Kastner of the Rochester Institute of Technology and Adam Frank of the University of Rochester.

For more information, contact Balick at balick@uw.edu.