An Early Discovery by Rubin Observatory

A field of stars seen by the NSF–DOE Vera C. Rubin Observatory
Credit: NSF–DOE Vera C. Rubin Observatory/NOIRLab/SLAC/AURA; CC BY 4.0

Title: Discovery of the Distant, Ultra-Faint Milky Way Satellite Aquarius IV with the Vera C. Rubin Observatory Early Data Preview 2

Authors: William Cerny et al.
First Author’s Institution: Yale University
Status: Published in RNAAS

Warming Up the World’s Largest Camera

Today’s bite covers one of the NSF–DOE Vera C. Rubin Observatory‘s first major discoveries, which was found in testing data before the observatory began its decade of observations. Perched atop a mountain in Chile, the brand-new Rubin Observatory is just beginning a 10-year survey called the Legacy Survey of Space and Time (LSST). LSST will be the deepest and widest sky survey ever conducted, taking images of the entire southern night sky every three nights. This ultra-wide, ultra-high-definition time-lapse of the universe will help answer fundamental questions about dark matter and dark energy, study objects in our solar system, find distant supernova explosions, and more.

LSST is a photometric survey, meaning its main data product is images in several filters. These images are taken with the largest digital camera ever constructed, about the size of a Mini Cooper. The LSST camera has a resolution of 3.2 gigapixels. To put that number into perspective, you would need about 13 copies of the Las Vegas Sphere to display just a single LSST image… and hundreds of these images will be taken every night!

The authors of today’s article use the first dataset from the LSST camera, called Early Data Preview 2 (EDP2). EDP2 was taken from April 2025 to January 2026, covered about 3,000 square degrees (about 7% of the entire night sky), and primarily served as a test before beginning the 10-year LSST (which began in June 2026).

Small Galaxies, Big Questions

Since LSST will survey a large area at unprecedented depths, one field of interest is to study extremely dim and small galaxies called ultra-faint dwarf galaxies (UFDs). These galaxies are so faint that we can only find them close to home, orbiting the Milky Way and other nearby galaxies as satellites. UFDs don’t have much luminous matter, meaning they are likely dominated by their dark matter halos. This makes them useful test beds for our theories of dark matter and galaxy formation, if we can spot them.

Many UFDs don’t look like normal galaxies that resemble blobs of diffuse light with stars; instead, they’re more like a handful of individual stars in an image that also contains foreground stars and background galaxies. So how do you identify them? The trick is that stars born together at the same time from the same gas follow a predictable track in color and brightness called an isochrone. The authors slide a model isochrone for an ancient, metal-poor population through the data at a range of assumed distances and ask: at any spot in EDP2, are there more stars sitting on that track than random chance would predict? Cerny and coauthors found a new spot, which they call Aquarius IV, a new UFD candidate (Figure 1).

Figure 1: Left: A Rubin image centered on Aquarius IV, combining images in the g, r, and z filters. The dashed circle marks the half-light radius, the region enclosing half the galaxy’s light. Aquarius IV is only a scattering of individual faint stars. The yellow star marks a likely blue horizontal-branch member. Right: A plot of brightness against color for the stars inside twice the half-light radius (first panel) and inside a ring of sky just outside the galaxy (second panel). Stars born at the same time from the same gas fall along the isochrone (blue line; any stars in the grey regions are deemed to follow the isochrone). All the stars follow the isochrone in the first panel but not the second, indicating that the stars are associated. Adapted from Cerny et al. 2026

Aquarius IV had not been identified previously by any other observatory. However, the authors combed through data from LSST’s predecessor (the Dark Energy Survey, which concluded taking data in 2019) and found previously missed evidence that supports their discovery, namely an excess of faint, blue, marginally resolved stars. As a sanity check, they confirm that all previously known UFDs within the EDP2 footprint (Sagittarius II, Aquarius II, Aquarius III, and Virgo III) are also detected using their methods.

The authors also infer several properties of Aquarius IV, including its centroid coordinates, half-light radius, ellipticity, distance, and absolute magnitude. They find that its radius is larger than almost all Milky Way globular clusters (tight gravitationally bound systems of old stars that don’t reside in their own dark matter halos), suggesting that Aquarius IV is a true dwarf galaxy

Currently, there are about 40 known UFDs around the Milky Way, and LSST is expected to roughly double this number (see this Astrobite), allowing us to study these tiny galaxies at a population level. This article proves that LSST has the potential to revolutionize many areas of astrophysics! If you are a researcher in the US or Chile and want to play with the EDP2 data yourself, you can access it via the Rubin Science Platform. For researchers from other countries, see more info here.

Original astrobite edited by Katya Gozman.

Source: American Astronomical Society/ASS-Nova

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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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About the author, Ben Sherwin:

I am a physics PhD student and NSF Graduate Research Fellow at Stanford University. I am interested in theoretical and observational cosmology, specifically in cross-correlations between the cosmic microwave background and tracers of large-scale structure. Outside of work, I enjoy seeing the latest movies in theaters and exploring the San Francisco Bay Area.

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Hubble Solves Merger Mystery From Milky Way’s Early Years

LKH Milky Way Merger Illustration

About 12 billion years ago, a dwarf galaxy known as LKH collided with a young Milky Way and merged with it. This artist’s concept portrays that collision. NASA’s Hubble Space Telescope uncovered definitive evidence of this collision by studying globular star clusters. Illustration: NASA, ESA, Joseph Olmsted (STScI)

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Our home galaxy, the Milky Way, grew to its current size in part by consuming smaller galaxies. Now, new data from NASA’s Hubble Space Telescope shows definitive evidence of a dwarf galaxy merging with the young Milky Way galaxy in the earliest phases of its evolution. This finding extends our knowledge of our galaxy’s history 1.8 billion years farther back in time than before.

The results published Monday in the journal Nature Astronomy.

The Milky Way today is a massive spiral galaxy home to hundreds of billions of stars. However, our galaxy wasn’t always so large; it has grown by forming new stars from its gas clouds as well as collecting stars, gas, and dark matter from other galaxies through mergers.

The most recent massive merger in our galaxy’s history took place with the Sagittarius dwarf galaxy, beginning over 6 billion years ago and still ongoing today. Looking back into the even more distant past, researchers learned that the Milky Way galaxy consumed another dwarf galaxy called Gaia-Sausage-Enceladus 10 billion years ago. This ancient merger greatly affected the structure of our galaxy’s disk of stars. Other, smaller mergers occurred between these two.

But our galaxy’s history doesn’t stop there. Both observations and simulations have suggested that another large merger preceded these two, though the specifics of the event have been heavily debated. Now, Hubble has uncovered definitive evidence of an earlier merger that occurred about 11.8 billion years ago, or just 2 billion years after the big bang.

“Our home is the Milky Way galaxy, but we do not know how our house was built,” said Davide Massari, lead author, Astrophysics and Space Science Observatory of Bologna in Italy. “In this paper we discover where the first significant batch of bricks came from: a dwarf galaxy that we call LKH.”

Cosmic archaeological sites

Immense astronomical surveys and precision data from spacecraft like ESA’s (European Space Agency’s) Gaia mission have been instrumental in piecing together the history of our galaxy. The farther back into our galaxy’s history that scientists attempt to look, the more difficult it becomes to tell what happened. When our galaxy was young, it was smaller and much closer in size to the galaxies it clashed with. It was also more chaotic, and it’s possible that the signs of mergers have been erased over billions of years.

It’s into this murky past that Hubble peered. Researchers used Hubble to study some of the Milky Way galaxy’s globular clusters: immense, roughly spherical collections of tens of thousands to a few million stars. Globular clusters contain some of the oldest stars in our galaxy, and they can act as cosmic archaeological sites that preserve stars from other galaxies the Milky Way galaxy has collected.

“Thanks to the high resolution and depth of Hubble imaging, we could measure the age and the metal content of these clusters with unprecedented precision,” said Chiara Zerbinati, study co-author, University of Bologna in Italy. “Coupled with measurements from Gaia, this made it possible to distinguish a population of globular clusters that are different from the others. These are the clusters that were born in LKH, and they tell us when that galaxy was devoured by ours, and how massive it was.”

The team analyzed Hubble observations of 39 globular clusters in the inner 20,000 light-years of our galaxy, where evidence of the most ancient mergers should be preserved. They expected this sample to contain globular clusters that formed within the young Milky Way galaxy as well as those collected from the Gaia-Sausage-Enceladus dwarf galaxy about 10 billion years ago.

Using Hubble’s sensitive observations to determine each cluster’s precise age and associated metallicity — the abundance of elements heavier than helium — they determined there was a third population of globular clusters in the inner regions of our galaxy. The team found that these clusters are older than the group collected in the Gaia-Sausage-Enceladus merger, but younger than those born in the Milky Way, regardless of their metal content. These clusters, therefore, came from a separate and even earlier merger — in which the Milky Way galaxy absorbed a dwarf galaxy containing roughly 500 million times the mass of the Sun in stars, a significant fraction of our galaxy’s mass at the time. They named this dwarf galaxy Low-energy-Kraken-Heracles, or LKH, in honor of three earlier research papers that championed the idea of a merger early in our galaxy’s history.

Such a large merger so early in the Milky Way galaxy’s formation has profound implications for the evolution of our galaxy.

“Some past studies have argued that the earliest phases of our galaxy’s evolution were defined by stars born only in our galaxy,” says Massari. “Here, we have shown that stars born in external galaxies also need to be considered.”

The team plans to continue their work to unravel the history of the Milky Way galaxy by studying its globular clusters, aiming to characterize all the massive mergers that our galaxy has experienced across cosmic history.

“Hubble is observing globular clusters that have never been studied before, and this will help us characterize the merger events that are far back in time in the Milky Way galaxy’s history,” said Fernando Aguado-Agelet, co-author, University of Vigo and the University of La Laguna in Spain.

The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: NASA's Hubble Space Telescope/News

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Details:

Last Updated: Aug 17, 2026
Editor: Andrea Gianopoulos
Location: NASA Goddard Space Flight Center

Contact Media:

Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov

Bethany Downer
ESA/Hubble
Baltimore, US

Christine Pulliam
Space Telescope Science Institute
Baltimore, Maryland

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NASA Webb Finds Early-Universe Analog’s Unexpected Talent for Making Dust

Sextans A PAHs Pull-out (NIRCam and MIRI Image)

Images from NASA’s James Webb Space Telescope of the dwarf galaxy Sextans A reveal polycyclic aromatic hydrocarbons (PAHs), large carbon-based molecules that can be a signifier of star formation. The inset at the top right zooms in on those PAHs, which are represented in green.Credit Image: NASA, ESA, CSA, Elizabeth Tarantino (STScI), Martha Boyer (STScI), Julia Roman-Duval (STScI); Image Processing: Alyssa Pagan (STScI)

Sextans A Context Image (Webb and KPNO)

NASA’s James Webb Space Telescope’s image of a portion of the nearby Sextans A galaxy is put into context using a ground-based image from the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory. Credit Image: STScI, NASA, ESA, CSA, KPNO, NSF's NOIRLab, AURA, Elizabeth Tarantino (STScI), Phil Massey (Lowell Obs.), George Jacoby (NSF, AURA), Chris Smith (NSF, AURA); Image Processing: Alyssa Pagan (STScI), Travis Rector (UAA), Mahdi Zamani (NSF's NOIRLab), Davide De Martin (NSF's NOIRLab)

Sextans A PAHs Pull-out (Compass Image)

This image of dwarf galaxy Sextans A, captured by NASA’s James Webb Space Telescope’s Near Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), shows compass arrows, scale bar, and color key for reference. Credit Image: NASA, ESA, CSA, Elizabeth Tarantino (STScI); Image Processing: Alyssa Pagan (STScI)

Giant Star in Dwarf Galaxy Sextans A (Spectrum)

This graph shows a spectrum of an Asymptotic Giant Branch (AGB) star in the Sextans A galaxy. It compares data collected by NASA’s James Webb Space Telescope with models of mostly silicate-free dust and dust containing at least 5% silicates.Credit Illustration: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI)

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Using NASA’s James Webb Space Telescope, astronomers have spotted two rare kinds of dust in the dwarf galaxy Sextans A, one of the most chemically primitive galaxies near the Milky Way. The finding of metallic iron dust and silicon carbide (SiC) produced by aging stars, along with tiny clumps of carbon-based molecules, shows that even when the universe had only a fraction of today’s heavy elements, stars and the interstellar medium could still forge solid dust grains. This research with Webb is reshaping ideas about how early galaxies evolved and developed the building blocks for planets, as NASA explores the secrets of the universe and our place in it.

Sextans A lies about 4 million light-years away and contains only 3 to 7 percent of the Sun’s metal content, or metallicity, the astrophysical term for elements heavier than hydrogen and helium. Because the galaxy is so small, unlike other nearby galaxies, its gravitational pull is too weak to retain the heavy elements like iron and oxygen created by supernovae and aging stars.

Galaxies like it resemble those that filled the early universe just after the big bang, when the universe was made of mostly hydrogen and helium, before stars had time to enrich space with ‘metals.’ Because it is relatively close, Sextans A gives astronomers a rare chance to study individual stars and interstellar clouds under conditions similar to those shortly after the big bang.

“Sextans A is giving us a blueprint for the first dusty galaxies,” said Elizabeth Tarantino, postdoctoral researcher at the Space Telescope Science Institute and lead author of the results in one of the two studies presented at a press conference at the 247th meeting of the American Astronomical Society in Phoenix. “These results help us interpret the most distant galaxies imaged by Webb and understand what the universe was building with its earliest ingredients.”

Forging dust without usual ingredients

One of those studies, published in the Astrophysical Journal, honed in on a half a dozen stars with the low-resolution spectrometer aboard Webb’s MIRI (Mid-Infrared Instrument). The data collected shows the chemical fingerprints of the bloated stars very late in their evolution, called asymptotic giant branch (AGB) stars. Stars with masses between one and eight times that of the Sun pass through this phase.

“One of these stars is on the high-mass end of the AGB range, and stars like this usually produce silicate dust. However, at such low metallicity, we expect these stars to be nearly dust-free,” said Martha Boyer, associate astronomer at the Space Telescope Science Institute and lead author in that second companion study. “Instead, Webb revealed a star forging dust grains made almost entirely of iron. This is something we’ve never seen in stars that are analogs of stars in the early universe.”

Silicates, the usual dust formed by oxygen-rich stars, require elements like silicon and magnesium that are almost nonexistent in Sextans A. It would be like trying to bake cookies in a kitchen without flour, sugar, and butter.

A normal cosmic kitchen, like the Milky Way, has those crucial ingredients in the form of silicon, carbon, and iron. In a primitive kitchen, like Sextans A, where almost all of those ingredients are missing, you barely have any proverbial flour or sugar. herefore, astronomers expected that without those key ingredients, stars in Sextans A couldn’t “bake” much dust at all.

However, not only did they find dust, but Webb showed that one of these stars used an entirely different recipe than usual to make that dust.

The iron-only dust, as well as silicon carbide produced by the less massive AGB stars despite the galaxy’s low silicon abundance, proves that evolved stars can still build solid material even when the typical ingredients are missing.

“Dust in the early universe may have looked very different from the silicate grains we see today,” Boyer said. “These iron grains absorb light efficiently but leave no sharp spectral fingerprints and can contribute to the large dust reservoirs seen in far-away galaxies detected by Webb.”

Tiny clumps of organic molecules

In the companion study, currently under peer review, Webb imaged Sextans A’s interstellar medium and discovered polycyclic aromatic hydrocarbons (PAHs), which are complex, carbon-based molecules and the smallest dust grains that glow in infrared light. The discovery means Sextans A is now the lowest-metallicity galaxy ever found to contain PAHs.

But, unlike the broad, sweeping PAH emission seen in metal-rich galaxies, Webb revealed PAHs in tiny, dense pockets only a few light-years across.

“Webb shows that PAHs can form and survive even in the most metal-starved galaxies, but only in small, protected islands of dense gas,” said Tarantino.

The clumps likely represent regions where dust shielding and gas density reach just high enough to allow PAHs to form and grow, solving a decades-long mystery about why PAHs seem to vanish in metal-poor galaxies.

The team has an approved Webb Cycle 4 program to use high-resolution spectroscopy to study the detailed chemistry of Sextans A’s PAH clumps further.

Connecting two discoveries

Together, the results show that the early universe had more diverse dust production pathways than the more established and proven methods, like supernova explosions. Additionally, researchers now know there’s more dust than predicted at extremely low metallicities.

“Every discovery in Sextans A reminds us that the early universe was more inventive than we imagined,” said Boyer. “Clearly stars found a way to make the building blocks of planets long before galaxies like our own existed.”

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/Webb/Latest News

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Related Links

Read more: Webb Science: Galaxies Through Time

Explore more: Massive stars: Engines of Creation

Explore more: Wolf-Rayet Apep Visualization

Read more: Spectroscopy 101

More Webb News

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Webb Mission Page

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A neighbouring vista of stellar birth

LMC N159

A field filled with stars and covered by clouds of gas and dust. In the centre, a thick column of dark black dust blocks light from stars that light it up from behind. More clouds behind those stars are illuminated in pale colours. Complex, layered filaments of red dust lie to the left and right. Blue, white and gold stars in various sizes can be seen around, within and through the colourful layers of dust. Credit: ESA/Hubble & NASA, R. Indebetouw

Today’s ESA/Hubble Picture of the Week highlights another view of a distant stellar birthplace. Captured in a parallel field to a recently released image, this scene reveals a neighbouring region of the N159 star-forming complex in the Large Magellanic Cloud, approximately 160 000 light-years away.

Thick clouds of cold hydrogen gas dominate the scene, forming a complex network of ridges, cavities, and glowing filaments. Embedded within these dense clouds, newly formed stars begin to shine, their intense radiation causing the surrounding hydrogen to glow in deep red tones.

The brightest regions mark the presence of hot, massive young stars whose powerful stellar winds and energetic light reshape their environment. These forces carve out bubble-like structures and hollowed cavities in the gas, clear signatures of stellar feedback in action. Dark clouds in the foreground are lit from behind by new stars. Together, the glowing clouds and sculpted bubbles reveal a dynamic interplay between star formation and the material from which stars are born, capturing the ongoing cycle of creation and transformation within this neighbouring galactic system.

N159 is one of the most massive star-forming clouds in the Large Magellanic Cloud, a dwarf galaxy that is the largest of the small galaxies that orbit the Milky Way. This image shows just a portion of this expansive star-forming complex, as the entire complex stretches over 150 light-years across.

Links

• Pan: N159

Source: ESA/Hubble/potw

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A sea monster and a Tarantula

A nebula. The top-left is dense with layers of fluffy pink and greenish clouds. Long strands of green clouds stretch out from here; a faint layer of translucent blue dust combines with them to create a three-dimensional scene. A sparse network of dark dust clouds in the foreground adds reddish-black patches atop the nebula. Blue-white and orange stars, from our galaxy and beyond, are spread amongst the clouds. Credit: ESA/Hubble & NASA, C. Murray

A scene from a star-forming factory shines in this NASA/ESA Hubble Space Telescope Picture of the Week. This Hubble picture captures incredible details in the dusty clouds in a star-forming region called the Tarantula Nebula. What’s possibly the most amazing aspect of this detailed image is that this nebula isn’t even in our galaxy. Instead, it’s in the Large Magellanic Cloud, a dwarf galaxy that is located about 160 000 light-years away in the constellations Dorado and Mensa.

The Large Magellanic Cloud is the largest of the dozens of small satellite galaxies that orbit the Milky Way. The Tarantula Nebula is the largest and brightest star-forming region not just in the Large Magellanic Cloud, but in the entire group of nearby galaxies to which the Milky Way belongs.

The Tarantula Nebula is home to the most massive stars known, some of which are roughly 200 times as massive as our Sun. The scene pictured here is located away from the centre of the nebula, where there is a super star cluster called R136, but very close to a rare type of star called a Wolf–Rayet star. Wolf–Rayet stars are massive stars that have lost their outer shell of hydrogen and are extremely hot and luminous, powering dense and furious stellar winds.

This nebula is a frequent target for Hubble, whose multiwavelength capabilities are critical for capturing sculptural details in the nebula’s dusty clouds. The data used to create this image come from an observing programme called Scylla, named for a multi-headed sea monster from the Greek myth of Ulysses. The Scylla programme was designed to complement another Hubble observing programme called ULYSSES (Ultraviolet Legacy library of Young Stars as Essential Standards). ULYSSES targets massive young stars in the Small and Large Magellanic Clouds, while Scylla investigates the structures of gas and dust that surround these stars.

Source: ESA/Hubble/potw

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Capturing candyfloss clouds

Large Magellanic Cloud

A part of a nebula in space. It is made of layers of gas and dust clouds in different colours, from blue and green shades to pink, red and black, indicating light emitted by different molecules. The background cloud layers are thicker and puffier, though still translucent, and the upper layers are thin and bright at the edges. Behind the clouds are very many small, mostly orange and some blue, stars. Credit: ESA/Hubble & NASA, C. Murray

Today’s NASA/ESA Hubble Space Telescope Picture of the Week features a sparkling cloudscape from one of the Milky Way’s galactic neighbours, a dwarf galaxy called the Large Magellanic Cloud. Located 160 000 light-years away in the constellations Dorado and Mensa, the Large Magellanic Cloud is the largest of the Milky Way’s many small satellite galaxies.

This view of dusty gas clouds in the Large Magellanic Cloud is possible thanks to Hubble’s cameras, such as the Wide Field Camera 3 (WFC3) that was used to collect the observations for this image. WFC3 is equipped with a variety of filters, each of which lets through only specific wavelengths, or colours, of light. This image combines observations made with five different filters, including some that capture ultraviolet and infrared light that the human eye cannot see.

The wispy gas clouds in this image resemble brightly coloured candyfloss. When viewing such a vividly coloured cosmic scene, it is natural to wonder whether the colours are ‘real’. After all, Hubble, with its 2.4 metre-wide mirror and advanced scientific instruments, doesn’t bear resemblance to a typical camera! When image-processing specialists combine raw filtered data into a multi-coloured image like this one, they assign a colour to each filter. Visible-light observations are typically matched to the colour that the filter allows through. Shorter wavelengths of light such as ultraviolet are usually coloured blue or purple, while longer wavelengths like infrared are typically coloured red.

This colour scheme closely represents reality while adding new information from the portions of the electromagnetic spectrum that humans cannot see. However, there are endless possible colour combinations that can be employed to achieve an especially aesthetically pleasing or scientifically insightful image.

Source: ESA/Hubble/potw

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Colourful clouds of a nearby neighbour

SMC 13

An area of space that is filled with stars. Most of the stars are small, distant dots in orange colours; closer stars shine with a bright glow and four thin spikes around them. These closer stars appear in both bluish and reddish colours. Clouds from a nebula cover the left half of the scene, giving it a blue-greenish cast. More pieces of cloud drift over the black background of space on the right. Credit: ESA/Hubble & NASA, C. Murray

Say hello to one of the Milky Way’s neighbours! Today’s NASA/ESA Hubble Space Telescope Picture of the Week features a scene from one of the closest galaxies to the Milky Way, the Small Magellanic Cloud (SMC). The SMC is a dwarf galaxy located about 200 000 light-years away. Most of the galaxy resides in the constellation Tucana, but a small section crosses over into the neighbouring constellation Hydrus.

Thanks to its proximity, the SMC is one of only a few galaxies that can be seen from Earth without the help of a telescope or binoculars. For viewers in the southern hemisphere and some latitudes in the northern hemisphere, the SMC resembles a piece of the Milky Way that has broken off, though in reality it’s much farther away than any part of our own galaxy.

With its 2.4-metre ‘eye’ and sensitive instruments, Hubble’s view of the SMC is far more detailed and vivid than what humans can see. Researchers used Hubble’s Wide Field Camera 3 instrument to observe this scene through four different filters. Each filter admits different wavelengths of light, creating a multicoloured view of dust clouds drifting across a field of stars. Hubble’s view, however, is much more zoomed-in than our eyes, the better for it to observe very distant objects. This image captures a small region of the SMC near the centre of NGC 346, a star cluster that is home to dozens of massive young stars.

Source: ESA/Hubble/potw

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Simulating the birth, life and dispersal of galactic star clusters

This illustration shows the galactic orbit (grey dots) of a star cluster (with 800 solar masses) that formed in a dwarf galaxy. The insets show individual cluster stars at three different times in the life-cycle of the star cluster: when the compact cluster has formed (red); after 50 Myr (half an orbit, green); and after 450 Myr (several orbits, blue), when the cluster is almost entirely disrupted. The background shows stars which have formed in the last 500 Myr (see movie below for details). © MPA

Most stars form in clusters, deeply embedded in the densest and coldest cores of giant molecular gas clouds. A few million years into the formation of a cluster the remaining gas is finally expelled by supernova explosions. Thereafter the clusters lose stars in the galactic tidal field and eventually disrupt. This entire life-cycle is very difficult to observe. Star clusters begin their lives deeply embedded in their birth clouds and are invisible to most observatories and the disruption of a single cluster can take tens of millions of years or more. An international team led by researchers at MPA has presented a new high-resolution supercomputer simulation, which can follow entire galactic star cluster life-cycles from birth to disruption and sheds light on the unobservable phases of star cluster evolution.

The complex life of star clusters

A typical young star cluster is a home to up to thousands of stars contained in a compact size of a few parsecs. The most massive ones, such as globular clusters, can exceed millions in their stellar count. Some of stars in these clusters are born with masses that exceed the mass of the Sun by tens or hundreds of times. Such massive stars are extremely rare (less than one in every 100 stars) and they live only for a few million years. They are, however, vitally important for creating new chemical elements through nuclear fusion, including those that are requisites for the formation of planets and the development of life.

Once massive stars form, they start releasing energetic photons and fast stellar winds that interact with the surrounding birth-cloud of gas. After a few million years, once the stars have exhausted their nuclear fuel, the most massive ones end their lives as explosive supernovae. These so called “feedback” processes deposit heat, momentum and heavy elements into the birth-cloud, eventually expelling the remaining gas that is left over from star formation.

This marks the transition of a young star cluster into a system that mainly evolves by gravitational interactions among its stars and with the surrounding tidal field. Through dynamical interactions, massive stars can sink to the centre of the cluster and stars can end up in binaries. Further gravitational interactions at the centre of the cluster force low mass stars on increasingly distant orbits. These stars can then become unbound and escape from the gravitational potential of the cluster into the galactic field. While orbiting in the host galaxy, the cluster continuously loses mass and ultimately disrupts entirely (Fig. 1).

More realistic star cluster simulations

Numerical simulations are an invaluable tool to probe the entire cycle of formation and disruption of star clusters on spatial and temporal scales that are inaccessible to observations (see previous Research Highlight December 2021 and Research Highlight October 2019). A recent study led by Postdoctoral Fellow Natalia Lahén at MPA presentedthe first star-by-star hydrodynamical galaxy simulations. Detailed modelling of individual stars is crucial for resolving the internal structure of star clusters. The simulation code for this project was first developed at MPA and further improved in international collaboration including researches at the University of Helsinki in Finland and Nicolaus Copernicus University in Poland. For the study presented here the team used a very accurate gravity solver to follow close gravitational interactions between stars. With this method it was possible to simulate, for the first time, the evolution of an entire dwarf galaxy with all its stars, gas and dark matter. At the same time, they could accurately follow the dynamical evolution of hundreds of individual star clusters, each containing at least hundreds or thousands of stars.

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Star cluster simulation

This movie follows the evolution of a low-mass galaxy for 500 million years modelled with the new method. The panels show the surface densities of stars (top left) and interstellar gas (top right), as well as the temperature (bottom left) and thermal pressure (bottom right) of the gas. Star clusters can be seen as concentrations of stellar mass, and the leading and trailing tidal tails extending from the clusters indicate that they are losing stars and being gradually disrupted. Energetic feedback from young massive stars can be seen as bubbles and cavities in the gas distribution.

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This figure shows the time evolution of the size and mass of a number of selected star clusters in the simulation. The color scale indicates the mean stellar age of the clusters and the black lines connecting the data points indicate the evolution of indiviual clusters. The clusters start embedded (triangles). They first contract and then expand once the star formation is halted and gas is removed (circles). The size evolution is compared to observed clusters in the Large and Small Magellanic clouds (green stars and crosses) and clusters in low-mass galaxies measured in the LEGUS galaxy survey (blue symbols). Even though the simulated clusters form very compact, they evolve to the observed range of sizes over ~10 million years. © MPA

Star cluster evolution in a galactic context

The new high-resolution simulations of a dwarf galaxy similar to Wolf–Lundmark–Melotte (WLM) in the Local Group (see the Movie for an illustration) show how gas and stars interact through cooling, collapse, star formation, and stellar feedback. The orbits as well as the release of energy and chemically enriched material of each star are followed individually along the stellar lifetime. Thanks to the new algorithm for gravitational force computation, in particular encounters with massive stars can be followed down to stellar radii and the dynamical evolution of the clusters embedded in the galactic interstellar medium can be followed at unprecedented accuracy.

The new simulations show that initially, while they are still embedded in the birth-cloud, star clusters can form very compact (see Figs. 1 and 2). During the following ten million years their sizes increase to the observed ~1 parsec due to dynamical evolution and stellar mass loss. The new methodology and its future expansion will play a key role in the next generation of simulations that aim to probe more extreme star forming systems called starbursts. Starbursts can be induced for example by compression of gas in galactic mergers or through gaseous inflows during the early cosmic epochs when galaxies themselves were still forming. The extreme gas densities promote the formation of increasingly massive star clusters.

The next step is to use the new methods to decipher the internal chemical and kinematic structure of the most massive clusters known as globular clusters. Globular clusters are the oldest bound star clusters observed in the Milky Way, dating back to the Cosmic Dawn. Understanding their birth conditions in synergy with state-of-the art observations of high-redshift star formation (from e.g. HST and JWST) as well as the Milky Way clusters (e.g. from Gaia and the upcoming 4MOST) may thus reveal how our home galaxy first started to form.

This work was supported by Gauss Centre for Supercomputing grants pn49qi and pn72bu at the GCS Supercomputer SUPERMUC-NG at Leibniz Supercomputing Centre and the Max Planck Computing and Data Facility.

Source: Max Planck Institute for Astrophysics/_Research Highlights

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Authors:

Natalia Lahén
Postdoc
tel: 2253
nlahen@mpa-garching.mpg.de

Antti Rantala
Postdoc
tel: 2253
anttiran@mpa-garching.mpg.de

Naab, Thorsten Naab
Scientific Staff
tel: 2295
tnaab@mpa-garching.mpg.de

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Original publications

1. Natalia Lahén, Antti Rantala, Thorsten Naab, Christian Partmann, Peter H. Johansson andJessica May Hislop

The formation, evolution and disruption of star clusters with improved gravitational dynamics in simulated dwarf galaxies

Monthly Notices of the Royal Astronomical Society, 2025

DOI

2. Natalia Lahén, Thorsten Naab, Guinevere Kauffmann, Dorottya Szécsi, Jessica May Hislop, Antti Rantala, Alexandra Kozyreva, Stefanie Walch and Chia-Yu Hu

Formation of star clusters and enrichment by massive stars in simulations of low-metallicity galaxies with a fully sampled initial stellar mass function

Monthly Notices of the Royal Astronomical Society, 2023, Volume 522, Issue 2, pp.3092-3116

Source

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New dwarf galaxy discovered in the halo of Andromeda galaxy

A series of plots showing the tentative detection of a candidate stellar overdensity (Pegasus VII) in the UNIONS photometric catalogs. Credit: arXiv (2025). DOI: 10.48550/arxiv.2502.09792

An international team of astronomers reports the discovery of a new dwarf galaxy, which they have named Pegasus VII. The newfound galaxy, which lies about 2.4 million light years away, was identified in the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). The discovery was detailed in a research paper published Feb. 13 on the arXiv preprint server.

Dwarf galaxies are low-luminosity and low-mass stellar systems, usually containing a few billion stars. Their formation and activity are thought to be heavily influenced by interactions with larger galaxies.

One of the great places to look for dwarf galaxies is the halo of the Andromeda galaxy (also known as Messier 31, or M31 for short), due to its relative proximity. UNIONS is so far the deepest available survey for exploring the far reaches of this galaxy's halo and now a team of astronomers led by Simon E. T. Smith of the University of Victoria in Canada, has found another such dwarf.

"We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 sub-group which has been uncovered in the ri photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada-France-Hawaii Telescope and the Gemini-North Telescope," the researchers wrote in the paper.

Pegasus VII was identified at a separation of about 1.08 million light years from the Andromeda galaxy. Therefore, Pegasus VII is just about to cross the virial radius of Andromeda and has likely been isolated up until this point.

According to the study, Pegasus VII has an absolute V-band magnitude of −5.7 mag, a central surface of 27.3 mag/arcsec2, and a physical half-light radius of approximately 577 light years. This means that Pegasus VII is the faintest known dwarf galaxy satellite of Andromeda and roughly five times larger than the most extended globular clusters in this galaxy.

The study found that Pegasus VII has an ellipticity at a level of 0.5 and this projected elongation is aligned within 18 degrees of the projected direction towards Andromeda. The astronomers suppose that the source of this elongation is a previous tidal interaction with the gravitational potential of the Andromeda galaxy.

Furthermore, the researchers calculated that Pegasus VII has a total stellar mass of 26,000 solar masses and its metallicity is at a level of -2.0 dex. The age of the dwarf galaxy was estimated to be around 10 billion years.

Summing up the results, the authors of the paper concluded that they hope to find many more dwarf galaxies in the halo of Andromeda.

"The discovery of Pegasus VII complements both the empirical and theoretical claim that a wealth of dwarf galaxy satellites remain undetected towards M31," the scientists wrote.

by Tomasz Nowakowski (Phys.org)

Source: Phys.org/Astronomy & Space news

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More information: Simon E. T. Smith et al, Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII dwarf galaxy in UNIONS, arXiv (2025). DOI: 10.48550/arxiv.2502.09792

Journal information: arXiv

© 2025 Science X Network

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Explore further

• Hubble observes an oddly organized satellite galaxy

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A Tarantula’s outskirts

Large Magellanic Cloud, Tarantula Nebula

A section of a nebula, made up of layers of coloured clouds of gas, of varying thickness. In the background are bluish, translucent and wispy clouds; on top of these are stretches of redder and darker, clumpy dust, mostly along the bottom and right. In the bottom left corner are some dense bars of dust that block light and appear black. Small stars are scattered across the nebula. Credit: ESA/Hubble

Today’s NASA/ESA Hubble Space Telescope Picture of the Week features a dusty yet sparkling scene from one of the Milky Way’s satellite galaxies, the Large Magellanic Cloud. The Large Magellanic Cloud is a dwarf galaxy situated about 160 000 light-years away in the constellations Dorado and Mensa.

Despite being only 10–20% as massive as the Milky Way galaxy, the Large Magellanic Cloud contains some of the most impressive star-forming regions in the nearby Universe. The scene pictured here is on the outskirts of the Tarantula Nebula, the largest and most productive star-forming region in the local Universe. At its center, the Tarantula Nebula hosts the most massive stars known, which weigh in at roughly 200 times the mass of the Sun.

The section of the nebula shown here features serene blue gas, brownish-orange dust patches and a sprinkling of multicoloured stars. The stars within and behind the dust clouds appear redder than those that are not obscured by dust. Dust absorbs and scatters blue light more than red light, allowing more of the red light to reach our telescopes and making the stars appear redder than they are. This image incorporates ultraviolet and infrared light as well as visible light. Using Hubble observations of dusty nebulae in the Large Magellanic Cloud and other galaxies, researchers will study these distant dust grains, helping to understand the role that cosmic dust plays in the formation of new stars and planets.

 

Source: Esa/Hunnle/potw

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New Species of Dwarf Galaxy in the Galaxy Cluster Ecosystem?

This Hubble Space Telescope image shows the spiral galaxy ESO 137-001, which has been transformed into a "jellyfish galaxy" trailing gaseous tentacles. Credit:NASA, ESA; Acknowledgements: Ming Sun (UAH), and Serge Meunier

Title: Dark-Matter-Free Dwarf Galaxy Formation at the Tips of the Tentacles of Jellyfish Galaxies
Authors: V. Lora et al.
First Author’s Institution: Institute of Nuclear Sciences, Mexico (UNAM)
Status: Published in ApJL

When Jellyfish Fly

Most galaxies are part of a galaxy cluster, which is exactly what it sounds like — a large collection of galaxies that are gravitationally bound to the larger cluster, much like how stars are gravitationally bound to a larger galaxy. In addition to the galaxies themselves, there is also gas between the galaxies in the cluster, referred to as the intracluster medium. When a disk-like galaxy moves through the intracluster medium in a galaxy cluster, some of the gas within the galaxy (the interstellar medium) gets stripped away from the galaxy. This creates long gaseous tails (or, if you will, tentacles), giving the galaxy an uncanny resemblance to a jellyfish!

Jellyfish galaxies, and their tentacles in particular, have been studied for decades. Astronomers have investigated how much of the gas in the tentacles comes from the intracluster medium versus the interstellar medium, as well as where and how star formation occurs within the tentacles. Interestingly, astronomers have found star-forming regions in the tentacles that have similar masses and sizes to ultra-compact dwarf galaxies. Today’s authors look to reproduce those results computationally and better understand how this dwarf galaxy formation channel works.

Hanging On by a Tentacle

The authors use data from the IllustrisTNG50 simulation, a cosmological simulation large enough to form dozens of galaxy clusters with enough resolution to accurately model features such as the arms of spiral galaxies. The authors identify a set of jellyfish galaxies within this simulation, then make additional cuts to:

• ensure the galaxies have obvious tentacles;
• find locations of star formation within the tentacles; and
• eliminate galaxies where tentacle-like features could be due to interactions with other galaxies.

These cuts leave only one galaxy with a mass of ~400 billion solar masses; compare this to the mass of the Milky Way, which is typically reported as ~1 trillion solar masses. (However, a 2023 study found that the Milky Way mass was closer to ~200 billion solar masses.)

The authors identify a star-forming site within one of the tentacles of this galaxy, highlighted in Figure 1. This both supports the observational evidence and suggests that this may be a new type of dwarf galaxy (more on this in a moment). Additionally, by tracking the galaxy’s history prior to the infall, they determine that the galaxy loses gas but not stars. This means that the gas in the tentacle came from the galaxy, but the stars are forming in the tentacle rather than being relocated from the galaxy. This is a consequence of ram-pressure stripping, the primary physical phenomenon that creates the tails of jellyfish galaxies. Another important finding about the dwarf galaxy candidate is that it lies well outside the dark-matter halo of the jellyfish galaxy, which has important ramifications for its status as a dwarf galaxy candidate.

Figure 1: Different visualizations of the selected galaxy. The top panel shows neutral gas (green), dark matter (white), and star formation (rainbow). The bottom panel shows the dark matter (white) and stellar mass (rainbow). The dwarf candidate is circled in magenta in both panels. Credit: Lora et al. 2024

Figure 2: Star formation rate (top panel) and oxygen abundance (proxy for metal concentration, bottom panel) of the ram-pressure-stripped candidate (magenta). Credit: Lora et al. 2024

Dark-Matter-Deficient Dwarfs

The authors perform additional analysis on the dwarf galaxy candidate. First, they determine that the gas and stars are gravitationally bound, meaning that they can be thought of as a single system much like how a galaxy is thought of as a single system. They also look at the dark-matter content of the dwarf galaxy candidate and find that none of it is gravitationally bound, making this a dark-matter-free dwarf galaxy. Furthermore, they estimate the mass and size of the dwarf galaxy candidate to be ~200 million solar masses and ~1–1.5 kiloparsecs. Based on these findings, the authors conclude that this system represents a new kind of dwarf galaxy, which they dub a ram-pressure-stripped dwarf galaxy; additionally, ram-pressure-stripped dwarf galaxies are unique among dwarf galaxies because they lack a dark-matter halo due to their creation via ram pressure stripping.

The authors also analyze the star formation and metallicity of the ram-pressure-stripped dwarf, shown in Figure 2. They find a high star formation rate compared to other star-forming regions created via ram pressure stripping. They also find that the ram-pressure-stripped dwarf is very metal rich compared to other dwarf galaxies of similar size and mass; this is because the jellyfish galaxy is also rich in metals, so the gas stripped into the tentacle to form stars has a higher concentration of metals.

Today’s authors have found evidence of a new type of dwarf galaxy, which they call a ram-pressure-stripped dwarf galaxy. These dwarf galaxies form via ram pressure stripping in the tentacles of jellyfish galaxies and are characterized as being gravitationally self-bound, hosting star formation, and lacking a dark-matter halo. The authors hope to continue studies of ram-pressure-stripped dwarf galaxies, noting that other cosmological simulations that can resolve smaller amounts of mass may lead to more discoveries of ram-pressure-stripped dwarfs with lower masses.

Original astrobite edited by Amaya Sinha

Source: American Astronomical Society/AAS-Nova

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About the author, Brandon Pries:

I am a graduate student in physics at Georgia Institute of Technology (Georgia Tech). I do research in computational astrophysics with John Wise, using machine learning to study the formation and evolution of supermassive black holes in the early universe. I’ve also done extensive research with the IceCube Collaboration as an undergraduate at Michigan State University, studying applications of neural networks to event reconstructions and searching for signals of neutrinos from dark matter annihilation.

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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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NSF NOIRLab Astronomers Discover the Fastest-Feeding Black Hole in the Early Universe

PR Image noirlab2427a
Artist’s Impression of Fastest-feeding Black Hole in the Early Universe

PR Image noirlab2427b
Artist concept of JWST

PR Image noirlab2427c
Chandra X-Ray Observatory

PR Image noirlab2427d
Artist’s Impression of Black Hole LID-568

PR Image noirlab2427e
Artist’s Impression of Early-Universe Dwarf Galaxy

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Videos

PR Video noirlab2427a
Cosmoview Episode 89: NSF NOIRLab Astronomers Discover the Fastest-Feeding Black Hole in the Early Universe

PR Video noirlab2427b
Cosmoview Episodio 88: Astrónomos de NOIRLab descubren el agujero negro más voraz del Universo primitivo

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Observations from JWST and Chandra reveal a low-mass supermassive black hole that appears to be consuming matter at over 40 times the theoretical limit

Using data from NASA's JWST and Chandra X-ray Observatory, a team of U.S. National Science Foundation NOIRLab astronomers have discovered a supermassive black hole at the center of a galaxy just 1.5 billion years after the Big Bang that is consuming matter at a phenomenal rate — over 40 times the theoretical limit. While short lived, this black hole’s ‘feast’ could help astronomers explain how supermassive black holes grew so quickly in the early Universe.

Supermassive black holes exist at the center of most galaxies, and modern telescopes continue to observe them at surprisingly early times in the Universe’s evolution. It’s difficult to understand how these black holes were able to grow so big so rapidly. But with the discovery of a low-mass supermassive black hole feasting on material at an extreme rate, seen just 1.5 billion years after the Big Bang, astronomers now have valuable new insights into the mechanisms of rapidly growing black holes in the early Universe.

LID-568 was discovered by a cross-institutional team of astronomers led by International Gemini Observatory/NSF NOIRLab astronomer Hyewon Suh. They used the James Webb Space Telescope (JWST) to observe a sample of galaxies from the Chandra X-ray Observatory’s COSMOS legacy survey. This population of galaxies is very bright in the X-ray part of the spectrum, but are invisible in the optical and near-infrared. JWST’s unique infrared sensitivity allows it to detect these faint counterpart emissions.

LID-568 stood out within the sample for its intense X-ray emission, but its exact position could not be determined from the X-ray observations alone, raising concerns about properly centering the target in JWST’s field of view. So, rather than using traditional slit spectroscopy, JWST’s instrumentation support scientists suggested that Suh’s team use the integral field spectrograph on JWST’s NIRSpec. This instrument can get a spectrum for each pixel in the instrument’s field of view rather than being limited to a narrow slice.

“Owing to its faint nature, the detection of LID-568 would be impossible without JWST. Using the integral field spectrograph was innovative and necessary for getting our observation,” says Emanuele Farina, International Gemini Observatory/NSF NOIRLab astronomer and co-author of the paper appearing in Nature Astronomy.

JWST’s NIRSpec allowed the team to get a full view of their target and its surrounding region, leading to the unexpected discovery of powerful outflows of gas around the central black hole. The speed and size of these outflows led the team to infer that a substantial fraction of the mass growth of LID-568 may have occurred in a single episode of rapid accretion. “This serendipitous result added a new dimension to our understanding of the system and opened up exciting avenues for investigation,” says Suh.

In a stunning discovery, Suh and her team found that LID-568 appears to be feeding on matter at a rate 40 times its Eddington limit. This limit relates to the maximum luminosity that a black hole can achieve, as well as how fast it can absorb matter, such that its inward gravitational force and outward pressure generated from the heat of the compressed, infalling matter remain in balance. When LID-568’s luminosity was calculated to be so much higher than theoretically possible, the team knew they had something remarkable in their data.

“This black hole is having a feast,” says International Gemini Observatory/NSF NOIRLab astronomer and co-author Julia Scharwächter. “This extreme case shows that a fast-feeding mechanism above the Eddington limit is one of the possible explanations for why we see these very heavy black holes so early in the Universe.”

These results provide new insights into the formation of supermassive black holes from smaller black hole ‘seeds’, which current theories suggest arise either from the death of the Universe’s first stars (light seeds) or the direct collapse of gas clouds (heavy seeds). Until now, these theories lacked observational confirmation. “The discovery of a super-Eddington accreting black hole suggests that a significant portion of mass growth can occur during a single episode of rapid feeding, regardless of whether the black hole originated from a light or heavy seed,” says Suh.

The discovery of LID-568 also shows that it’s possible for a black hole to exceed its Eddington limit, and provides the first opportunity for astronomers to study how this happens. It’s possible that the powerful outflows observed in LID-568 may be acting as a release valve for the excess energy generated by the extreme accretion, preventing the system from becoming too unstable. To further investigate the mechanisms at play, the team is planning follow-up observations with JWST.

Source: NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab)/News

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More information

This research was presented in a paper entitled “A super-Eddington-accreting black hole ~1.5 Gyr after the Big Bang observed with JWST” to appear in Nature Astronomy. DOI: 10.1038/s41550-024-02402-9

The team is composed of Hyewon Suh (International Gemini Observatory/NSF NOIRLab, USA), Julia Scharwächter (International Gemini Observatory/NSF NOIRLab, USA), Emanuele Paolo Farina (International Gemini Observatory/NSF NOIRLab, USA), Federica Loiacono (INAF – Astrophysics and Space Science Observatory, Italy), Giorgio Lanzuisi (INAF – Astrophysics and Space Science Observatory, Italy), Günther Hasinger (Institute of Nuclear and Particle Physics/DESY/German Center for Astrophysics, Germany), Stefano Marchesi (INAF-Astrophysics and Space Science Observatory, Italy), Mar Mezcua (Institute of Space Sciences/Institute of Spatial Studies of Catalonia, Spain), Roberto Decarli (INAF – Astrophysics and Space Science Observatory, Italy), Brian C. Lemaux (International Gemini Observatory/NSF NOIRLab, USA, Institute of Astrophysics, Italy), Marta Volonteri (Paris Institute of Astrophysics, France), Francesca Civano (NASA Goddard Space Flight Center, USA), Sukyoung K. Yi (Department of Astronomy and Yonsei University Observatory, Republic of Korea), San Han (Department of Astronomy and Yonsei University Observatory, Republic of Korea), Mark Rawlings (International Gemini Observatory/NSF NOIRLab, USA), Denise Hung (International Gemini Observatory/NSF NOIRLab, USA)

NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

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Links

• Read the paper
• Chandra press release
• ICE-CSIC press release
• INAF press release
• JWST website
• Check out other NOIRLab Science Releases

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Contacts:

Hyewon Suh
Associate Scientist
International Gemini Observatory/NSF NOIRLab
Email: hyewon.suh@noirlab.edu

Julia Scharwächter
Scientist
International Gemini Observatory/NSF NOIRLab
Email: julia.scharwaechter@noirlab.edu

Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email: josie.fenske@noirlab.edu

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Playing against type

NGC 4694

An oval-shaped galaxy seen tilted at an angle. It glows brightly at its central point, with the radiated light dimming out to the edge of the oval. Reddish-brown, patchy dust spreads out from the core and covers much of the galaxy’s top half, as well as the outer edge, obscuring some of its light. Stars can be seen around and in front of the galaxy.Credit: ESA/Hubble & NASA, D. Thilker

Most galaxies we are familiar with fall into one of two easily-identified types. Spiral galaxies are young and energetic, filled with the gas needed to form new stars and sporting spiral arms hosting hot, bright stars. Elliptical galaxies have a much more pedestrian look, their light coming from a uniform population of older and redder stars. But other galaxies require in-depth study to understand: such is the case with NGC 4694, a galaxy located 54 million light-years from Earth in the Virgo galaxy cluster, and the subject of this Hubble Picture of the Week.

NGC 4694 has a smooth-looking, armless disc which — like an elliptical galaxy — is nearly devoid of star formation. However its stellar population is still relatively young and new stars are still actively forming in its core, powering the brightness we can see in this image and giving it a markedly different stellar profile from that of a classic elliptical galaxy. The galaxy is also suffused by the kinds of gas and dust normally seen in a young and sprightly spiral; elliptical galaxies often do host significant quantities of dust, but not the gas needed to form new stars. NGC 4694 is surrounded by a huge cloud of invisible hydrogen gas, fuel for star formation. This stellar activity is the reason for Hubble’s observations here.

As this Hubble image shows, the dust in this galaxy forms chaotic structures that indicate some kind of disturbance. It turns out that the cloud of hydrogen gas around NGC 4694 forms a long bridge to a nearby, faint dwarf galaxy named VCC 2062. The two galaxies have undergone a violent collision, and the larger NGC 4694 is accreting gas from the smaller galaxy. Based on its peculiar shape and its star-forming activity, NGC 4694 has been classified as a lenticular galaxy: lacking the unmistakable arms of a spiral, but not so bereft of gas as an elliptical galaxy, and still with a galactic bulge and disc. Some galaxies just aren’t so easy to classify as one type or the other!

Link

• Pan of NGC 4694

Source: ESA/Hubble/potw

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