The Neutron Star That Doesn't Stop Spinning Up

A combined optical, H-alpha, and X-ray image of NGC 7793, indicating the position of the remarkably bright X-ray source P13. Image credit: NASA/CXC/ESO/VLT/NOAO/AURA/NSF/Univ of Strasbourg/M. Pakull et al. Download Image

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Last week, NuSTAR performed the first of two planned observations of the ultraluminous X-ray source NGC 7793 P13. Like its fellow ultraluminous source M82 X-2, P13 is a pulsar, meaning that its extraordinary luminosity comes from extreme levels of accretion onto a tiny neutron star, and its spin period decreases over time as the accreting material spins it up by adding angular momentum. Every now and again, P13 appears to fade dramatically in brightness but, unusually for this class of objects, when it returns to its usual luminosity again its rate of spin has increased further rather than slowing down, suggesting that it doesn't stop spinning up even when it is in a faint state. Additionally, this binary system has an orbital period a little over 60 days long, with a variation in the ultraviolet emission that is very slightly out of sync with it, which might indicate some unusual interaction between different parts of the accreting system. These NuSTAR observations will continue to track its changing period over time, helping to piece together the shape of this system and the reasons for its strange behavior.

Author: Hannah Earnshaw (NuSTAR Project Scientist, Caltech)

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

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Hunting for the Source of Superfast Electrons with NuSTAR

A multi-wavelength image of the supernova remnant shell of PWN G0.9+0.1, combining high-energy X-ray data from NuSTAR (green), low-energy X-ray data from XMM-Newton (blue), and radio data from MeeRKAT (red). The pulsar remnant of the supernova explosion is the compact X-ray source at the center of the image, while the brighter cnewsompact X-ray source to the lower right is unrelated. The radio data shows the shape of the nebula, as well as the fainter outer shell of the supernova remnant. Image credit: Brunelli et al. (2026)/MeerKAT (Heywood et al. 2022)/H. Earnshaw. Download Image

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Earth is continuously bombarded with cosmic rays—particles such as protons and electrons flying through space incredibly fast. The faster a particle travels, the more energy it has, and a small fraction of these cosmic rays have energies greater than a petaelectronvolt, or PeV. This is about the energy of a buzzing housefly, which might not seem like a lot, but it's all contained in one single, incredibly energetic electron moving at mind-blowing, relativistic speed. Accelerating electrons to such extreme speeds takes a cosmic-scale particle accelerator, which astronomers have nicknamed a 'PeVatron'. But what kind of astronomical source could be capable of such a feat?

Pulsar wind nebulae are some of the most fascinating objects in our Galaxy. They are created in the aftermath of a supernova, the explosion of a massive star at the end of its life when it has exhausted its fuel supply. Supernovae usually leave behind a compact remnant, either a black hole or a neutron star, and a rapidly spinning neutron star can appear to pulse, almost like a light house. This inspired the term “pulsar” to describe such remnants. A rapidly spinning pulsar will illuminate the extended bubble of outflowing material from the explosion, producing highly energetic particles accelerated by the strong magnetic field of the nebula. Pulsar wind nebulae can be detected at X-ray and even gamma-ray energies, making these cosmic powerhouses ideal candidates in the hunt for PeVatrons.

Dr. Kaya Mori of Columbia University is leading a large program with NASA’s NuSTAR X-ray satellite to hunt for PeVatrons in pulsar wind nebulae in our Galaxy. NuSTAR is the first satellite to focus high-energy X-ray photons, making it the most sensitive instrument for studying the Universe at X-ray energies above 10 keV, roughly the energy of X-ray machines you'd find at a hospital. One of the nebulae studied is this program is G0.9+0.1, a young supernova remnant in the Galactic Center. In a recent paper published in the Astrophysical Journal led by PhD student Giulia Brunelli at INAF Bologna, high-energy X-ray data from NuSTAR is combined with multiwavelength data from radio and gamma-ray observatories. Modeling these observations, the team determined that this pulsar wind nebula is very young—about 2,200 years old—and capable of accelerating electrons up to 2 PeV. This makes G0.9+0.1 a compelling PeVatron candidate, meaning that it—and perhaps other pulsar wind nebulae churning away in the Galactic Center—may be one of the objects responsible for some of the highest-energy particles arriving at Earth.

Source: NASA's Nuclear Spectroscopic Telescope Array (NuSTAR)/News Release

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How Galaxies Keep the Fuel Flowing

Montage of the NOEMA Telescopes and the detected massive disk galaxies with spiral arms and bars that actively transported cold gas inward. © Jean-Baptiste Jolly

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Spiral Arms and Bars Drive Gas Transport at Cosmic Noon

Studies from the Infrared & Submillimeter Astronomy Group at the Max Planck Institute for Extraterrestrial Physics (MPE) using NOEMA and JWST reveal that during cosmic noon, massive disk galaxies with spiral arms and bars actively transported cold gas inward. This process sustained star formation by distributing gas efficiently across galactic disks, challenging previous views of early chaotic galaxies.

Galaxies need a continuous supply of cold gas to form new stars. This was especially true during "cosmic noon", roughly 8 to 10 billion years ago, when galaxies across the universe were forming stars at rates far exceeding those seen today. A key question in galaxy evolution is therefore how this gas was distributed within galaxies, and how it was transported from the outer disk into the regions where stars, bulges, and central black holes form and grow. Two new studies from the NOEMA3D survey, led by the Infrared-Submillimeter-Astronomy Group at the Max Planck Institute for Extraterrestrial Physics (MPE) and collaborators, now provide one of the clearest observational views yet of these processes.

Using the NOrthern Extended Millimeter Array (NOEMA), a radio interferometer located in the French Alps, the team obtained the deepest millimeter-wave observations to date of cold molecular gas — traced via CO emission — in ten massive, star-forming galaxies at redshifts z ~ 1.1–1.6. With integration times of typically more than 20 hours per galaxy, the NOEMA3D survey resolves both the distribution and kinematics of molecular gas on kiloparsec scales. These observations were combined with high-resolution infrared imaging from the James Webb Space Telescope (JWST), which reveals the underlying stellar structure of the same galaxies in unprecedented detail.

What JWST shows is itself striking: many of these distant systems are not the chaotic, merger-dominated objects that early galaxies were long assumed to be. Instead, they are well-ordered disk galaxies with clear spiral arms and, in four out of ten cases, bars. Structural features previously thought to be rare or absent at these redshifts.

The NOMA3D sample: 10 large massive galaxies on the star forming main sequence, at 1.1 < z < 1.6, showing clear spiral arms and for 4 of them bars. © Jean-Baptiste Jolly

G4_38065 is a massive spiral galaxy at z = 1.12. The velocity residuals, obtained by subtracting a model velocity map from the observed one, show clear patterns along the spiral arms which we interpret as inflowing gas refueling the galaxy. © Jean-Baptiste Jolly

Cold Gas Distribution Supports Star Formation Across Galactic Disks

The first study analyzes the kinematics of the molecular gas. All ten galaxies show ordered rotation consistent with a rotating disk. But after subtracting the best-fitting disk model, coherent velocity residuals remain in nearly every system, gas motions that cannot be accounted for by simple rotation alone. These residuals reach typical in-plane velocities of 50 to 100 km/s, substantially larger than comparable non-circular motions in nearby disk galaxies. Crucially, they are spatially correlated with the non-axisymmetric structures seen in the JWST images: spiral arms and bars. “For the first time, we can directly link spiral arms and bars to the motions of cold gas within galaxies,” says Jean-Baptiste Jolly. “This provides compelling evidence that these structures were already driving gas transport when the Universe was at the peak of its star-forming activity.”.

Spiral arms and bars are therefore not merely aesthetic features in galaxy images. They are dynamical structures that actively redistribute gas within the disk. When interpreted as radial inflows, the inferred molecular gas transport rates are often comparable to the galaxies' star formation rates, of order tens of solar masses per year. Such flows could move gas inward to feed central star formation, contribute to the growth of bulges, and potentially supply material to central supermassive black holes.

The companion study examines where the cold gas and dust are actually located. Comparing the spatial distributions of CO emission, neutral carbon [C I], dust continuum, stars, and star formation across the same ten galaxies, it finds that molecular gas and dust are generally extended over the full galactic disk, with sizes broadly comparable to the stellar component. This stands in sharp contrast to merger-driven compact starburst galaxies at similar redshifts, where dust and star formation are typically concentrated in small central regions. The resolved measurements further show that both the molecular gas fraction and the gas depletion time remain broadly flat across the disk, out to approximately twice the stellar effective radius. “The depth of the NOEMA observations allows us to trace the cold-gas reservoirs that fueled galaxy growth during cosmic noon,” says Jianhang Chen. “We can now see, in unprecedented detail, how galaxies sustained star formation across their disks over billions of years.”

Taken together, the two studies present a coherent picture of how massive disk galaxies sustained their star formation during a crucial epoch in cosmic history. Gas was present across the full disk; star formation proceeded with broadly similar efficiency at different radii. Internal structures, like spiral arms and bars, provided an efficient mechanism for moving gas inward. The NOEMA3D observations thereby connect the large-scale gas reservoirs of galaxies to the internal dynamical processes that regulate their growth.

These results also highlight the power of combining NOEMA and JWST. NOEMA provides the cold-gas kinematics and molecular gas maps; JWST reveals the stellar structures that shape the gas motion. Only by combining both telescopes can the link between morphology and gas dynamics be directly observed.

The broader implication is significant. By z ~ 1–2, massive star-forming galaxies already possessed organized disks with spiral arms and bars capable of driving significant gas transport. These structures likely played an important role in keeping galaxies on the star-forming main sequence and in shaping the buildup of disks, bulges, and black holes over cosmic time. The findings challenge the long-held view that early galaxies were predominantly turbulent and merger-driven. Many were already mature, well-ordered systems — not unlike our own Milky Way, but younger and considerably more active.

Source: Max Planck Institute for Extraterrestrial Physics/News

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Contacts:

Dr. Jean-Baptiste Jolly
Postdoc Infrared-Group
Tel: +49 89 30000-3335
Email: jbjolly@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching

Dr. Jianhang Chen
Postdoc Infrared-Group
Tel: +49 89 30000-3374
Email: jhchen@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching

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Original Publication

1. Chen, J., L. Tacconi, R. Genzel, R. Neri, K. Schuster, N. Förster Schreiber, J.-B. Jolly et al.
NOEMA3D: Spatially resolved dust, CO, and [C I] in massive star-forming main sequence galaxies at cosmic noon
A & A

DOI

2. Jolly, J.-B., L.J. Tacconi, R. Genzel, R. Neri, K. Schuster, J. Chen et al.
NOEMA3D: Resolving radial gas flows in disk galaxies at z ∼ 1.1 − 1.6 with high-resolution CO observations
A & A

Source | DOI

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Further Information

Series: Research Highlight

The series “Research Highlight” features a scientific highlight of MPE researchers.

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Galaxy Evolution with SINS/KMOS3D/ PHIBSS/NOEMA3D/ GALPHYS

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NOEMA in the search for our origins

September 22, 2014

With the official inauguration of the first of six planned NOEMA antennas on 22 September, the Max Planck Society and its partner institution IRAM are taking a crucial step towards one of the largest Franco-German projects in astronomy: the expansion of the Plateau de Bure observatory in the French Alps into the most powerful and most sensitive millimetre radio telescope in the northern hemisphere. The scientists are hoping that this state of the art observatory will provide answers to questions about our origins and the formation of the universe.

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Tracing the Origins of Mysterious Gas Clouds near the Galactic Center

April 08, 2026

New observations and simulations by a team of researchers led by MPE reveal that a massive binary star near our Galaxy’s center is responsible for creating a series enigmatic gas clouds — compact gas clumps that help feed the supermassive black hole Sagittarius A*.

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ALMA and VLA Reveal a Vast Reservoir of Star-Forming Fuel in a Galaxy Near Cosmic Dawn

Image of the galaxy REBELS-25, taken by the Atacama Large Millimeter/submillimeter Array (ALMA).
Credit: ALMA (ESO/NAOJ/NRAO)/L. Rowland et al.

This illustration traces the universe’s evolution from the Big Bang to the present day, highlighting REBELS-25, a very distant galaxy seen during the Epoch of Reionization 13 billion years ago. New deep observations with the NSF VLA and ALMA reveal that REBELS-25 already had an enormous reservoir of cool molecular gas—the direct fuel for star formation—when the universe was just 700 million years old.

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Highlights

• Astronomers used ALMA and the NSF Very Large Array (VLA) to detect molecular gas in REBELS-25, a massive star-forming galaxy observed just 700 million years after the Big Bang.

• The observations reveal a reservoir of roughly 100 billion solar masses of cool gas — the raw fuel for star formation — in one of the earliest and most distant galaxies ever studied in this way.

• The VLA achieved the most distant detection to date of a key molecular gas tracer, while ALMA provided a detailed picture of the galaxy’s star-forming environment.

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Astronomers have directly detected a vast reservoir of cool molecular gas in REBELS-25, a massive star-forming galaxy seen just 700 million years after the Big Bang. The discovery, made using the NSF Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), provides a rare direct measurement of the star-forming fuel available to a galaxy in the early universe.

REBELS-25 is observed at a cosmic distance so vast that its light has been stretched – or redshifted – by the expansion of the universe to a redshift of z = 7.31. Astronomers see the galaxy as it was roughly 13 billion years ago, during the Epoch of Reionization — the period when the first stars and galaxies were transforming the young universe, just 5% of its current age.

Galaxies grow by turning gas into stars, and molecular gas is the primary raw material for that process. Until now, astronomers had strong indirect evidence that some early, massive galaxies contained large gas supplies, but directly detecting this material at such early cosmic times has been extremely difficult.

The team, led by Karin Cescon of Leiden University, used deep VLA observations to search for faint radio emission from carbon monoxide, or CO, a molecule commonly used to trace molecular gas. The VLA detected a low-energy CO transition that traces relatively cool gas – the most distant detection of this kind ever reported, and the first in a star-forming galaxy this early in cosmic history.

“Our results show galaxies just 700 million years after the Big Bang already contained large reservoirs of cold gas available for star formation,” said Karin Cescon, PhD student at Leiden University and lead author. “With these deep NSF VLA observations, we were able to overcome the observational challenges posed by the cosmic microwave background.”

That background – the ancient glow of radiation left over from the early universe – makes these observations especially challenging. At high redshift, it is warmer and brighter than it is today, like trying to spot a faint light against an increasingly bright sky. By accounting for this effect, the team derived a molecular gas mass of roughly 100 billion solar masses, a figure independently supported by modeling of both the CO and dust emission.

ALMA played a crucial role in completing the picture. Its observations detected higher-energy carbon monoxide emission and provided measurements of dust and ionized carbon, together revealing the gas’s physical conditions and confirming that the CO emission lines up spatially with other star-formation tracers. The results confirm that REBELS-25 is strongly gas-dominated, with a reservoir large enough to sustain vigorous star formation. They also suggest that ionized carbon emission, one of ALMA’s most powerful tools for studying early galaxies, remains a viable – if imperfect – tracer of molecular gas at these distances.

“This NSF VLA detection is an exciting sneak peek of what’s to come with the ngVLA,” noted Karin’s PhD advisor, Professor Jacqueline Hodge. “The ngVLA will allow us to find and study cool gas in many more young galaxies, including those at even earlier times. This will be crucial for understanding how the first galaxies formed and grew.”

The discovery helps explain how some early galaxies grew so large, so fast. The direct confirmation of such a massive gas reservoir – assembled when the universe was still in its infancy – places REBELS-25 among the most informative laboratories for studying how galaxies built up their ordinary matter, formed stars, and enriched the chemical content of their interstellar medium during the first billion years of cosmic history.}

Together, ALMA and current and future radio facilities are opening a new window onto the fuel supply of the earliest galaxies. Expanding the sample of galaxies with these kinds of measurements at z>7 will be essential for understanding how efficiently the first galaxies formed stars – and ultimately, how the universe came to look the way it does today.

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

Scientific Paper

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Additional Information

This research is presented in “Direct detection of cool molecular gas in a star-forming galaxy at z = 7.31,” by K. Cescon et al., published in Monthly Notices of the Royal Astronomical Society.

The Atacama Large Millimeter/submillimeter Array (ALMA) data used in this study include observations from project 2021.1.01495.S. The VLA observations are available under project 21A-335.

This article is based on the original press release by the U.S. National Science Foundation National Radio Astronomy Observatory (NRAO), an ALMA partner on behalf of North America.

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

Jill Malusky
Public Information Officer
NRAO
Phone: +1 304-456-2236
Email: jmalusky@nrao.edu

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Phone: +49 89 3200 6670

Email: press@eso.org

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

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'Crisis averted' as experts confirm universe's expansion IS accelerating

Studying Type Ia supernovae – violent, luminous white dwarf star explosions – led to the Nobel Prize-winning discovery that the universe's expansion is accelerating. This image combines data from four space telescopes to create a multi-wavelength view of all that remains of RCW 86, the oldest documented example of a supernova. Credit: X-ray: NASA/CXC/SAO & ESA; Infared: NASA/JPL-Caltech/B. Williams (NCSU)

Licence type: Attribution (CC BY 4.0)

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Our universe's expansion is still accelerating despite recent claims suggesting otherwise, an international team of astrophysicists say.

They refuted a study published last year claiming the growth of the universe is slowing and insist there is no flaw in the widely-accepted theory that a mysterious force known as dark energy is driving the expanding cosmos.

The researchers, who include two Nobel Laureates and represent institutions worldwide, say the debate that followed last November’s revelations was the result of a scientific misunderstanding rather than a cosmic grenade threatening to blow apart everything we know about the universe.

Their paper has been published today in Monthly Notices of the Royal Astronomical Society.

It is a direct rebuttal of a study by a team of South Korean researchers that made the erroneous claim the universe's expansion may have entered a deceleration phase, caused by the influence of dark energy – which acts as a kind of anti-gravity – weakening over time.

"The previous and well accepted measurements were, in fact, fine and our current understanding of the fate of the universe remains robust," said lead author Dr Phil Wiseman, from the University of Southampton.

"Thankfully we have averted this crisis, but the mystery about why the rate of expansion of the universe is still accelerating remains.

"By proving our measurements are correct, we can get back to trying to understand what this dark energy actually is, rather than wondering if it exists at all."

The international team of researchers involved in the new study included Professor Adam Riess and Professor Brian Schmidt, who won the 2011 Nobel Prize in Physics alongside Professor Saul Perlmutter.

The trio studied Type Ia supernovae – violent, luminous white dwarf star explosions – and determined that more distant objects appeared to move faster, leading to their conclusion that the universe's expansion was accelerating.

This has been the globally-accepted theory ever since, although last year's research by the South Korean team threatened to upset the apple cart. It claimed that, as the universe aged, these supernovae had different maximum brightnesses, tricking astronomers into thinking the cosmos was accelerating when it was in fact slowing.

But the University of Southampton-led researchers found an error in how the age of these stars was estimated. They say the previous findings incorrectly assumed the age of a galaxy was the same as the age of the star that exploded.

The experts also said the South Korean paper failed to account for the mass of host galaxies, a standard correction used in modern cosmology to prove accuracy.

Professor Riess added: "Extraordinary claims require especially careful testing.

"What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent."

Professor Mark Sullivan, also from the University of Southampton, said challenging accepted theories and observations was fundamental to science.

"This is how progress is made. Although this idea did not turn out to be correct, it has opened up new ways of thinking about how supernovae explode and how we can measure dark energy more accurately," he added.

Fellow co-author Dr Brodie Popovic agreed. "We've recently been really focused on astrophysics of the explosions and how they impact cosmology," he said.

"This was a good opportunity to go back and go over all of our assumptions – it turns out, yes, we do understand this stuff and we're accounting for it in our cosmology measurement."

Source: Royal Astronomical Society (RAS)/Latest News

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Media contacts:

Sam Tonkin
Royal Astronomical Society
Mob: +44 (0)7802 877 700
Email: press@ras.ac.uk

James Haigh
University of Southampton
Mob: +44 (0)7584 368684
Email: J.haigh@soton.ac.uk

Science contacts:

Dr Phil Wiseman
University of Southampton
Email: P.S.Wiseman@soton.ac.uk

Dr Brodie Popovic
University of Southampton
Email: B.A.Popovic@soton.ac.uk

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Images & video

Supernova

Caption: Studying Type Ia supernovae – violent, luminous white dwarf star explosions – led to the Nobel Prize-winning discovery that the universe's expansion is accelerating. This image combines data from four space telescopes to create a multi-wavelength view of all that remains of RCW 86, the oldest documented example of a supernova. Credit: X-ray: NASA/CXC/SAO & ESA; Infared: NASA/JPL-Caltech/B. Williams (NCSU)

Type Ia supernova animation

Caption: This animation shows the explosion of a Type Ia supernova, where the white dwarf's gravity steals material away from a nearby stellar companion until it can no longer sustain its own weight and blows up. Credit: NASA/JPL-Caltech

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Further information

The paper 'Still Accelerating: Type Ia supernova cosmology is robust to host galaxy age evolution' by Wiseman et al. has been published in >Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stag797.

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Notes for editors

About the Royal Astronomical Society

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

The RAS organises scientific meetings, publishes international research journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of successful peer review, following which experts on the Editorial Boards accept the papers for publication. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

Keep up with the RAS on Instagram, Bluesky, LinkedIn, Facebook and YouTube.

Download the RAS Supermassive podcast

Submitted by Sam Tonkin on Thu, 11/06/2026 - 00:01

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NASA Webb, Hubble Reveal History of Relic of Milky Way’s Formation

Bulge Fossil Fragment Terzan 5 (Webb and Hubble Image)

New observations from Webb combined with multiple observations from Hubble prove that Terzan 5 is a self-contained, self-enriching stellar system that contains up to four distinct star populations. It orbits within our Milky Way galaxy’s central bulge.Credit Image: NASA, ESA, CSA, STScI, Giorgia Zullo (University of Bologna), Francesco Ferraro (University of Bologna); Image Processing: Alyssa Pagan (STScI)

Terzan 5 (Webb and Hubble Compass Image)

Yhis image of bulge fossil fragment Terzan 5 was captured by the James Webb and Hubble space telescopes. Webb’s data are from its NIRCam (Near-Infrared Camera) and Hubble’s from its Advanced Camera for Surveys (ACS). The image shows a scale bar, compass arrows, and color key for reference. The scale bar is labeled in light-years along the bottom, which is the distance that light travels in one Earth-year. (It takes two years for light to travel a distance equal to the length of the scale bar.) One light-year is equal to about 5.88 trillion miles or 9.46 trillion kilometers. The north and east compass arrows show the orientation of the image on the sky. Note that the relations hip between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). This image shows visible and near-infrared wavelengths of light that have been translated into visible-light colors. The color key shows which NIRCam and ACS filters were used when collecting the light. The color of each filter name is the visible-light color used to represent the infrared light that passes through that filter. Credit Image: NASA, ESA, CSA, STScI, Giorgia Zullo (University of Bologna), Francesco Ferraro (University of Bologna); Image Processing: Alyssa Pagan (STScI)

Zoom to See Terzan 5 Near Our Milky Way Galaxy’s Bulge

Zoom in to Terzan 5, a star cluster that lies within the crowded central region of our Milky Way galaxy known as the bulge. The scene starts with a ground-based image of our Milky Way bulge and zooms in on and circles Terzan 5, ending with the composite image of the star system from the James Webb and Hubble Space Telescopes. The Milky Way is shaped like a giant fried egg. The yolk in the middle is the galactic bulge, a crowded region packed with ancient stars of various masses and brightnesses. It’s also home to a number of globular star clusters that formed early in our galaxy’s history, which typically have only one ancient star population. In contrast, Terzan 5 was recently reclassified as a bulge fossil fragment because it has four generations of stars and has maintained its separate identity. Credit Video: NASA, ESA, CSA, Alyssa Pagan (STScI); Acknowledgment: ESO, Pan-STARRS, DSS2, Akira Fujii

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Researchers using two of humanity’s most powerful observatories — NASA’s James Webb and Hubble Space Telescopes — have definitively shown that Terzan 5 is not a globular star cluster as it was once classified, offering new insight into how galaxies like our own form and evolve over time. A globular star cluster typically has only one ancient star population. New data not only confirms the existence of two distinct populations of stars in Terzan 5, but also provides evidence for two more recent rounds of star formation. Although located within the crowded bulge of our Milky Way, our galaxy’s central, spherical region of older stars, Terzan 5 was massive enough to maintain its separate identity while lighter weight systems spread out and mixed to form the bulge billions of years ago. It’s like a lump in an otherwise well-mixed cake batter.

“Webb’s new near-infrared observations, cross-referenced with Hubble’s archival observations, have given us a much clearer picture of the history of Terzan 5,” said Giorgia Zullo, who led the research and is a PhD student at the University of Bologna in Italy.

These results were presented at a press conference Tuesday at the 248th meeting of the American Astronomical Society in Pasadena, and were published in Astronomy & Astrophysics.

Four generations of stars

Discovered in 1968 by astronomer Azop Terzan, Terzan 5 resembles a globular cluster in many ways. However, in 2009 this system was discovered to harbor two distinct populations of stars. In 2016 Hubble provided the first estimate of their ages, showing that one formed roughly 12 billion years ago — as the Milky Way itself was assembling — and the other about 5 billion years ago, just before Earth started forming. This pointed to a more complex history than a typical globular cluster.

Studying Terzan 5 is complicated by its location in a region of our galaxy crowded with stars and heavily obscured by dust. This is where Webb stepped in. Its infrared view allowed the research team to peer through the dust and catalog many more stars, and fainter stars, than previous work. By measuring star colors and brightnesses, astronomers can classify them into populations of different ages and chemistries.

Webb was able to measure these key properties for every star within the field of view in the sky — both stars within Terzan 5 and unrelated foreground stars. To isolate the stars of Terzan 5, the team relied on the power and longevity of Hubble. The 12-year separation allowed the team to measure very small movements of individual stars, known as proper motions, to determine which stars belong to Terzan 5 and which are part of the Milky Way bulge.

By combining data from both Webb and Hubble, the researchers found strong evidence for two more stellar populations, one that formed 3.8 billion years ago and another only 2.5 billion years ago. They also were able to determine the ages of the previously known stellar populations with unprecedented precision, finding that they formed 12.5 billion and 4.7 billion years ago.

With the previously known two generations of stars, astronomers could not rule out the possibility that Terzan 5 interacted with another object, like a globular cluster or a giant molecular cloud, becoming enriched with new gas and dust that set off a second round of star formation. With four stellar generations, those explanations are ruled out.

Measurements of the stellar composition of Terzan 5 populations made at the W. M. Keck Observatory and European Southern Observatory’s Very Large Telescope also point toward very distinct populations. “Along with the ages of these populations, the cluster preserves a fossil record of progressive enrichment of heavy elements by supernovae,” said co-author R. Michael Rich, a research astronomer at the University of California, Los Angeles. Terzan 5 formed multiple generations of stars because it was able to retain the necessary raw materials. There is evidence of powerful supernova explosions in Terzan 5 that forged heavier elements that were swept up by subsequent generations of stars. In lighter weight systems, the force of the explosions themselves could have ejected the resulting elements as well as sweeping out leftover gas and dust. The progenitor of Terzan 5 had enough mass to retain those stars’ ejections, allowing new generations of stars to form over billions of years.

‘Bulge fossil fragment’

The results show that Terzan 5 is most likely the remnant of a much more massive stellar system that initially formed 12.5 billion years ago. Terzan 5 is extraordinary because it survived — and never merged or fully “mixed in” with the Milky Way’s bulge. “For some reason, this peculiar clump of stars formed separately from the bulge and was not destroyed as the bulge itself formed,” said Francesco R. Ferraro, a professor at the University of Bologna and principal investigator of the Webb observations. “Terzan 5 is what we now call a bulge fossil fragment because it resembles the primordial clumps that contributed to the formation of the bulge.”

To date, there’s one other known cosmic object like Terzan 5. Liller 1 was the second to be reclassified from a globular star cluster to a bulge fossil fragment. It also contains multiple generations of stars. There may be more objects like it. Between 40 to 50 additional globular clusters that orbit within the bulge will be examined by Ferraro’s team to determine if their stellar populations are all the same, like globular clusters, or have several generations, like bulge fossil fragments.

Source: NASA's Hubble Space Telescope/News

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Details:

Last Updated: Jun 16, 2026
Location: NASA Goddard Space Flight Center

Contact Media:

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

Christine Pulliam
Space Telescope Science Institute
Baltimore, Maryland

Claire Blome
Space Telescope Science Institute
Baltimore, Maryland

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NASA Webb Finds Strongest Evidence Yet for ‘Black Hole Stars’

Abell S1063 with Pullout of GLIMPSE-17775 (NIRCam Image)

While the primary purpose of NASA’s James Webb Space Telescope’s observations of galaxy cluster Abell S1063 was to look for a certain population of stars, scientists obtained a detailed spectrum of GLIMPSE-17775 from the dataset. This little red dot is located behind Abell S1063. Credit Image: NASA, ESA, CSA, Vasily Kokorev (UT Austin); Image Processing: Alyssa Pagan (STScI)

Evidence of a 'Black Hole Star'

NASA’s James Webb Space Telescope captured the deepest spectrum to date of a little red dot. More than 40 spectral lines have been discerned from the data, many of which independently support the theory that GLIMPSE-17775 is a black hole enshrouded by a hot, dense gas cocoon. Credit Illustration: NASA, ESA, CSA, Vasily Kokorev (UT Austin); Designer: Leah Hustak (STScI)

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The complex puzzle known as little red dots has become more complete since their initial discovery by NASA’s James Webb Space Telescope in 2022. Now a particular little red dot’s spectrum is helping connect many of the pieces.

A team of astronomers led by Vasily Kokorev at the University of Texas at Austin identified the lucky dot in question: GLIMPSE-17775. By carefully analyzing the dot’s spectrum captured by Webb — the deepest spectrum to date of a little red dot — the research team has identified multiple lines of evidence, all of which support the interpretation that GLIMPSE-17775 is a supermassive black hole enveloped in a dense cocoon of partially ionized gas, a model referred to as the BH* (black hole star) scenario. A paper describing the results was published today in The Astrophysical Journal.

“I think part of the scientific community is converging on a singular picture — that little red dots can be explained by black hole star models. But none of the previous little red dots have all of the pieces of evidence in the same place,” said Kokorev, lead author of the study. “With GLIMPSE-17775 we can test these models because of how deep and amazing this source’s spectrum is.”

Connecting puzzle pieces

Soon after Webb first began science operations, it discovered a new, mysterious type of object in the very early universe – abundant red objects that emerged about 600 million years after the big bang. Scientists have explored multiple explanations for these little red dots, including the black hole star scenario.

A set of fortunate circumstances brought about this new, elaborate spectrum of a little red dot. The little red dot that would come to be known as GLIMPSE-17775 was fortunately included in Webb’s imaging and spectroscopy efforts for a project that sought to look for Population III stars and faint galaxies in galaxy cluster Abell S1063. This little red dot is more distant than the galaxy cluster and magnified by gravitational lensing. (GLIMPSE-17775 has a cosmological redshift of 3.5, meaning it existed about 1.8 billion years after the big bang.)

While Webb provided a 30-hour spectrum of the little red dot, the effect of gravitational lensing made it equivalent to 80 hours of telescope time. This combination of Webb’s infrared sensitivity and nature’s own “magnifying glass” amplified the amount of detail that could be gleaned from GLIMPSE-17775. The result was more than 40 spectral lines from this small, red source, which is the most detailed little red dot spectrum to date.

“When we saw the spectrum for the first time, it was like having all the pieces of a puzzle scattered on the floor,” said Kokorev. “We picked up each piece of the puzzle, measured the lines, and started combining the different pieces into a mosaic. Maybe a few pieces looked like nothing at first, but then a couple of them came together, and we realized that there was something there.”

The spectroscopic data collected by Webb contains multiple lines of evidence that support the interpretation that little red dot GLIMPSE-17775 is a black hole star: a rapidly accreting, or growing, black hole enveloped in a dense gas cocoon, which is reprocessing the light emitted from near the black hole and producing the features seen in the spectrum.

Lines of evidence

Among the 40-plus lines that the team detected in GLIMPSE-17775’s spectrum were various independent indicators that all align with the BH* scenario. For example, the team found that many of the spectral lines, such as hydrogen, oxygen, and helium, do not fit a simple model of a rotating gas cloud. Instead, the best fit model includes a broadening effect known as electron scattering, a telltale sign that a dense, layered gas cocoon is enshrouding this source.

The strength and ratios of certain lines to each other, most notably the 16 iron lines that compose what the team has dubbed an “iron forest” and certain oxygen lines, require a high-energy source to produce them, like a rapidly accreting black hole. Additionally, astronomers noted the fluorescence and absorption of helium in the spectrum, both of which individually suggest that there is a dense medium enveloping a powerful source.

The BH* scenario not only fits GLIMPSE-17775; it also accounts for why most little red dots are faint in X-rays, since any such emission is likely absorbed by the dense gas cocoon.

One missing element of the GLIMPSE-17775 puzzle piece is the part of the spectrum that would reveal what’s known as a Balmer break, or a strong dip in the emitted light that’s a signature characteristic of little red dots. To build a more comprehensive understanding of this little red dot, the team incorporated ancillary data from two observing programs that used NASA’s Hubble Space Telescope: the Frontier Fields and BUFFALO (Beyond Ultra-deep Frontier Fields And Legacy Observations) programs.

The Webb and Hubble data together help explain why the Balmer break is weaker than what typically is found in other little red dots: A giant host galaxy is surrounding GLIMPSE-17775. Although a little red dot’s host galaxy is not something that has been usually seen at such scale before, it isn’t inconsistent with the dense gas cocoon model. The black hole star model of little red dots attributes excess blue light to stars in the host galaxy.

When Webb first discovered little red dots, some researchers thought these objects had “broken cosmology,” unsure how galaxies could have grown so big so quickly in the early universe to account for all this light coming from their stars. However, the team believes the GLIMPSE-17775 puzzle piece fits nicely in the existing framework of the universe’s evolutionary history, because black hole masses don’t need to be as high in order to explain the broad emission lines.

“Everything fits, nothing is broken, and I think that makes the puzzle that is our universe even better,” said Kokorev. “Looking ahead, I’m eager to dive deeper and learn about what is powering the central engines of little red dots. While we think it’s a black hole, there are some other interesting theories being proposed, which is exciting. Maybe in a year or two, we’ll have the final answer to what powers these sources.”

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

Source: NASA's James Webb Space Telescope/News

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Details:

Last Updated: Jun 10, 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

Christine Pulliam
Space Telescope Science Institute
Baltimore, Maryland

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Webb unveils young stars across every stage of formation

Star-forming molecular cloud - Constellation Orion 

An area inside a star-forming molecular cloud. The background is covered with layers of gas and dust in blue, green and yellowish colours. Thicker clumps of cold dust, dark brown to black, block out light completely. Stars lie among and atop the clouds, from small orange ones to large white or blue ones. Waves and streams of glowing whitish gas are created by jets from protostars colliding with the surrounding material. Credit: ESA/Webb, NASA & CSA, T. Megeath, M. Zamani (ESA/Webb) - Acknowledgement: M. H. Özsaraç

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For this NASA/ESA/CSA James Webb Space Telescope Picture of the Month we return to the constellation Orion (the Hunter), a location familiar to Webb. This area of the sky is replete with star-forming clouds that make up a complex hundreds of light-years across. We find ourselves in the giant molecular cloud Orion A, of which the familiar Orion Nebula (also known as M42) is just a part; Webb has taken both close-up and wide-angle looks at M42 before.

The target of these observations, however, requires us to look behind the Orion Nebula. Behind the stars, gas and dust of M42 is a long, massive filament of cold gas and dust called (somewhat confusingly) the Orion Molecular Clouds, which is divided into four parts, OMC-1 through OMC-4. OMC-1 sits immediately behind M42, to the north are OMC-2 and OMC-3, and OMC-4 lies to the south.

This image shows just a small, northern portion of OMC-2, located 1280 light-years from Earth and a little north of the Orion Nebula. Every stage of star formation — from the youngest stellar embryos, to protoplanetary discs, to newly-minted pre-main sequence stars — is contained within just this scene, which stretches 150 light-years across. The intense star-forming activity has produced an impressive display of billowing outflows and sparkling stars atop swirling layers of gas and dark, obscuring clouds.

Molecular clouds such as OMC-2 are vast clumps of gas much more dense than the rest of interstellar space. This density allows complex molecules to form, protected from the radiation given off by other stars, and it means that gravity can cause the cloud to collapse and form stars. The earliest stage of this process is a protostar - a growing star that is being fed gas from the surrounding cloud through a spinning disc of gas. As gas falls onto the protostar, it heats up, powering the glow of the protostar. The immense amount of energy acquired during this process is unleashed in fierce jets of gas from the poles of the star, frequently seen as twin glowing outflows that mark the location of a protostar.

The abundance of protostars forming here in OMC-2 has created many spectacular outflows, large and small. Jets emitted from the young stars form high-speed shockwaves that sweep through the dense material around them; where the shockwaves are impacting the gas, it heats up and glows brightly, creating sharp ridges. Zoom in to observe the fine details in these shockwaves, as well as spot the smaller outflows from younger protostars. See if you can spot the location of hidden protostars, still so deeply obscured by their dusty cradles that they can’t be seen directly, by following outflows! Compare these very young protostars to the most evolved examples: the large, bright stars which have cleared away the clouds that surrounded them and now illuminate OMC-2.

Webb’s Near-Infrared Camera (NIRCam) was used to capture this view of OMC-2. The thick gas and dust in and around the Orion Nebula blocks any light coming from OMC-2 at visible wavelengths, and the clouds in OMC-2 itself obscure the protostars that astronomers really want to find. Only in the infrared do we see these protostars begin to shine out from their cocoons of dust. In many places, the cold dust is so dense that it absorbs all or almost all light, creating dark globules. Orange, brown and some of the red colours mark warmer dust that absorbs some light and emits some of its own. The yellow to green gradient is largely emission from polycyclic aromatic hydrocarbons (PAHs), while light from stars and protostars scattered by dust grains is seen here primarily as blue and cyan hazes. Gas heated by the outflows creates the detailed, glowing red ridges.

The data was collected in observing programme #5804, which aims to study the star formation in OMC-2 and its immediate neighbour, OMC-3. Since these molecular clouds are so near to Earth, they are excellent laboratories to learn about the earliest stages of stellar evolution. Astronomers will use the data from Webb to investigate how the many outflows affect star formation in the two regions, how the ultraviolet emission from the young stars impacts chemistry in the circumstellar discs which one day will form planets, and how gas and dust accretes onto the tens of protostars in the region.

Source: ESA/Webb/potm

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Links

• Pan video: OMC-2
• Zoom video: OMC-2
• Space Sparks episode: OMC-2
• Image on ESA website

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What Powers the X-ray Emission from Distant Supermassive Black Holes?

An artist’s concept of a supermassive black hole surrounded by a swirling disk of material falling into it. The purpish ball of light above the black hole, a feature called the corona, contains highly energetic particles that generate X-ray light. Credit: NASA/JPL-Caltech/R. Hurt (IPAC). Download Image

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Supermassive black holes don't give off any light themselves, but at those times in their existence when they are actively accreting material, they are encircled by a disk of hot, glowing material. The gravity of a black hole pulls swirling gas in, heating that material and causing it to shine at energies ranging from the ultraviolet to X-rays depending on the mass of the black hole. Another major source of radiation near a black hole is the so-called “corona”. Coronae are made up of highly energetic particles that generate X-ray light, though details about their geometry, location, appearance, and how they form remain uncertain and are driving questions for X-ray astrophysicists. In the artist’s concept shown here, the corona is envisioned as a hot spot of energetic plasma above (and below) the black hole, though other models suggest the corona is a hot atmosphere to the inner accretion disk.

In a new study submitted to the Astrophysical Journal, an international team led by Dr. Xiurui Zhao of the California Institute of Technology systematically studied the X-ray coronae in some of the most distant and luminous accreting supermassive black holes ever observed. These coronae, composed of ultra-hot electrons, produce high-energy X-rays by boosting lower-energy light emitted by the accretion disk. The expansion of the universe then shifts these high-energy emitted photons to lower observed energies, similar to the Doppler shift we hear as an ambulance or police car speeds away from us and the tone of the siren shifts to lower notes. By targeting luminous accreting supermassive black holes in the distant universe, known as quasars, the team leveraged this cosmological shift to bring key spectral features into NuSTAR’s energy range. This enabled direct measurements of the coronal properties which had been out of reach of previous X-ray satellites.

By combining NuSTAR observations with observations by the European Space Agency-led XMM-Newton satellite, which is sensitive to lower energy X-rays, the team constructed the most comprehensive view to date of coronae in active galaxies across cosmic time. The results provide new constraints on how energy is dissipated and radiated near supermassive black holes, offering critical tests for state-of-the-art theoretical models and simulations.

The study reveals that coronae in these powerful, distant quasars are significantly cooler than those found in the nearby universe, where quasars are typically less luminous. This result suggests that the most luminous black holes operate in a fundamentally different physical regime. The findings also indicate that these distant coronae are denser and more efficiently cooled, likely due to intense radiation fields near rapidly accreting black holes. Together, these results challenge standard models of black hole coronae and point toward a more complex interplay between heating, cooling, and particle acceleration in these extreme environments.

In a related study to be presented at the 248^th meeting of the American Astronomical Society later this month, Dr. Zhao and collaborators report on dramatic X-ray variability detected in the corona of the galaxy Mrk 509. Mrk 509 is a relatively nearby galaxy, just shy of 500 million light years away, that hosts an actively accreting supermassive black hole. This new work, relying on observations from the NuSTAR satellite, finds very strong variations in the temperature of the corona, at a level not previously found from either Mrk 509 or similar sources. Both the distant quasar survey and this detailed study of the nearby galaxy Mrk 509 have important implications for understanding the physical processes occurring very close to supermassive black holes.

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

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Galaxy Roasts Clouds, Makes "BBQ Sauce"

Figure: Schematic illustration of an evolutionary scenario connecting LRDs (left), BBQSORS (center), and ordinary QSOs (right). In LRDs, a supermassive black hole is thought to be surrounded by thick gas clouds. In BBQSORS, the surrounding clouds are being roasted off, and the region around the black hole may be partially emerging into view. In a QSO, the region around the black hole is visible. (Credit: Illustration generated by ChatGPT [OpenAI]; edited by Kohei Ichikawa)

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Galaxies in the early Universe which shine brightly due to gas falling into a supermassive blackhole at the galaxy center were originally regarded as puzzling Quazi-Stellar Objects, abbreviated as QSO. Even though we now know that they are not stars, but entire galaxies, the abbreviation QSO, now pronounced as "quasar," is still used. QSOs are some of the brightest objects in the Universe, but the recipe nature uses to create them has remained a secret.

Now, thanks to data from the new wide-field multi-object spectrograph, ʻŌnohiʻula PFS, on the Subaru Telescope, astronomers think that they have discovered the special sauce needed to understand the secret recipe. The data comes from observations of an object known as "BBQSORS," which is an abbreviation for "Blackbody QSO and Radio Source," and is pronounced "barbecue sauce."

As the name implies, BBQSORS seems to be a QSO, but has some idiosyncrasies. It was originally identified as a radio-bright QSO candidate. Follow-up observations to determine the true nature of the candidate were conducted as part of ʻŌnohiʻula PFS’s filler observations program. Under this program, astronomers can request observations of an object when ʻŌnohiʻula PFS is scheduled to observe other targets in the same area of the sky. This filler observation program allows astronomers to make simultaneous observations, which use the instrument more efficiently without detracting from the main observations. The PFS observations revealed that BBQSORS shows the characteristic of high-speed gas around a black hole, but, unlike ordinary QSOs, also has features similar to black body emission from gas at around 10,000 degrees.

A research team including researchers from the Japanese institutions Tohoku University, Ehime University, and Ritsumeikan University analyzed data for BBQSORS from other observations and found that it has properties similar to those of a class of objects called "Little Red Dots" (LRDs). Researchers think that in LRDs, a growing supermassive black hole may be obscured by very dense clouds of gas which absorb the intense light from the center and re-emit it at different wavelengths. From this early "cloudy stage," LRDs are thought to change into QSOs.

BBQSORS seems to be shrouded in gas clouds, similar to LRDs, but the gas may be hotter than that surrounding LRDs. In other words, BBQSORS may be roasting off its surrounding clouds in the process of cooking up a QSR. If this interpretation is correct, BBQSORS is a valuable candidate object capturing the transition from a thick-gas-enshrouded stage to an ordinary quasar.

This research result was published on June 3, 2026, in The Astrophysical Journal Letters (Zhong, Chen, Ichikawa et al., "Blackbody Quasar and Radio Source (BBQSORS): A Candidate of Transitional Little Red Dots with a T ~ 104 K Blackbody Spectrum").

This research was supported by JSPS KAKENHI (Grant No. 25K01043), JST FOREST Program (JPMJFR2466), and the Inamori Foundation Research Grant.

Source: Subaru Telescope/Distant Univers

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Relevant Links

• Ritsumeikan University June 3, 2026 News
• Frontier Research Institute for Interdisciplinary Sciences, Tohoku University June 3, 2026 Topics

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About the Subaru Telescope

The Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences with the support of the MEXT Project to Promote Large Scientific Frontiers. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawai`i.

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The new LIGO-Virgo-KAGRA catalog sets records in precision gravitational-wave astronomy

The spectrograms of all gravitational-wave events in the new catalog GWTC-5.0 that were found in O4b and have a false-alarm rate of less than one per year. Credit: Derek Davis / University of Rhode Island / LIGO-Virgo-KAGRA

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To the point

• New gravitational-wave catalog: The LIGO-Virgo-KAGRA collaboration releases the largest gravitational-wave catalog, GWTC-5, with 161 new events, totaling 390 confirmed detections since 2015.


• A wealth of results: The catalog contains many astrophysical highlights: the gravitational-wave source with the most precise sky localization, the first measurement of three gravitational-wave tones from a black hole, evidence for the existence of second-generation black holes, and new measurements of how fast the Universe is expanding.


• More results to come: Data from the last part of the fourth observing run are being analyzed at the moment. Information on the 68 signal candidates and new discoveries will be published in a catalog update in the coming months.

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Researchers at the Max Planck Institute for Gravitational Physics contribute to discoveries in the largest gravitational-wave catalog ever compiled.

Today, the LIGO-Virgo-KAGRA (LVK) collaboration published an updated catalog of the gravitational-wave events observed by its international network of gravitational-wave detectors in the United States, Italy, and Japan. The new version of the catalog, called Gravitational-Wave Transient Catalogue-5.0 (GWTC-5), has been posted as three core and three companion papers on the arXiv preprint server. These will be submitted to The Astrophysical Journal and The Astrophysical Journal Letters.

The detector network collected the data analyzed in this work between April 2024 and the end of January 2025, during O4b, the second part the fourth joined observing run (O4). A total of 161 new gravitational-wave events were discovered, of which scientists extracted parameters from 104. The latest revision of the catalog increases the grand total of confirmed events observed by the network since the first detection in September 2015 to 390.

As detector upgrades make the instruments increasingly more sensitive, the number of events detected in each successive observing run is growing significantly. This is underlined by the fact that 75% of all gravitational-wave signals observed so far have been discovered in the first and second part of O4.

An ever-growing treasure trove of data

“Our detectors have now become so sensitive that we discover new gravitational-wave signals about three to four times each week of our observing runs, unlocking an ever-growing treasure trove of data,” says Frank Ohme, group leader in the Precision Interferometry and Fundamental Interactions department at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover. “Each new signal helps to deepen our understanding of the dark, invisible side of the Universe.”

“Ten years after our first discoveries, we are now entering the era of precision gravitational-wave astronomy,” adds Karsten Danzmann, director emeritus at the AEI in Hannover. “What we can do with gravitational-wave astronomy today is truly amazing! We can study the population of coalescing black holes, conduct some of the most precise tests of general relativity, and obtain completely new measurements of the expansion of our Universe.”

“Our new catalog includes several exceptional and record-breaking signals,” says Alessandra Buonanno, director of the Astrophysical and Cosmological Relativity department at the AEI in the Potsdam Science Park. “We have found evidence for the existence of second-generation black holes, have pinpointed the sky position of a gravitational-wave source more precisely than ever before, and have for the first time measured or constrained three gravitational-wave tones from a black hole in the clearest gravitational-wave signal observed to date.” “The collaboration did an extraordinarily careful and comprehensive analysis of the detected gravitational waves,” confirms Harald Pfeiffer, group leader at AEI in Potsdam and the lead reviewer for the internal quality control of data-taking and analysis of the GWTC-5.0 results paper. “This makes today’s announcements not only scientifically extraordinarily important, but also very reliable.”

Pinpointing a black hole coalescence

One signal in the catalog, observed on 15 June 2024, sets a new record for the most precise sky localization of all gravitational-wave events. Its source was found to lie within an area of just 6 square degrees – a patch of the sky that could be covered by about 28 full moons. This exceptional performance was possible because LVK researchers could combine data from both LIGO instruments and the Virgo detector, which observed the gravitational waves.

Determining where a gravitational-wave source is located is crucial when searching for possible electromagnetic signals generated by events such as binary neutron star or black-hole–neutron-star coalescences. The smaller the sky region, the easier it is to point other astronomical observatories at them.

The record-setting event came from the coalescence of two black holes, weighing 34 and 26 times as much as our Sun, respectively. The gravitational waves were emitted from their merger about 3.4 billion years ago – at a time when the earliest known forms of life emerged on Earth – and traveled at the speed of light until reaching our planet in 2024.

Data analysis expertise and new waveform models

Whenever gravitational-wave signals reached Earth, an international expert team reviewed the performance of the algorithms that identified the potential signals and also discussed the next analysis steps. AEI members contributed week-long shifts of data analysis expertise during the observing run.

Gravitational-wave astronomy goes far beyond simply detecting a signal’s presence. Using highly sophisticated data analyses, it must be extracted it from the detectors’ background noise and its astrophysical properties must be inferred and understood. The clearer a signal stands out from the noise background, the “louder” it is and the better its astrophysics can be understood.

Extracting astrophysical properties from these loud signals requires a detailed understanding of the characteristic fingerprints these properties leave in the data. For this purpose, researchers at the AEI in Potsdam and Hannover have developed and made key contributions to the latest generation of improved waveform models. LVK researchers use these models to predict the gravitational waves emitted from binary black holes and to understand new signals once found.

“Our improved waveform models are more physically consistent and accurate and are key to reliably infer the properties of black hole mergers from the detector data,” explains Héctor Estellés Estrella, a former postdoc at AEI Potsdam, now a Postdoctoral Fellow at the Institute of Space Sciences in Barcelona.

“The additional physics incorporated by us into existing waveform models, now used in GWTC-5, brings us a step closer to precisely modeling these complex astrophysical systems,” adds Shrobana Ghosh a postdoc in the Precision Interferometry and Fundamental Interactions department at AEI Hannover.

Visualization of a binary black hole ringdown consistent with the gravitational-wave event GW250114.The gravitational waves are separated into two modes of the ringing remnant black hole, identified in the observation: the fundamental mode (green) and its first overtone (red). It also shows a predicted third tone (yellow) that the data places limits on. Visualization performed at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), based on a numerical relativity simulation of the Simulating Extreme Spacetimes (SXS) Project. Credit: H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics), K. Mitman (Cornell University)

The clearest gravitational-wave signal

GWTC-5 contains five exceptionally loud binary black hole mergers including the by far clearest gravitational-wave signal seen to date. GW250114, reported earlier, came from a coalescence of black holes with masses 34 and 32 times that of our Sun about 1.3 billion light-years away. It was observed on 14 January 2025 and its “clarity” made it possible to achieve outstanding scientific results, among them the most precise test of general relativity ever performed and confirmation of Stephen Hawking’s black hole area theorem.

During the ringdown phase, when the black hole settles into its final state right after the merger, the gravitational-wave signal contains a characteristic spectrum of modes, or tones. Characterizing multiple gravitational-wave tones – measuring the frequencies of the tones and how quickly they fade – enables unique and powerful tests of general relativity. GW250114 was clear enough for the researchers to measure two tones and constrain a third. All three agree with Einstein’s general relativity and the Kerr solution for rotating black holes.

Characterizing black holes with DINGO

In the past years, researchers at the AEI and at the Max Planck Institute for Intelligent Systems (MPI-IS) have been developing DINGO, a machine learning algorithm for gravitational-wave data analysis. In the production of GWTC-5 it has been used routinely for the first time.

“Our approach called DINGO employs deep neural networks. It is just as accurate and reliable as the conventional methods the LVK collaboration uses to determine the astrophysical characteristics of the gravitational-wave sources, but it only takes minutes instead of hours or days for the same task,” explains Annalena Kofler, a PhD student at the MPI-IS and the AEI in Potsdam.

“The LVK investigated 104 of the 161 of the new gravitational-wave signals, in detail. For 42 of those 104 signals in the new catalog, DINGO served as a cross-validation tool. The DINGO results agree exactly with those obtained with the conventional methods,” adds Nihar Gupte, a PhD student in the Astrophysical and Cosmological Relativity department at the AEI in the Potsdam Science Park.

Infographic about the two gravitational-wave events GW241011 and GW241110.
Credit: Shanika Galaudage / Northwestern University / Adler Planetarium

Second-generation black holes

In October and November 2024, just one month apart, the detector network observed gravitational waves from two very special black hole coalescences. GW241011 and GW241110 came from distances of approximately 700 million and 2.4 billion light-years, respectively. As reported earlier, certain characteristics of these mergers – in particular how fast and around which axis the black holes were spinning – indicate the objects involved could be “second-generation” black holes. These are black holes that themselves were formed in previous black hole coalescences, likely in very dense and crowded cosmic environments, such as stellar clusters. There black holes are more likely to collide and merge repeatedly.

The growing number of observed events has also enabled the LVK researchers to study and identify the properties of different populations of black holes. One of the articles accompanying the catalog deals with this specific aspect.

Studying the expansion of our Universe

LVK researchers have used the improving ability of the detector network to localize events and the increased number of events to measure the rate at which our Universe is expanding. They combined gravitational-wave based measurements of the distances to the sources with other measurements of how fast they are traveling away from Earth because of the Universe’s expansion.

The LVK improved the precision of its estimate of the Hubble constant, which measures the Universe’s expansion rate, by more than 25% compared to the value derived from the previous catalog. The estimated value is consistent with existing measurements from both our cosmic neighborhood and the early Universe. It is, however, not yet precise enough to resolve the “Hubble Tension” between those long-established measurements.

More signals in the next catalog update and the upcoming observing run

The analysis of O4c, the final part of O4 from the end of January 2025 until mid November 2025, is currently underway. The LVK collaboration will publish the results in the coming months. The 68 signal candidates already identified during O4c will further expand the catalog and offer new opportunities to study our Universe and the fundamental laws of physics.

At the moment, the detectors of the international network are undergoing upgrades to improve their sensitivity towards the next six-month observing run, called IR1, beginning in late October or mid November of 2026. More sensitive instruments will help discovering gravitational-wave signals at an even higher rate – potentially uncovering additional rare cosmic events.

Source: Max Planck Institute for Gravitational Physics/News

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Contacts:

Dr. Benjamin Knispel
Press Officer AEI Hannover
Tel: +49 511 762-19104
Email: benjamin.knispel@aei.mpg.de

Dr. Elke Müller
Press Officer AEI Potsdam, Scientific Coordinator
Tel: +49 331 567-7303
Email: elke.mueller@aei.mpg.de

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Scientific contacts:

Prof. Dr. Alessandra Buonanno
Director | LSC Principal Investigator
Tel: +49 331 567-7220
Fax: +49 331 567-7298
Email: alessandra.buonanno@aei.mpg.de
Homepage of Alessandra Buonanno

Prof. Dr. Dr. h.c. Karsten Danzmann
Director Emeritus | LSC Principal Investigator
Tel: +49 511 762-2356
Fax: +49 511 762-5861
Email: karsten.danzmann@aei.mpg.de
Homepage of Karsten Danzmann

Dr. Frank Ohme
Research Group Leader | LSC Principal Investigator
Tel: +49 511 762-17171
Fax: +49 511 762-2784
Email: frank.ohme@aei.mpg.de
Homepage of Frank Ohme

Dr. Héctor Estellés
Research Scientist
Email: hestelles@ice.csic.es
Institute of Space Sciences, Barcelona

Dr. Shrobana Ghosh
Postdoc
Tel: +49 511 762-14659
Email: shrobana.ghosh@aei.mpg.de

Nihar Gupte
PhD Student
Tel: +49 331 567-7169
Email: nihar.gupte@aei.mpg.de

Annalena Kofler
PhD Student / MPI for Intelligent Systems
Tel: +49 331 567-7369
Email: annalena.kofler@tuebingen.mpg.de

Prof. Harald Pfeiffer
Group Leader
Tel: +49 331 567-7328
Fax: +49 331 567-7298
Email: harald.pfeiffer@aei.mpg.de

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Additional experts:

Dr. Angela Borchers Pascual
Postdoc
Tel: +49 511 762-17172
Email: angela.borchers.pascual@aei.mpg.de
Dr. Raffi Enficiaud
Research Software Engineer
Tel: +49 331 567-7123
Email: raffi.enficiaud@aei.mpg.de

Cheng Foo
PhD Student
Tel: +49 331 567-7241
Email: cheng.foo@aei.mpg.de

Jannik Mielke
PhD Student
Tel: +49 511 762-14659
Email:jannik.mielke@aei.mpg.de

Dr. Gonzalo Morrás
Postdoc
Tel: +49 331 567-7321
Email: gonzalo.morras@aei.mpg.de

Dr. Lorenzo Pompili
Research Fellow
Email: Lorenzo.Pompili@nottingham.ac.uk
University of Nottingham, School of Mathematical Sciences

Elise Sänger
PhD Student
Email: elise.saenger@aei.mpg.de

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Core publications:

1.The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration

GWTC-5.0: An Introduction to Version 5.0 of the Gravitational-Wave Transient Catalog
arXiv:2605.27223 (2026)

Source | DOI

2. The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration

GWTC-5.0: Methods for Identifying and Characterizing Gravitational-wave Transients
arXiv:2605.27224 (2026)

Source | DOI

3. The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration

GWTC-5.0: Observations from the Second Part of the Fourth LIGO-Virgo-KAGRA Observing Run and Updates to the Gravitational-Wave Transient Catalog

arXiv:2605.27225 (2026)

Source | DOI

4. The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration

GWTC-5.0: Constraints on the Cosmic Expansion Rate and Modified Gravitational wave Propagation
arXiv:2605.27227 (2026)

Source | DOI

5. The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration

Open Data from LIGO, Virgo, and KAGRA through the Second Part of the Fourth Observing Run
arXiv:2605.27090 (2026)

Source | DOI

6. The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration
GWTC-5.0: Population Properties of Merging Compact Objects
arXiv:2605.27226 (2026)

Source | DOI

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