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

---

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

---

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

---

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.

---

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.

---

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

---

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

---

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

---

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

---

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

---

Explore further

• Hubble observes an oddly organized satellite galaxy

---

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

---

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

---

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.

---

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.

---

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

---

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

---

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

---

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.

---

Links

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

---

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

---

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

---

Galaxies in miniature

IC 3430

A relatively small, oval-shaped galaxy, tilted diagonally. It glows brightly at the centre and dims gradually to its edge. At the centre it is crossed by some wisps of dark dust, and a few small, blue, glowing spots are visible, where stars are forming. The galaxy is on a dark background in which many background galaxies and foreground stars can be seen. Credit: ESA/Hubble & NASA, M. Sun

The Hubble Picture of the Week this week reveals the subtle glow of the galaxy named IC 3430, located 45 million light-years from Earth in the constellation Virgo. It is part of the Virgo cluster, a rich collection of galaxies both large and small, many of which are very similar in type to this diminutive galaxy.

IC 3430 is a dwarf galaxy, a fact well reflected by this view from Hubble, but it is more precisely known as a dwarf elliptical or dE galaxy. Like its larger cousins, this galaxy has a smooth, oval shape lacking any recognisable features like arms or bars, and it is bereft of gas to form very many new stars. Interestingly, IC 3430 does feature a core of hot, massive blue stars, an uncommon sight in elliptical galaxies that indicates recent star-forming activity. It’s believed that ram pressure from the galaxy ploughing through gas within the Virgo cluster has ignited what gas does remain in IC 3430’s core to form some new stars.

Dwarf galaxies are really just galaxies with not many stars, usually fewer than a billion, but that is often enough for them to reproduce in miniature the same forms as larger galaxies. There are dwarf elliptical galaxies like IC 3430, dwarf irregular galaxies, dwarf spheroidal galaxies and even dwarf spiral galaxies! The so-called Magellanic spiral is a distinct type of dwarf galaxy, too, the best example being the well-known dwarf galaxies that are the Magellanic Clouds.

Source: ESA/Hubble/potw

---

NASA's Hubble Traces Dark Matter in Dwarf Galaxy Using Stellar Motions

Draco Dwarf Spheroidal

Credits: Science: NASA, ESA, Eduardo Vitral (STScI), Roeland van der Marel (STScI), Sangmo Tony Sohn (STScI), DSS. Image Processing: Joseph DePasquale (STScI)

Images

---

The qualities and behavior of dark matter, the invisible "glue" of the universe, continue to be shrouded in mystery. Though galaxies are mostly made of dark matter, understanding how it is distributed within a galaxy offers clues to what this substance is, and how it's relevant to a galaxy's evolution.

While computer simulations suggest dark matter should pile up in a galaxy's center, called a density cusp, many previous telescopic observations have indicated that it is instead more evenly dispersed throughout a galaxy. The reason for this tension between model and observation continues to puzzle astronomers, reinforcing the mystery of dark matter.

A team of astronomers has turned toward NASA's Hubble Space Telescope to try and clarify this debate by measuring the dynamic motions of stars within the Draco dwarf galaxy, a system located roughly 250,000 light-years from Earth. Using observations that spanned 18 years, they succeeded in building the most accurate three-dimensional understanding of stars' movements within the diminutive galaxy. This required scouring nearly two decades of Hubble archival observations of the Draco galaxy.

"Our models tend to agree more with a cusp-like structure, which aligns with cosmological models," said Eduardo Vitral of the Space Telescope Science Institute (STScI) in Baltimore and lead author of the study. "While we cannot definitively say all galaxies contain a cusp-like dark matter distribution, it's exciting to have such well measured data that surpasses anything we've had before."

Charting the Movements of Stars

To learn about dark matter within a galaxy, scientists can look to its stars and their movements that are dominated by the pull of dark matter. A common approach to measure the speed of objects moving in space is by the Doppler Effect – an observed change of the wavelength of light if a star is approaching or receding from Earth. Although this line-of-sight velocity can provide valuable insight, only so much can be gleaned from this one-dimensional source of information.

Besides moving closer or further away from us, stars also move across the sky, measured as their proper motion. By combining line-of-sight velocity with proper motions, the team created an unprecedented analysis of the stars' 3D movements.

"Improvements in data and improvements in modeling usually go hand in hand," explained Roeland van der Marel of STScI, a co-author of the paper who initiated the study more than 10 years ago. "If you don't have very sophisticated data or only one-dimensional data, then relatively straightforward models can often fit. The more dimensions and complexity of data you gather, the more complex your models need to be to truly capture all the subtleties of the data."

A Scientific Marathon (Not a Sprint)

Since dwarf galaxies are known to have a higher proportion of dark matter content than other types of galaxies, the team honed in on the Draco dwarf galaxy, which is a relatively small and spheroidal nearby satellite of the Milky Way galaxy.

"When measuring proper motions, you note the position of a star at one epoch and then many years later measure the position of that same star. You measure the displacement to determine how much it moved," explained Sangmo Tony Sohn of STScI, another co-author of the paper and the principal investigator of the latest observational program. "For this kind of observation, the longer you wait, the better you can measure the stars shifting."

The team analyzed a series of epochs spanning from 2004 to 2022, an extensive baseline that only Hubble could offer, due to the combination of its sharp stable vision and record time in operation. The telescope's rich data archive helped decrease the level of uncertainty in the measurement of the stars' proper motions. The precision is equivalent to measuring an annual shift a little less than the width of a golf ball as seen on the Moon from Earth.

With three dimensions of data, the team reduced the amount of assumptions applied in previous studies and considered characteristics specific to the galaxy – such as its rotation, and distribution of its stars and dark matter – in their own modeling efforts.

An Exciting Future

The methodologies and models developed for the Draco dwarf galaxy can be applied to other galaxies in the future. The team is already analyzing Hubble observations of the Sculptor dwarf galaxy and the Ursa Minor dwarf galaxy.

Studying dark matter requires observing different galactic environments, and also entails collaboration across different space telescope missions. For example, NASA's upcoming Nancy Grace Roman Space Telescope will help reveal new details of dark matter's properties among different galaxies thanks to its ability to survey large swaths of the sky.

"This kind of study is a long-term investment and requires a lot of patience," reflected Vitral. "We're able to do this science because of all the planning that was done throughout the years to actually gather these data. The insights we've collected are the result of a larger group of researchers that has been working on these things for many years."

These results are published today in The Astrophysical Journal.

The Hubble Space Telescope has been operating for over 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, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: HubbleSite/News

---

About This Release

Credits:

Media Contact:

Abigail Major
Space Telescope Science Institute, Baltimore, Maryland

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Science Contact:

Eduardo Vitral
Space Telescope Science Institute, Baltimore, Maryland

Roeland van der Marel
Space Telescope Science Institute, Baltimore, Maryland

Sangmo Tony Sohn
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 Eduardo Vitral et al., PDF (2.62 MB)
• NASA's Hubble Portal
• HSTPROMO: The High-resolution Space Telescope Proper Motion Collaboration
• Vitral's STScI Public Science Lecture Series Talk (on YouTube)

---

Channelling light from starbursts

NGC 5253

An oval-shaped galaxy, made up of many point-like stars. It is softly lit from the centre, brightest and slightly blue at the very centre and fading to darkness at the edges. Surrounding the galaxy’s core are reddish clouds of gas and dust, most around or behind the core, but a few wisps are in front of it and block some light. Some faraway galaxies and two foreground stars can be seen around the galaxyCredit: ESA/Hubble & NASA, A. Zezas, D. Calzetti

The focus of this week’s Hubble Picture of the Week is the blue compact dwarf galaxy NGC 5253, located in the constellation Centaurus around 11 million light-years from Earth. This new image combines data taken with Hubble’s Advanced Camera for Surveys (ACS), using its Wide Field Channel, and with the older Wide Field and Planetary Camera 2 (WFPC2). As a bonus for this Picture of the Week, there is also a second new image made using data from the High Resolution Channel (HRC) of ACS, a sub-instrument only operational for a few years that was optimised for detailed studies of environments dense with stars.

What has interested astronomers so much about this galaxy that three of Hubble’s instruments were used to study it in depth over ten years? It turns out to lie at the focus of a few areas of research where Hubble’s capabilities are essential. Dwarf galaxies are considered important for understanding the evolution of both stars and galaxies through time, since they resemble ancient, distant galaxies. NGC 5253 is called both a 'starburst galaxy' and a 'blue compact dwarf': these names mean it is forming clusters of bright, massive stars at an exceptional rate. This Hubble image clearly shows the dense nebula which is being consumed to birth these stars, and which makes NGC 5253 a laboratory in which to investigate stellar composition, star formation and star clusters, all at once.

A tremendously high rate of star formation is a recipe for star clusters, but NGC 5253 goes beyond that: in a small region of the core, the star formation is so intense that the galaxy contains no fewer than three 'super star clusters' (SSCs). SSCs are very bright, populous and massive open clusters which are believed to evolve into globular clusters. Globular clusters themselves offer unique insights into how stars form and evolve, but their origins are poorly understood. Astronomers were therefore eager to make use of the HRC sub-instrument, with its superb resolution, to home in on these small, very dense clusters of stars.

Links

• NGC 5253 High Resolution Channel image of nucleus
• NGC 5253 galaxy collage
• Pan of NGC 5253

Source: ESA/Hubble/potw

---

KKR 25（Dwarf Galaxy）

KKR 25 (Dwarf Galaxy)
Credit: NAOJ - Download image (2.70 MB)
Distance from Earth: 6.2 million light-years
Instrument: Hyper Suprime-Cam (HSC)

Small galaxies like Large and Small Magellanic Clouds are called dwarf galaxies. In this image, the KKR 25 dwarf galaxy is visible as an extended dim object behind the middle bright star in the Milky Way Galaxy. The straight lines observed on the bright stars are photographic artifacts. These lines appear when a star's intense light spills into adjacent CCD pixels.

KKR 25 is a unique, isolated dwarf galaxy and does not belong to any group of galaxies. In contrast, many dwarf galaxies exist as satellite galaxies, such as Large and Small Magellanic Clouds as satellite galaxies of the Milky Way. This image, taken by the Hyper Suprime-Cam (HSC), shows every single star dissolved in the dwarf galaxy. Explore the high-resolution image and see the stars in another galaxy by enlarging it, located 6.2 million light-years away.

Discover this dwarf galaxy on the hscMap website, where you can freely explore the vast cosmic images captured by HSC. From the menu bar, select “Bookmarks” > “Recommended Objects” > Dwarf Galaxy KKR25.

Source: Subaru Telescope

---

Dwarf galaxies stripped of their stars prove to be the missing link in the formation of rare ultra-compact dwarf galaxies

This illustration shows a dwarf galaxy in the throes of transitioning to an ultra-compact dwarf galaxy as it’s stripped of its outer layers of stars and gas by a nearby larger galaxy. Ultra-compact dwarf galaxies are among the densest stellar groupings in the Universe. Being more compact than other galaxies with similar mass, but larger than star clusters — the objects they most closely resemble — these mystifying objects have defied classification. The missing piece to this puzzle has been a lack of sufficient transitional, or intermediate objects to study. A new galaxy survey, however, fills in these missing pieces to show that many of these enigmatic objects are likely formed from the destruction of dwarf galaxies. Credit:NOIRLab/NSF/AURA/M. Zamani, download Large JPEG

A continuum of galaxies captured at different stages of the transformation process from a dwarf galaxy to an ultra-compact dwarf galaxy (UCD). These objects are located near the supergiant elliptical galaxy M87, the dominant member of the neighboring Virgo Cluster. Credit: NOIRLab/NSF/AURA/NASA/R. Gendler/K. Wang. download Large JPEG

NGC 3628 and an example of an ultra-compact dwarf galaxy (no annotations)

ANGC 3628, sometimes nicknamed the Hamburger Galaxy or Sarah's Galaxy, is an unbarred spiral galaxy about 35 million light-years away in the constellation Leo. Extending to the left of NGC 3628 for around 300,000 light-years is a ‘tidal tail’ — an elongated region of stars that arises as a result of gravitational interaction with another galaxy. Embedded within this tidal tail is the ultra-compact dwarf galaxy known as NGC 3628-UCD1. Credit: CTIO/NOIRLab/DOE/NSF/AURA. Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab), & D. de Martin (NSF’s NOIRLab). download Large JPEG

NGC 3628 and an example of an ultra-compact dwarf galaxy (annotated)

NGC 3628, sometimes nicknamed the Hamburger Galaxy or Sarah's Galaxy, is an unbarred spiral galaxy about 35 million light-years away in the constellation Leo. Extending to the left of NGC 3628 for around 300,000 light-years is a ‘tidal tail’ — an elongated region of stars that arises as a result of gravitational interaction with another galaxy. Embedded within this tidal tail is the ultra-compact dwarf galaxy known as NGC 3628-UCD1. Credit: CTIO/NOIRLab/DOE/NSF/AURA. Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab), & D. de Martin (NSF’s NOIRLab).  download Large JPEG

---

Astronomers using the Gemini North telescope, one half of the International Gemini Observatory operated by NSF’s NOIRLab, have captured the eroding remains of more than 100 dwarf galaxies as they transition into ultra-compact dwarf galaxies, objects with masses much greater than star clusters yet much smaller than dwarf galaxies. These findings confirm that many ultra-compact dwarf galaxies are likely the fossil remains of normal dwarf galaxies that have been stripped of their outer layers.

Ultra-compact dwarf galaxies (UCDs) are among the densest stellar groupings in the Universe. Being more compact than other galaxies with similar mass, but larger than star clusters — the objects they most closely resemble — these mystifying objects have defied classification. The missing piece to this puzzle has been a lack of sufficient transitional, or intermediate objects to study. A new galaxy survey, however, fills in these missing pieces to show that many of these enigmatic objects are likely formed from the destruction of dwarf galaxies.

The idea that UCDs are remnants of disrupted dwarf galaxies has been proposed since they were discovered over two decades ago. However, previous searches have not revealed the large population of galaxies-in-transition that you would expect to find. So an international team of astronomers conducted a systematic search for these intermediate-stage objects around the Virgo Cluster, a grouping of thousands of galaxies in the direction of the constellation Virgo. Using the Gemini North telescope near the summit of Maunakea in Hawaiʻi, the team identified more than 100 of these missing-link galaxies that show every stage of the transformation process.

“Our results provide the most complete picture of the origin of this mysterious class of galaxy that was discovered nearly 25 years ago,” said NOIRLab astronomer Eric Peng, a co-author on the paper describing these results appearing in the journal Nature. “Here we show that 106 small galaxies in the Virgo cluster have sizes between normal dwarf galaxies and UCDs, revealing a continuum that fills the ‘size gap’ between star clusters and galaxies.”

The team compiled their sample by first looking at images from the Next Generation Virgo Cluster Survey, taken with the Canada-France-Hawaiʻi Telescope. And though they were able to identify hundreds of candidate UCD progenitors, they were unable to confirm their true nature. The obstacle was that UCDs that are surrounded by envelopes of stars are indistinguishable from normal galaxies that are located farther away beyond the Virgo Cluster.

To distinguish the candidate UCD progenitors from the background galaxies, the team performed follow-up spectroscopic studies with Gemini North to obtain more concrete measurements of their distances. These observations allowed the astronomers to eliminate all of the background galaxies from their samples until only the UCDs within the Virgo Cluster remained.

Scattered among this vast survey are many dwarf galaxies that contain ultra-compact central star clusters. These galaxies represent the early stages of the transformation process and suggest that after neighboring massive galaxies strip these dwarfs of their outer layers of stars and gas, what remains will be an object identical to the late-stage UCDs that have already been identified.

The researchers also found many objects with very extended and diffuse stellar envelopes around them, indicating that they are currently in the throes of transitioning as their stars and dark matter is stripped away. Within their extensive sample the team identified objects at several other stages of the evolutionary process that, when placed in sequence, tell a compelling story of the morphology of UCDs. Furthermore, nearly all the candidates were near to massive galaxies, suggesting that their local environment plays an important role in their formation.

“Once we analyzed the Gemini observations and eliminated all the background contamination, we could see that these transition galaxies existed almost exclusively near the largest galaxies. We immediately knew that environmental transformation had to be important,” said Kaixiang Wang, a PhD student at Peking University and lead author of the paper.

Besides identifying the environment UCDs live in, these results also lend valuable insight into how many of these objects there are and what the full sequence of their evolutionary change looks like. “It’s exciting that we can finally see this transformation in action,” said Peng. “It tells us that many of these UCDs are visible fossil remnants of ancient dwarf galaxies in galaxy clusters, and our results suggest that there are likely many more low-mass remnants to be found,” he added.

“This study illustrates how large surveys can improve our understanding of the biggest questions in astronomy, like galaxy evolution,” says Chris Davis, NSF Program Director for NOIRLab. “NSF’s NOIRLab is a world leader in supporting astronomical surveys and — importantly — providing community and public access to the data and the amazing resulting discoveries.”

Source: Gemini Observatory

---

More information

This research was presented in a paper appearing in Nature. DOI: 10.1038/s41586-023-06650-z

The team is composed of K. Wang (Peking University), E. W. Peng (NSF’s NOIRLab), C. Liu (Shanghai Jiao Tong University), J. Christopher Mihos (Case Western Reserve University), P. Côté (National Research Council of Canada), L. Ferrarese (National Research Council of Canada), M. Taylor (University of Calgary), J. P. Blakeslee (NSF’s NOIRLab), J. Cuillandre (Universite! Paris Diderot), P. Duc (Université de Strasbourg), P. Guhathakurta (University of California Santa Cruz), S. Gwyn (National Research Council of Canada), Y. Ko (Korea Astronomy and Space Science Institute), A. Lançon (Université de Strasbourg), S. Lim (Yonsei University), L. A. MacArthur (Princeton University), T. Puzia (Pontificia Universidad Católica de Chile), J. Roediger (National Research Council of Canada), L. V. Sales (University of California), R. Sanchez-Janssen (Royal Observatory Edinburgh), C. Spengler (Pontificia Universidad Católica de Chile), E. Toloba (University of the Pacific), H. Zhang (University of Science and Technology of China), & M. Zhu (Peking University).

NSF’s NOIRLab, the US 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 Iolkam 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.

---

Links

• Research Paper
• Photos of Gemini North
• Videos of Gemini North

---

Contacts:

Eric Peng
NSF’s NOIRLab
Email: eric.peng@noirlab.edu

Kaixiang Wang
Peking University
Email: kaixiang.wang@pku.edu.cn

Josie Fenske
NSF’s NOIRLab Communications
Email: josie.fenske@noirlab.edu

---