Black holes outgrow their galaxies

An AI-generated visualisation of a distant galaxy with an overly massive black holes (black sphere, not to scale). The vicinity of the black hole glows as a bright quasar.© MPE (generated with AI)

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To the Point:

• Black Holes and Galaxies: Eight black holes that were studied are extremely massive compared to their host galaxies and grew disproportional to the galaxies themselves.


• Unusual Mass Ratios: The ratio of black hole mass to stellar mass in the galaxies is at least 1 to 20, which is significantly higher than the typical value of about 1 to 200.


• Black Hole Growth Phase: The black holes are currently accreting matter at a rate that could double their mass within about one billion years.


• Future Research: Additional eROSITA data and high-resolution observations will help determine how common these systems are and how the host galaxies evolve.

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eROSITA identifies active black holes with unusually high mass fractions

An international team of astronomers has identified eight active black holes whose masses account for at least five per cent of the total stellar mass of their host galaxies. In the nearby Universe, the corresponding fraction is typically about half a per cent. The result challenges the widely held view that galaxies and the black holes at their centres always grow in close step.

The study, led by the Max Planck Institute for Extraterrestrial Physics (MPE), is based primarily on data from the eROSITA X-ray telescope and observations at ultraviolet, optical and infrared wavelengths.

The team searched a 140-square-degree region of the sky containing 22,079 quasars. Quasars are active galactic nuclei in which matter falls towards a supermassive black hole and releases large amounts of radiation. The intense X-ray emission detected by eROSITA reveals that the black holes in the eight selected systems are actively accreting matter.

“Astronomers assumed that central black holes always grow closely coupled to their host galaxies. Our results show that this is not always the case,” says Johannes Buchner, Postdoc at MPE, who led the study with international collaborators.

An extreme mass ratio

In the eight systems, the mass ratio between the black hole and the total stellar mass of the host galaxy is at least about 1:20. The black hole therefore accounts for at least roughly five per cent of the host galaxy’s stellar mass – more than ten times the typical value in the nearby Universe.

For a statistically well-defined subsample, the researchers also examined the 200 brightest quasars in a particularly deep part of the survey field. Three of the eight extreme objects were among the 200 brightest quasars in the survey. Simulations that account for the selection procedure and measurement uncertainties indicate that the systems are not simply isolated outliers, but represent a distinct population at the extreme end of the distribution.

The black holes have masses between approximately 800 million and four billion solar masses. They are therefore roughly a thousand times more massive than Sagittarius A*, the black hole at the centre of the Milky Way.

"Think of it like finding a Great Dane living in a studio apartment. The black hole has simply grown too large for its home.", says Prof. Kirpal Nandra.

Measuring the black holes

The researchers estimated the black-hole masses from optical spectra obtained by the Sloan Digital Sky Survey. The analysis relied in particular on the broad H-beta emission line, produced by ionised gas moving in the vicinity of the black hole.

The width of the line provides information about velocity, indicating that gas is circling the black hole with 40,000,000 km/h. Combined with an estimate of its luminosity, this allowed doctoral students Catarina Aydar and Qiaoya Wu to infer the black-hole mass. The method is calibrated for the mass range and cosmic epoch covered by the study. The uncertainty for individual black-hole masses is nevertheless approximately a factor of three. The conclusion therefore rests not on the exact mass of any one object, but on the statistical evidence for the population as a whole.

“The spectra reveal black holes with masses of roughly one to four billion Suns. What is particularly unusual, however, is their mass relative to the stellar mass of their host galaxies,” says Qiaoya Wu, a doctoral researcher at the University of Illinois Urbana-Champaign.

Animation of a black hole in a galaxy, growing in mass as matter falls in, glowing bright as a quasar. The growth of the black hole causes the mass ratio between black hole and stars to change, finally becoming "overmassive", like the found objects. Download video

Faint host galaxies

The black holes are clearly detected as active quasars through their X-ray emission. Their host galaxies, by contrast, are very faint or not unambiguously detected in the available images.

The team analysed observations across several wavelength ranges, including ultraviolet data from the GALEX satellite, optical images from the DESI Legacy Imaging Survey, near-infrared data from the VISTA Hemisphere Survey and infrared observations from the WISE satellite. The researchers modelled the quasar and galaxy light separately.

If the host galaxies had stellar masses comparable to that of the Milky Way, they would be substantially brighter in the available images. The observations therefore indicate that the galaxies contain considerably fewer stars. They do not yet establish whether the galaxies are small, compact or largely inactive, nor whether they are still forming stars.

“The faintness of the host galaxies shows that they cannot contain a stellar population comparable to that of a Milky-Way-sized galaxy. If they did, they would be much more clearly visible,” says Johannes Buchner.

Higher-resolution observations will be needed to determine the morphology and stellar populations of the host galaxies.

The black holes are still growing

The X-ray emission shows that the black holes are currently accreting matter. The team estimates an average growth rate of approximately 40 million solar masses per billion years. At that rate, their masses could double on a timescale of roughly one billion years.

If accretion continues, the mass ratio between the black hole and the stellar component of the host galaxy will become even more extreme.

“These black holes are already unusually massive compared with their host galaxies, yet they are still growing,” says Catarina Aydar, a doctoral researcher at MPE.

Results of measurements of stellar mass (from ultraviolet to infrared images) and black hole mass (from spectra). Optical galaxy image cutouts are positioned at the measured values. Most galaxies lie close to the orange line, with a mass ratio of 0.5%. The largest ratios of black hole to stellar mass are found in the upper left, above the dashed line marking 5%. Left-pointing triangles indicate cases where only an upper limit on the stellar mass could be determined, meaning the true ratio could be much higher than 5%. © Buchner et al., 2026

A challenge for galaxy-evolution models.

The observations point to a possible growth channel in which black holes temporarily gain mass faster than the stellar populations of their host galaxies. Current cosmological simulations do not produce systems with such extreme mass ratios.

The researchers compared their results to the Illustris, TNG, Horizon-AGN, EAGLE, Simba, Magneticum and ASTRID computer simulations. These models predominantly produce stellar to black hole mass ratios near the local value of 1 to 200. Systems as extreme as the ones observed are not produced.

The results therefore expose a limitation in existing models of the co-evolution of galaxies and their central black holes. They also provide a possible link to the overmassive black holes observed in the early Universe, where similarly extreme systems have raised questions about how rapidly black holes can grow. An important open question is: How could the black hole grow to be so massive, without the galaxy forming stars proportionally?

“These results are exciting and unexpected. We had assumed that galaxies and their central black holes grow closely connected to one another. These observations indicate that black holes can become extremely massive relative to their galaxies, apparently to a large extent independently of the evolution of the stellar population. This challenges us to rethink how black holes grow over cosmic history,” says Roberto Maiolino, a professor at the University of Cambridge, who was not involved in the study.

The eight quasars are likely to represent only the active, observable part of a larger population. Inactive or heavily obscured black holes cannot be identified as easily using the method applied here. Further eROSITA data and spectroscopic surveys will help determine how common these systems are.

The key open question is how the black holes gained so much mass without a corresponding increase in the stellar mass of their host galaxies. High-resolution observations will show whether the galaxies are still forming stars, how they are structured and how gas reached their central black holes over extended periods.

Source: Max Planck Institute for Extraterrestrial Physics/News

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Contacts:

Dr. Johannes Buchner
Postdoc High-Energy Astrophysics
Tel: +49 89 30000-3558
Email: jbuchner@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

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

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Original Publication

Buchn.er, J., I. Gauger, Q. Wu et al.
A lar,brge population of overmassive black hole quasars at z=0.3-0.8 revealed by eROSITA
A&A

Source | DOI

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Further Information

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

July 31, 2026
Second data release nearly doubles the previously known eROSITA X-ray sources to two million

An appetizer to the all-sky banquet

June 28, 2021
First eROSITA X-ray data release to the public

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.

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.

eROSITA sees changes in the most powerful quasar

May 19, 2023

Researchers have observed the X-ray emission of the most luminous quasar seen in the last 9 billion years of cosmic history. Significant changes in the quasar’s emission give a new perspective on the inner workings of quasars and how they interact with their environment.

Space Telescope Studies Solar System X-ray Glow

April 16, 2026
SRG/eROSITA reveals how our Solar System modifies the appearance of the X-ray sky

eROSITA witnesses the awakening of massive black holes

April 29, 2021

Using the SRG/eROSITA all-sky survey data, scientists at the MPE have found two previously quiescent galaxies that now show quasi-periodic eruptions.

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ALMA Watches a Massive Binary Assemble in Real Time

T 

The inset circle shows an ALMA 0.9 mm continuum image of the central binary system of IRAS 07299−1651 with the reconstructed orbital trajectories overlaid. The red- and blue-shifted hydrogen recombination line emission traces the rotation of the ionized circumstellar disks around the two forming stars, while the arrows indicate the directions of the bipolar jets. Background: Mid-infrared image of the region obtained with JWST (red = F470N, green = F405N, blue = F360M). Credit: NASA, ESA, CSA, STScI, J. DePasquale (STScI), ALMA (ESO/NAOJ/NRAO), Y. Zhang

 

An artist’s impression of the formation of a close massive binary system, showing misaligned disks around two young stars.
Credit: Y. Zhangdiv

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Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have captured one of the most detailed three-dimensional views yet of a massive binary star system while it is still being born. By tracking the motions of two young, massive stars over nearly eight years, the team found that the pair follows a highly stretched-out orbit and is surrounded by strongly tilted gas disks, both relative to each other and to the stars' orbit. The findings suggest the two stars didn't form together from a single spinning disk of material, as is often assumed, but instead formed independently and later came together in a close gravitational encounter, revealing a new way close massive binary star systems may form.

Most massive stars are born with stellar companions, and at least 90% are thought to exist in binary or higher-order multiple systems. These massive binaries go on to shape their surroundings dramatically, through supernova explosions and the production of heavy elements. But because most known massive binaries are only studied long after they've finished forming, astronomers have had few opportunities to catch the actual moment of assembly.

An international team led by Yichen Zhang of Shanghai Jiao Tong University set out to change that by studying IRAS 07299−1651, a system containing two massive protostars, stars still growing by pulling in surrounding gas and dust. The team had studied this system before, in 2019, when ALMA observations first provided direct dynamical constraints on the pair. At the time, the results seemed broadly consistent with the standard picture: two stars forming together from the fragmentation of one large disk. But one detail didn't quite fit: the disks around the two stars already looked oddly misaligned.

To dig deeper, the researchers spent nearly eight years measuring extremely subtle shifts in the two stars' positions on the sky, a technique that requires exceptional precision and is well within ALMA's capabilities. "For the first time, we were able to watch two massive stars move around one another while they were still being born," said Yichen Zhang, corresponding author of the study.

The team combined this long-term ALMA monitoring with data from the U.S. National Science Foundation's Very Large Array (VLA), as well as infrared images from the James Webb Space Telescope (JWST) and ESO's Very Large Telescope (VLT), which traced jets of material streaming away from the young stars. Together, these observations let the team reconstruct, for the first time, the system's full three-dimensional architecture, how the stars orbit each other, how their disks are tilted, and how their jets point into space.

"Each telescope revealed a different piece of the puzzle," said Rubén Fedriani, a co-author of the study. "The combination of radio and infrared observations provides the most exquisite detail on the formation of this massive protobinary system."

What they found surprised them. Instead of a neat, roughly circular orbit, the stars are following a highly eccentric trajectory, with the preferred orbital solutions lying close to a parabolic path. And rather than being aligned, as would be expected if the stars formed from the same disk, their surrounding disks are tilted at a sharp angle to each other and to the orbit itself. "It felt like solving a three-dimensional puzzle," said Yao Wang, the study's first author. "Each new observation added another piece, and eventually the orbit, disks, and jets all came together into a single, coherent picture."

This mismatched, chaotic-looking architecture is hard to explain if the two stars grew up together in the same disk — in that scenario, they'd be expected to inherit similar, well-aligned spins. Instead, the evidence points to a different origin story: the two stars likely began forming separately, in their own individual pockets of gas, before a chance close encounter brought them into their present configuration while they were still wrapped in their birth cloud. In representative orbital solutions, the stars passed closest to each other only about 60 years before the observations, practically an instant on cosmic timescales. The compact disks seen today appear to have survived the encounter, retaining well-defined rotational structures.

"This study demonstrates that the early lives of stars can be quite chaotic, with a chance encounter leading to this gravitational dance and stellar coupling," said Jonathan C. Tan, a co-author of the study. It's still not certain whether the two stars will stay gravitationally bound to each other for good — their current motion sits close to the dividing line between a bound orbit and one that could eventually fly apart, and interactions with the surrounding gas may still nudge their fate one way or the other. Future observations will help pin that down.

More broadly, the study opens a new way of investigating how massive binary stars come together. By applying the same long-term monitoring approach to other young massive binaries, astronomers hope to learn how often close encounters like this one—rather than shared birth in a single disk—build the massive binary systems seen across our galaxy.

Source: ALMA (Atacama Large Millimeter/submillimeter Array)/Press Releases

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Additional Information

The results of this research appear in Nature Astronomy as "An eccentric massive protobinary assembled via a core-merger parabolic encounter" by Y. Wang et al.

This article is based on the original press release by the National Astronomical Observatory of Japan (NAOJ), an ALMA partner on behalf of East Asia.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning, and operation of ALMA.

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Contacts:

Nicolás Lira
Education and Public Outreach Officer
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cel: +56 9 9445 7726
Email: nicolas.lira@alma.cl

Seiichiro Naito
NAOJ EPO Lead
Email: naito.seiichiro@nao.ac.jp

Jill Malusky
Public Information Officer
NRAO
Email: jmalusky@nrao.edu

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: press@eso.org

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NASA’s Hubble, Webb Find Far-out Solar System Objects ‘Remember’ Past

Trans-Neptunian Object Illustration

This artist’s concept depicts a Trans-Neptunian Object, a small, faint, icy body orbiting the Sun beyond the orbit of Neptune. These objects are so small that even with NASA’s Hubble and Webb space telescopes, they appear only as tiny points of light. Credit Artwork: NASA, ESA, Leah Hustak (STScI)

Tiny Worlds Discovered by Hubble and Webb

This video explains how Hubble and Webb are giving scientists a new look at some of the solar system’s oldest survivors and revealing new clues about how the building blocks of planets, including Earth, first formed. Credit: NASA's Goddard Space Flight Center.

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For the first time, scientists used the joint power of NASA’s Hubble and James Webb Space Telescopes to study some of the most far-flung bodies in our solar system, Trans-Neptunian Objects (TNOs). Some of these are the smallest and faintest ever directly seen. The researchers unexpectedly found fewer small TNOs than they expected, and that the colors of these bodies followed the same relationships as their larger family members

. These objects are typically small, faint, icy bodies orbiting the Sun beyond the orbit of Neptune. Most are more than 100 million times dimmer than objects visible to the unaided eye. In two complementary papers published Tuesday in The Astronomical Journal, teams analyzed the color, composition, and size distribution of 27 newly discovered tiny, dim TNOs.

This class of small bodies offers the best view into an early stage of planet-building, when a disk of dust and pebbles in orbit around the Sun coalesced into city-sized “planetesimals” — the solid building blocks that clump together to form planets — but had not yet merged into full-sized worlds. Beyond Neptune, this second stage never happened, leaving behind a frozen population of planetesimals.

In the deepest TNO survey to date, teams led by PhD candidates from the University of Victoria in Canada, under the guidance of the National Research Council of Canada, and Northern Arizona University in Flagstaff examined a patch of sky simultaneously with Hubble, observing the TNOs’ visible light, and Webb, observing their infrared light. The team of researchers measured the objects' colors, which are like a fingerprint of the surface composition, as well as their sizes and determined their orbits.

In the coordinated observations, the teams studied two different types of TNOs. The first, dynamically “cold” TNOs, are on their original, relatively circular orbits around the Sun in the plane of the solar system. The second type, dynamically “hot” TNOs, formed between the current locations of Uranus and Neptune but were pushed outward where they are today when the outer gas giants migrated early in the solar system’s history. Today they reside in highly elliptical orbits and move in and out of the plane of our solar system.

Prior to these observations, astronomers thought that small TNOs from both hot and cold populations would have undergone many collisions, changing their surfaces compared to larger TNOs. But that's not what the observations showed. Instead, the small bodies look like their larger counterparts. This implies that collisions are not changing the surfaces significantly—perhaps because there are fewer collisions than expected, or because the TNOs somehow retain their primordial, pre-collision compositions. The teams are still trying to unravel this mystery.

“You could imagine a scenario where getting knocked around and fragmented would change the surface composition, and then you would see a different surface color for tiny TNOs compared to their larger siblings. So it's really fascinating to see that the smallest objects are somehow 'remembering' and preserving the history of how they were made,” said Northern Arizona University PhD candidate Anastasia Morgan, who led the study of color and composition.

“These dynamically ‘hot’ TNOs retain a signature of where they were born, even though they’ve been orbitally scrambled since then,” said co-author David Trilling of Northern Arizona University.

Both the “hot” and “cold” populations seem to keep the same colors as when they were formed, with little change since the birth of the solar system.

The Webb data also allowed researchers to measure the number of objects of each size. They found that the overall size distributions for both populations were surprisingly similar.

“It's very interesting that the process of planetesimal formation ends up producing the same distribution of sizes for both cold and hot populations, despite forming in different regions of the early solar system. The process seems to be insensitive to disk conditions, producing similar planetesimal sizes whether the disk is hot or cold, and dense or fluffy,” said University of Victoria PhD candidate Marielle Eduardo, who led the study on size distribution.

Researchers also found fewer of these very small bodies than they expected based on some planet formation models. Webb discovered 27 new, remarkably dim TNOs, one so faint it is equivalent to standing on Earth and seeing a small swarm of fireflies on the Moon. The smallest one they observed has a diameter of about 3 miles (5 kilometers), which is about five times smaller than what is possible to detect with the most sensitive ground-based telescopes.

This project would not have been possible without Hubble and Webb working together to detect and characterize these TNOs. With Hubble’s sensitivity in visible light and Webb’s in infrared, the space telescopes provide more insights than either can on its own.

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.

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

Source: NASA's Hubble Space Telescope/News

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A superbubble scene

LHA 120-N44

TA dense field of stars fills the image, surrounded by wispy clouds of gas and dust. Pale blue and grey nebulosity forms an intricate web across the scene, with darker clouds of dust concentrated towards the lower right. Numerous bright stars appear in shades of blue, white and orange. Credit: ESA/Hubble & NASA, D. Gouliermis.

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This sprawling cosmic vista and subject of today’s ESA/Hubble Picture of the Month comes from the Large Magellanic Cloud, or LMC. The LMC is the largest of the small galaxies that orbit our Milky Way galaxy. At just 160 000 light-years away, the LMC offers a close look at highly active stellar birthsites like the nebula shown here. This nebula is named LHA 120-N44, or N44 for short, and it’s located in the constellation Dorado.

The appearance of this photogenic nebula is dominated by two features: a vast central void and a shell of dense, dusty gas. The central void is a ‘superbubble’ spanning roughly 210 by 140 light-years. The glittering stars at the centre of the void are responsible for its creation; through their powerful stellar winds and explosive supernovae, these stars have expelled much of the gas from which they were born.

When the stars of N44’s central star cluster swept away this gas, the expelled gas formed a shell around the superbubble. New stars are forming in this compressed gas shell, making N44 an interesting target for researchers studying the process of star formation. In particular, astronomers have turned to this nebula as an ideal place to time this process from start to finish. Their goal is to understand how long it takes from the collapse of cold gas clouds into dense knots to the moment nuclear fusion ignites in the heart of a newborn star.

Researchers used Hubble to survey N44 and take a census of its stars, cataloguing nearly half a million stars within the cluster as well as interlopers drifting in front of it. Of the stars surveyed, nearly 30 000 are what astronomers call pre-main-sequence stars, which have yet to begin fusing hydrogen into helium in their cores. This treasure trove of baby stars was discoverable thanks to the high sensitivity and fine spatial resolution of Hubble’s instruments that can pick out faint objects in crowded clusters.

The gas shell surrounding the superbubble is energised by ultraviolet radiation from massive stars, causing it to glow and highlighting several distinct features. Each feature within the broader N44 star-forming complex was catalogued by astronomer Karl Henize in the 1950s. One feature is a smaller bubble, catalogued as N44F, that is located near the upper-right corner of this image. N44F is an interstellar bubble blown by the intense stellar winds of a single hot and massive star. As this previously released Hubble closeup shows, the star’s furious winds and radiation have sculpted the surrounding bubble and created pillars of dusty gas.

The data used to create this image come from an observing programme (#14689; PI: Gouliermis) that aimed to probe stars in the N44 complex that have not yet begun fusing hydrogen into heavier elements in their cores. These data help to determine how long the process of star formation takes, as well as what masses newborn stars typically have. Hubble's sensitive observations of the lowest-mass stars in this region open a new window onto star formation in regions that, like the LMC or the galaxies of the early Universe, are poor in elements heavier than helium.

Source: ESA/Hubble/potm

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Links

• Image on ESA website
• Video: Space Sparks episode 28
• Video: Pan of LHA 120-N44
• Video: Zoom into LHA 120-N44

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An inside-out view of active supermassive black holes and their host galaxies

Different telescopes reveal different signatures of active black holes. LOFAR (left) detects radio jets; WISE (centre) detects hot dust; SDSS/MaNGA (right) provides spatially resolved optical spectra of stars and gas. Credits: ASTRON, NASA/JPL-Caltech, SDSS, MPA

Active supermassive black holes do not all look the same. Some are obscured by hot dust, some are surrounded by fast-moving ionised gas, and some can eject giant radio jets extending over millions of light-years. By mapping about two thousand such objects from their galactic centres outward, researchers at the Max Planck Institute for Astrophysics found that these variations are related to the properties of their host galaxies. Infrared and optical AGNs are found in star-forming galaxies with young centres and ionised winds, whereas radio AGNs are mostly found in older, quieter systems. A small group showing both kinds of activity sits in between.

Seeing Active Black Holes in a Different Light

An active galactic nucleus (AGN) can appear in several forms, such as a hot, dusty torus that glows in infrared light; broad emission lines from gas moving close to the black hole; narrow lines from gas farther out; or a radio jet blasting away from the centre. Some of this diversity is simply due to our viewing angle. For example, an AGN seen edge-on through its dusty torus looks different from one seen face-on. However, orientation alone cannot explain everything. A long-standing question is whether these different 'faces' of AGN activity are also connected to what is happening in the surrounding galaxy, and if so, how

Host-galaxy properties change systematically from the nucleus outward for different AGN types. Each column shows one AGN class, with radial profiles of star formation (top), stellar age (middle), and gas ionisation (bottom); grey lines show reference profiles for normal galaxies. Infrared and optical AGN hosts show enhanced central star formation and younger stellar populations, while radio AGN hosts resemble quiescent galaxies at all radii. Credit: SDSS, MPA/G. Jin

From the Nucleus to the Outskirts

To find out, the team combined data on around ten thousand nearby galaxies, including nearly two thousand identified AGNs, taken from three surveys, each of which contributes a different piece of the picture. WISE, an infrared satellite, reveals hot dust. MaNGA is an integral-field spectroscopic survey that supplies optical AGN signatures and spectra at multiple positions across each galaxy. This allows the team to map properties rather than just measuring them in aggregate. LoTSS, a state-of-the-art radio survey using the LOFAR telescope, traces synchrotron emission from jets. Together, these datasets enable the researchers to trace the evolution of each galaxy from its inner regions to its outskirts.

The first differences appear in the central regions. Galaxies hosting infrared AGN exhibit the clearest boost in central star formation, forming stars at a faster rate near their nuclei than similar galaxies without AGN activity. These infrared and optical AGN hosts also have younger stellar populations at their centres, as determined by a spectral indicator of stellar age. In contrast, radio AGN hosts have old central populations and reduced central star formation, much like normal quiescent galaxies. The simultaneous presence of black-hole growth and central star formation in the same populations is consistent with both processes being fed by the same gas supply, though the data do not show one triggering the other.

The gas emission and kinematics also carry the AGN's signature. Infrared, broad-line and narrow-line AGNs all exhibit stronger gas ionisation towards the centre, and this excess compared to normal galaxies extends over several kiloparsecs before fading. Fast-moving, ionised winds are strongest in infrared and broad-line AGNs, and their average signal extends to around 2 kiloparsecs from the nucleus. Radio AGNs show no comparable outflow on average. These winds clearly disturb the ionised gas around the black hole. However, the data do not show that star formation is immediately shut down by the current AGN. The link between black-hole and stellar growth is strongest near the centre and gradually weakens towards the outskirts.

A schematic view of the proposed AGN population sequence created with the help of AI. Left: a radiative AGN with abundant gas and a prominent dusty torus, typical of star-forming hosts. Centre: a mixed AGN with compact radio emission alongside radiative signatures. Right: a radio-dominated AGN with extended jets, typical in quiescent hosts. This is a map of connected AGN-galaxy states, not a timeline for any individual galaxy. Credit: MPA/G. Jin

A Bridge Between AGN Modes

A small group of AGNs exhibits both optical/infrared and radio signatures. Several independent measurements show that these 'mixed' AGNs lie between the radiative and radio-dominated populations, providing an observational link rather than a clear boundary between the two. Their radial star-formation profiles lie between those of optical/infrared-only and radio-only AGNs. Their stacked spectra reveal a combination of strong emission lines and a significant 4000-Ångström break, suggesting ongoing black-hole accretion within an ageing stellar population. While their radio emission is present, it remains relatively compact compared with the extended jets of radio-only AGNs.

These findings suggest a possible population-wide sequence running from radiative AGNs in star-forming hosts to radio AGNs in quiescent ones, with mixed AGNs marking an intermediate stage. However, it is important to note that this sequence should be interpreted as a map of connected AGN-galaxy states rather than as a time-lapse of a single galaxy. AGN episodes last far less time than the galaxy evolution, and any one galaxy may experience repeated AGN cycles throughout its lifetime. Changes in large-scale gas supply may contribute to the pattern, but the available data cannot identify the underlying cause.

What's missing?

Several observations could clarify this picture. Molecular gas from CO observations would reveal the fuel reservoir directly. X-ray observations could reveal the hot atmospheres thought to exist around radio-mode AGNs. Higher-resolution radio images would clarify whether the compact jets in mixed AGNs are younger. Comparing these with spatially resolved simulations would reveal whether the observed states arise from one evolutionary route or several. Ultimately, these observations will reveal whether the empirical map uncovered here reflects a common evolutionary route, repeated cycles or multiple paths through black hole and galaxy growth.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Authors:

Gaoxiang Jin
PhD student
Tel: 2298
Email: gxjin@mpa-garching.mpg.de/a>

Guinevere Kauffmann
Director
Tel: 2013
Email: gamk@mpa-garching.mpg.de

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Original publication

Jin et al.
'A spatially resolved evolutionary sequence of multi-wavelength AGN host galaxies
Monthly Notices of the Royal Astronomical Society, Volume 546, Issue 4

DOI

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A Supermassive Cosmic Dance

Artist's impression of a pair of supermassive black holes orbiting each other, surrounded by accreting material from a circumbinary disk. Image credit: NAOJ. Download Image

Over the past week, NuSTAR observed 4C +37.11, the only confirmed supermassive black hole binary in an active galaxy with spatially resolved orbital motion. This system was originally identified in 2004 by the Very Long Baseline Array (VLBA) as a pair of central, compact, flat-spectrum, variable radio sources with a measured separation of 7.3 pc—evidence of a pair of gravitationally bound supermassive black holes. Subsequent VLBA observations claim the detection of relative proper motion between the binary components. Numerical simulations predict that accretion in supermassive black hole binaries can generate excess hard X-ray emission above 20 keV through shocks and heated mini-disks fed by circumbinary gas streams. NuSTAR will test those predictions of a significant hard excess, or see if the X-ray spectrum follows a standard AGN power law. This test of binary accretion physics in a wide-separation supermassive black hole binary will establish whether a hard X-ray diagnostic that can be applied to unresolved binary AGN candidates identified by LSST and future time-domain surveys.

Author: Daniel Stern (NuSTAR Deputy Principal Investigator, Caltech)

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

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Hitchhiking PAHs Caught Catching a Ride on Galactic Winds

JWST's view of the spiral galaxy IC 5332. JWST's infrared instruments are sensitive to emission from molecules called polycyclic aromatic hydrocarbons.Credit: NASA, ESA, CSA, STScI, PHANGS Team, Janice Lee (STScI), Thomas Williams (Oxford), Rupali Chandar (UToledo)

Title: JWST Discovery of Warm Dust in the Circumgalactic Medium of the Makani Galaxy
Authors: Sylvain Veilleux et al.
First Author’s Institution: University of Maryland
Status: Published in ApJ

The Windy Galaxy

Billions of light-years away lies Makani, a record-breaking galaxy discovered in 2019 by researchers at the Keck Observatory atop Maunakea, Hawaiʻi. The galaxy shows evidence of a large merger event, where two galaxies collided to form a larger galaxy. This event triggered starburst activity, or several waves of intense star formation, that changed the makeup of not just Makani, but the region around it.

There are several processes that can create galactic winds. An active supermassive black hole at the center of the galaxy can slingshot particles out of the galaxy at close to the speed of light, or supernovae leftover from previous starburst activity can help to expel material from the galaxy. Makani, whose name in Hawaiian just so happens to mean “wind,” has both factors contributing to its galactic winds: massive amounts of star formation and a very active black hole in its center.

This contributes to some of the strongest galactic winds discovered to date, stretching approximately 100 kiloparsecs (330,000 light-years) beyond the galaxy, roughly ten times the extent of a typical galactic wind. These galactic winds remove gas from the galaxy and help to enrich the circumgalactic medium around the galaxy. There is still much to discover about how galactic winds change the makeup of such galaxies, and what exactly they take with them on their way out.

Figure 1: Makani’s spectrum overlaid on top of the JWST filters. The peaks in the spectrum are PAH features that neatly overlap with JWST’s observing bands. Credit: Veilleux et al. 2025

PAHs Gone Extragalactic

Using JWST, the authors scrutinized Makani for any signs of PAHs. They found that not only did PAHs exist within the galaxy, these molecules were found up to 30 kpc (~100,000 light-years) outside the galaxy. Makani’s strong galactic winds were ejecting the dust grains from the galaxy over an estimated timescale of a billion years.

Previously, astronomers had not expected to find high quantities of dust grains outside the protection of a galaxy. The journey across a galaxy is long and hot, with temperatures in the millions of degrees. A dust grain would likely not survive the trip, as it would be destroyed by high-energy photons. This suggests that the PAHs were somehow shielded from the hotter parts of the interstellar medium and circumgalactic medium in large enough volumes to make it beyond the edge of Makani.

This answered questions about how galaxies enrich the circumgalactic medium, but it also added several more. Since today’s authors were limited by the sensitivity and range of their instruments, they were unable to confirm if there were PAHs along Makani’s entire wind structure, or just the first 35 kpc (114,000 light-years) of it. They also would like to turn their sights towards the intergalactic medium to see if PAHs could make it even farther beyond the reach of their host galaxy.

Earth’s Favorite Carcinogen: Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs, pronounced P-A-Hs or “paws”) are small flat dust grains scattered into every corner of the universe, from the atmosphere of Earth in the form of exhaust and wildfire smoke to the circumgalactic medium (the mostly empty space between galaxies). These PAHs contribute to regulating the temperature of the interstellar medium, but astronomers have long wondered how they migrate across galaxies.

Even though they are smaller than a human hair, PAHs are still easily observable even in very distant galaxies. These dust grains emit infrared light, and if there are enough PAHs in a region, they are bright enough to be observed with modern telescopes, such as JWST. By combining multiple observations across multiple filters, astronomers can calculate ratios that reveal information about the PAHs’ size, temperature, and charge, allowing reserachers to further discern properties about the regions in which these PAHs reside.

With redshifted galaxies like Makani, the light from PAHs is stretched beyond its usual wavelength, but fortunately for today’s authors, the light was stretched just enough to land known PAH features well within JWST filters, as seen in Figure 1. The authors were then able to use this information to track the distribution of these PAHs across Makani.

Original astrobite edited by Chloe Klare.

Source: American Astronomical Society/AAS-Nova

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About the author, Natalie Price:

As a first-year master’s student at Wesleyan University, I study how stellar winds interact with the local interstellar medium. Outside of the observatory, you can find me dancing, with my nose in a book, or running at non-relativistic speeds.

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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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NASA’s Hubble Tracks New Decagon Encircling Saturn’s South Pole

Decagon on Saturn’s South Pole (Color)

Recent NASA Hubble Space Telescope images show the gas giant Saturn and its southern pole, where astronomers have discovered a 10-sided atmospheric wave. Observations show the decagon extends through multiple layers of Saturn’s atmosphere.Credit Image: NASA, ESA, STScI, Agustin Sánchez-Lavega (UPV), Amy Simon (NASA-GSFC), Michael Wong (UC Berkeley); Image Processing: Alyssa Pagan

Decagon on Saturn’s South Pole (Single Filter)

A single filter from NASA’s Hubble Space Telescope distinctly shows a 10-sided wave encircling Saturn’s south pole, labeled “decagon”. An “X” denotes where data was not captured. Credit Image: NASA, ESA, STScI, Agustin Sánchez-Lavega (UPV), Amy Simon (NASA-GSFC), Michael Wong (UC Berkeley); Image Processing: Alyssa Pagan

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Recent observations with NASA’s Hubble Space Telescope have revealed a giant, evolving, 10-sided atmospheric wave encircling Saturn's south pole. This discovery marks the first time a large, regular-sided jet pattern has been observed in the planet's southern hemisphere. The feature appears remarkably similar to Saturn's famous hexagon at its northern pole, but is also distinctly different, suggesting scientists may be witnessing a new atmospheric phenomenon develop on the iconic gas giant.

The results published Wednesday in the journal Science Advances.

By piecing together several years of Hubble observations dating back to 2023, researchers found subtle hints of the structure beginning to emerge before it became a clearly defined pattern. Those observations were taken as part of Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, which has photographed the outer planets annually for more than a decade.

"We've never seen anything quite like this in Saturn's southern hemisphere," said Amy Simon, study co-author and OPAL principal investigator, NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The northern hexagon has been there every time we've looked for more than 40 years. This feature is different — it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop."


The discovery was possible because Saturn's changing seasons gradually brought the planet's south pole back into view from Earth, where astronomers who collectively analyze images of Saturn from ground-based observatories first identified it.

Agustín Sánchez-Lavega, lead author of the new study, is a researcher at the University of the Basque Country in Spain. The university manages a website, called Planetary Virtual Observatory Laboratory, that accepts ground-based images of solar system planets contributed by observers all over the world. It was in those images, first in 2024, that Sánchez-Lavega and amateur astronomers Trevor Barry and Jean-Paul Oger noticed a subtle undulating band along the southern pole. Additional 2025 imagery taken from the ground hinted even more strongly toward this decagon structure.

That’s when the Hubble observations come into the picture. Hubble’s view from space offers unmatched image sharpness and spatial resolution over full rotations of Saturn, without smearing by Earth’s atmosphere.

“Given Saturn’s symmetry in its north-south jet stream system, we have been searching for a counterpart to Saturn’s northern hexagon on the south pole in Hubble images since 1990,” Sánchez-Lavega said. “Images from NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017, showed no inkling of a long-lived formation, either. The Hubble data confirmed the feature’s presence back to 2023.”

The wave sits within one of Saturn's powerful jet streams and extends through multiple layers of the atmosphere, indicating it is not just a cloud-level feature, but a vertically extended atmospheric structure. The decagon’s apparent position shifts slightly, because Hubble captures images from different wavelengths. Those different wavelengths probe different altitudes in Saturn's atmosphere.

“The most intriguing part to me is that this seems to have just formed recently,” said Simon. “The question is, why did it suddenly form now when we haven't seen one before?”

The authors say further study is needed from Hubble and NASA’s James Webb Space Telescope, as well as analysis of computer models, to understand how the decagon formed, how long it may last, and how it compares to the long-lived hexagon in the north.

Hubble’s long duration in operation has allowed astronomers to track changes over time in solar system planets and other astronomical objects as well.

Rather than providing a single snapshot, the OPAL program allows scientists to follow seasonal changes, track short-lived storms, and identify other atmospheric features that evolve slowly over time.


"When we started the OPAL program, we expected compelling surprises, but we didn't know what to expect specifically,” said Mike Wong, study co-author, University of California, Berkeley. “A lot of the discoveries we see coming from OPAL are not just based on one observation, but on years and years of data. Regular observations over time are enabling a lot of new findings."

The team plans to continue observing Saturn to determine whether the decagon settles into a long-lived, stable configuration like the northern hexagon or continues to evolve. Future observations also could help scientists determine what drives the wave, what it reveals about the atmospheric dynamics of giant planets throughout the solar system, and how they may relate to those we see here on Earth.

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

Source: NASA's Hubble Space Telescope/News

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Details:

Last Updated: Sep 02, 2026
Editor: Andrea Gianopoulos
Location: NASA Goddard Space Flight Center

Contact Media:

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

Hannah Braun
Space Telescope Science Institute
Baltimore, Maryland

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Hawai‘i Students Name Image of Glittering Galaxy Pair Nā ʻUhane Māhoe Huki Pū i ke Ola

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Nā ʻUhane Māhoe Huki Pū i ke Ola

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Project Hōkūlani Interns Summer 2026

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Project Hōkūlani Galaxy Presentation

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Project Hōkūlani Stargazing on Maunakea

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Project Hōkūlani Interns Fall 2025

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Project Hōkūlani Interns Shadow Nighttime Operations

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Videos


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Pan on NGC 7253


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Zooming into NGC 7253

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Project Hōkūlani interns researched and named this new Gemini North image featuring the stunning pair of interacting galaxies known as NGC 7253

Nā ʻUhane Māhoe Huki Pū i ke Ola is the Hawaiian name given to this image of NGC 7253 — a pair of spiral galaxies caught in each other’s gravity. Captured by the Gemini North telescope on Maunakea in Hawai‘i, this image created a spectacular symbolic display for this year’s interns participating in Project Hōkūlani.

Over 200 million light years away, deep within the constellation Ka Lupe o Kawelo (Pegasus), is NGC 7253 — a pair of gravitationally interacting galaxies separated by a distance of about four million light years. This glittering view of their meeting was captured by the Gemini North telescope, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab. The new image offers viewers the closest look yet at NGC 7253, and has been named Nā ʻUhane Māhoe Huki Pū i ke Ola, which translates to “The Twin Spirits Pulling Together Creating Life.”

The creation of this image began in October 2025 with three local students from Waiākea High School and the Volcano School of Arts and Sciences participating in the Project Hōkūlani internship. Interns Raiyan Rahman, Rafan Rahman, and Alia Tamanha spent one week at the Gemini North Hilo Base Facility with three goals: learn about observatory operations and how scientific data is collected; deepen their own appreciation for Maunakea; and select an astronomical object for Gemini North to image.

“NGC 7253 is a fascinating object because it’s two galaxies that are merging into one over billions of years. But we mainly picked this object because it was one of the few that actually lay within a Hawaiian constellation, Ka Lupe o Kawelo,” says Raiyan Rahman. “After spending so much time on Maunakea, it was important to us to pick something that was both culturally and astronomically significant.”

In June 2026, three more local students from Keaʻau High School and Kamehameha Schools joined the Project Hōkūlani internship program. Mylin Wilson, Manu Silva-Sampaio, and Samantha Silva-Sampaio shared many of the same goals as their predecessors, and built upon their work by creating a name for the new image of NGC 7253.

The chosen name, Nā ʻUhane Māhoe Huki Pū i ke Ola, is inspired by the dual nature of the interacting galaxies and symbolizes the transformative experience the students had during their summer internship. Each portion of the name corresponds to a different part of the interns’ experience.

Nā ʻUhane Māhoe represents the two similarly sized galaxies and their wispy spiral arms. It also represents the twin nature of the International Gemini Observatory, composed of the Gemini North telescope in Hawai‘i and the Gemini South telescope on Cerro Pachón in Chile.

“ʻUhane (spirit) was an important theme for our group. Our experiences throughout the week — ʻoli (stargazing), visiting the summit, and learning about the awesome scientific discoveries made possible by Maunakea — ignited our own spirits as we prepare for life after high school,” says Samantha Silva-Sampaio.

“ʻUhane in this image reminds us that astronomy is not just science or spirit; it's both at the same time,” adds Manu Silva-Sampaio.

Huki Pū represents the physical and literal aspect of the galaxies being pulled together, driven by the force of each other's gravity. It also represents the communities that came together to make Project Hōkūlani a reality.

“Many people from around the world and different areas of expertise came together to make our internship possible, and we learned so much from everyone,” says Wilson. “Our experience, and astronomy itself, is a kākou (collective) type of practice.”

Finally, i ke Ola represents the life that can be created by interacting galaxies. To choose a fitting name for this image, the interns researched interacting galaxies and galaxy mergers. They learned that when spiral galaxies begin to merge, the gas and dust in their spiral arms collide, causing a significant burst in star formation. Extremely hot radiation from the newly born stars ionizes, or energizes, the surrounding gas. When atomic hydrogen is ionized, it forms what are known as H II (pronounced “h-two”) regions, which are visible in this image as concentrations of bright pink light. Manu Silva-Sampaio says, “Stars are sources of life and health for us as human beings, because our Sun is a star, and we cannot live without it.”

Project Hōkūlani operates through a partnership between the International Gemini Observatory and the Project Hōkūlani team at the University of Hawaiʻi at Mānoa. Project Hōkūlani supports middle and high school students in entering postsecondary science, technology, engineering, and math (STEM) fields through strengths- and work-based enrichment programs.

This image was taken as part of the NOIRLab Legacy Imaging Program — a continuation of the program started at the International Gemini Observatory in 2002, called the Gemini Legacy Imaging Program. Its aim is to use observing time on NOIRLab telescopes that is dedicated to acquiring data specifically for color images to share with the public.

Through both of these programs, six local high school students on Hawaiʻi Island get to contribute to the selection, imaging, and naming of a new astronomical image from the Gemini North telescope on Maunakea each year.

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

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More information

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.

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Links

• Explore Nā ʻUhane Māhoe Huki Pū i ke Ola in more detail
• Learn more about Project Hōkūlani
• Photos of the Gemini North telescope
• Videos of the Gemini North telescope
• Check out other NOIRLab Photo Releases

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Contacts:

Leinani Lozi
Hawaiʻi Education and Engagement Manager
International Gemini Observatory/NSF NOIRLab
Email: leinani.lozi@noirlab.edu

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

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An inside-out view of active supermassive black holes and their host galaxies September 01, 2026

Different telescopes reveal different signatures of active black holes. LOFAR (left) detects radio jets; WISE (centre) detects hot dust; SDSS/MaNGA (right) provides spatially resolved optical spectra of stars and gas. Credits: ASTRON, NASA/JPL-Caltech, SDSS, MPA

A schematic view of the proposed AGN population sequence created with the help of AI. Left: a radiative AGN with abundant gas and a prominent dusty torus, typical of star-forming hosts. Centre: a mixed AGN with compact radio emission alongside radiative signatures. Right: a radio-dominated AGN with extended jets, typical in quiescent hosts. This is a map of connected AGN-galaxy states, not a timeline for any individual galaxy. Credit: MPA/G. Jin

Host-galaxy properties change systematically from the nucleus outward for different AGN types. Each column shows one AGN class, with radial profiles of star formation (top), stellar age (middle), and gas ionisation (bottom); grey lines show reference profiles for normal galaxies. Infrared and optical AGN hosts show enhanced central star formation and younger stellar populations, while radio AGN hosts resemble quiescent galaxies at all radii. Credit: SDSS, MPA/G. Jin

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Active supermassive black holes do not all look the same. Some are obscured by hot dust, some are surrounded by fast-moving ionised gas, and some can eject giant radio jets extending over millions of light-years. By mapping about two thousand such objects from their galactic centres outward, researchers at the Max Planck Institute for Astrophysics found that these variations are related to the properties of their host galaxies. Infrared and optical AGNs are found in star-forming galaxies with young centres and ionised winds, whereas radio AGNs are mostly found in older, quieter systems. A small group showing both kinds of activity sits in between.

Seeing Active Black Holes in a Different Light

An active galactic nucleus (AGN) can appear in several forms, such as a hot, dusty torus that glows in infrared light; broad emission lines from gas moving close to the black hole; narrow lines from gas farther out; or a radio jet blasting away from the centre. Some of this diversity is simply due to our viewing angle. For example, an AGN seen edge-on through its dusty torus looks different from one seen face-on. However, orientation alone cannot explain everything. A long-standing question is whether these different 'faces' of AGN activity are also connected to what is happening in the surrounding galaxy, and if so, how.

From the Nucleus to the Outskirts

To find out, the team combined data on around ten thousand nearby galaxies, including nearly two thousand identified AGNs, taken from three surveys, each of which contributes a different piece of the picture. WISE, an infrared satellite, reveals hot dust. MaNGA is an integral-field spectroscopic survey that supplies optical AGN signatures and spectra at multiple positions across each galaxy. This allows the team to map properties rather than just measuring them in aggregate. LoTSS, a state-of-the-art radio survey using the LOFAR telescope, traces synchrotron emission from jets. Together, these datasets enable the researchers to trace the evolution of each galaxy from its inner regions to its outskirts.

The first differences appear in the central regions. Galaxies hosting infrared AGN exhibit the clearest boost in central star formation, forming stars at a faster rate near their nuclei than similar galaxies without AGN activity. These infrared and optical AGN hosts also have younger stellar populations at their centres, as determined by a spectral indicator of stellar age. In contrast, radio AGN hosts have old central populations and reduced central star formation, much like normal quiescent galaxies. The simultaneous presence of black-hole growth and central star formation in the same populations is consistent with both processes being fed by the same gas supply, though the data do not show one triggering the other. The gas emission and kinematics also carry the AGN's signature. Infrared, broad-line and narrow-line AGNs all exhibit stronger gas ionisation towards the centre, and this excess compared to normal galaxies extends over several kiloparsecs before fading. Fast-moving, ionised winds are strongest in infrared and broad-line AGNs, and their average signal extends to around 2 kiloparsecs from the nucleus. Radio AGNs show no comparable outflow on average. These winds clearly disturb the ionised gas around the black hole. However, the data do not show that star formation is immediately shut down by the current AGN. The link between black-hole and stellar growth is strongest near the centre and gradually weakens towards the outskirts.

A Bridge Between AGN Modes

A small group of AGNs exhibits both optical/infrared and radio signatures. Several independent measurements show that these 'mixed' AGNs lie between the radiative and radio-dominated populations, providing an observational link rather than a clear boundary between the two. Their radial star-formation profiles lie between those of optical/infrared-only and radio-only AGNs. Their stacked spectra reveal a combination of strong emission lines and a significant 4000-Ångström break, suggesting ongoing black-hole accretion within an ageing stellar population. While their radio emission is present, it remains relatively compact compared with the extended jets of radio-only AGNs.

What's missing?

Several observations could clarify this picture. Molecular gas from CO observations would reveal the fuel reservoir directly. X-ray observations could reveal the hot atmospheres thought to exist around radio-mode AGNs. Higher-resolution radio images would clarify whether the compact jets in mixed AGNs are younger. Comparing these with spatially resolved simulations would reveal whether the observed states arise from one evolutionary route or several. Ultimately, these observations will reveal whether the empirical map uncovered here reflects a common evolutionary route, repeated cycles or multiple paths through black hole and galaxy growth.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Authors:

Jin Gaoxiang
PhD student
Tel: 2298
Email: gxjin@mpa-garching.mpg.de

Guinevere Kauffmann
Director
Tel: 2013
Email: gamk@mpa-garching.mpg.de

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Original publication

Jin et al.
'A spatially resolved evolutionary sequence of multi-wavelength AGN host galaxies
Monthly Notices of the Royal Astronomical Society, Volume 546, Issue 4

DOI

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