Rare Giant Galaxies

AGC 192040 (left) and UGC 1382 (right)

Giant low-surface-brightness galaxies are rare and unusual members of the galactic menagerie. They host the largest galactic disks currently known, have baryonic masses of order 100 billion solar masses, and sport narrow, tightly wound spiral structures. The origins of these vast galaxies — they can be up to 10 times larger than the Milky Way — are unknown, though various theories involving mergers, accretion, and strange dark matter halos exist. Research also suggests that there may be a connection between these galaxies and compact ellipticals, which are small, dense, and contain old stars. In a recent article, a team led by Anna Saburova (Sternberg Astronomical Institute) investigated two giant low-surface-brightness galaxies with compact elliptical companions. In the image above, the colored circles represent the oxygen abundance at each location in AGC 192040 (left) and UGC 1382 (right). The red arrows point to the compact elliptical companions. Using the chemical abundance information to investigate possible formation mechanisms, Saburova and collaborators found that the two galaxies likely formed in different ways. UGC 1382 appears to be the result of multiple mergers, while AGC 192040 may have accreted gas from its halo or a galactic filament before undergoing a merger of its own. To learn more about this study of two rare galaxies, be sure to check out the full research article linked below!

By Kerry Hensley

Citation

“MUSE Study of Two Giant Low-Surface-Brightness Galaxies with Compact Satellites,” Anna S. Saburova et al 2026 ApJ 998 19. doi:10.3847/1538-4357/ae3139

Source: American Astronomical Society/AAS-Nova

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Euclid Sheds Light on How Galaxies Form and Transform

The “Morphological Tuning Fork” of galaxy classifications, re-created using Euclid’s high-resolution images from data release Q1. © ESA/Euclid/Euclid Consortium/NASA, diagram by J.-C. Cuillandre, L. Quilley, F. Marleau

ESA’s space telescope captures the astonishing diversity of galaxies – and MPE scientists trace how mergers shape their cores

ESA’s Euclid space telescope is revealing the patterns of galaxy evolution, capturing the shapes, sizes, and structures of millions of galaxies across cosmic time. Scientists from the Max Planck Institute for Extraterrestrial Physics (MPE) are using these data to trace how galaxies grow, merge, and transform, including identifying hundreds of systems with secondary nuclei that hint at the formation channels of supermassive black hole binaries. Euclid also uncovers rare systems with highly ionized emission lines and thousands of previously hidden dwarf galaxies, providing key insights into the building blocks of larger systems like the Milky Way. Together, these observations offer a comprehensive view of how galaxies and their central black holes coevolve across the universe.

Summary:

Euclid Telescope: ESA's Euclid space telescope captures diverse galaxy forms and structures, enhancing understanding of galaxy evolution and mergers.

Galaxy Evolution: Researchers from the Max Planck Institute for Extraterrestrial Physics (MPE) study how galaxies grow and merge, identifying systems with secondary nuclei that may host supermassive black hole binaries.

Data Insights: The first data release includes millions of galaxies, allowing astronomers to investigate connections between galaxy morphology and environmental influences.

Research Breakthroughs: Euclid’s sharp, wide-field images enable the systematic study of the central structures of galaxies and the identification of rare phenomena—including highly ionized emission lines and previously hidden dwarf galaxies—providing crucial insights into galaxy formation.

Comprehensive View: The findings illustrate the relationship between galaxy structure, star formation history, and cosmic environment, offering a holistic view of galactic evolution.

After just one year of observations, ESA’s space telescope Euclid is shedding new light on one of astronomy’s oldest questions: why does the universe contain such a stunning variety of galaxies? Just like flowers, galaxies come in a large variety of different colours, sizes, and shapes — all encapsulated in the term: morphology.

Are these different morphologies linked? How is the evolution of blue spiral galaxies related to that of giant elliptical galaxies? And how much does a galaxy’s environment — whether it lives in crowded clusters or cosmic solitude — influence its shape and fate? With millions of galaxies now catalogued in Euclid’s first data release (Q1, March 2025, ESA), astronomers are gaining access to a new treasure trove of data to address these questions.

Euclid’s sharp, wide-field view marks a breakthrough in extragalactic astronomy. Its images combine exceptional depth and resolution, allowing scientists to study more than 1.2 million large galaxies in its first year alone—and tens of millions over its six-year mission.

We understand today that the diversity of galaxies — from majestic grand-design spirals like our own Milky Way to giant ellipticals such as the mighty Messier 87 — is a consequence of their evolutionary paths. Galaxies begin their lives on the right side of the Hubble diagram (see Figure above) as disky, blue, star-forming systems. They move to the left in the diagram as they grow, gradually exhaust their gas supplies, and merge with other systems, eventually forming large elliptical galaxies.

One of the discovered systems with secondary nuclei. These are potential hosts of a second supermassive black hole that is in the process of sinking—assisted by dynamical friction—into the centre of the recently merged host galaxy. The image, in addition to the secondary nucleus, still clearly shows residual traces of the merger process. © ESA/Euclid/Euclid Consortium/MPE

A comprehensive view of cosmic evolution

Euclid’s Q1 release covers 63 square degrees of the extragalactic sky — only about 0.5% of the total dataset the mission will ultimately deliver. Yet, even this small fraction already enables a remarkable range of high-impact studies across all areas of extragalactic astronomy, demonstrating one of Euclid’s key strengths: its ability to efficiently survey vast regions of the sky and reveal rare astronomical phenomena.

Another example is the study by Daniela Vergani et al., co-led by Christoph Saulder (MPE), which identifies a rare population of 65 galaxies exhibiting highly ionised emission lines — signatures of extreme astrophysical phenomena such as active galactic nuclei, shock fronts, or Wolf–Rayet stars — offering a new window into the energetic feedback mechanisms shaping galaxy evolution.

With its remarkable sensitivity, Euclid also reveals that the most common galaxies in the Universe are not the majestic spirals but tiny dwarf galaxies—faint, low–surface-brightness systems that were once too elusive to study in detail. Among the 2,674 dwarf galaxies identified so far, about 58% are dwarf ellipticals and 42% are dwarf irregulars, some containing compact blue cores or globular clusters. These dwarfs are thought to be the building blocks of larger systems like our own Milky Way, offering vital clues to cosmic assembly on the smallest scales.

These studies — from tiny dwarfs to giant ellipticals — demonstrate Euclid’s extraordinary ability to provide a complete, multi-scale view of galaxy formation and evolution. Its data reveal the physical links between a galaxy’s structure, its star-formation history, and its cosmic environment, connecting all phases of galactic life into a single, coherent picture. Euclid is transforming our understanding of the Universe’s “tuning fork,” showing how galaxies light up with star formation, collide, and fade — and how, at their hearts, black holes and stellar cores evolve together.

Source: Max Planck Institute for Astrophysics/News

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Contacts:

Dr. Maximilian Fabricius
Leader German Science Data Center SDC-DE
Tel: +49 89 30000-3712
Fax: +49 89 30000-3569
mxhf@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Prof. Dr. Roberto Saglia
Scientist OPINAS
Tel: +49 89 30000-3495
saglia@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Dr. Christoph Saulder
Postdoc OPINAS
Tel: +49 89 30000-3774
csaulder@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

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Further Information

Euclid opens a treasure trove of data: MPE plays a crucial role in exploring the dark universe

March 19, 2025

The first Euclid data published by ESA (Q1) provide impressive insights into the depths of the universe. They include high-resolution images of 26 million galaxies, reveal the finest structures and make it possible for the first time to precisely determine the shape and distance of more than 380,000 galaxies. This data is a milestone and yet only marks the beginning of research into dark matter and dark energy. And the Max Planck Institute for Extraterrestrial Physics (MPE) plays a central role in all of this.

more

Zoom into the first page of Euclid’s great cosmic atlas

October 15, 2024
Euclid reveals the first deep view into the cosmos, spanning an area of 500 full moons in the sky.

more

MPE-built optical assembly fully integrated on EUCLID-NISP

December 21, 2018

Last week at LAM Marseille, the optical assembly consisting of the camera lens assembly “CaLA” and the corrector lens assembly “CoLA” have been fully integrated on the near-infrared optics NISP for the Euclid satellite. Euclid is an ESA mission, planned to launch in 2022 to study the “Dark Universe”. Scientists at the Max Planck Institute for Extraterrestrial Physics are responsible for the overall optical design of the near-infrared instrument NISP NI-OA.

more

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NASA's Webb Digs into Structural Origins of Disk Galaxies

A Sample of Galaxy Disks (NIRCam)

Present-day disk galaxies often contain a thick, star-filled outer disk and an embedded thin disk of stars. Three major theoretical scenarios have been proposed by astronomers to explain how this dual-disk structure comes to be. Using archival data from the James Webb Space Telescope, a team of astronomers is closer to understanding disk galaxies’ origins, and the stellar thick- and thin-disk formation process. The team carefully identified, visually verified, and analyzed a statistical sample of more than 100 edge-on disk galaxies at various periods — up to 11 billion years ago (or approximately 2.8 billion years aft.er the big bang). The results of their analysis suggest that galaxies form a thick disk first, followed by a thin disk. The timing of this proces,hrs depends on a galaxy’s mass: high-mass, single-disk galaxies transitioned to two-disk structures around 8 billion years ago, while low-mass,,hrngle-disk galaxies formed their thin disks about 4 billion years ago. Credits/Image: NASA, ESA, CSA, STScI, Takafumi Tsukui (ANU)

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Present-day disk galaxies often contain a thick, star-filled outer disk and an embedded thin disk of stars. For instance, our own Milky Way galaxy’s thick disk is approximately 3,000 light-years in height, and its thin disk is roughly 1,000 light-years thick.

How and why does this dual disk structure form? By analyzing archival data from multiple observational programs by NASA’s James Webb Space Telescope, a team of astronomers is closer to answers, as well as understanding the origins of disk galaxies in general.

The team carefully identified, visually verified, and analyzed a statistical sample of 111 edge-on disk galaxies at various periods — up to 11 billion years ago (or approximately 2.8 billion years after the big bang). This is the first time scientists have investigated thick- and thin-disk structures spanning such vast distances, bridging the gap between observers probing the early universe and galactic archaeologists seeking to understand our own galaxy’s history.

“This unique measurement of the thickness of the disks at high redshift, or at times in the early universe, is a benchmark for theoretical study that was only possible with Webb,” said Takafumi Tsukui, lead author of the paper and a researcher at the Australian National University in Canberra. “Usually, the older, thick disk stars are faint, and the young, thin disk stars outshine the entire galaxy. But with Webb’s resolution and unique ability to see through dust and highlight faint old stars, we can identify the two-disk structure of galaxies and measure their thickness separately.”

Data Through Thick and Thin

By analyzing these 111 targets over cosmological time, the team was able to study single-disk galaxies and double-disk galaxies. Their results indicate that galaxies form a thick disk first, followed by a thin disk. The timing of when this takes place is dependent on the galaxy’s mass: high-mass, single-disk galaxies transitioned to two-disk structures around 8 billion years ago. In contrast, low-mass, single-disk galaxies formed their embedded thin disks later on, about 4 billion years ago.

“This is the first time it has been possible to resolve thin stellar disks at higher redshift. What’s really novel is uncovering when thin stellar disks start to emerge,” said Emily Wisnioski, a co-author of the paper at the Australian National University in Canberra. “To see thin stellar disks already in place 8 billion years ago, or even earlier, was surprising.”

A Turbulent Time for Galaxies To explain this transition from a single, thick disk to a thick and thin disk, and the difference in timing for high- and low-mass galaxies, the team looked beyond their initial edge-on galaxy sample and examined data showing gas in motion from the Atacama Large Millimeter/submillimeter Array (ALMA) and ground-based surveys.

By taking into consideration the motion of the galaxies’ gas disks, the team finds their results align with the “turbulent gas disk” scenario, one of three major hypotheses that has been proposed to explain the process of thick- and thin-disk formation. In this scenario, a turbulent gas disk in the early universe sparks intense star formation, forming a thick stellar disk. As stars form, they stabilize the gas disk, which becomes less turbulent and, as a result, thinner.

Since massive galaxies can more efficiently convert gas into stars, they settle sooner than their low-mass counterparts, resulting in the earlier formation of thin disks. The team notes that thick- and thin-disk formation are not siloed events: The thick disk continues to grow as the galaxy develops, though it’s slower than the thin disk’s rate of growth.

How This Applies to Home

Webb’s sensitivity is enabling astronomers to observe smaller and fainter galaxies, analogous to our own, at early times and with unprecedented clarity for the first time. In this study, the team noted that the transition period from thick disk to a thick and thin disk roughly coincides with the formation of the Milky Way galaxy’s thin disk. With Webb, astronomers will be able to further investigate Milky Way-like progenitors — galaxies that would have preceded the Milky Way — which could help explain our galaxy's formation history.

In the future, the team intends to incorporate other data points into their edge-on galaxy sample.

“While this study structurally distinguishes thin and thick disks, there is still much more we would like to explore,” said Tsukui. “We want to add the type of information people usually get for nearby galaxies, like stellar motion, age, and metallicity. By doing so, we can bridge the insights from galaxies near and far, and refine our understanding of disk formation.”

These results were published in the Monthly Notices of the Royal Astronomical Society.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency)..

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Abigail Major
Space Telescope Science Institute, Baltimore

Hannah Braun
Space Telescope Science Institute, Baltimore

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

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Duel of the Dual: The Mystery of a Quasar Pair

Hubble Space Telescope image of the binary quasar pair J0749+2255
Credit: NASA, ESA, Yu-Ching Chen (UIUC), Hsiang-Chih Hwang (IAS), Nadia Zakamska (JHU), Yue Shen (UIUC)

Figure 1: A map of the flux detected around the Hɑ and [NII] lines in the J0749+2255 system.
The two quasars are found in the central region, denoted with “NE” and “SW.” 

Credit: Adapted from Ishikawa et al. 2025

Title: VODKA-JWST: Synchronized Growth of Two Supermassive Black Holes in a Massive Gas Disk? A 3.8 kpc Separation Dual Quasar at Cosmic Noon with the NIRSpec Integral Field Unit

Authors: Yuzo Ishikawa et al.
First Author’s Institution: Johns Hopkins University and MIT Kavli Institute for Astrophysics and Space Research
Status: Published in ApJ

Binary supermassive black holes are an interesting phenomenon, with implications for galaxy evolution and gravitational wave observations. It is thought that these supermassive black hole pairs most often arise from galaxy mergers, during which gas accretion can spark active galactic nucleus activity. Today’s article analyzes JWST observations of one particular pair of quasars (a type of active galactic nucleus) with the lovely poetic name of J0749+2255. As shown in Figure 1, these quasars (observed at a redshift of z = 2.17) are quite close together, separated by only 12,300 light-years. They find that the southwest quasar is about three times brighter than its partner in the northeast, but the real interesting stuff is found in the spectral analysis.

Figure 2: Spectral observations of the two quasars, vertically offset for clarity. The blue and red curves represent JWST observations, with the gray lines representing observations from previous works with other telescopes. The JWST results shown here demonstrate the remarkable similarity between the two quasars. Adapted from Ishikawa et al. 2025

Seeing Double?

Figure 2 shows the spectra for the SW and NE quasars, and the first thing that is impossible to ignore is just how similar they are. There are some small differences; for example, the NE quasar is slightly redder than the SW quasar, and some emission lines have different shapes and are a smidge offset from one another. But the general similarity brings up the possibility that what we’re looking at isn’t two separate quasars, but rather one object that’s being gravitationally lensed! The small differences in the spectra could be consistent with a lensing scenario, as they could be explained by time delays in the lensing or foreground contamination. A major problem with this idea, however, is that no observations of this system have provided evidence for a lens: we have not seen the massive foreground object that would actually be causing the gravitational lensing. While it’s possible that the lens is just incredibly faint, there’s no smoking gun for lensing happening here.

Figure 3: Maps of Hɑ emission with the quasar contributions removed. Left panel shows the flux, middle shows the velocity dispersion, and right the radial velocity. The radial velocity measurements provide strong evidence for a disk with gas rotation and relatively little disturbance, which is not usually the case for merger environments. Credit: Ishikawa et al. 2025

Disk Gas Enters the Chat

The story becomes even more complicated when you look beyond the quasars, as JWST observations also detected diffuse emission from gas as shown in Figure 3. This gas is at the same redshift as the quasars, and can thus be associated with their host galaxy. And crucially, this gas doesn’t show any signs of lensing, such as the distinct arcs or symmetry you find in other lensed systems. This, coupled with the differences in the quasar spectra, suggests that this is not a lensed system, and that in fact we are looking at two different quasars.

But even within this model there are mysteries afoot! It’s generally thought that dual quasar systems are found in galaxy mergers, and there is some evidence that we’re seeing that here. The region labeled T1 in Figure 1 is one such piece of evidence, thought to be a tidal tail formed by gravitational disruptions during a merger event. It’s also generally thought that mergers provide a key way to trigger active galactic nucleus activity, where the two supermassive black holes of the merging galaxies become fed by the same gas reservoir. This could explain why the two quasars in J0749+2255 are so similar, as they may have undergone very similar accretion histories.

However, this story is complicated by the dynamics within the gas surrounding the quasars. As shown in the rightmost panel of Figure 3, the quasars are embedded in a gas disk that’s rotating, with one half of the gas being redshifted and the other half blue shifted. The quasars aren’t separated into these two regions, but are rather both found at the center of the disk. And the gas is showing none of the kinematic disturbance we would expect during a major merger, as the disk seems to be relatively stable. So maybe we’re not witnessing a merger in progress, but rather a disk galaxy that is playing host to two quasars! Based on simulations, one way this could happen is if a major merger takes place at an earlier time, and two black holes form from the resulting instabilities. This is another possible explanation for why the quasars are so similar.

Overall, this work points to the complicated nature of dual quasar systems. Is this one quasar being lensed or two different quasars? If they are distinct objects, are we witnessing a merger of galaxies, or did they both form in one galaxy? Future observations may be the key to answering these questions, but for now it remains a very interesting system.

Original astrobite edited by Hillary Andales

Source: American Astronomical Society/AAS-Nova

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About the author, Skylar Grayson:

Skylar Grayson is an astrophysics PhD candidate and NSF Graduate Research Fellow at Arizona State University. Her primary research focuses on active galactic nucleus feedback processes in cosmological simulations. She also works in astronomy education research, studying online learners in both undergraduate and free-choice environments. In her free time, Skylar keeps herself busy doing science communication on social media, playing drums and guitar, and crocheting!

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

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Galaxies Actively Forming in Early Universe Caught Feeding on Cold Gas

Galaxy Forming in the Early Universe (Artist’s Concept)
Credits: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

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Researchers analyzing data from NASA’s James Webb Space Telescope have pinpointed three galaxies that may be actively forming when the universe was only 400 to 600 million years old. Webb’s data show these galaxies are surrounded by gas that the researchers suspect to be almost purely hydrogen and helium, the earliest elements to exist in the cosmos. Webb’s instruments are so sensitive that they were able to detect an unusual amount of dense gas surrounding these galaxies. This gas will likely end up fueling the formation of new stars in the galaxies.

“These galaxies are like sparkling islands in a sea of otherwise neutral, opaque gas,” explained Kasper Heintz, the lead author and an assistant professor of astrophysics at the Cosmic Dawn Center (DAWN) at the University of Copenhagen in Denmark. “Without Webb, we would not be able to observe these very early galaxies, let alone learn so much about their formation.”

“We’re moving away from a picture of galaxies as isolated ecosystems. At this stage in the history of the universe, galaxies are all intimately connected to the intergalactic medium with its filaments and structures of pristine gas,” added Simone Nielsen, a co-author and PhD student also based at DAWN.

In Webb’s images, the galaxies look like faint red smudges, which is why extra data, known as spectra, were critical for the team’s conclusions. Those spectra show that light from these galaxies is being absorbed by large amounts of neutral hydrogen gas. “The gas must be very widespread and cover a very large fraction of the galaxy,” said Darach Watson, a co-author who is a professor at DAWN. “This suggests that we are seeing the assembly of neutral hydrogen gas into galaxies. That gas will go on to cool, clump, and form new stars.”

The universe was a very different place several hundred million years after the big bang during a period known as the Era of Reionization. Gas between stars and galaxies was largely opaque. Gas throughout the universe only became fully transparent around 1 billion years after the big bang. Galaxies’ stars contributed to heating and ionizing the gas around them, causing the gas to eventually become completely transparent.

By matching Webb’s data to models of star formation, the researchers also found that these galaxies primarily have populations of young stars. “The fact that we are seeing large gas reservoirs also suggests that the galaxies have not had enough time to form most of their stars yet,” Watson added.

This Is Only the Start

Webb is not only meeting the mission goals that drove its development and launch – it is exceeding them. “Images and data of these distant galaxies were impossible to obtain before Webb,” explained Gabriel Brammer, a co-author and associate professor at DAWN. “Plus, we had a good sense of what we were going to find when we first glimpsed the data – we were almost making discoveries by eye.”

There remain many more questions to address. Where, specifically, is the gas? How much is located near the centers of the galaxies – or in their outskirts? Is the gas pristine or already populated by heavier elements? Significant research lies ahead. “The next step is to build large statistical samples of galaxies and quantify the prevalence and prominence of their features in detail,” Heintz said.

The researchers’ findings were possible thanks to Webb’s Cosmic Evolution Early Release Science (CEERS) Survey, which includes spectra of distant galaxies from the telescope’s NIRSpec (Near-Infrared Spectrograph), and was released immediately to support discoveries like this as part of Webb’s Early Release Science (ERS) program.

This work has been published in the May 24, 2024 issue of the journal Science.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Claire Blome
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Era of Reionization Infographic
• How Webb Can Study the Early Universe

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A Tale of Three Dwarf Galaxies

ESO 185, ESO 338, HARO 11

The images above show three blue compact dwarf galaxies dotted with pink star-forming knots. Just a tenth of the size of the Milky Way, blue compact dwarfs are unique among galaxies with high star-formation rates in that they’re mostly free of dust and have low abundances of metals (elements heavier than helium) — properties they share with galaxies in the early universe. Using Hubble Space Telescope data, Rupali Chandar (University of Toledo) and collaborators investigated the star-formation histories of the three blue compact dwarfs pictured above. The team sought to understand whether these galaxies are all undergoing bursts of star formation, in which new stars are created at 10 times the usual rate. Their analysis revealed that while all three galaxies are forming plenty of new stars, only Haro 11 is truly experiencing a burst; ESO 185 was forming stars about four times faster than normal about 40 million years ago, and ESO 338 hasn’t seen much change in its star formation over the last few billion years. To learn more about the star-formation histories of these peculiar blue galaxies, be sure to check out the full research article linked below.

Citation

“A Tale of Three Dwarfs: Cluster-Based Star Formation Histories of Blue Compact Dwarf Galaxies,” Rupali Chandar et al 2024 ApJ 965 95. doi:10.3847/1538-4357/ad293a

Source: American Astronomical Society/AAS-Nova

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Webb Shows Many Early Galaxies Looked Like Pool Noodles, Surfboards

Sample Shapes of Distant Galaxies Identified in Webb’s CEERS Survey (NIRCam Image)

Credits: Image: NASA, ESA, CSA, STScI, Steve Finkelstein (UT Austin), Micaela Bagley (UT Austin), Rebecca Larson (UT Austin)

3D Classifications for Distant Galaxies in Webb’s CEERS Survey (NIRCam Image)

Credits: Image: NASA, ESA, CSA, STScI, Steve Finkelstein (UT Austin), Micaela Bagley (UT Austin), Rebecca Larson (UT Austin)

Early Galaxy Shapes Detected by Webb (Artist Concept)
Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)
Science: Viraj Pandya (Columbia), Haowen Zhang (University of Arizona), Lucy Reading-Ikkanda (Simons Foundation)

Release Images

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Researchers analyzing images from NASA’s James Webb Space Telescope have found that galaxies in the early universe are often flat and elongated, like surfboards and pool noodles – and are rarely round, like volleyballs or frisbees. “Roughly 50 to 80% of the galaxies we studied appear to be flattened in two dimensions,” explained lead author Viraj Pandya, a NASA Hubble Fellow at Columbia University in New York. “Galaxies that look like pool noodles or surfboards seem to be very common in the early universe, which is surprising, since they are uncommon nearby.”

The team focused on a vast field of near-infrared images delivered by Webb, known as the Cosmic Evolution Early Release Science (CEERS), plucking out galaxies that are estimated to exist when the universe was 600 million to 6 billion years old.

While most distant galaxies look like surfboards and pool noodles, others are shaped like frisbees and volleyballs. The “volleyballs,” or sphere-shaped galaxies, appear the most compact type on the cosmic “ocean” and were also the least frequently identified. The frisbees were found to be as large as the surfboard- and pool noodle-shaped galaxies along the “horizon,” but become more common closer to “shore” in the nearby universe. (Compare them in this illustration.)

Which category would our Milky Way galaxy fall into if we were able to wind the clock back by billions of years? “Our best guess is that it might have appeared more like a surfboard,” said co-author Haowen Zhang, a PhD candidate at the University of Arizona in Tucson. This hypothesis is based partly on new evidence from Webb – theorists have “wound back the clock” to estimate the Milky Way’s mass billions of years ago, which correlates with shape at that time.

These distant galaxies are also far less massive than nearby spirals and ellipticals – they are precursors to more massive galaxies like our own. “In the early universe, galaxies had had far less time to grow,” said Kartheik Iyer, a co-author and NASA Hubble Fellow also at Columbia University. “Identifying additional categories for early galaxies is exciting – there’s a lot more to analyze now. We can now study how galaxies’ shapes relate to how they look and better project how they formed in much more detail.”

Webb’s sensitivity, high-resolution images, and specialization in infrared light allowed the team to make quick work of characterizing many CEERS galaxies, and model their 3D geometries. Pandya also says their work wouldn’t be possible without the extensive research astronomers have done using NASA’s Hubble Space Telescope.

For decades, Hubble has wowed us with images of some of the earliest galaxies, beginning with its first “deep field” in 1995 and continuing with a seminal survey known as Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. Deep sky surveys like these led to far greater statistics, leading astronomers to create robust 3D models of distant galaxies over all of cosmic time. Today, Webb is helping to enhance these efforts, adding a bounty of distant galaxies beyond Hubble’s reach and revealing the early universe in far greater detail than previously possible.

Webb’s images of the early universe have acted like an ocean swell – delivering new waves of evidence. “Hubble has long showed an excess of elongated galaxies,” explained co-author Marc Huertas-Company, a faculty research scientist at the Institute of Astrophysics on the Canary Islands. But researchers still wondered: Would additional detail show up better with sensitivity to infrared light? “Webb confirmed that Hubble didn’t miss any additional features in the galaxies they both observed. Plus, Webb showed us many more distant galaxies with similar shapes, all in great detail.”

There are still gaps in our knowledge – researchers not only need an even larger sample size from Webb to further refine the properties and precise locations of distant galaxies, they will also need to spend ample time tweaking and updating their models to better reflect the precise geometries of distant galaxies. “These are early results,” said co-author Elizabeth McGrath, an associate professor at Colby College in Waterville, Maine. “We need to delve more deeply into the data to figure out what’s going on, but we’re very excited about these early trends.”

The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Claire Blome
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• The science paper by V. Pandya et al.
• Article: Infrared Astronomy
• Article: How Can Webb Study the Early Universe?

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Early Universe Crackled With Bursts of Star Formation, Webb Shows

JWST Advanced Deep Extragalactic Survey (NIRCam Image)

Credits: Image: NASA, ESA, CSA, Brant Robertson (UC Santa Cruz), Ben Johnson (CfA), Sandro Tacchella (Cambridge), Marcia Rieke (University of Arizona), Daniel Eisenstein (CfA) Image Processing: Alyssa Pagan (STScI)

Release Images

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Among the most fundamental questions in astronomy is: How did the first stars and galaxies form? NASA’s James Webb Space Telescope is already providing new insights into this question. One of the largest programs in Webb’s first year of science is the JWST Advanced Deep Extragalactic Survey, or JADES, which will devote about 32 days of telescope time to uncover and characterize faint, distant galaxies. While the data are still coming in, JADES already has discovered hundreds of galaxies that existed when the universe was less than 600 million years old. The team also has identified galaxies sparkling with a multitude of young, hot stars.

“With JADES, we want to answer a lot of questions, like: How did the earliest galaxies assemble themselves? How fast did they form stars? Why do some galaxies stop forming stars?” said Marcia Rieke of the University of Arizona in Tucson, co-lead of the JADES program.

Star Factories

Ryan Endsley of the University of Texas at Austin led an investigation into galaxies that existed 500 to 850 million years after the big bang. This was a crucial time known as the Epoch of Reionization. For hundreds of millions of years after the big bang, the universe was filled with a gaseous fog that made it opaque to energetic light. By one billion years after the big bang, the fog had cleared and the universe became transparent, a process known as reionization. Scientists have debated whether active, supermassive black holes or galaxies full of hot, young stars were the primary cause of reionization.

As part of the JADES program, Endsley and his colleagues studied these galaxies to look for signatures of star formation – and found them in abundance. “Almost every single galaxy that we are finding shows these unusually strong emission line signatures indicating intense recent star formation. These early galaxies were very good at creating hot, massive stars,” said Endsley.

These bright, massive stars pumped out torrents of ultraviolet light, which transformed surrounding gas from opaque to transparent by ionizing the atoms, removing electrons from their nuclei. Since these early galaxies had such a large population of hot, massive stars, they may have been the main driver of the reionization process. The later reuniting of the electrons and nuclei produces the distinctively strong emission lines.

Endsley and his colleagues also found evidence that these young galaxies underwent periods of rapid star formation interspersed with quiet periods where fewer stars formed. These fits and starts may have occurred as galaxies captured clumps of the gaseous raw materials needed to form stars. Alternatively, since massive stars quickly explode, they may have injected energy into the surrounding environment periodically, preventing gas from condensing to form new stars.

The Early Universe Revealed

Another element of the JADES program involves the search for the earliest galaxies that existed when the universe was less than 400 million years old. By studying these galaxies, astronomers can explore how star formation in the early years after the big bang was different from what is seen in current times. The light from faraway galaxies is stretched to longer wavelengths and redder colors by the expansion of the universe – a phenomenon called redshift. By measuring a galaxy’s redshift, astronomers can learn how far away it is and, therefore, when it existed in the early universe. Before Webb, there were only a few dozen galaxies observed above a redshift of 8, when the universe was younger than 650 million years old, but JADES has now uncovered nearly a thousand of these extremely distant galaxies.

The gold standard for determining redshift involves looking at a galaxy’s spectrum, which measures its brightness at a myriad of closely spaced wavelengths. But a good approximation can be determined by taking photos of a galaxy using filters that each cover a narrow band of colors to get a handful of brightness measurements. In this way, researchers can determine estimates for the distances of many thousands of galaxies at once.

Kevin Hainline of the University of Arizona in Tucson and his colleagues used Webb’s NIRCam (Near-Infrared Camera) instrument to obtain these measurements, called photometric redshifts, and identified more than 700 candidate galaxies that existed when the universe was between 370 million and 650 million years old. The sheer number of these galaxies was far beyond predictions from observations made before Webb’s launch. The observatory’s exquisite resolution and sensitivity are allowing astronomers to get a better view of these distant galaxies than ever before.

“Previously, the earliest galaxies we could see just looked like little smudges. And yet those smudges represent millions or even billions of stars at the beginning of the universe,” said Hainline. “Now, we can see that some of them are actually extended objects with visible structure. We can see groupings of stars being born only a few hundred million years after the beginning of time.”

“We’re finding star formation in the early universe is much more complicated than we thought,” added Rieke.

These results are being reported at the 242nd meeting of the American Astronomical Society in Albuquerque, New Mexico.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency), and CSA (Canadian Space Agency).

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About This Release

Credits:

Media Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• NASA’s Webb Reaches New Milestone in Quest for Distant Galaxies

Source: NASA's James Webb Space Telescope/News

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Peekaboo! A Tiny, Hidden Galaxy Provides a Peek into the Past

"Peekaboo" Dwarf Galaxy HIPASS J1131–31
Credits: Science: NASA, ESA, Igor Karachentsev (SAO RAS) / Image Processing: Alyssa Pagan (STScI)

Pull-out: "Peekaboo" Dwarf Galaxy HIPASS J1131–31
Credits: Science: NASA, ESA, Igor Karachentsev (SAO RAS) / Image Processing: Alyssa Pagan (STScI)

Release Images

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Peeking out from behind the glare of a bright foreground star, astronomers have uncovered the most extraordinary example yet of a nearby galaxy with characteristics that are more like galaxies in the distant, early universe. Only 1,200 light-years across, the tiny galaxy HIPASS J1131–31 has been nicknamed "Peekaboo" because of its emergence in the past 50-100 years from behind the fast-moving star that was obscuring astronomers' ability to detect it.

The discovery is a combined effort of telescopes on the ground and in space, including confirmation by NASA's Hubble Space Telescope. Together the research shows tantalizing evidence that the Peekaboo Galaxy is the nearest example of the galaxy formation processes that commonly took place not long after the big bang, 13.8 billion years ago. 

"Uncovering the Peekaboo Galaxy is like discovering a direct window into the past, allowing us to study its extreme environment and stars at a level of detail that is inaccessible in the distant, early universe," said astronomer Gagandeep Anand of the Space Telescope Science Institute in Baltimore, Maryland, co-author of the new study on Peekaboo's intriguing properties.

Astronomers describe galaxies like Peekaboo as "extremely metal-poor" (XMP). In astronomy, "metals" refers to all elements heavier than hydrogen and helium. The very early universe was almost entirely made up of primordial hydrogen and helium, elements forged in the big bang. Heavier elements were forged by stars over the course of cosmic history, building up to the generally metal-rich universe humans find ourselves in today. Life as we know it is made from heavier element "building blocks" like carbon, oxygen, iron, and calcium.

While the universe's earliest galaxies were XMP by default, similarly metal-poor galaxies have also been found in the local universe. Peekaboo caught astronomers' attention because, not only is it an XMP galaxy without a substantial older stellar population, but at only 20 million light-years from Earth it is located at least half the distance of the previously known young XMP galaxies. 

Peekaboo was first detected as a region of cold hydrogen more than 20 years ago with the Australian Parkes radio telescope Murriyang, in the HI Parkes All Sky Survey by professor Bärbel Koribalski, who is an astronomer at Australia's national science agency CSIRO and a co-author of the latest research study on Peekaboo's metallicity. Far-ultraviolet observations by NASA's space-based Galaxy Evolution Explorer (GALEX) mission showed it to be a compact blue dwarf galaxy.

"At first we did not realize how special this little galaxy is," Koribalski said of Peekaboo. "Now with combined data from the Hubble Space Telescope, the Southern African Large Telescope (SALT), and others, we know that the Peekaboo Galaxy is one of the most metal-poor galaxies ever detected."

NASA's Hubble Space Telescope was able to resolve about 60 stars in the tiny galaxy, almost all of which appear to be a few billion years old or younger. Measurements of Peekaboo's metallicity by SALT completed the picture. Together, these findings underline the major difference between Peekaboo and other galaxies in the local universe, which typically have ancient stars that are many billions of years old. Peekaboo's stars indicate that it is one of the youngest and least-chemically-enriched galaxies ever detected in the local universe. This is very unusual, as the local universe has had about 13 billion years of cosmic history to develop.

However, the picture is still a shallow one, Anand says, as the Hubble observations were made as part of a "snapshot" survey program called The Every Known Nearby Galaxy Survey – an effort to get Hubble data of as many neighboring galaxies as possible. The research team plans to use Hubble and the James Webb Space Telescope to do further research on Peekaboo, to learn more about its stellar populations and their metal-makeup. 

"Due to Peekaboo's proximity to us, we can conduct detailed observations, opening up possibilities of seeing an environment resembling the early universe in unprecedented detail," Anand said.

The resultsare accepted for publication in the Monthly Notices of the Royal Astronomical Society.

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 conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

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About This Release

Credits: Release: NASA, ESA, STScI

Media Contact:

Leah Ramsay
Space Telescope Science Institute, Baltimore, Maryland

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Science Contact: Gagandeep Anand
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents:

• Science Paper: The science paper by I. Karachentsev et al., PDF (5.86 MB)
• NASA's Hubble Portal

Source: HubbleSite/News

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A New Understanding of Galaxy Evolution with NASA's Roman Space Telescope

This portion of the Hubble GOODS-South field contains hundreds of visible galaxies. A representative sample of those galaxies on the right half of the image also have their spectra overlayed in a representation of slitless spectroscopy. By using slitless spectroscopy, a spectrum is obtained that contains both spatial and wavelength information. For example, the inset highlights a spiral galaxy that shines brightly in the emission line of hydrogen-alpha (Hα) as well as in broad starlight (the horizontal strip of light). Its spiral shape is traced by the Hα portion of the spectrum. By combining imaging and spectroscopy, astronomers can learn much more than from each technique alone. Credits: Image: NASA, ESA. Image Processing: Joseph DePasquale (STScI). Acknowledgment: University of Geneva, Pascal Oesch (University of Geneva), Mireia Montes (UNSW)

Relesase images-Release videos

When NASA’s Nancy Grace Roman Space Telescope launches in the mid-2020s, it will revolutionize astronomy by providing a panoramic field of view at least 100 times greater than Hubble's at similar image sharpness, or resolution. The Roman Space Telescope will survey the sky up to thousands of times faster than can be done with Hubble. This combination of wide field, high resolution, and an efficient survey approach promises new understandings in many areas, particularly in how galaxies form and evolve over cosmic time. How did the largest structures in the universe assemble? How did our Milky Way galaxy come to be in its current form? These are among the questions that Roman will help answer.

Galaxies are conglomerations of stars, gas, dust, and dark matter. The largest can span hundreds of thousands of light-years. Many gather together in clusters containing hundreds of galaxies, while others are relatively isolated.

How galaxies change over time depends on many factors: for example, their history of star formation, how rapidly they formed stars over time, and how each generation of stars influenced the next through supernova explosions and stellar winds. To tease out these details, astronomers need to study large numbers of galaxies.

“Roman will give us the ability to see faint objects and to view galaxies over long intervals of cosmic time. That will allow us to study how galaxies assembled and transformed,” said Swara Ravindranath, an astronomer at the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

While wide-field imaging will be important for galaxy studies, just as important are Roman’s spectroscopic capabilities. A spectrograph takes light from an object and spreads it into a rainbow of colors known as a spectrum. From this range of colors, astronomers can glean many details otherwise unavailable, like an object’s distance or composition. Roman’s ability to provide a spectrum of every object within the field of view, combined with Roman imaging, will enable astronomers to learn more about the universe than from either imaging or spectroscopy alone.

Revealing When and Where Stars Were Born Galaxies don’t form stars at a constant rate. They speed up and slow down—forming more or fewer stars—under the influence of a variety of factors, from collisions and mergers to supernova shock waves and galaxy-scale winds powered by supermassive black holes.

By studying a galaxy’s spectrum in detail, astronomers can explore the history of star formation. “Using Roman we can estimate how fast galaxies are making stars and find the most prolific galaxies that are producing stars at an enormous rate. More importantly, we can find out not only what’s happening in a galaxy at the moment we observe it, but what its history has been,” stated Lee Armus, an astronomer at IPAC/Caltech in Pasadena, California.

Some precocious galaxies birthed stars very rapidly for a short time, only to cease forming stars surprisingly early in the universe’s history, undergoing a rapid transition from lively to “dead.”

“We know galaxies shut off star formation, but we don’t know why. With Roman’s wide field of view, we stand a better chance of catching these galaxies in the act,” said Kate Whitaker, an astronomer at the University of Massachusetts in Amherst.

Growing the Cosmic Web

Even as galaxies themselves have grown over time, they also have gathered together in groups to form intricate structures billions of light-years across. Galaxies tend to collect into bubbles, sheets, and filaments, creating a vast cosmic web. By combining high-resolution imaging, which yields a galaxy’s position on the sky, with spectroscopy, which provides a distance, astronomers can map this web in three dimensions and learn about the universe’s large-scale structure.

The expansion of the universe stretches light from distant galaxies to longer, redder wavelengths—a phenomenon called redshift. The more distant a galaxy is, the greater its redshift. Roman’s infrared detectors are ideal for capturing light from those galaxies. More distant galaxies are also fainter and harder to spot. Combining this with the fact that that some galaxy types are rare, you have to search a larger area of the sky with a more sensitive observatory to find the objects that often have the most interesting stories to tell.

“Right now, with telescopes like Hubble we can sample tens of high-redshift galaxies. With Roman, we’ll be able to sample thousands,” explained Russell Ryan, an astronomer at STScI.

Seeking the Unknown

While astronomers can anticipate many of the discoveries of the Roman Space Telescope, perhaps most exciting is the possibility of finding things that no one could have predicted. Typical high-resolution observations from space-based observatories like Hubble, target specific objects for detailed investigation. Roman’s survey approach will cast a wide net, thereby opening up a new “discovery space.”

“Roman will excel in unknown unknowns. It will certainly find rare, exotic things that we don’t expect,” said Ryan.

“Roman’s combined imaging and spectroscopy surveys will gather the ‘gold nuggets’ that we never would have mined otherwise,” added Ravindranath.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will provide Roman’s Mission Operations Center. The Space Telescope Science Institute in Baltimore, Maryland, will host Roman’s Science Operations Center and lead the data processing of Roman imaging. Caltech/IPAC in Pasadena, California, will house Roman’s Science Support Center and lead the data processing of Roman spectroscopy.

Credits:

Release: NASA

Media Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

 

Contact Us: Direct inquiries to the News Team.

 

Source: HubbleSite/News 

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Gas content and quenching of local galaxies

Top panel: gas fraction (fgas) and bottom panel: star formation efficiency (SFE) plotted as functions of distance from the MS in four bins of total stellar mass. Each point corresponds to a median value with a bootstrapped error estimate. The grey shaded area covers the range in ∆SFMS with 10% completeness in each bin.

During galactic transition towards quiescence 'it is not only the gas reservoir of a galaxy which decreases but also the efficiency with which the gas is turned into stars' - suggests a new study led by KICC researchers.

Galaxies in the observable Universe divide into two broad categories: blue, star-forming and red, quiescent. When observed across cosmic, time the distribution of galaxies shifts from the star-formation dominated to passive (quiescent) and hence these two states are interpreted as an evolutionary sequence.

Understanding the physical processes responsible for ceasing star formation is one of the long-standing questions in the area of galaxy evolution. Ultimately, galaxies may quench either due to a lack of fuel or a decrease in star formation efficiency (i.e. an increase in thedepletion time). In order to differentiate between the two possibilities one needs to measure the dense neutral gas within galaxies. However, observing the faint gas emission typically requires long exposure times on premier facilities, thus limiting the sample sizes to only a few hundred detections.

In this work led by Joanna Piotrowska, a PhD student at the Kavli, the KICC researchers use an indirect method to obtain gas mass estimates for ~62 000 local galaxies in the Sloan Digital Sky Survey which allows them to investigate the variation of gas fraction and star formation efficiency of objects on their path towards quiescence. They show that as galaxies deviate from the star-forming Main Sequence (a tight relation between the galaxy stellar mass and star formation rate) it is not only the gas reservoir of a galaxy which decreases but also the efficiency with which the gas is turned into stars as shown in the figure at the above of the page.

These results call for a better understanding of the physical processes driving the decrease in star formation efficiency, which has received relatively little attention in the theory of quenching until now.

You can freely access the article at this link  or with a subscription in the MNRAS Letters here.

Source: Kavli Institute for Cosmology (KICC)/News

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Milky Way Raids Intergalactic 'Bank Accounts,' Hubble Study Finds

Artist’s Impression of Milky Way Inflows and Outlfows

Artist's Illustration: NASA, ESA, and D. Player (STScI )
Science: NASA, ESA, and A. Fox (STScI )

Audit of the Milky Way's gas flow rates reveals a mysterious surplus of inflowing gas.

Astronomers have discovered an unexplained surplus of gas flowing into our Milky Way after conducting a galaxy-wide audit of outflowing and inflowing gas. Rather than a gas equilibrium and "balanced books," 10 years of data from NASA's Hubble Space Telescope show there is more gas coming in than going out.

It is no secret that the Milky Way is frugal with its gas. The valuable raw material is recycled over billions of years—thrown out into the galactic halo via supernovas and violent stellar winds, and then used to form new generations of stars once it falls back to the galactic plane. The surplus of inflowing gas, however, was a surprise.

Hubble distinguished between outflowing and inflowing clouds using its sensitive Cosmic Origins Spectrograph (COS), which detects the movement of the invisible gas. As the gas moves away it appears redder, while gas falling back toward the Milky Way is bluer.

The source of the excess gas inflow remains a mystery. Astronomers theorize that the gas could be coming from the intergalactic medium, as well as the Milky Way raiding the gas "bank accounts" of its small satellite galaxies using its considerably greater gravitational pull.

Our Milky Way is a frugal galaxy. Supernovas and violent stellar winds blow gas out of the galactic disk, but that gas falls back onto the galaxy to form new generations of stars. In an ambitious effort to conduct a full accounting of this recycling process, astronomers were surprised to find a surplus of incoming gas.

"We expected to find the Milky Way's books balanced, with an equilibrium of gas inflow and outflow, but 10 years of Hubble ultraviolet data has shown there is more coming in than going out," said astronomer Andrew Fox of the Space Telescope Science Institute, Baltimore, Maryland, lead author of the study to be published in The Astrophysical Journal.

Fox said that, for now, the source of the excess inflowing gas remains a mystery.

One possible explanation is that new gas could be coming from the intergalactic medium. But Fox suspects the Milky Way is also raiding the gas "bank accounts" of its small satellite galaxies, using its considerably greater gravitational pull to siphon away their resources. Additionally, this survey, while galaxy-wide, looked only at cool gas, and hotter gas could play a role, too.

The new study reports the best measurements yet for how fast gas flows in and out of the Milky Way. Prior to this study, astronomers knew that the galactic gas reserves are replenished by inflow and depleted by outflow, but they did not know the relative amounts of gas coming in compared to going out. The balance between these two processes is important because it regulates the formation of new generations of stars and planets.

Astronomers accomplished this survey by collecting archival observations from Hubble’s Cosmic Origins Spectrograph (COS), which was installed on the telescope by astronauts in 2009 during its last servicing mission. Researchers combed through the Hubble archives, analyzing 200 past ultraviolet observations of the diffuse halo that surrounds the disk of our galaxy. The decade's worth of detailed ultraviolet data provided an unprecedented look at gas flow across the galaxy and allowed for the first galaxy-wide inventory. The gas clouds of the galactic halo are only detectable in ultraviolet light, and Hubble is specialized to collect detailed data about the ultraviolet universe.

"The original Hubble COS observations were taken to study the universe far beyond our galaxy, but we went back to them and analyzed the Milky Way gas in the foreground. It's a credit to the Hubble archive that we can use the same observations to study both the near and the more distant universe. Hubble's resolution allows us to simultaneously study local and remote celestial objects," noted Rongmon Bordoloi of North Carolina State University in Raleigh, North Carolina, a co-author on the paper.

Because the galaxy's gas clouds are invisible, Fox's team used light from background quasars to detect these clouds and their motion. Quasars, the cores of active galaxies powered by well-fed black holes, shine like brilliant beacons across billions of light-years. When the quasar's light reaches the Milky Way, it passes through the invisible clouds.

The gas in the clouds absorbs certain frequencies of light, leaving telltale fingerprints in the quasar light. Fox singled out the fingerprint of silicon and used it to trace the gas around the Milky Way. Outflowing and inflowing gas clouds were distinguished by the Doppler shift of the light passing through them—approaching clouds are bluer, and receding clouds are redder.

Currently, the Milky Way is the only galaxy for which we have enough data to provide such a full accounting of gas inflow and outflow.

"Studying our own galaxy in detail provides the basis for understanding galaxies across the universe, and we have realized that our galaxy is more complicated than we imagined," said Philipp Richter of the University of Potsdam in Germany, another co-author on the study.

Future studies will explore the source of the inflowing gas surplus, as well as whether other large galaxies behave similarly. Fox noted that there are now enough COS observations to conduct an audit of the Andromeda galaxy (M31), the closest large galaxy to the Milky Way.

The Hubble Space Telescope is a project of international cooperation between the European Space Agency (ESA) and NASA. 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.

Source: HubbleSites/News

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Contact:

Leah Ramsay / Ray Villard

Space Telescope Science Institute, Baltimore, Maryland

667-218-6439 / 410-338-4514

lramsay@stsci.edu/villard@stsci.edu

Andrew Fox

Space Telescope Science Institute, Baltimore, Maryland

afox@stsci.edu

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Related Links:

• The science paper by A. Fox et al.
• NASA's Hubble Portal

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