EXCELlent Work, Detectives! Solving the Murder of Star Formation in Galaxies with JWST

This JWST image shows a pair of interacting galaxies, collectively known as Arp 142. The galaxy on the right ("the Penguin") is alight with recent star formation, while the galaxy on the left ("the Egg") contains mostly old stars. Credit: NASA, ESA, CSA, STScI

Title: The JWST EXCELS Survey: Insights into the Nature of Quenching at Cosmic Noon
Authors: Maya Skarbinski et al.
First Author’s Institution: Johns Hopkins University
Status: Published in ApJ

How to Quench a Galaxy

Look at an image of the sky taken with a sufficiently sensitive telescope, and you’ll quickly notice that galaxies tend to cluster into two main types: blue spiral galaxies, which have flat disk shapes with a central bulge, and red elliptical galaxies, which look like spherical or elliptical balls of red stars. Blue spiral galaxies can form tens to hundreds of stars every year, while elliptical galaxies have completely stopped forming stars, meaning that some process has to transform star-forming spirals into non-star-forming, or “quiescent,” elliptical galaxies. To form the current population of massive elliptical galaxies, this process had to be common about 2–3 billion years after the Big Bang at “cosmic noon,” the period when star formation in the universe peaked. The processes that “quench” star formation in massive galaxies are still being studied, and one of the best ways to study them is to find galaxies that recently quenched and look for clues about the processes that quenched them.

Post-starburst galaxies are galaxies that have rapidly quenched after a short burst of star formation. Because these galaxies quenched so quickly and so recently, it’s often possible to find signs of whatever quenched them, like the signatures of past galaxy mergers, feedback from supermassive black hole accretion, or the shutoff of gas flowing into the galaxy. Rapid quenching is pretty uncommon now, but it was a much more common way for galaxies to quench at cosmic noon. Understanding post-starburst galaxies at cosmic noon is therefore critical for understanding the formation of massive elliptical galaxies in the local universe.

The Quest for Quenched Galaxies

Today’s article uses data from the JWST Early eXtragalactic Continuum and Emission Line Survey (EXCELS) to identify post-starburst galaxies at cosmic noon and try to determine why they quenched. EXCELS is a spectroscopic survey, so the authors get a spectrum for every galaxy. The spectrum encodes information about the galaxy’s stellar population, including the mass of stars in the galaxy, the number of stars forming every year, and the history of star formation throughout the galaxy’s life.

The authors use a technique called principal component analysis to further divide the sample into young and old post-starbursts. Principal component analysis is a machine-learning technique that learns the most important features of a data set. This technique is used for “dimension reduction,” or reducing the number of data points needed to learn something about the object. A typical spectrum has hundreds or even thousands of data points, which means performing data analysis on a spectrum can be very computationally expensive. Principal component analysis takes these thousands of data points and learns broad patterns that correlate with each other. These patterns are called “supercolors” in the context of spectral data, and they encode things like the overall shape and color of the spectrum as well as the spectral shape around key features (see Figure 1 for a visualization). Since the overall shape, color, and emission/absorption line features of a spectrum come from the galaxy’s stellar population, this method can be used to identify galaxies with lots of star formation a billion years ago but very little star formation today — in other words, post-starburst galaxies.

Figure 1: An example of principal component analysis for sample star-forming (SF), quiescent (Qu), and post-starburst (PSB) galaxy spectra (left-hand side). Principal component analysis simplifies a many-dimensional data set (for example, spectra) into fewer dimensions. In this case, Super-Color 1 measures the overall color of the spectrum (shown on the left-hand side as the slope of the spectra, marked with red lines), while Super-Color 2 measures the shape of the spectrum around 4,000 angstroms (orange box). The authors use principal component analysis to identify post-starburst galaxies for further analysis (right-hand side). Adapted from Skarbinski et al. 2026

The authors apply principal component analysis to the galaxies in their sample and find that 11 of the galaxies in their sample are classified as post-starburst, 9 are quiescent, and 4 still have some star formation. To further analyze the stellar populations of the post-starbursts in their sample, the authors use a program called Bagpipes to fit the galaxies’ spectra. Bagpipes is a spectral energy distribution fitting software, which means that it takes the observed spectrum of a real galaxy and tries to match it to a library of different stellar spectra. By measuring the relative contribution of different kinds of stars (which all have different lifetimes), Bagpipes can compute the likely history of star formation in the galaxy (e.g., when the star formation rate peaked) as well as the present-day properties of the galaxy (things like the mass in stars versus dust and the current star formation rate). The authors use the galaxies’ star formation histories to try to find clues as to how they quenched.

Figure 2: Possible evolutionary tracks in supercolor for two example galaxies as they quench. The galaxy in the top panel quenches quickly and has post-starburst supercolors for about a billion years, while the galaxy in the bottom panel quenches without ever going through the post-starburst phase. The authors use these tracks to determine how important the post-starburst phase is for quenching massive galaxies. Credit: Skarbinski et al. 2026

How Quickly Do Post-Starbursts Quench?

First, the authors measure something called a “quenching timescale,” which they define as the length of time between when the galaxy’s star formation rate peaked and when it fell low enough that the galaxy was quenched. The quenching timescale depends on which process shut down star formation in the galaxy — feedback from black hole accretion or star formation should cause fast quenching, while galaxies that are starved of gas from the intergalactic medium should quench more slowly. The authors find that 15 of their galaxies quenched in under 500 million years, 6 took between 500 million and 1 billion years, and 3 took longer than 1 billion years to quench. The galaxies that had the highest peak star formation rates quenched the fastest, suggesting that feedback from star formation could have played a role in quenching these galaxies.

Next, the authors measure how important the post-starburst phase is to form massive quiescent galaxies. Not all galaxies that quench go through a post-starburst phase; some objects, especially those that quench slowly, will transition directly from star forming to quiescent. The authors use the star formation histories from their spectral energy distribution fits to predict how the galaxies’ supercolors changed after their star formation peaked (Figure 2) and find that six of the nine quiescent galaxies went through a post-starburst phase in the past, while the other three did not. For the objects that went through a post-starburst phase, the median time spent as a post-starburst was around 600 million years.The authors can use this measured “visibility timescale” to constrain whether the post-starburst phase is important for forming massive quiescent galaxies. If the fraction of post-starburst galaxies in a sample is high, that can be for two reasons: either a larger fraction of galaxies will eventually go through a post-starburst phase, or the post-starburst phase is very long, making it easy to find post-starburst galaxies. Using the measured timescale of 600 million years and combining with results from another article, the authors find that 40% of quiescent galaxies likely went through a post-starburst phase; for the more massive end of the sample, this fraction increases to around 73% due to the shorter visibility timescale. This suggests that the post-starburst phase is very important for forming the kind of massive quiescent galaxies we see in the local universe.

While the post-starburst phase is important, the different quenching timescales present across the sample suggest that multiple pathways existed to quench galaxies at cosmic noon, similar to what has been found in less-distant galaxies and at cosmic noon in other samples. This is also supported by the fact that four of the five galaxies with sufficient data show evidence of an actively accreting supermassive black hole that may help shut down star formation in many (but perhaps not all) massive galaxies. While the precise processes that quench massive galaxies are still uncertain, one thing is clear: JWST EXCELS at solving the mystery!

Original astrobite edited by Anavi Uppal.

Source: American Astronomical Society/AAS-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, Margaret Verrico:

I am a fourth.-year graduate student at the University of Illinois Urbana-Champaign. I study the connection between supermassive black hole transients and their host galaxies. I am also an avid knitter and reader, and I am passionate about opening up STEM opportunities for people of all backgrounds.

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Venus Isn't Dead After All

There are huge rift valleys on Venus. They suggest that the planet is still geologically active.
Credit: NASA/JPL/USGS

When it comes to literary allegories, Venus is about as close to Dante's description of hell as one can get! Its atmosphere is 93 times as dense as Earth's, which is equal to the pressure found 900 m (3,000 ft) underwater, enough to crush the human body. It's also the hottest planet in the Solar System, with temperatures reaching 467 °C (872 °F), which is hot enough to melt lead. Unlike Earth, its surface is not composed of tectonic plates that are constantly shuffling around, but a single-piece crust.

Until recently, scientists believed that this meant Venus was geologically inactive, though recent findings have challenged this. According to a new study by ETH researchers, Venus is not only geologically "alive" but hosts many active volcanoes. This is evident from Venus' rift valleys, which can measure up to 10,000 km (mi) in diameter. On Venus, they can span up to 10,000 kilometers.

lowland features that resemble those found on Earth and form when tectonic plates move apart. While the timing of their formation is not yet certain, the team's simulations indicate that they could have formed about 100 million years ago.

Rift valleys, which indicate tectonic activity, can be vast and resemble those on Earth, such as the African Rift Valley.

ETH researchers, led by Taras Gerya, Professor of Geodynamics at the Department of Earth and Planetary Sciences, have used a new computer model to demonstrate that some rift valleys may have formed relatively recently. The planetary scientists also addressed the long-standing question of whether Venus is geologically active. This study has been published in Nature Geoscience. Lead author Xi Yang conducted the research as part of his Master’s studies under Gerya’s supervision. Add ETH Zurich as a preferred Google source

With only one click, you can select which sources you want to see prioritized in your Google search. This allows you to quickly see what's truly relevant to you. Select ETH Zurich as a preferred source on Google now.

Yang and his team used a new computer model to simulate high-resolution, 3D rifts for the first time. This allowed them to accurately replicate these rift structures in simulations and provide better explanations of their formation. Earlier models had relied on simplified material assumptions and been mostly two-dimensional.

The models indicate that broad ridges, known as rift flanks, form along the edges of rift valleys when the rifts are geologically young and either still actively moving or have only recently stopped moving. The simulations also suggest that these rifts widen more rapidly than had been previously believed, at a rate of 3 to 10 centimetres per year.

Yang and his colleagues also show that the rift flanks tend to flatten rapidly after movement ceases; the older the rift system, the less steep and narrow its flanks. Unlike Earth, where erosion gradually wears down features, Venus’s flanks subside due to crustal relaxation.

Wide and high rift flanks are not only produced by the computer model but can also be seen in images of the Venusian surface from the Magellan probe during its 1990’s mission.

Based on their simulations and observational data, the researchers conclude that Venus remains an active planet with a more dynamic interior than had been previously believed. “The results help us to better assess the tectonic activity on Venus,” says Gerya.

The results of the ETH researchers’ model could help pinpoint active regions worthy of detailed investigation for these missions. Additionally, the study enhances our understanding of how rocky planets form. Importantly, the researchers aim to uncover clues that could improve the detection of rocky exoplanets. Growing interest in our neighbouring planet.

Interest in Venus is increasing as NASA and ESA prepare multiple missions to explore Earth’s neighbouring planet.

ETH geophysics professors Paul Tackley and Taras Gerya, along with their collaborators, are participating in ESA’s EnVision mission. They are developing instruments for the Venus orbiter to analyse the planet’s surface. The mission, scheduled for launch in the early 2030s, will explore the planet more thoroughly, from its core to its upper atmosphere.

Further Reading: ETH Zurich

By Matt Williams  [1]

Source: Universe Today

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[1] Matt Williams is a space journalist, science communicator, and author with several published titles and studies. His work is featured in The Ross 248 Project and Interstellar Travel edited by NASA alumni Les Johnson and Ken Roy. He also hosts the podcast series Stories from Space at ITSP Magazine. He lives in beautiful British Columbia with his wife and family. For more information, check out his website.

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eROSITA delivers the most comprehensive census of the high-energy Universe to date

The colour image shows X-ray sources in the western galactic hemisphere of the X-ray sky. The Galactic plane lies horizontally through the centre of the image. Sources in the eROSITA catalogue are plotted with their red, green and blue brightness showing their count rate in soft (0.5-1.0 keV), medium (0.5-1.0 keV) and hard (1.0-2.0 keV), respectively. The sky is plotted using an azimuthal equal area projection. © Jeremy Sanders / MPE

This figure compares the build-up of mass locked in super-massive black holes with the rescaled growth of the stellar population in inactive galaxies over cosmic time. The eROSITA X-ray census traces the fraction of super-massive black hole growth that is directly visible in the soft X-rays, while estimates including obscured sources show that much of the total growth is hidden from this view. The gap implies that roughly 70-90% of super-massive black holes' growth likely occurred in soft X-ray-suppressed phases. The shape similarity of all growth curves supports the claim that accreting super-massive black holes and galaxies evolved in lockstep, growing over broadly similar cosmic epochs. © William Roster / MPE

eROSITA DR2 Representation of the Active Galactic Nuclei (AGN)

This animation shows a representation of the active galactic nuclei (AGN) identified in the DR2 catalogue. Each dot shows a single object, where the distance from the three-dimensional centre increases with the source's redshift, i.e. how far away it is from us. We and our neighbouring objects lie at this centre. Sources at the same distance lie on shells, where the position of the dot on the shell is the position in the sky. The stationary circles, shown horizontally, represent the radii of the shells at redshifts of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5. The animation rotates about the western Galactic hemisphere, highlighting the clumpy nature of structure in the universe.

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To the Point

• Catalogue contents, source types: DR2 lists over 1.9 million pointlike sources such as stars and supermassive black holes, plus about 64,000 extended sources including galaxy clusters and supernova remnants.


• Survey depth, sensitivity: Combining data from three fullsky scans, DR2 detects fainter X-ray fluxes and reveals many previously unknown sources.


• Multiwavelength identification: DR2 links X-ray detections to optical and infrared counterparts using six new catalogues, improving the understanding and classification of cosmic objects.


• Collaboration with SDSS: The release coincides with the Sloan Digital Sky Survey's twentieth data release, enabling 3D mapping of active black holes and studies on their growth across cosmic time.

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Second data release nearly doubles the previously known eROSITA X-ray sources to two million

The German eROSITA Consortium (eROSITA-DE), led by the Max Planck Institute for Extraterrestrial Physics (MPE), has released its second major public dataset, eROSITA Data Release 2 (DR2). The new catalogue comprises close to two million X-ray sources—approximately doubling the number of previously released eROSITA sources in the X-ray sky and marking a major step forward in mapping the high-energy Universe. Built from the first three all-sky scans of the eROSITA telescope aboard the Spectrum-Roentgen-Gamma (SRG) mission, DR2 provides the most comprehensive catalogue of the X-ray Universe currently available to the scientific community. By combining multiple passes over the sky, the release significantly increases the survey depth and reveals large populations of previously undetected sources.

The main DR2 catalogue contains nearly two million X-ray sources detected in the 0.2–2.3 keV band and includes more than 1.9 million point-like sources, primarily stars and actively accreting supermassive black holes, as well as around 64,000 extended sources such as galaxy clusters, nearby galaxies, and supernova remnants. Compared to the first data release, the number of detected sources has roughly doubled.
v A complementary hard-band catalogue adds nearly 15,000 sources detected at higher energies (2.3–5.0 keV), tracing heavily obscured and intrinsically energetic systems that are often missed at softer X-ray energies. Together, these catalogues capture the full diversity of the X-ray sky, from nearby stellar coronae to distant supermassive black holes and massive galaxy clusters. Many of these objects are newly identified in X-rays, while others can now be studied with substantially improved precision.

After the start of operations in December 2019, eROSITA surveyed the entire sky every six months, progressively increasing depth and sensitivity. DR2 combines data collected over the mission’s first 556 days, spanning three full sky surveys (eRASS1–3). By stacking these observations, the survey reaches significantly fainter fluxes than the first release, enabling the large increase in detected sources.

“DR2 is the best inventory of the X-ray sky we have to date and opens the door to robust statistical studies of cosmic populations,” says Miriam E. Ramos-Ceja, Ground Segment Manager of the eROSITA instrument and lead author of the DR2 publication.

Linking X-rays to the broader Universe

To enable physical interpretation, DR2 includes multi-wavelength information that associates the X-ray detections with their most likely optical and infrared counterparts. Based on this information, roughly 88% are extragalactic, dominated by accreting supermassive black holes.

“X-ray detection is only the first step,” explains Mara Salvato, eROSITA spokesperson and chair of the follow-up working group. “By linking X-ray sources to their counterparts at other wavelengths, we can work out what these objects are, where they sit on the cosmic distance ladder, and build clean, well-defined samples on an unprecedented scale.”

A joint milestone with SDSS

The release coincides with the twentieth data release of the Sloan Digital Sky Survey (SDSS), which includes extensive optical spectroscopy of eROSITA-DE sources. Together, these datasets represent the culmination of nearly a decade of collaboration between the German eROSITA Consortium and the SDSS collaboration. By combining SDSS spectroscopy with eROSITA’s X-ray data, researchers can build three-dimensional maps of active black holes across the sky, revealing how these rapidly growing objects are distributed and evolve across cosmic time.

Combining eROSITA’s X-ray catalogue with spectroscopic and photometric redshifts enabled one of the largest and most detailed studies of accreting supermassive black holes to date. These elusive objects formed surprisingly early in the history of the Universe, and eROSITA has provided a new census of their growth at high redshift. “The most luminous black holes at high redshift are like needles in a haystack. Thanks to DR2 we found more needles than expected, suggesting that rapidly growing black holes were more abundant in the early Universe than previously thought” says William Roster, lead author of the corresponding study.

A focused, catalogue-driven release

In contrast to the first public data release, DR2 is a catalogue-focused release. It provides rigorously validated source lists derived from the combined eRASS:3 observations, along with an updated upper-flux-limit service that allows researchers to quantify non-detections across the sky.

The data cover the western Galactic hemisphere, reflecting the agreed data-sharing arrangement between the German and Russian eROSITA consortia. Within this region, DR2 represents the largest and most homogeneous public X-ray dataset currently available.

Enabling the next wave of discoveries

“This is a dataset of unprecedented scale and completeness, now in the hands of the global astronomical community,” says eROSITA Principal Investigator Andrea Merloni. “With nearly 2 million sources, DR2 provides a unique foundation for discoveries ranging from rare objects to large-scale population studies.” MPE Director Kirpal Nandra adds: “eROSITA just set another world record in terms of X-ray source numbers – and it won’t be the last.”

The eROSITA-DE DR2 catalogues, upper-flux-limit server, and full documentation are publicly accessible via the eROSITA-DE Science Data Archive.

Source: Max Planck Institute for Extraterrestrial Physics/Press Releases

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Contacts:

Dr. Miriam Ramos-Ceja
Postdoc High-Energy Astrophysics
Tel: +49 89 30000-3603
Email: mramos@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

William Roster
PhD-Student High-Energy Astrophysics
Tel: +49 89 30000-3879
Email: wroster@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

Dr. Andrea Merloni
Senior Scientist High-Energy Astrophysics; PI eROSITA
Tel: +49 89 30000-3893
Email: am@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Dr. Mara Salvato
Senior Scientist High-Energy Astrophysics
Tel: +49 89 30000-3815
Email: mara@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

Dr. Jeremy Sanders
Scientist High-Energy Astrophysics
Tel: +49 89 30000-3340
Email: jsanders@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

Prof. Dr. Kirpal Nandra
Director of the High-Energy Astrophysics
Tel: +49 89 30000-3401
Email: knandra@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching

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Original publication

1. Ramos-Ceja, M.E., G. Lamer, M. Salvato, A. Merloni, J.S. Sanders et al. The SRG/eROSITA All-Sky Survey DR2: Cumulative X-ray catalogues from the first three surveys and multi-wavelength counterparts in the western Galactic hemisphere
A&A

Source | DOI

2. Roster, W., J. Buchner, M. Salvato, R. Shirley, A. Merloni et al.
Accrete, shine, repeat: AGN X-ray luminosity function
The SRG/eROSITA All-Sky Survey DR2
A & A

Source | DOI

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Further Information

eROSITA website of the MPE

The X-ray sky opens to the world

With about 900 000 distinct sources, the first eROSITA All-Sky Survey (eRASS1) has yielded the largest X-ray catalogue ever published. Based on just the first six months of observations, eROSITA has already detected more sources than had previously been known in the 60-year history of X-ray astronomy.

eROSITA relaxes cosmological tension

February 14, 2024

Results from the first X-ray sky survey resolve the previous inconsistency between competing measurements of the structure of the Universe

Baryons at the Edge: SRG/eROSITA Survey Detects “Missing” Cosmic Gas at the Outskirts of Galaxy Clusters

May 05, 2026
Missing baryons found in galaxy cluster outskirts.
Research uncovers 90% of missing baryonic matter in galaxy cluster outskirts, enhancing cosmic structure understanding.

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Solving the Mystery of Gaia’s Quiet Black Holes

The location of the first three black holes discovered by ESA’s Gaia mission in the Milky Way. Gaia Black Hole 1 (BH1) is located just 1560 light-years away from us in the direction of the constellation Ophiuchus; Gaia BH2 is 3800 light-years away in the constellation Centaurus; Gaia BH3 is in the constellation Aquila, at a distance of 1926 light-years from Earth. With a mass of about 33 times that of the Sun, BH3 is the heaviest black hole of stellar origin discovered in our galaxy. Credit: ESA/Gaia/DPAC

AI-rendered visualization of the three discovered Gaia black hole systems Gaia BH1, BH2 and BH3. Each system consists of a low-mass stellar companion orbiting a stellar-mass black hole with large orbital periods. © MPA/A. Olejak

Evolutionary stages of the progenitors of the Gaia black hole systems. After leaving the main sequence, the massive star (blue) expands and fills its Roche lobe, initiating a non-conservative mass-transfer phase. Eventually, the currently observed system, consisting of a black hole and a low-mass stellar companion, is formed. © MPA/A. Olejak

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In addition to the spectacular black hole systems that produce high-energy transients, there should exist a much larger hidden population of black holes that remain silent and can be detected only through their gravitational influence on companion stars. So far, the ESA Gaia mission has identified three such quiescent black hole binaries, with many more potentially to be released in December this year. However, two of these systems pose a major challenge to our understanding of binary evolution because of their unexpectedly wide orbits and extreme mass ratios. A new study by the Max Planck Institute for Astrophysics proposes a solution: if most of the mass transferred from the massive star escapes the system without carrying away a significant fraction of the orbital angular momentum, the binary can survive without its orbit shrinking or the stars merging. These findings suggest that low-angular-momentum mass loss may also play an important role in other types of systems, with significant implications for our understanding of how binary systems evolve.

Black hole discoveries are often associated with some of the most energetic phenomena in the Universe: powerful X-ray outbursts from matter falling onto a black hole, or spectacular mergers detected through gravitational waves. Yet the vast majority of black holes are expected to be remarkably quiet. They may drift through the Galaxy alone or orbit a normal star without producing any detectable radiation, making them almost impossible to find.

In recent years, the European Space Agency’s Gaia mission has opened a new window for discovering these hidden black holes. Gaia detects their presence through the subtle motion they induce on their stellar companions. By precisely measuring the positions and movements of billions of stars in the Milky Way, Gaia can reveal tiny “wobbles” caused by the gravitational pull of an unseen companion.

So far, three such “sleeping” black holes have been publicly confirmed through Gaia observations. These systems consist of a relatively low-mass star orbiting a black hole at a large distance, with orbital periods ranging from over a hundred to a few thousand days. Because the black holes are not actively feeding on their companions, they remain invisible, detectable only through their gravitational influence.

However, two of the discovered systems, Gaia BH1 and Gaia BH2, came as a surprise. According to the standard picture of binary star evolution, systems like these should be extremely difficult, if not impossible, to form.

A Problem for Stellar Evolution

Massive stars rarely evolve in isolation. Most are born in binary systems, where the interactions between the two stars can profoundly influence their lives. Through processes such as mass transfer, one star can lose material to its companion, altering the evolution and even the final fate of the entire system. One important process is called Roche-lobe overflow, a stage in which an expanding star spills material onto its companion. While Gaia BH3 is in a wide enough orbit to avoid this Roche-lobe overflow, Gaia BH1 and Gaia BH2 are expected to undergo this phase during their evolution.

The systems Gaia BH1 and Gaia BH2 each contain a black hole with a mass of about 9 times that of the Sun orbiting a much lighter companion star. Their black hole progenitors must once have been much more massive stars – around 20 times the mass of the Sun – paired with significantly smaller companions. Such massive stars reach the end of their main sequence phase quickly and then expand dramatically. Eventually, they should have been transferring material onto their companion stars.

This mass transfer phase creates a major theoretical challenge for the Gaia systems. Binary systems with such an extreme difference in stellar masses between the two stars were traditionally expected to undergo unstable mass transfer, leading to a so-called common envelope phase. During this phase, the smaller companion becomes engulfed inside the envelope of the massive star, and the system is expected either to merge into a single star or to emerge with a much tighter orbit – unlike the wide black hole binaries observed by Gaia.

An Alternative Mass-Loss Channel

The new study by Max Planck Institute for Astrophysics (MPA) stellar department team provides a possible solution to this puzzle, using detailed stellar evolution calculations to explore a different pathway for the formation of Gaia’s quiet black hole binaries.

Usually, in binary evolution models most of the transferred material is captured and lost from the vicinity of the companion star. Instead, the team investigated a scenario in which the majority of the material escapes directly from the vicinity of the massive star (the donor star).

The crucial difference is how much orbital angular momentum is removed from the system. If matter leaves close to the donor star, it carries away relatively little angular momentum compared with scenarios where mass is lost from the outer regions of the binary. As a result, the orbit does not shrink dramatically, allowing the two stars to avoid a catastrophic merger.

With this alternative mass-loss channel, the binary can survive and naturally evolve into a system with properties similar to Gaia BH1 and Gaia BH2.

Why would stars behave this way?

The obvious next question is whether and when nature can actually produce such a mass loss mode. The study identifies several possible physical mechanisms. Massive stars close to the end of their lives develop high opacity outer layers where radiation pressure can become extremely strong. These layers may drive powerful eruptions similar to those observed in luminous blue variable stars, ejecting material directly away from the donor star.

At the same time, the enormous difference in the sizes of the two stars' gravitational domains may prevent much of the transferred gas from ever reaching the companion. Current one-dimensional stellar evolution models cannot fully capture these complex hydrodynamic processes. Nevertheless, the agreement between our evolutionary models and the observed Gaia systems suggests that these effects deserve much closer attention.

Beyond the Gaia black holes

The implications extend far beyond the two unusual black hole binaries. Several other classes of post-interacting binary stars (including systems containing neutron stars, white dwarfs, and stripped Wolf-Rayet stars) seem to face similar difficulties within the standard picture of mass transfer. If low-angular-momentum mass loss proves to be common in certain binaries, it could reshape our understanding of how many compact-object binaries form with important implications for other populations, such as gravitational wave sources.

Future data releases from Gaia are expected to uncover many more dormant black hole binaries, providing a much larger sample against which theoretical models can be tested. Combined with discoveries from other observational techniques and increasingly sophisticated three-dimensional simulations of mass transfer, these observations will help determine whether this alternative evolutionary pathway is indeed a common outcome of binary star evolution.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Author:

Olejak, Aleksandra Olejak
Postdoc
Tel: 2231
Email: aolejak@mpa-garching.mpg.de

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Original publication

A. Olejak et al.
Nonconservative Mass Transfer as a Formation Channel for Gaia Black Hole Systems
ApJ1006 13

Source ! DOI

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NSF–DOE Rubin Observatory Opens Deep Window on Famous Cosmic Field

PR Image noirlab2618a
Rubin Looks Deep Into a Famous Cosmic Field

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Rubin Looks Deep Into a Famous Cosmic Field (selected excerpts)

PR Image noirlab2618c
Footprints on COSMOS

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Videos


PR Video noirlab2618a
Zoom on Rubin Observatory’s Image of the COSMOS Field


PR Video noirlab2618b
Pan on Rubin Observatory’s Image of the COSMOS Field

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A new NSF–DOE Vera C. Rubin Observatory image featuring hundreds of thousands of distant galaxies in and around the COSMOS field marks the Observatory’s first LSST Camera image and catalog release for science

A new image from NSF–DOE Vera C. Rubin Observatory offers a spectacularly deep view into a famous region of sky known as the COSMOS field. Located in the constellation Sextans, COSMOS is one of the most observed patches of the Universe — and Rubin’s new image adds a powerful new view of this well-known cosmic landmark.

Packed into this single image from Rubin Observatory are many different kinds of galaxies: spirals with delicate arms, smooth elliptical galaxies, distorted merging galaxies, and faint red galaxies from the distant Universe. Only a relatively small number of bright stars from our own Milky Way appear in the foreground, leaving an unusually clear view of galaxies stretching far into the distance.

Rubin Observatory is jointly funded by the U.S. National Science Foundation (NSF) and the U.S. Department of Energy's Office of Science (DOE/SC).

This image was captured with Rubin’s 3.2-gigapixel LSST Camera — the largest digital camera in the world, mounted on the 8.4-meter Simonyi Survey Telescope. It features the well-known and well-studied region of sky known as the COSMOS field. It was created by stacking hundreds of individual observations and contains more than half a million galaxies and more than 50,000 stars.

The COSMOS field is especially valuable to astronomers because it looks away from the crowded plane of our Milky Way. With fewer nearby stars and clouds of dust blocking the view, telescopes can see enormous numbers of distant galaxies, many so far away that their light has traveled for billions of years before reaching Earth. Looking deeper into space also means looking farther back in time, allowing scientists to study galaxies at many different stages in the history of the Universe.

Astronomers have studied COSMOS for more than two decades. Beginning with observations by the Hubble Space Telescope in 2003, researchers around the world have pointed many of the world’s leading telescopes at this same area, observing it in wavelengths ranging from radio waves to X-rays. Because the field has been observed so extensively, it serves as an important reference point for testing new data, comparing measurements, and combining information from many observatories.

Rubin now brings something new to this familiar field: a combination of depth, wide-field coverage, and repeated observations. By imaging COSMOS again and again with the LSST Camera, Rubin will complement earlier observations and add a dynamic view of the field. This perspective will help astronomers study not only what distant galaxies look like, but also how the sky changes over time.

Because of its scientific value, the COSMOS field is among the regions that will be observed more frequently than most areas included in the Legacy Survey of Space and Time (LSST) — Rubin’s ten-year survey aimed at creating the most comprehensive, cinematic record of the Universe in history. With added observations, Rubin will create an even deeper view, revealing fainter galaxies and finer details than can be seen in this first image.

This image is being released today to mark the occasion of Rubin’s Early Data Preview 2, or EDP2 — the first phase of Rubin’s Data Preview 2 release. EDP2 is Rubin’s first data preview based on observations from the LSST Camera [1]. It combines Rubin’s science validation observations collected between April 2025 and January 2026. It provides the Rubin science community with a deep co-added (stacked) image covering 3000 square degrees of night sky, which is around one-sixth of the entire visible Southern Hemisphere sky.

“The COSMOS deep image is just the beginning for Rubin in this region. Repeated visits to the field over the next few years will demonstrate the power of our survey design for discovery by providing our science community with a huge number of transient and variable objects like supernovae and other explosive transients for follow-up and detailed study,” says Bob Blum, Director of Rubin Observatory at NSF NOIRLab.

While EDP2 is not a release of data from the full LSST, which has only recently begun, it is a scientifically valuable data release in and of itself. The data preview gives scientists a rich look at the Southern Hemisphere sky, while allowing the Rubin science community to test tools, validate data products, and prepare for the decade-long survey ahead. Notably, EDP2 includes the COSMOS field, as well as the region of sky captured in Rubin’s Ocean of Stars image, which was released to celebrate the beginning of the LSST.

“The COSMOS field is a very important one for LSST science,” says Phil Marshall, Deputy Director of Rubin Observatory at SLAC. “Its wealth of prior observations, and its repeated targeting both during commissioning and as one of the LSST’s deep fields, will make it very valuable as a testing ground for scientists as they get ready to take on the survey data.”

With this new view of COSMOS, Rubin offers an early glimpse of the science to come: an extraordinarily deep and wide view of the Universe, revealing both the vast population of distant galaxies and the changing sky above Earth. Visit the Rubin Skyviewer app to explore this field in more detail.

Bob Blum adds: “As we celebrate the start of science with Rubin Observatory, our thoughts are with our staff and the community of Chile impacted by the recent devastating storms in the region of Coquimbo and beyond. Our priority is to ensure the well-being of our staff in the region and support the community where we live and work. This image marking the start of LSST science is dedicated to the people of the region of Coquimbo and is a small token of our gratitude for their decades of support for astronomy and the AURA Observatories in Chile.”

The second phase of EDP2, expected in the October–December 2026 timeframe, will add products derived from individual images. This includes the processed visit images from individual observations, difference images that show only detected changes, and the template images, which are compared to the individual visit images to produce the difference images

Access to EDP2 is available right now to researchers in the U.S. and Chile, as well as authorized international Rubin data-rights holders. In keeping with Rubin Observatory’s data-access policy, the data products will be made openly available to the public after a two-year proprietary period.

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

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Notes

[1] Rubin’s Data Preview 1 (DP1), released in June 2025, contained observations from October–December 2024 taken with the LSST Commissioning Camera — a much smaller version of the LSST Camera that was used to conduct test campaigns.

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More information

NSF–DOE Vera C. Rubin Observatory, funded by the U.S. National Science Foundation and the U.S. Department of Energy’s Office of Science, is a groundbreaking new astronomy and astrophysics observatory on Cerro Pachón in Chile. It is named after astronomer Vera Rubin, who provided the first convincing evidence for the existence of dark matter. Using the largest camera ever built, Rubin will repeatedly scan the sky for 10 years to create an ultra-wide, ultra-high-definition, time-lapse record of our Universe.

NSF–DOE Vera C. Rubin Observatory is a joint initiative of the U.S. National Science Foundation (NSF) and the U.S. Department of Energy’s Office of Science (DOE/SC). Its primary mission is to carry out the Legacy Survey of Space and Time, providing an unprecedented data set for scientific research supported by both agencies. Rubin is operated jointly by NSF NOIRLab and SLAC National Accelerator Laboratory. NSF NOIRLab is managed by the Association of Universities for Research in Astronomy (AURA) and SLAC is operated by Stanford University for the DOE. France provides key support to the construction and operations of Rubin Observatory through contributions from CNRS/IN2P3. The Science and Technology Facilities Council supports the wide range of UK contributions to Rubin operations provided through the LSST:UK Science Centre programme. Rubin Observatory is privileged to conduct research in Chile and gratefully acknowledges additional contributions from more than 40 international organizations and teams.

The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

The DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.

NSF NOIRLab, the U.S. National Science Foundation 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), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’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 scientific 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 of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

SLAC National Accelerator Laboratory explores how the Universe works at the biggest, smallest and fastest scales and invents powerful tools used by researchers around the globe. As world leaders in ultrafast science and bold explorers of the physics of the Universe, we forge new ground in understanding our origins and building a healthier and more sustainable future. Our discovery and innovation help develop new materials and chemical processes and open unprecedented views of the cosmos and life’s most delicate machinery. Building on more than 60 years of visionary research, we help shape the future by advancing areas such as quantum technology, scientific computing and the development of next-generation accelerators. SLAC is operated by Stanford University for the U.S. Department of Energy’s Office of Science.

Forty-three international teams outside the U.S. and Chile are contributing to Rubin Observatory and LSST Science through the In-kind Program, in exchange for LSST data rights. These contributions are recognized in the International Data Rights Holder list, which includes all individuals nominated by their respective international programs.

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Links

• Explore Rubin’s COSMOS Field in more detail
• Press release on rubinobservatory.org
• Vera C. Rubin Observatory website
• Vera C. Rubin Observatory image gallery
• More Rubin images
• More Rubin videos

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Contacts:

Bob Blum
Director for Operations
NSF–DOE Vera C. Rubin Observatory/NSF NOIRLab
Email: bob.blum@noirlab.edu

Phil Marshall
Deputy Director of Operations
SLAC National Accelerator Laboratory
Email: pjm@slac.stanford.edu

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

Manuel Gnida
Head of External Communications
SLAC National Accelerator Laboratory
Email: mgnida@slac.stanford.edu

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Chandra Sees Black Hole Stirring "Pot" Containing Galactic Potato

Red Potato Galaxy (MQN01 J004131.9-493704)
Credit: X-ray: NASA/CXC/Univ. Milano-Bicocca/W. Wang et al.; Infrared: NASA/ESA/CSA/STScI;
Radio: ESO/NRAO/NAOJ/ALMA; Image processing: NASA/CXC/SAO/N. Wolk & P. Edmonds

JPEG (128.9 kb) - Large JPEG (939.4 kb) - Tiff (77.2 MB) - More Images

A Tour of the Red Potato Galaxy - More Videos

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• A jet from a black hole in the early universe is churning the gas around a neighboring galaxy, tamping down star formation.


• NASA’s Chandra provided evidence that this jet is striking the gas cloud pumping particles and energy into it.


• This galaxy was nicknamed the "red potato" galaxy because of its appearance in images from NASA’s James Webb.


• This result informs how and when stars & galaxies formed in the early universe — and the effects black holes may have on them.

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A black hole may be stirring a "pot" of gas containing a neighboring galaxy in the early universe, according to a new study using NASA's Chandra X-ray Observatory, as described in our latest press release. This galaxy, officially named MQN01 J004131.9-493704, has been nicknamed the "red potato" by astronomers because of its appearance in images from NASA's James Webb Space Telescope.

The red potato galaxy is located about 11.7 billion light-years from Earth at an intersection where gigantic web-like structures of galaxies and gas meet. Astronomers targeted this area with Webb because they knew it contains one of the heaviest concentrations of galaxies and growing supermassive black holes yet identified in the early universe.

A composite image shows this galaxy in X-rays from Chandra (blue) and radio light data from ALMA, the Atacama Large Millimeter/submillimeter Array (red). The X-rays reveal a growing supermassive black hole and the jet it has produced, while the radio light shows relatively cool gas in the region. Infrared data from Webb (red, green, and blue) completes the view.

Astronomers expected that the red potato galaxy, which is surrounded by the ingredients to form new stars in the form of the cool gas, would be producing many young stars. However, the amount of star formation was relatively low, which led the researchers to look for a reason why.

One important clue is that the cloud of gas surrounding the red potato galaxy is unusually turbulent compared to large gas clouds surrounding other galaxies. Such turbulence could be preventing most of the gas from falling onto the red potato galaxy to form large numbers of new stars.

Using Chandra, the team discovered that a jet of particles from a growing black hole in a neighboring galaxy is pointed toward and may be striking the gas cloud around the red potato galaxy, possibly causing the turbulence.

The Red Potato galaxy, MQN01 J004131.9-493704, and the surrounding region in X-ray, infrared, and radio light. Credit: X-ray: NASA/CXC/Univ. Milano-Bicocca/W. Wang et al.; Infrared: NASA/ESA/CSA/STScI; Radio: ESO/NRAO/NAOJ/ALMA; Image processing: NASA/CXC/SAO/N. Wolk & P. Edmonds

A labeled version of the image highlights the red potato galaxy, the neighboring galaxy hosting the growing supermassive black hole, the jet from this black hole and the cloud of cool gas the jet may be striking. Apart from the jet, the blue Chandra emission from the neighboring galaxy is a point source of X-rays, rather than including diffuse X-rays. The large, diffuse appearance of the X-ray source is caused by the difference in resolving power of JWST and Chandra, and the processing required to show the faint jet.

While the red potato galaxy mostly has older, cooler stars and therefore appears red in infrared data, the galaxy hosting the black hole with the jet does not. Instead, this galaxy, which is located about 200,000 light-years from the red potato, is very actively forming stars, including massive, hot stars, as are most of the other nearby galaxies.

Astronomers want to learn how galaxies and black holes interact with each other – especially at this critical epoch in the universe’s history – and how that impacts when and how stars form.

A paper describing these results, led by Weichen Wang of the University of Milan-Bicocca in Italy, has been recently published in the Astronomy & Astrophysics journal. NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Quick Look: The Red Potato Galaxy

Source: NASA’s Chandra X-ray Observatory

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Visual Description:

This release includes a composite image featuring two galaxies in the early universe, some 11.7 billion light-years from Earth.

Near the center of the image is a small, irregular, pale yellow oval with a red outer ring, in the heart of a bright, hazy red cloud. This is a galaxy nicknamed the “red potato” by astronomers studying this region of the early universe. Those astronomers expected the red potato to be producing scores of new stars. When they instead discovered relatively low star growth, they looked to a neighboring galaxy for reasons why.

To our upper right of the red potato and its hazy red cloud of gas, is a neighboring galaxy in a pool of blue haze. This galaxy is also pale yellow in color, but has a less defined, less tuber-like shape than its counterpart. The blue pool represents X-rays from a growing supermassive black hole in the heart of the galaxy. The pool has a stubby tail, or X-ray jet, pointed toward the red cloud, and faint pockets of red and blue overlap within the composite image.

Astronomers now believe that the X-ray jet from the neighboring supermassive black hole may have struck the red gas cloud around the red potato. This may be causing turbulence within the gas cloud, preventing the gas from falling onto the red potato. Without the ingredients from that gas, new stars struggle to grow.

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Fast Facts for Red Potato Galaxy (MQN01 J004131.9-493704):

Credit: X-ray: NASA/CXC/Univ. Milano-Bicocca/W. Wang et al.; Infrared: NASA/ESA/CSA/STScI; Radio: ESO/NRAO/NAOJ/ALMA; Image processing: NASA/CXC/SAO/N. Wolk & P. Edmonds

Release Date: July 21, 2026
Scale: Image is about 20 arcsec (500,000 light-years) across.
Category: Groups & Clusters of Galaxies, Quasars & Active Galaxies
Coordinates (J2000): RA 00h 41m 31.9s | Dec -49° 37´ 3.7"
Constellation: Phoenix
Observation Dates: 22 observations from July 2022 to Sept. 2023
Observation Time: 176 hours (7 days 8 hours)
Obs. ID: 25375, 25711-25730, 27667
Instrument: ACIS
References: Wang W., et al., 2026, A&A, In press. DOI: 10.1051/0004-6361/202659351
Color Code: X-ray: blue; Infrared: red, green, and blue; Radio: red
Distance Estimate: About 11.7 billion light-years from Earth (z=3.25)

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Active Galaxy M77

M77 (NGC 1068)
Detail: Low Res. (240 KB) / Mid. Res. (600 KB)  / High Res. (7.0 MB)

M77 (NGC 1068) is a spiral galaxy located relatively close to our Milky Way. At its center lies a supermassive black hole about 10 million times the mass of the Sun. As enormous amounts of energy are released around the black hole, M77 is known as an active galaxy.

Because of its proximity, M77 has been extensively studied across the electromagnetic spectrum, from X-rays to radio waves, using various telescopes, including the Subaru Telescope and ALMA. Recently, observations with the Subaru Telescope's Hyper Suprime-Cam (HSC) have revealed evidence that M77 experienced a previously hidden minor merger with a low-mass satellite galaxy billions of years ago. Credit: NAOJ/SDSS/David Hogg/Michael Blanton. Image Processing: Ichi Tanaka)

Distance from Earth: 48 million light-years
Instrument: Hyper Suprime-Cam (HSC)

Relevant Links

• Minor Merger Kicks Supermassive Black Hole into High Gear (Subaru Telescope October 30, 2017 Science Results)

Source: Subaru Telescope

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A bright X-ray flare from a tidal disruption event

An artist's i,br,brmpression of a tidal disruption event in an active galaxy, in which a star is torn up by the gravitational force from a nearby supermassive.. black hole. Image credit: NASA/CXC/M.Weiss. - Download Image

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This week's significant event is from Maya Nunez, a rising sophomore at California State University, Long Beach, who is doing a Summer Undergraduate Research Fellowship (SURF) with the NuSTAR group at Caltech. Maya is working with Murray Brightman, a NuSTAR Staff Scientist, on transient X-ray sources—that is, X-ray sources that rapidly change in brightness, such as new X-ray sources that suddenly appear in the sky. X-ray transients can be caused by a wide variety of astrophysical processes, including Tidal Disruption Events (TDEs), which occur when a star passes too close to a supermassive black hole and is torn apart. Maya identified a bright X-ray flare from a galaxy hosting an actively accreting supermassive black hole, i.e., an active galaxy. Back in 2019, this galaxy had hosted the bright optical and infrared transient AT2019fdr, whose origin has been under much debate. AT2019fdr is hypothesized to be either a superluminous supernova, a flare from a supermassive black hole, or a TDE. Maya led an approved NuSTAR Director's Discretionary Time proposal to observe this source, and the observations, obtained last week, detected the source in the 3–8 keV NuSTAR energy band. The NuSTAR data provide a late-time X-ray detection from AT2019fdr which, in combination with recent literature, solidifies AT2019fdr’s categorization as a TDE as opposed to a superluminous supernova, since late-time X-ray emission is not common for such supernovae. A flare from a supermassive black hole is also less probable, but not completely ruled out. These new data and findings will expand our understanding of TDEs, particularly TDEs in galaxies with actively accreting supermassive black holes, which have not been as well-studied as TDEs in inactive or quiescent galaxies.

Source: NASA's Nuclear Spectroscopic Telescope Array (NuSTAR)/Weekly Highlights

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NASA Webb Explores Family Tree of Newly Discovered Distant Objects

Saguaro in GOODS-North Field (NIRCam)

Scientists have proposed one pathway little red dots can follow as the universe matures based on their analysis of spiral galaxy WISEA J123635.56+621424.2, nicknamed the “Saguaro.” They suggest little red dots may be a temporary phase of highly active supermassive black holes. Credit Image: NASA, ESA, CSA, STScI, Pierluigi Rinaldi (Steward Observatory); Image Processing: Alyssa Pagan (STScI)

Little Red Dot at Redshift 2: Real and Simulated Graphic

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Scientists synthetically shifted the Saguaro, a lower-redshift spiral galaxy, to a higher redshift to find out how it would appear if it was in the early universe. Its compact red appearance suggests that little red dots are a phase of highly active supermassive black holes. Credit Image: NASA, ESA, CSA, Pierluigi Rinaldi (Steward Observatory); Image Processing: Alyssa Pagan (STScI); Illustration: Leah Hustak (STScI)

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Since their discovery by NASA’s James Webb Space Telescope in 2022, little red dots (LRDs) have been the subject of great interest to astronomers. Understanding the nature of these extremely distant, compact red sources has been a puzzling scientific endeavor.

One popular theory is that little red dots are supermassive black holes known as active galactic nuclei, although they display characteristics unlike nearby active galactic nuclei. While they appear abundant at high redshift early in the universe, they rapidly decrease in number at lower redshifts. (The higher the redshift, the greater the distance the light has traveled across the universe.) This perplexing shift in number raises the question: What happens to little red dots as the universe matures?

A team of researchers led by Pierluigi Rinaldi of the University of Arizona’s Steward Observatory, now at the Space Telescope Science Institute (STScI) in Baltimore, has built upon their previous research in a new study published on July 29 in The Astrophysical Journal and proposed one pathway LRDs can follow as the universe ages: Though they may look like a unique galaxy population, these dots are affected by observational bias — some features just don’t appear at higher redshifts with current technology.

Their conclusions are based on their analysis of lower-redshift spiral galaxy WISEA J123635.56+621424.2, nicknamed the “Saguaro” for its prominent arms, like the cactus native to the Sonoran Desert in the Southwestern United States. A particularly intriguing feature of this redshift 2 galaxy, which corresponds to approximately 3.3 billion years after the big bang, is its little red dot-like center that is reminiscent of the ruby red fruit produced by the desert plant.

“Everything created in the early universe must evolve into something around us. We have had little idea of what LRDs become, but these results finally show us how to find their progeny,” said co-author George Rieke of the University of Arizona. Previous studies by NASA’s retired Spitzer Space Telescope provided the first hint of the dust-obscured, compact galaxy population in the lower-redshift universe that the Saguaro belongs to, paving the way for NASA’s Hubble and James Webb space telescopes’ high-resolution analyses.

“The Saguaro is important because it’s a prototypical little red dot and is one of the few we have found at lower redshift. It can be used to study the pathway of these dots throughout cosmic time,” said Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a co-author of the study.

Among the thousands of sources Rinaldi looked at across several surveys, the Saguaro was an example of the right place — with one of Webb’s microshutter arrays perfectly framed over the galaxy’s core to take spectroscopic data — and right time — being at lower redshift. To get as broad a view of the spiral galaxy as possible across the electromagnetic spectrum, the team used Hubble’s ultraviolet- and Webb’s infrared-imaging and spectroscopic archival data, respectively.

“Because the Saguaro is at lower redshift, we can see the very beautiful and bright host galaxy in high resolution and detail with Webb and Hubble,” said Zihao Wu of the Harvard-Smithsonian Center for Astrophysics, and a co-author of the study. “Webb’s observations can help us understand how the galaxy and its little red dot-like nucleus are connected.”

The team took multiple approaches to verify that the Saguaro’s compact red nucleus matched the characteristics of a prototypical LRD. In particular, the Hubble and Webb data showed that the nucleus is brighter in both ultraviolet and infrared light than in visible light, just like distant LRDs. The team also carefully disentangled the light emitted from the host and nucleus, and considered the presence of X-ray emission from the source.

Although the majority of little red dots at high redshift are not detectable in X-ray light, NASA’s Chandra X-ray Observatory detected weak X-ray emission from the Saguaro.

“What the X-ray light observations show is that this galaxy has an active galactic nucleus, and a very obscured one at that,” said Carys Gilbert, a Master’s student at the University of Cape Town in South Africa and a co-author of the paper. “It’s not only obscured but also X-ray weak. That kind of combination could explain the lack of X-ray emission that we see from all other little red dots. It fits the puzzle of little red dots nicely.”

In addition to demonstrating how the Saguaro’s central compact red source fits the little red dot criteria, the team synthetically shifted the galaxy to a higher redshift to explore how this galactic environment would appear to observers if located in the early universe. As expected, the Saguaro’s surrounding galactic structure fades so that only the bright, LRD-like source at its center is visible.

“Our theory is that most of these distant sources are affected by this cosmological effect, creating an observational bias,” said Rinaldi. “We simply are not able to sample the immediate environment of high-redshift little red dots because their surroundings are just too faint to be observed even with Webb. Little red dots are far more complex than just being a dot. They’re just the tip of the iceberg — of a supermassive black hole interacting with its nearby surroundings.”

Considering the Saguaro case study, the team believes that LRDs may not be a unique galaxy population, but instead a temporary phase of highly active supermassive black holes. Could this theory be the link between the populous high-redshift little red dots seen by Webb and the local universe?c While the Saguaro is not representative of all LRDs, the team proposes that this is one phase of these compact red sources. To build more confidence, further study of the Saguaro is necessary, as well as seeking other Saguaro-like galaxies at lower redshift. The team also intends to comb through Webb’s bountiful archival data to build a census of little red dots to study how their environments may impact how they mature. These different approaches are all geared to helping uncover the family tree of little red dots.

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).

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, 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 James Webb Space Telescope/News

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Details:

Last Updated: Jul 29, 2026
Location: NASA Goddard Space Flight Center

Contact Media:

Laura Betz
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
laura.e.betz@nasa.gov

Abigail Major
Space Telescope Science Institute
Baltimore, Maryland

Hannah Braun
Space Telescope Science Institute
Baltimore, Maryland

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