Hidden X-ray phase revealed in likely neutron star merger

Artist's impression of satellites observing high-energy prompt emission from a binary neutron star merger. SVOM and HXMT detected the short gamma-ray burst, while Einstein Probe captured the accompanying long-lasting X-ray emission. Credit: Yi-Han Iris Yin; reference images: EPSC, SVOM collaboration, NSSDC.

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An international team of astronomers, including researchers from the Department of Physics and the Hong Kong Institute for Astronomy and Astrophysics (HKIAA) at The University of Hong Kong (HKU), has discovered a previously hidden phase of high-energy activity following the merger of compact stars.

This fleeting cosmic explosion, known as EP250704a in X-rays and GRB 250704B in gamma rays, was jointly captured by the China-led Einstein Probe (EP), the Space Variable Objects Monitor (SVOM) and the Insight-Hard X-ray Modulation Telescope (HXMT)..

EP's wide-field X-ray telescope detected the event from its onset and continued to observe several episodes of soft X-ray emission after the gamma-ray signal disappeared. While the gamma-ray burst lasted only about 0.4 seconds, the source continued to shine in soft X-rays for nearly 10 minutes, revealing a phase of activity that conventional gamma-ray observations would likely have missed. These findings have been published as a cover article in Science Bulletin..

How Einstein Probe revealed the hidden X-ray phase.

Short gamma-ray bursts are commonly associated with the merger of compact objects such as neutron stars. As the two objects spiral together and collide, they release an intense burst of high-energy radiation. Traditionally, astronomers have identified these events mainly through gamma rays. Most X-ray telescopes can only turn to a burst after a gamma-ray detector has first located it, meaning the earliest X-ray emission may already be over by the time observations begin..

Einstein Probe changes this picture by continuously monitoring a wide area of the sky at soft X-ray energies. In this case, it revealed that what appeared to be a brief gamma-ray event was accompanied by much longer-lasting X-ray activity.

Yi-Han Iris Yin, a Ph.D. student at HKU's Department of Physics and the Hong Kong Institute for Astronomy and Astrophysics (HKIAA), is a co-corresponding author of the study. She led the analysis of the high-energy prompt emission and contributed to the physical interpretation of the event.

Yin's analysis of the X-ray signal revealed key insights into the merger's aftermath:

• The source remained active long after the gamma-ray burst. The soft X-ray emission continued for nearly 10 minutes after the brief gamma-ray flash.


• The X-rays point to continued central engine activity. Their rapid variability and changing spectrum indicate that the central engine created by the merger continued to release energy.


• The remnant may be a magnetar. One possible explanation is a rapidly rotating, highly magnetized neutron star that continued to power the X-ray emission.


• Similar X-ray activity may have been missed before. This suggests prolonged soft X-ray emission could be more common in compact-object mergers than previously recognized and may provide another way to study gravitational-wave sources.

Working with an international team led by An Li of Beijing Normal University (BNU) and Bin-Bin Zhang of Nanjing University (NJU), the researchers found that similar soft X-ray emission may have been present in previous short gamma-ray bursts but remained undetected because it was too soft and faint for conventional gamma-ray instruments.

"Einstein Probe is allowing us to uncover a part of compact star mergers that was hidden from previous gamma-ray observations," said Yin. "The short gamma-ray flash may represent only the beginning of the high-energy activity. By observing the universe at soft X-ray energies, we can now follow these systems for much longer and obtain a more complete view of what happens during and after the merger."

Fostering young scientific leadership

Bing Zhang, founding director of HKIAA and chair of astrophysics at HKU's Department of Physics, co-authored the study and contributed to the physical interpretation of the event. He has long proposed that binary neutron star mergers could produce fast X-ray transients detectable by missions such as Einstein Probe. Beyond the scientific findings, Zhang highlighted the significance of the study in nurturing young researchers and strengthening international collaboration.

"One of our goals at HKIAA is to create an environment where talented young researchers can take on scientific leadership and work at the forefront of international astronomy," Zhang said. "It is particularly encouraging to see our Ph.D. student Yin taking a leading role as one of the corresponding authors in this international collaboration."

"Her contribution reflects the quality and potential of the young researchers we are training at HKIAA, and this collaboration also demonstrates how Hong Kong can connect with major scientific facilities and research teams in mainland China and around the world."

International collaboration

The study brought together researchers from HKU, Nanjing University, the University of Rome "Tor Vergata," the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the Institute of High Energy Physics of the Chinese Academy of Sciences and many other institutions worldwide.

The co-first authors include BNU's Li and colleagues from the Institute of High Energy Physics, the University of Rome "Sapienza" and the University of Chinese Academy of Sciences. The corresponding authors include NJU's Bin-Bin Zhang, Eleonora Troja from the University of Rome "Tor Vergata," HKU's Ph.D. student Yin and colleagues from NAOC.

Source: Phys.org/news

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More information

An Li et al, Minutes-long soft X-ray prompt emission from a compact object merger, Science Bulletin (2026).
DOI: 10.1016/j.scib.2026.08.021

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Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →

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Explore further

A possible first-ever Einstein probe observation of a black hole tearing apart a white dwarf

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Stratospheric Observatory Sunrise-III Reveals Intricate Solar Magnetic Structures

Magnetic fields in the chromosphere above a quiet-Sun region observed by the SCIP instrument onboard Sunrise-III (right box), and magnetic structures reproduced by a numerical simulation (left box). The thin, thread-like magnetic structures detected by SCIP are reproduced in the simulation as twisted magnetic field lines (enlarged view inside the circle at the lower left). （Credit: NAOJ / MPS / Sunrise-III/SCIP） Image (1.3MB)

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A team of researchers led by the National Astronomical Observatory of Japan discovered unexpectedly intricate magnetic structures above quiet-Sun regions by observing the Sun with the balloon-borne solar observatory Sunrise-III during its 2024 flight in Earth’s stratosphere.

Sunrise-III observations revealed thin, elongated, thread-like magnetic structures embedded within the magnetic canopy above a quiet-Sun region. The magnetic canopy forms in the solar atmosphere (chromosphere) as magnetic fields concentrated at the solar surface (photosphere) arc outwards with increasing altitude above the photosphere, creating an arch of magnetic structures. The new observations show that this canopy is not a simple, uniformly expanding structure, but instead contains numerous thin elongated magnetic substructures. A numerical simulation reproduced the thread-like structures seen by Sunrise-III and showed that they are associated with magnetic field lines twisted by motions at the solar surface.

In separate observations of a quiet-Sun region near the solar limb (visible edge of the Sun), Sunrise-III mapped the magnetic fields of spicules, jet-like structures extending upward from the solar surface, and revealed how the distribution of the magnetic field varies with height above the limb.

Regions of the Sun without activity such as sunspots are referred to as “quiet.” Quiet-Sun regions cover most of the solar surface. The magnetic fields in the quiet-Sun regions are weaker than in active regions, making detailed measurements difficult for ground-based telescopes because of blurring due to Earth’s atmosphere.

Sunrise-III is an international collaborative project that observes the Sun with a 1-meter telescope carried by a balloon floating in the stratosphere at an altitude of 35 km. At this altitude, the Sun can be observed with very little atmospheric blurring. The gondola carried three instruments developed by different countries. Among them, the near-infrared spectropolarimeter SCIP (Sunrise Chromospheric Infrared spectroPolarimeter), developed under NAOJ's leadership, can continuously observe the magnetic field from the photosphere up through the chromosphere. The high-precision observations from the stratosphere made it possible to map the structure of the chromospheric magnetic field above quiet-Sun regions in fine detail. These findings provide important clues to understanding how energy is transported up from the solar surface to heat the solar atmosphere.

Source: National Astronomical Observatory of Japan (NAOJ)/News

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Detailed Article(s)

Balloon-Borne Solar Observatory Sunrise-III Reveals Intricate Magnetic Structures above the Quiet Sun
Solar Science Observatory

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Release Information

Researcher(s) Involved in this Release

Masahito Kubo (NAOJ SOLAR-C Project)
Yoshihiro Naito (The Graduate University for Advanced Studies)
Yukio Katsukawa (NAOJ Solar Science Observatory)

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Coordinated Release Organization(s)

National Astronomical Observatory of Japan, NINS

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Paper(s)

Masahito Kubo et al. “Three-dimensional Magnetic Field Structure of a Quiet-Sun Region Revealed by Sunrise III/SCIP”, in The Astrophysical Journal Letters, DOI:10.3847/2041-8213/ae909b

Yoshihiro Naito et al. “Magnetic Field Distribution along Spicules Revealed with SUNRISE III/SCIP”, in The Astrophysical Journal Letters DOI:10.3847/2041-8213/ae8f38

Patrick A. Ondratschek et al. “Cause of Chromospheric Opposite Polarity Intrusions Discovered in Sunrise III/SCIP Data: MURaM-ChE Simulations Point to Twisted Flux Ropes”, in The Astrophysical Journal Letters, DOI: 10.3847/2041-8213/ae9607

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Related Link(s)

First Solar Images from Sunrise-Ⅲ (January 16, 2025)

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Clouds in turbulence: How do cold clouds survive turbulent galactic winds?

A typical absorption profile produced by a cloud embedded in a turbulent wind along a quasar sightline. Including turbulence in the wind (purple curve) leads to multiple kinematic components and a larger equivalent width compared to its laminar-wind counterpart (yellow curve). © MPA

Visualising the difference in the evolution of the projected column densities of clouds in laminar (top) and turbulent winds (bottom). Turbulent winds result in shorter, clumpier, and much more laterally extended clouds, in contrast to the filamentary clouds found in laminar winds. Video here

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Turbulent outflows can strip away cold gas from galactic disks – yet, some cold clouds survive and travel tens of kiloparsecs, challenging the notion that turbulence inevitably destroys them. Using three-dimensional hydrodynamic simulations, MPA researchers reveal that turbulence can actually enhance cloud survival by increasing the surface area for radiative cooling, enabling hot gas to condense onto the cold phase and boost its mass by up to an order of magnitude. This also leads to clumpier, laterally extended structures instead of long comet-like tails. These findings reshape our understanding of cloud evolution in galactic outflows, not only reshaping and sustaining cold gas but also enriching spectral signatures with multiple kinematic components.

Galactic winds are powerful, turbulent outflows of hot gas that sweep cooler, denser clouds away from galactic disks. Despite being immersed in these harsh environments, some cold clouds manage to survive and travel vast distances of several kiloparsecs — that is to say, further than the thickness of a typical galaxy disk. This raises the interesting question of how cold clouds survive their journey through a hot, fast-moving galactic wind.

Simulations to explain this observation have so far been limited to idealised 'wind-tunnel' scenarios, where the surrounding wind is treated as a smooth, laminar flow. However, in reality, galactic winds are turbulent and are driven by processes such as stellar feedback and AGN activity. In a recent study, researchers from the Max Planck Institute for Astrophysics in Garching and the Indian Institute of Science in Bangalore explored this question using three-dimensional hydrodynamic simulations. They examined how a cold cloud evolves when moving through a hot wind in which turbulence is continuously driven.

The results are surprising. Turbulence does not necessarily destroy the cold cloud; in regimes where radiative cooling is efficient, turbulence can actually help the cloud to grow. Turbulent motions stretch and deform the cold gas, dramatically increasing the surface area of interaction between the cold and hot phases. This creates more areas where radiative cooling can be efficient, allowing more hot gas to condense onto the cold phase. Consequently, the mass of the cold gas can increase by up to an order of magnitude compared to a laminar wind..

Turbulence also alters the motion of the cloud. As newly cooled gas from the wind joins the cold phase, it transfers momentum to the cloud, enabling it to become entrained in the wind much more rapidly. In other words, the turbulence that reshapes the cloud also helps to accelerate it..

The visual difference is striking, too. Instead of the long, narrow, comet-like tails produced by laminar winds, turbulent winds produce shorter, clumpier, and much more laterally extended clouds. The cold gas is stretched and dispersed over a much larger area, which could potentially change how we interpret observations of cold atomic and molecular phases in galactic outflows. From different viewing angles, this more complex, spatially extended gas could produce richer spectral features, with multiple kinematic components in quasar spectra indicating gas moving at different velocities..

Together, these results demonstrate that turbulence is not merely a force that tears cold clouds apart. It can also reshape them, help them grow and carry them along with the wind. Therefore, the fate of a cloud depends on a delicate balance between turbulent driving, hydrodynamic mixing, and radiative cooling..

The team is now looking to simulate the cooler molecular phase and dust, as such observations are becoming increasingly abundant with JWST. This will involve understanding the influence of additional physical processes, particularly magnetic fields and thermal conduction, on the evolution of cold gas in these turbulent galactic outflows. Exploring these effects will help to build a more complete picture of the broader role played by galactic outflows in shaping their host galaxies.

Source: Max Planck Institute for Astrophysics/Research Highlights

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Author:

Alankar Dutta
Tel: 2254
alankard@mpa-garching.mpg.de

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Original publication

Ritali Ghosh, Max Gronke, Prateek Sharma, Alankar Dutta
Woven by the whirls: the growth and entrainment of cold clouds in turbulent hot winds
Monthly Notices of the Royal Astronomical Society, Volume 550, Issue 1, July 2026

DOI

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NASA’s Webb Provides Crash Course on Planet-Shattering Collisions

Extreme Debris Disk (Artist’s Concept)

The types of collisions within young stellar systems known as extreme debris disks are relevant to scientists’ understanding of our own solar system, which is thought to have undergone similar impact events that created our Moon and shaped Earth’s initial state.Credit Artwork: NASA, ESA, CSA, Joseph Olmsted (STScI)

Composition of Extreme Debris Disks Across Time

By investigating the compositions of extreme debris disks, scientists inferred that silica-rich disks are produced by high-energy impacts of Mars-sized objects, while silica-poor disks are created by less energetic events from Moon-sized bodies. Credit Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

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The environment surrounding a star changes as it ages, beginning with a juvenile, gas-rich protoplanetary disk where forming planets can reside, before evolving to a gas-poor debris disk. During its mission lifetime, NASA’s retired Spitzer Space Telescope examined the debris disk stage and discovered a subclass termed extreme debris disks. These systems harbor unusually large amounts of warm dust close to the star, in the region comparable to where rocky planets orbit in our solar system. A team of astronomers led by Kate Su of the Space Science Institute in Boulder, Colorado investigated these intriguing objects with Webb.

Contrary to theoretical predictions, which suggest we should observe many extreme debris disks, observations indicate that these environments are rare. Scientists estimate roughly only 1% of young stars show observable signatures of this phase based on the data collected so far, including possibly our own solar system during its formation. Despite their rarity, the team was able to compile a sample of 21 extreme debris disks, including five from Spitzer’s archival data and 16 from Webb, with 12 newly observed disks and follow-up observations on four of Spitzer’s.

“This is the first time we have gathered enough systems to truly understand this subclass that we call extreme debris disks,” said Su, lead author of the paper. “Before Webb, we had limited information. We knew that they are weird and very different from the typical cold debris disks that we know, like Vega and Fomalhaut. Now that we have more data, we can pin down what these disks represent for planet formation and evolution.”

The team confirmed that extreme debris disks share three key properties: smaller dust grains than those in protoplanetary or classic debris disks, a high concentration of warm dust, and irregular brightness variations, all revealed by mid-infrared spectra from Webb and Spitzer.

To determine the driving factor for these qualities, the team studied the mineralogical makeup of the disks. They found that their sample could be categorized into silica-rich and silica-poor disks. Volcanic glass like obsidian is one example of silica-rich material found on Earth, whereas the silica-poor mineral forsterite appears as green sand grains on some beaches in Hawaii. An extreme debris disk’s category relays information on the type of collisions producing the impact debris and may help account for its variability in infrared brightness.

“To just see their mid-infrared emission and beautiful spectral features with Webb, which allowed us to identify their compositions, was the most exciting thing for me,” said Agnes Kospal of Konkoly Observatory in Budapest, Hungary, and a coauthor of the study. “We have no other way to study these planetary embryos directly because they are too small.”

Of their sample, about one-third is silica-rich, suggesting these disks are produced by high-energy impacts between Mars-sized bodies where a significant portion of the material is vaporized. The remaining two-thirds of their sample is silica-poor, indicating that the collisions are occurring on smaller scales, like grazing, between Moon-sized objects. Silica-rich disks are found only around stars younger than 300 million years, while silica-poor disks persist across a broad range of ages and often show greater brightness variability. The team proposes that this variability is driven by the rapid evolution of fresh debris through orbital changes and additional impacts.

Their findings can be applied to our own solar system, which may have experienced more than one extreme debris disk phase.

“How rocky planets formed and giant planets evolved are part of the broader story of the solar system’s formation. It’s all one story,” said Su. “Our work on extreme debris disks helps us bring together the big picture of what we currently understand.”

Simulations suggest that terrestrial planets, such as Earth, should form within the first few hundred million years of a solar system’s formation. This period fits with the ages of silica-rich extreme debris disks observed so far and aligns with the estimation that Earth and the Moon formed around 100 million years after the Sun formed, with the Moon likely being the result of a collision between Earth and a Mars-sized object.

As for whether our Sun underwent a silica-poor extreme disk phase, if older silica-poor disks and their random intervals of infrared brightness do reflect orbital instability, this would be broadly consistent with the Late Heavy Bombardment hypothesis for our solar system. In that scenario, the gas giant planets migrated significant distances, gravitationally disrupting the orbits of smaller bodies and triggering catastrophic collisions that generated the short-lived, dust-rich phases observed in extreme debris disks.

“Of course, there’s many things we still don’t know about these disks,” said Attila Moor of Konkoly Observatory, a coauthor of the study. “We expect no silica-rich systems among older extreme debris disks. We only have three disks in our sample that fit that age criteria, so it’ll be nice to observe more of these systems to confirm our hypothesis.”

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/Latest News

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Details

Last Updated: Oct 01, 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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A Cleaner Look at Our Galactic Center's Hot Mess

Sagittarius A East (Labeled)
Credit: X-ray: NASA/CXC/McGill Univ./M. Balakrishnan et al.;
Radio: NSF/NRAO/VLA; Sub-mm: EAO/James Clerk Maxwell Telecope;
Image Processing: NASA/CXC/SAO/P. Edmonds, N. Wolk

JPEG (352.3 kb) - Large JPEG (2 MB) - Tiff (74.1 MB) -More Images

Tour: NASA Connects Little Red Dots With Chandra, Webb (Video)

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The center of the Milky Way galaxy is a chaotic place. In addition to the 4-million-solar mass black hole, known as Sagittarius A* (Sgr A*), the region is full of gas, dust, strong magnetic fields, and stars in various stages of life — from birth to death.

Now, astronomers have released the clearest view yet of the remains of an exploded star that sits amid this cluttered galactic environment. The supernova remnant is named Sagittarius A East, or Sgr A East, and it is the closest remnant to Sgr A* that astronomers know about.

Sgr A East emits light in many wavelengths, including X-rays that NASA’s Chandra X-ray Observatory can see. Supernova remnants like Sgr A East give off X-rays because powerful shock waves rumble outward into space after the explosion and the stellar debris is superheated to millions of degrees.

In this packed galactic landscape, it is difficult to tease out what light is coming from the Sgr A East supernova remnant and what emanates from other objects. Astronomers previously have identified the primary contributors. The two main sources of X-rays in this image, besides the supernova remnant itself, are colliding winds from a cluster of hot, massive stars and a diffuse commingled glow from many fainter overlapping X-ray sources. (This latter category is composed mainly of double star systems including stars like our Sun orbiting white dwarf stars.)

This new composite image of Sgr A East and the region around it contains X-rays from Chandra that are not — for the first time — contaminated by X-rays from other sources in this crowded field. A team of astronomers used a special technique to separate the three main sources of X-rays and create this new cleaner view of Sgr A East. This analysis also allowed the authors to make maps of the elements within the supernova remnant, including iron, sulfur, argon, and calcium.

The new image of Sgr A East shows lower-energy X-rays detected by Chandra in green and high-energy ones in light blue, which appear purple in the middle of the supernova remnant. The researchers removed the point-like sources of X-rays so they could study the diffuse emission in more detail. The X-ray data have been combined with radio data from the NSF’s Very Large Array in red and submillimeter-wavelength data from the James Clerk Maxwell Telescope in dark blue to complete this new composite view.

The bright radio emission surrounds X-rays from Sgr A East as well as the region around Sgr A*. The supermassive black hole is located at the center of the yellow spiral structure to the right of the purple X-rays from Sgr A East.

This new image will also allow scientists to examine how the winds from the stars in the nearby cluster have shaped the supernova remnant’s evolution. This could help reveal the identity of the star that exploded to create Sgr A East and whether the supernova remnant has triggered outbursts from Sgr A* in the past.

Because Sgr A East is so close to Sgr A*, astronomers have long wondered if they influence one another. The authors’ new work supports the idea that Sgr A East has played an active role in the black hole’s environment by injecting energy into the region and keeping the gas surrounding Sgr A* hot and turbulent over its lifetime of about 10,000 years, although its exact age remains uncertain. They have shown that Sgr A East has expanded into, compressed and heated the gas surrounding it, shaping its three-dimensional asymmetrical structure. A paper describing these results with these authors appeared in The Astrophysical Journal, and was led by Mayura Balakrishnan from McGill University in Montreal, Canada.

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Source: NASA’s Chandra X-ray Observatory

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Visual Description:

This release features a composite image of a supermassive black hole and supernova remnant close to each other at the center of our Milky Way Galaxy. In a packed galactic landscape such as this, it is often difficult to discern what light emanates from which object. For this image, astronomers used a special technique to separate the glowing X-ray sources. The result is a picture with distinct elements, and an overall look not unlike an impressionist oil painting with patches of diffused color.

At the heart of the image is a light purple cloud and a spiraling, bright yellow tangle. The purple cloud represents X-rays from the center of the supernova remnant, Sagittarius A East. Inside the bright yellow tangle is the supermassive black hole, Sagittarius A*, which has the mass of 4-million suns. Surrounding the remnants of the exploded star and its black hole neighbor, is a neon red gas cloud with trails drifting toward our upper right. Here, red represents radio data from the NSF’s Very Large Array.

A faint, dark blue cloud, barely discernible when set against the blackness of space, begins at our upper left and exits the bottom of the frame. This is submillimeter-wavelength data from the James Clerk Maxwell Telescope. Mottled, faint patches of forest green stretch across the image from our lower left to our upper right. These are lower-energy X-rays detected by Chandra that are possibly linked to past outbursts from Sagittarius A*.

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Fast Facts for Sagittarius A East

Credit: X-ray: NASA/CXC/McGill Univ./M. Balakrishnan et al.; Radio: NSF/NRAO/VLA; Sub-mm: EAO/James Clerk Maxwell Telecope; Image Processing: NASA/CXC/SAO/P. Edmonds, N. Wolk

Release Date: September 30, 2026
Scale: Image is about 7 arcmin (53 light-years) across.
Category: Black Holes, Supernovas & Supernova Remnants
Coordinates (J2000): RA 17h 45m 40.0s | Dec -20° 00´ 28.1"
Constellation: Sagittarius
Observation Dates: 35 observations from Sept 1999 to Aug 2020
Observation Time: 422 hours 51 minutes (5 days 6 hours 51 minutes)

Obs. ID: 242, 1561, 2943, 2951-2954, 3392, 3393, 3549, 3663, 3665, 4683, 4684, 5950-5954, 6363, 9169-9174, 10556, 11843, 13016, 13017, 14941, 14942, 22707, 22937, 23295

Instrument: ACIS
References: Balakrishnan, M, et al., 2026, ApJ, 1003,128.
Color Code: X-ray: green and cyan; Radio: red; Sub-mm: blue
Distance Estimate: About 26,000 light-years from Earth

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An Early Discovery by Rubin Observatory

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

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

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

Warming Up the World’s Largest Camera

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

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

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

Small Galaxies, Big Questions

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

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

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

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

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

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

Original astrobite edited by Katya Gozman.

Source: American Astronomical Society/ASS-Nova

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

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About the author, Ben Sherwin:

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

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More precise than ever before

Next-generation gravitational-waveforms from inspiraling black holes are calculated using mathematical methods from particle physics, such as Feynman diagrams, originally developed for the evaluation of quantum scattering amplitudes. This breakthrough was achieved by calculating the most complex Feynman diagrams ever. Credit: R. Patil (Max Planck Institute for Gravitational Physics), background image: James Webb Space Telescope, ESA/Webb, NASA & CSA, H. Dannerbauer

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To the point:

• New detectors: Over the next decade, new gravitational-wave observatories on Earth and in space will begin operations. They will be much more sensitive than current detectors and will observe signals in much greater detail.


• New models: The waveform models used for data analysis — mathematical methods for calculating the expected signals — must be about 100 times more accurate than the current models in order to exploit the full potential of the new observatories.


• Important milestone: Researchers at the Max Planck Institute for Gravitational Physics in Potsdam, together with international colleagues, have now taken the most difficult step towards new, more precise analytical waveform models. They have improved methods from particle physics, enabling predictions to be made with unprecedented precision across the four fundamental forces.

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Breakthrough on the path to highly accurate prediction of gravitational-wave signals

The key to understanding black holes

Pairs of merging black holes reveal their presence only through their gravitational waves and remain invisible to other astronomical methods. The first gravitational wave, detected 11 years ago by the LIGO detectors, originated from such a merger. Even today, the vast majority of the nearly 400 published signals originate from merging black holes. Gravitational-wave astronomy has evolved into a successful method of observing and studying the dark side of the universe.

To detect and understand these signals, scientists need not only highly sensitive laser interferometers but also precisely tailored waveform models. These mathematical predictions provide the templates that researchers use to identify the signals in the observational data.

They also use these models to identify the sources of the detected gravitational waves and determine their properties. How massive were the two black holes? Where and when did they merge? Did they merely orbit each other, or did they also spin around their own axes? How fast were they rotating, and around which axes? If researchers can answer these questions using precise waveform models, they can decipher how the black holes formed. They can also put Einstein's general theory of relativity to increasingly rigorous tests.

The next generation of gravitational-wave detectors and waveform models

A new era is dawning for gravitational-wave astronomy in the coming decade. The LISA detector in space is designed for low-frequency gravitational waves that cannot be detected from the ground. At the same time, the planned 'third-generation' ground-based detectors — the Einstein Telescope and Cosmic Explorer — will observe gravitational waves similar to those detected by current instruments. However, these detectors will be up to ten times more sensitive in their final design and will capture a large number of very long and very loud signals.

The waveform models must also become significantly more accurate so that researchers can correctly interpret the data. “Our waveform models must be around 100 times more accurate than the current models,” says Jan Steinhoff, group leader in the Astrophysical and Cosmological Relativity department at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in the Potsdam Science Park. “Only with such precise theoretical models can we fully exploit the potential of the new observatories and gain new insights into the universe.”

Complex mathematics for a precision record

As a first step towards developing such highly precise waveform models, the researchers have focused on the initial phase of the merger. During this phase, two black holes orbit each other at a greater distance, emit gravitational waves and slowly continue to draw closer. The effects of general relativity are still very small during this phase. Therefore, their motion can be described by post-Newtonian theory: This essentially adds corrections from Einstein's general theory of relativity to Newton's theory of gravity. Complex mathematical methods originally developed in particle physics are employed to continually refine these corrections, accounting for parameters such as the black holes’ intrinsic spin.

Calculating black holes? Try particle physics!

In their study, published recently in the journal Physical Review Letters, the scientists treat black holes as particles to describe the initial phase of the merger and the resulting gravitational waves, using post-Newtonian theory.

This enabled the scientists to make predictions on the motion of black holes around each other with unprecedented accuracy across the four fundamental forces: gravity, electromagnetism, the weak interaction and the strong interaction.

Raj Patil, a doctoral student at the AEI, explains: “We had to perform highly complex calculations to take this most difficult step towards the new waveform models. Never before have researchers been able to calculate fundamental interactions with such precision.” Patil adds: 'While there is still a lot of work ahead of us before we have the final waveform templates, we are now very confident that we will achieve our goal following this breakthrough.”

Source: Max Planck Institute for Gravitational Physics/News

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Media contact:

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

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Science Contacts:

Raj Patil
PhD Student
Tel: +49 331 567-7186
Email: raj.patil@aei.mpg.de

Dr. Jan Steinhoff
Group Leader
Tel: +49 331 567-7125
Email: jan.steinhoff@aei.mpg.de

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Publication:

Brunello, G.; Mandal, M. K.; Mastrolia, P.; Patil, R.; Pegorin, M.; Ronca, J.; Smith, S.; Steinhoff, J.; Torres Bobadilla, W. J.
Six-loop gravitational interactions at the sixth post-Newtonian order. Physical Review Letters 137, 111401 (2026)
 MPG.PuRe | | DOI | pre-print

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Further information

Homepage of the “Astrophysical and Cosmological Relativity” Department

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A galaxy spinning out of sync

NGC 4698
Credit: ESA/Hubble & NASA, D. Thilker, the MAUVE-HST Team

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A spiral galaxy viewed at an angle, with a bright central bulge and winding spiral arms. The arms form a ring around the galaxy, without appearing to reach its centre. Prominent red-brown dust lanes weave through the arms, which are also dotted with bright blue and reddish regions of star formation. The galaxy is set against a dark background scattered with s,b.t,brars and faint distant galaxies.

Though the spiral galaxy in this ESA/Hubble Picture of the Month seems serene, it hides a chaotic secret. This galaxy is NGC 4698, and it lies about 55 million light-years away in the constellation Virgo. It’s one of over one thousand galaxies in the Virgo Cluster, the nearest large cluster of galaxies bound together by gravity.

As a spiral galaxy similar to our own Milky Way galaxy, NGC 4698 has spiral arms that curl around within a thin disc of stars, gas and dust. These arms are marked by opaque clumps of brown dust and dotted with small collections of bright blue stars. Unlike many other spiral galaxies, like this one recently photographed by Hubble, NGC 4698’s delicate spiral arms are only prominent in the outer reaches of the disc; spiral arms often wind down to the very centre of a galaxy, but NGC 4698’s spiral arms appear to shy away from its glowing centre. The arms instead hover in a ring-like structure around the perimeter of the galaxy.

NGC 4698’s centre is dominated by a galactic bulge. The diffuse off-white glow of the galaxy’s bulge comes from stars smaller, older, and cooler than the massive blue stars that dot the galaxy’s outer disc. These tightly packed stars orbit a supermassive black hole containing millions of times the Sun’s mass. Scientists have found signs that this black hole is actively growing, drawing gas inward with its gravitational pull.

With a flat, starry disc and diffusely glowing centre, NGC 4698 looks a lot like a typical spiral galaxy — but this galaxy is far from normal. NGC 4698 is one of only a few known spiral galaxies with a bulge that extends out from the disc at a right angle. The elongation is faintly visible in this Hubble image, which shows the ghostly glow of the starry bulge peeking above and below the dusty disc. What’s more, the stars and gas nearest the galaxy’s centre rotate perpendicular to the rest of the disc!

What could cause a galaxy to be so out of sync? Astronomers have found that the culprit likely lies outside the galaxy. If NGC 4698 funneled in gas from an outside source, the newly collected gas could have formed a disc of gas and stars in the galaxy’s centre, at an angle relative to the rest of the disc. Some observations suggest that this galaxy once experienced a minor galactic merger, as evidenced by a short ‘tail’ of hydrogen streaming from one side of the galaxy.

The data used to create this image come from an observing programme (#18103; PI: Thilker) focusing on galaxies in the Virgo Cluster. This programme zooms in on the details of these relatively nearby galaxies, such as individual star clusters and nebulae. At the same time, researchers will use these data to take stock of the larger picture, learning how a galaxy’s journey through a cluster affects the galaxy’s evolution and ability to. form new stars.

Source: ESA/Hubble/potm

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More information

Webb is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

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Links

• Image on ESA website
• Pan video: NGC 4698
• Zoom video: NGC 4698

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Contacts:

Bethany Downer
ESA/Hubble/Webb Chief Science Communications Officer
Email: Bethany.Downer@esahubble.org

ESA Newsroom and Media Relations Office
Email: media@esa.int

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Edge-on Galaxy Pair NGC 7332 and NGC 7339

NGC 7332 and NGC 7339

Detail: Low Res. (310 KB) / Mid. Res. (1.5 MB) / High Res. (7.0 MB)

two edge-on galaxies in the Pegasus constellation are thought to form a gravitationally bound pair. An edge-on galaxy is one observed almost exactly from the side, so even if it is a spiral galaxy, its spiral structure is not visible. In contrast, when a galactic disk is viewed almost head-on, it is called a “face-on galaxy.”

A close look at the bulge, the bright central region of NGC 7332 on the right, reveals that it is not simply elliptical but appears somewhat boxy. This structure is known as a “peanut bulge” and is believed to be a bar-shaped bulge viewed edge-on.

In NGC 7339 on the left, a prominent dust lane, where interstellar dust is concentrated, extends across much of the galaxy's central disk. This indicates that large amounts of gas, material for star formation, are present in the galactic plane. By contrast, NGC 7332 on the right shows little obvious visual evidence of such dust, yet active star formation is observed.. (Credit: NAOJ; Image provided by Masayuki Tanaka)

Distance from Earth: 70 million light-years
Instrument: Hyper Suprime-Cam (HSC)

Source: ubaru Telescope

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Observing in phase with binary orbits September 25th, 2026

An artist's impression of a high-mass X-ray binary, in which a compact object such as a neutron star accretes matter from a massive companion star. Image credit: ESO/L. Calçada/M.Kornmesser. Download Image

The recent NuSTAR observing schedule has been dominated by Target of Opportunity observations and coordinated observations with other high energy observatories. Among the time-constrained observations, several were scheduled to study precise moments in the orbital phases of binary systems. These include an observation of AXJ1700.2-4220, a recently rediscovered X-ray pulsator found while searching the HEASARC archive of X-ray data. Most systems discovered in this way are likely white dwarf binary systems, but the archival data for AXJ1700.2-4220 suggest the presence of an accreting neutron star in a rare binary system. With the goal of unambiguously assessing the nature of this unusual system, NuSTAR observed the source during the orbital phase when pulsations were expected to be strongest. NuSTAR has also obtained multiple observations of the gamma-ray binary system LS I +61 303 to sample key phases across its 26.5-day orbit. The NuSTAR observations were originally planned for later this year, but an independent campaign of observations with the Nordic Optical Telescope, timed to be performed around the expected peak of X-ray flaring activity, persuaded the NuSTAR Science Operations Center to bring forward those observations. The NuSTAR and multi-observatory data from these observing campaigns, which include a Director's Discretionary Time observation by ESA's XMM-Newton observatory, will be part of a collaboration between multiple teams of researchers.

Author: Karl Forster (NuSTAR Science Operations Manager, Caltech)

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

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The Heartbeat of a Windy Black Hole

An artist's impression of a black hole accreting matter from a companion star and driving powerful winds from its accretion disk. Credit: John A. Paice.  Download Image

The past few weeks of the NuSTAR program has been heavily dominated by target-of-opportunity (ToO) investigations, including observations of X-ray binaries in outburst, Galactic novae, variable stars, and magnetars. As part of this regular diet of ToOs, over the past week NuSTAR observed 4U 1630-47—a candidate black hole X-ray binary in our Galaxy—as part of a comprehensive spectroscopic campaign coordinated with the IXPE, XMM-Newton, and XRISM observatories. 4U 1630-47 is an intriguing source that exhibits variable disk wind signatures, abnormally high X-ray polarization, and multiple classes of outbursts on a quasi-annual recurrence time. NuSTAR observations are crucial for determining the temperature and distribution of the hot plasma of electrons near the black hole known as the corona, and these observations have already sampled three different states of the central engine. Meanwhile, coordinated lower-energy X-ray observations by XMM and XRISM will measure atomic transitions, allowing study of the corona's reflection off the encircling accretion disk as well as the associated wind of ionized plasma.

Of particular note, NuSTAR had its first detection of 4U 1630-47 transitioning between a high-energy-dominated “heartbeat" state and a more stable low-energy-dominated state. The NuSTAR heartbeat of 4U 1630-47 appears very different from the famed heartbeat of the Galactic black hole binary GRS 1915+105, which is generally seen at lower X-ray energies. NuSTAR's unique broadband capabilities will be essential for testing whether the two oscillation modes have the same physical origin, and the multi-facility coordinated campaign will provide insight into how matter falls into stellar mass black holes in our Galaxy, and how the energy released leads to material being ejected in a powerful wind.

Author: Maxime Parra (JSPS Postdoctoral Fellow, Ehime University, Japan)

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

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A Sneak Peek into Early-Universe Star Formation with Boötes I

This image from the Hubble Space Telescope shows the Large Magellanic Cloud nebula N44, which is home to a large star cluster. Credit: ESA/Hubble & NASA, D. Gouliermis; CC BY 4.0

Title: Probing the IMF in the Early Universe — Direct Measurements in the Boötes I UFD with JWST/NIRCam
Authors: Keyi Ding et al.
First Author’s Institution: University of Maryland
Status: Accepted ApJ
The Stellar Initial Mass Function

Figure 1: Several different formulations for the IMF. Astronomers have found that the Milky Way IMF seems to follow either a broken power law (Kroupa), or a log-normal (Chabrier) distribution. Credit:JohannesBuchner; CC BY-SA 4.0

A fundamental concept in astronomy is the stellar initial mass function (IMF). The IMF describes the number of stars of each mass that form from a single birth cloud. If the IMF has a negative slope, it means most stars are low in mass; if it has a positive slope, it means most stars are high in mass. Figure 1 shows some examples of commonly used IMFs, all of which have a negative slope, since we see far more low-mass stars than high-mass stars in the Milky Way. You may notice that several models deviate from a straight line at about 0.5 solar mass. This point, known as the turnover or critical mass, is crucial in determining the exact shape of the IMF.

For a relatively simple concept, the IMF is shaped by incredibly complicated underlying physical mechanisms. Things like turbulence, magnetic fields, and chemical enrichment all play a role in shaping the observed IMF. Additionally, the IMF is a pretty fundamental quantity. An enormous amount of astronomy research relies on assumptions made about the IMF. For example, since most stars are low in mass, and low-mass stars are dimmer, astronomers use the IMF to convert the amount of light in a galaxy to the number of stars; if there are more or fewer low-mass stars than we expect, our measurements will be wrong.

A big question surrounding the IMF is whether or not it’s universal. In the Milky Way, astronomers have been able to measure the IMF accurately, and they have found that it seems to be the same regardless of which bunch of stars we use to measure it.¹ However, we know that galaxies in the early universe were very different compared to today. Things get tricky when you acknowledge that most measurements made of early-universe galaxies rely on modeling tools that are entirely reliant on assuming an IMF. This gnarly little detail makes measuring the IMF in the early universe especially valuable to astronomers.

What Makes Ultra-Faint Dwarfs So Special?

Today’s authors attempt to measure the early-universe IMF using a local relic, an ultra-faint dwarf galaxy (UFD). You might describe UFDs as “incredibly funky little galaxies.” They’re much less massive than the Milky Way, with about 10,000 times less stellar mass. What stars they do have tend to be very old and metal poor. The nature of UFDs has led many astronomers to think of them as fossils: relatively untouched galaxies formed in the early universe. Since we think UFDs are fossils of earlier galaxies, measuring the IMF in a UFD tells us whether the IMF was the same in the early universe as it is today. The authors focus on Boötes I, a relatively luminous UFD orbiting the Milky Way. Figure 2 shows Boötes I as seen by the Sloan Digital Sky Survey.

Figure 2: Boötes I as seen by the Sloan Digital Sky Survey. Because they’re so diffuse, UFDs look less like galaxies and more like groups of stars. Credit: Vasily Belokurov – SDSS-II Collaboration

The IMF in Boötes I

Measuring the IMF can get tricky — it’s typically pretty difficult to measure the mass of each individual star in a galaxy. Thankfully, Boötes I is close enough that we can do exactly that! Using JWST’s NIRCam instrument, today’s authors obtain imaging of Boötes I that is sensitive enough to extract roughly 10,000 stars belonging to the galaxy.

To measure the IMF from the observed population of stars, the authors use a modified version of Starwave, a Bayesian inference tool. In short, the tool takes in some assumptions about the population of stars in the galaxy, then generates many potential color–magnitude diagrams for various parameter selections. You can then assess how well each simulated color–magnitude diagram fits the observed data, thus determining likely parameters for the stellar population. The authors apply their tool for three different IMF models, testing how close the IMF in Boötes I is to that of the Milky Way. This allows them to determine how well the IMF compares to that of the Milky Way, which is typically thought of as a broken power law or log-normal distribution. If the IMF in Boötes I aligns with the Milky Way’s IMF, we’ll have a solid piece of evidence for a truly invariant IMF across cosmic time, allowing astronomers to rest easy knowing our modeling efforts haven’t been bunk this whole time.

So… What Did We Learn?

The authors find that a single power law can be ruled out to a good degree of confidence. This is good, as Milky Way studies show undeniable evidence of a turnover in the distribution. The broken power law and log-normal models both fit the observed data relatively well, aligning well with Milky Way–derived IMFs. All in all, they find solid evidence for an invariant IMF in the early universe.

However, they are unable to say with absolute certainty that the IMF is invariant. Given that their data are nearly perfect (that is, it’s pretty much impossible to get better data for Boötes I), the authors emphasize that a larger sample of UFD IMFs is needed to truly rule out an invariant IMF, but we’re certainly taking steps in the right direction! As the age-old saying goes, “more data are needed!”

Original astrobite edited by Maggie Verrico.

Source: American Astronomical Society/AAS-Nova

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Editor’s Note: The Milky Way IMF may vary from star cluster to star cluster; as described in this AAS Nova highlight from 8 July 2026, recent research using data from the Gaia spacecraft has found evidence for IMF variation in our galaxy. ↩︎

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About the author, Drew Lapeer:

Drew is a first-year PhD student at the University of Massachusetts Amherst. They are broadly interested in the evolution of galaxies, with a focus on the impact of cosmic feedback on the galactic ecosystem. In their free time, they enjoy reading, rock climbing, hiking, and baking!

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Youngest Exoplanet Yet Discovered Found Hiding in Keck Observatory Data

Elias 2-24 b

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Astronomers confirm a giant planet still forming around its young star, offering a rare glimpse into how planetary systems take shape

Maunakea, Hawaiʻi -Astronomers have confirmed the youngest exoplanet detected so far, offering a rare glimpse into the earliest stages of planetary formation. The planet, known as Elias 2-24 b, is still actively gathering material from the disk of gas and dust surrounding its young host star, allowing scientists to study a giant planet while it is still growing.

The study, led by Diego Portales University in Chile and published in The Astrophysical Journal Letters, combines observations from W. M. Keck Observatory, the Atacama Large Millimeter/submillimeter Array (ALMA), and the European Southern Observatory’s Very Large Telescope (VLT). The findings support the core accretion model of giant planet formation and provide strong evidence linking gaps in protoplanetary disks to planets forming within them.

“What makes Elias 2-24 b so remarkable is its age,” said Andrea Bernardi, a doctoral student at Diego Portales University and lead author of the study. “This is the youngest planet detected so far, and because it is still actively accreting material from its surroundings, we’re able to observe a stage of planet formation that is rarely seen directly.”

Seeing a Planet in the Making

Young stars are often surrounded by rotating disks of gas and dust known as protoplanetary disks. Over time, material within these disks collects and grows into planets.

In recent years, ALMA has produced striking images of these disks, revealing rings and dark gaps in the surrounding material. Many astronomers suspected that emerging planets were carving those gaps as they formed, but direct evidence remained limited.

Elias 2-24 b provides one of the clearest examples yet of a planet occupying one of these gaps.

Elias 5 4k 5 (Artist’s animation depicting Elias 2-24 b)

“We can now connect the presence of gaps in protoplanetary disks to the presence of planets with much greater confidence,” Bernardi said. “This discovery provides direct evidence that these structures can be produced by planets forming within the disk.”

The finding also supports a specific stage of the core accretion model, the leading theory of giant planet formation. According to the team’s analysis, the planet is currently undergoing a brief but critical growth phase during which it rapidly accumulates gas from the surrounding disk and builds its atmosphere.

“In a way, we’re observing a much younger version of a planetary system like our own,” said Lucas Cieza, co-author of the study and professor at Universidad Diego Portales. “Because our solar system is billions of years old, we can only reconstruct how it formed. Systems like Elias 2-24 b allow us to study that process while it is still underway.”

Alice Zurlo, a professor at Universidad Diego Portales and one of the study’s authors, conducted the initial research on the system in 2018. “This planet is a rare gem, as it is currently undergoing a stage of its evolution for which theoretical models still struggle to reliably predict its mass, entropy, and, consequently, its expected luminosity,” said Zurlo. “This system will therefore provide key insights once we are able to further constrain its dynamical mass, helping us refine and recalibrate evolutionary models for young planets.”

A Decade-Long Search and a Discovery in the Archive

The discovery began with observations conducted at Keck Observatory in 2018.

That year, Alice Zurlo, then part of the research team studying young stars with structured protoplanetary disks, observed Elias 2-24 with Keck’s Near Infrared Camera 2 (NIRC2). At the time, the observations revealed a faint signal, but not enough evidence to identify it as a planet.

Years later, Bernardi returned to the data through the Keck Observatory Archive (KOA), a NASA-funded partnership between Keck Observatory and the NASA Exoplanet Science Institute (NExScI) at Caltech/IPAC. The archive serves all data taken at Keck Observatory, making it available for new scientific research long after the observations were originally obtained.

By reanalyzing the 2018 observations with new data-processing techniques, Bernardi identified a signal consistent with a forming planet. Additional archival Keck observations obtained in 2020, together with independent observations from the VLT and supporting evidence from ALMA, helped confirm the discovery.

“This object sits right at the limit of what current technology can detect,” said Cieza. “It was the combination of observations from multiple observatories that allowed us to show the planet is really there.”

The discovery also highlights the scientific value of preserving astronomical observations for future researchers.

“Astronomical data can have a remarkably long shelf life,” said Keck Observatory Chief Scientist John O’Meara. “The observations existed for years, but new techniques, improved models, and a fresh look at the data revealed something extraordinary. KOA allows scientists to return to those observations and ask new questions, sometimes uncovering discoveries that weren’t possible when the data were first collected.”

Looking Ahead

The research team continues to study the planet and hopes to obtain spectroscopy and other measurements that could reveal more about its atmosphere, temperature, mass, and ongoing accretion.

For now, Elias 2-24 b offers a rare opportunity to witness a giant planet in the midst of formation.

“This system has become a laboratory for understanding how planets form,” Cieza said. “Every new observation helps us piece together one of the most complex puzzles in modern astrophysics, the origin of planetary systems like our own.”

Source: W.M. Keck Observatory/News

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Related Link:

Science Paper | NASA Release

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Science Contact:

Andrea Bernardi
andrea.bernardi@mail.udp.cl

Media Contact:

Meagan O’Shea
moshea@keck.hawaii.edu

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'Born-again' star offers rare chance to watch stellar evolution in real time

This image captures the ancient planetary nebula ejected by Sakurai's Object when the star died for the first time. The star itself is not visible, as it was captured before it began brightening again. Credit :ESO, 2004

Licence type: Attribution (CC BY 4.0)

Astronomers have confirmed that one of the fastest-changing stars ever observed has entered a new stage of its evolution, offering a rare opportunity to watch a star's life unfold on human timescales.

Using the European Southern Observatory's Very Large Telescope (VLT) in Chile, researchers, involving scientists from The University of Manchester and The Valongo Observatory, studied Sakurai's Object, a rare 'born-again' star that unexpectedly burst back to life in 1996 after reaching the final stages of its evolution.

Their findings, published today in Monthly Notices of the Royal Astronomical Society, show that the star has entered a new phase of its evolution, developing the powerful stellar wind characteristic of Wolf-Rayet stars.

The research provides new insight into the final stages of stellar evolution and helps astronomers test theories that would otherwise take thousands or millions of years to verify.

Professor Albert Zijlstra, from Jodrell Bank Centre for Astrophysics at The University of Manchester, said: "Most stars evolve so slowly that major changes take place over timescales far longer than a human lifetime. As a result, we usually have to piece together snapshots of stellar evolution by comparing different stars at different stages of their lives.

"Sakurai's Object offers something far rarer. It is one of the very few stars known to have changed dramatically within just a few decades, giving us the opportunity to watch stellar evolution unfold in real time. Thirty years ago, the star had a temperature similar to our Sun. Now, it is five times as hot, the fastest rate of increase ever seen.

'Born-again' star animation

"With our observations, we can test theories of how stars evolve and gain new insights into one of the shortest and least understood phases in the life of a dying star."

The scientists believe the star was similar to our Sun, but had already ended nuclear burning and begun its journey towards becoming a white dwarf - the hot, dense core left behind after an ordinary star dies. It underwent a rare event known as a "very late thermal pulse", when a layer of helium deep inside the dead star suddenly reignites. The event caused the star to rapidly expand, cool and eject large amounts of material into space, temporarily returning to an earlier stage of its life, leading astronomers to describe it as a "born-again" star.

Only two stars have ever been directly observed undergoing this type of dramatic rebirth: Sakurai's Object and V605 Aquilae. Following its outburst, Sakurai's Object became hidden behind thick clouds of gas and dust released during the eruption, making it difficult to study directly.

To investigate its current state, the team analysed light collected by the VLT and compared it with sophisticated computer models that simulate the atmospheres and powerful winds of Wolf-Rayet stars.

The observations revealed distinctive signatures of carbon and helium, allowing the researchers to find its temperature, chemical composition and the characteristics of its stellar wind.

Their analysis suggests the star's surface temperature is currently between around 27,000 and 36,000 degrees Kelvin, showing that it is reheating following its dramatic eruption nearly three decades ago.

Professor Zijlstra added: "One of the key questions is how quickly Sakurai's Object should recover after its dramatic eruption.

"Our measurements show that the star is reheating more gradually than some earlier models predicted. That gives us an important way of testing which theories best describe what happens when a dying star briefly springs back to life.

"As we continue to monitor the star over the coming years, we expect to learn much more about this remarkable phase of stellar evolution."

The findings also suggest that Sakurai's Object is at an earlier stage of its evolution than V605 Aquilae, which experienced a similar event around 80 years ago.

The team will continue observing Sakurai's Object as it continues reheating and resumes its journey towards becoming a white dwarf, learning more about one of the most rapid and unusual phases of stellar evolution ever observed.

Source: Royal Astronomical Society (RAS)/Research Highlights

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Media contacts:

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

Jessica Marsh
The University of Manchester
Mob: +44 (0)7780 281312
jessica.marsh@manchester.ac.uk

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Science contacts:

Professor Albert Zijlstra
The University of Manchester
albert.zijlstra@manchester.ac.uk

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Images & captions

Sakurai's Object

Caption: This image captures the ancient planetary nebula ejected by Sakurai's Object when the star died for the first time. The star itself is not visible, as it was captured before it began brightening again.

Credit: ESO, 2004

‘Born-again’ star still

Caption: A still image of the animation showing Sakurai's Object as it was captured three years ago.

Credit: Peter van Hoof

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Further information

The paper 'The emergence of a [WC] star in Sakurai's object' by Marcolini et al. has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stag1533.

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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 Wed, 16/09/2026 - 10:00

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