NASA's Hubble Provides Bird's-Eye View of Andromeda Galaxy's Ecosystem

Survey of Andromeda's Satellite Galaxies
Credits/Image: NASA, ESA, Alessandro Savino (UC Berkeley), Joseph DePasquale (STScI), Akira Fujii DSS2.

The Distribution of Satellite Galaxies around M31
Credits/Visualization: NASA, ESA, Christian Nieves (STScI)
Science: Alessandro Savino (UC Berkeley)
Acknowledgment:Joseph DePasquale (STScI), Frank Summers (STScI), Robert Gendler

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Located 2.5 million light-years away, the majestic Andromeda galaxy appears to the naked eye as a faint, spindle-shaped object roughly the angular size of the full Moon. What backyard observers don't see is a swarm of nearly three dozen small satellite galaxies circling the Andromeda galaxy, like bees around a hive.

These satellite galaxies represent a rambunctious galactic "ecosystem" that NASA's Hubble Space Telescope is studying in unprecedented detail. This ambitious Hubble Treasury Program used observations from more than a whopping 1,000 Hubble orbits. Hubble's optical stability, clarity, and efficiency made this ambitious survey possible. This work included building a precise 3D mapping of all the dwarf galaxies buzzing around Andromeda and reconstructing how efficiently they formed new stars over the nearly 14 billion years of the universe's lifetime.

In the study published in The Astrophysical Journal, Hubble reveals a markedly different ecosystem from the smaller number of satellite galaxies that circle our Milky Way. This offers forensic clues as to how our Milky Way galaxy and Andromeda have evolved differently over billions of years. Our Milky Way has been relatively placid. But it looks like Andromeda has had a more dynamic history, which was probably affected by a major merger with another big galaxy a few billion years ago. This encounter, and the fact that Andromeda is as much as twice as massive as our Milky Way, could explain its plentiful and diverse dwarf galaxy population.

Surveying the Milky Way's entire satellite system in such a comprehensive way is very challenging because we are embedded inside our galaxy. Nor can it be accomplished for other large galaxies because they are too far away to study the small satellite galaxies in much detail. The nearest galaxy of comparable mass to the Milky Way beyond Andromeda is M81, at nearly 12 million light-years.

This bird's-eye view of Andromeda's satellite system allows us to decipher what drives the evolution of these small galaxies. "We see that the duration for which the satellites can continue forming new stars really depends on how massive they are and on how close they are to the Andromeda galaxy," said lead author Alessandro Savino of the University of California at Berkeley. "It is a clear indication of how small-galaxy growth is disturbed by the influence of a massive galaxy like Andromeda."

"Everything scattered in the Andromeda system is very asymmetric and perturbed. It does appear that something significant happened not too long ago," said principal investigator Daniel Weisz of the University of California at Berkeley. "There's always a tendency to use what we understand in our own galaxy to extrapolate more generally to the other galaxies in the universe. There's always been concerns about whether what we are learning in the Milky Way applies more broadly to other galaxies. Or is there more diversity among external galaxies? Do they have similar properties? Our work has shown that low-mass galaxies in other ecosystems have followed different evolutionary paths than what we know from the Milky Way satellite galaxies."

For example, half of the Andromeda satellite galaxies all seem to be confined to a plane, all orbiting in the same direction. "That's weird. It was actually a total surprise to find the satellites in that configuration and we still don't fully understand why they appear that way," said Weisz.

The brightest companion galaxy to Andromeda is Messier 32 (M32). This is a compact ellipsoidal galaxy that might just be the remnant core of a larger galaxy that collided with Andromeda a few billion years ago. After being gravitationally stripped of gas and some stars, it continued along its orbit. Galaxy M32 contains older stars, but there is evidence it had a flurry of star formation a few billion years ago. In addition to M32, there seems to be a unique population of dwarf galaxies in Andromeda not seen in the Milky Way. They formed most of their stars very early on, but then they didn't stop. They kept forming stars out of a reservoir of gas at a very low rate for a much longer time.

"Star formation really continued to much later times, which is not at all what you would expect for these dwarf galaxies," continued Savino. "This doesn't appear in computer simulations. No one knows what to make of that so far."

"We do find that there is a lot of diversity that needs to be explained in the Andromeda satellite system," added Weisz. "The way things come together matters a lot in understanding this galaxy's history."

Hubble is providing the first set of imaging where astronomers measure the motions of the dwarf galaxies. In another five years Hubble or NASA's James Webb Space Telescope will be able to get the second set of observations, allowing astronomers to do a dynamical reconstruction for all 36 of the dwarf galaxies, which will help astronomers to rewind the motions of the entire Andromeda ecosystem billions of years into the past.

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

Source: HubbleSite/News

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About This Release

Credits:

Media Contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Science Contact:

Alessandro Savino
University of California, Berkeley, California

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Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Science Paper: The science paper by Alessandro Savino et al. (on ApJ), PDF (5.77 MB)
• NASA's Hubble Portal

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New dwarf galaxy discovered in the halo of Andromeda galaxy

A series of plots showing the tentative detection of a candidate stellar overdensity (Pegasus VII) in the UNIONS photometric catalogs. Credit: arXiv (2025). DOI: 10.48550/arxiv.2502.09792

An international team of astronomers reports the discovery of a new dwarf galaxy, which they have named Pegasus VII. The newfound galaxy, which lies about 2.4 million light years away, was identified in the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). The discovery was detailed in a research paper published Feb. 13 on the arXiv preprint server.

Dwarf galaxies are low-luminosity and low-mass stellar systems, usually containing a few billion stars. Their formation and activity are thought to be heavily influenced by interactions with larger galaxies.

One of the great places to look for dwarf galaxies is the halo of the Andromeda galaxy (also known as Messier 31, or M31 for short), due to its relative proximity. UNIONS is so far the deepest available survey for exploring the far reaches of this galaxy's halo and now a team of astronomers led by Simon E. T. Smith of the University of Victoria in Canada, has found another such dwarf.

"We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 sub-group which has been uncovered in the ri photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada-France-Hawaii Telescope and the Gemini-North Telescope," the researchers wrote in the paper.

Pegasus VII was identified at a separation of about 1.08 million light years from the Andromeda galaxy. Therefore, Pegasus VII is just about to cross the virial radius of Andromeda and has likely been isolated up until this point.

According to the study, Pegasus VII has an absolute V-band magnitude of −5.7 mag, a central surface of 27.3 mag/arcsec2, and a physical half-light radius of approximately 577 light years. This means that Pegasus VII is the faintest known dwarf galaxy satellite of Andromeda and roughly five times larger than the most extended globular clusters in this galaxy.

The study found that Pegasus VII has an ellipticity at a level of 0.5 and this projected elongation is aligned within 18 degrees of the projected direction towards Andromeda. The astronomers suppose that the source of this elongation is a previous tidal interaction with the gravitational potential of the Andromeda galaxy.

Furthermore, the researchers calculated that Pegasus VII has a total stellar mass of 26,000 solar masses and its metallicity is at a level of -2.0 dex. The age of the dwarf galaxy was estimated to be around 10 billion years.

Summing up the results, the authors of the paper concluded that they hope to find many more dwarf galaxies in the halo of Andromeda.

"The discovery of Pegasus VII complements both the empirical and theoretical claim that a wealth of dwarf galaxy satellites remain undetected towards M31," the scientists wrote.

by Tomasz Nowakowski (Phys.org)

Source: Phys.org/Astronomy & Space news

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More information: Simon E. T. Smith et al, Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII dwarf galaxy in UNIONS, arXiv (2025). DOI: 10.48550/arxiv.2502.09792

Journal information: arXiv

© 2025 Science X Network

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Explore further

• Hubble observes an oddly organized satellite galaxy

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Subaru Telescope Observes Near Earth Asteroid 2024 YR4

Asteroid 2024 YR₄ (marked by the crosshairs) as observed by the Subaru Telescope around 21:00 on February 20, 2025 (HAST). This image is 1 arcminute north-to-south and 2 arcminutes east-to-west. Exposure time 120 s in the r-band (550-700 nanometer wavelength). Credit: NAOJ. Download image (2.2MB)

Time animation of the Subaru Telescope observations of 2024 YR4． Near the center of the image with the field of view of 30 arcsec, the asteroid can be seen moving with respect to the background stars and galaxies over the course of the 15 minutes required for this observation. Credit: NAOJ

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On February 20, 2025 (Hawaii-Aleutian Standard Time, HAST), the Subaru Telescope captured images of asteroid 2024 YR₄, which will pass close to the Earth in 2032. The positional data obtained from these observations was used to refine the asteroid’s orbit, and assure us that the asteroid will not actually hit the Earth.

Discovered in December 2024, asteroid 2024 YR₄ is estimated to be 40–90 meters in diameter. It follows a long elliptical orbit around the Sun with a period of approximately four years. For most of its orbit, it remains far from the Earth; however, when it approaches the Sun, it crosses Earth's orbit and occasionally comes close to the Earth. The International Asteroid Warning Network (IAWN)—coordinated by the United Nations Office for Outer Space Affairs—issued the first-ever official impact risk notification in history for 2024 YR₄ because there was a slight possibility it could collide with the Earth in December 2032. Now global efforts are working to observe the asteroid with better precision to refine the estimates of its trajectory.

The Subaru Telescope observations of 2024 YR₄ were conducted at the request of the JAXA Planetary Defense Team, responding to IAWN’s call for improved orbital tracking. On February 20, 2025 (HAST), Hyper Suprime-Cam (HSC), a wide-field prime-focus camera mounted on the Subaru Telescope, successfully imaged 2024 YR₄ and precisely measured its position. The asteroid's brightness was also measured and found to be 24.3 magnitude in r-band (red visible light).

Dr. Tsuyoshi Terai of the Subaru Telescope, National Astronomical Observatory of Japan (NAOJ), who led the observations, comments: “Although 2024 YR₄ appeared relatively bright at the time of its discovery, it has been steadily fading as it moves away from the Earth. By late February, observations would have been extremely challenging without a large telescope. This mission was successfully accomplished thanks to the Subaru Telescope’s powerful light-gathering capability and HSC’s high imaging performance.”

The observation results have been reported to the Minor Planet Center (MPC) of the International Astronomical Union, contributing to a more precise determination of 2024 YR₄’s orbital elements. Based on new information, IAWN has revised its estimate of the asteroid colliding with the Earth in 2032, downgrading it to only a 0.004 percent chance of collision, much lower than the estimate at the beginning of February.

Source: Subaru Telescope/Topics

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Related Link(s)

• Subaru Telescope Observes Near Earth Asteroid 2024 YR4 (Subaru Telescope)
• FINAL NOTIFICATION: NO SIGNFICANT POTENTIAL FOR FUTURE IMPACT WITH EARTH BY NEAR-EARTH ASTEROID 2024 YR4 (PDF) (IAWN)

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Lifting the veil

Veil Nebula

A colourful, glowing nebula that reaches beyond the top and bottom of the image. It is made of translucent clouds of gas: wispy and thin with hard edges in some places, and puffy and opaque in others. Blue, red and yellow colours mix together, showing light emitted by different types of atoms in the hot gas. Bright and pointlike stars are scattered across the nebula. The background is black. Credit: ESA/Hubble & NASA, R. Sankrit

In this NASA/ESA Hubble Space Telescope Picture of the Week, Hubble has once again lifted the veil on a famous — and frequently photographed — supernova remnant: the Veil Nebula. This nebula is the remnant of a star roughly 20 times as massive as the Sun that exploded about 10 000 years ago. Situated about 2400 light-years away in the constellation Cygnus, this photogenic nebula made an appearance as the Picture of the Week previously in 2021.

This view combines images taken in three different filters by Hubble’s Wide Field Camera 3 instrument, highlighting emission from hydrogen, sulphur and oxygen atoms. This image shows just a small fraction of the Veil Nebula; if you could see the entire nebula without the aid of a telescope, it would be as wide as six full Moons placed side by side. Look in the sidebar of this page to see this image superimposed on its location in the sky, and try zooming out to compare the size of the full nebula!

Although this image captures the Veil Nebula at just a single point in time, it will help researchers understand how the supernova remnant has evolved over decades. Combining this snapshot with Hubble observations from 1994 will reveal the motion of individual knots and filaments of gas over that span of time, enhancing our understanding of this stunning nebula.

Source: ESA/Hubble/potw

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Supernova Signatures on Life in the Local Bubble

Winds from a central massive hot star cause the expansion of interstellar material, blowing outwards to create the Bubble Nebula. Credit: NASA, ESA, Hubble Heritage Team; CC BY 4.0

As the solar system travels through the Milky Way, our planet and the life it harbors are exposed to a variety of environments. A recent study suggests that a nearby supernova may have played a role in the evolution of life on Earth

The Local Bubble

About 6 million years ago, the solar system wandered into a 1,000 light-year-wide void known as the Local Bubble. Winds from massive stars and ionizing radiation from an estimated 15 supernovae carved out this bubble over the last 15 million years. As the solar system traveled from the bubble’s edge to its current position in the center, at least nine of the bubble-sculpting supernovae exploded, showering the Earth with supernova byproducts and intense radiation.

Evidence of these past explosions is embedded within the Earth’s crust — radioactive isotopes formed only in supernovae have decayed over time in deep-sea sediments. Less conspicuous are the ways cosmic rays from supernovae may have impacted the Earth; high-energy charged particles rained into the solar system, exposing the planet and the life on it to powerful radiation. Studying the Local Bubble and tracing the history of supernova explosions within it will allow researchers to gauge how the local environment has impacted our planet and the life it harbors.

Map of the Local Bubble showing the locations of surrounding stellar associations. The solar system lies near the center of the Local Bubble, and the surrounding stellar associations hosted supernovae that blew up the bubble. Modified from Nojiri et al 2025

Modeling Nearby Supernovae and Cosmic Radiation

Starting with the decay rate of the deep-sea isotopes, scientists estimate peaks in radioactive iron deposits approximately 2–3 and 5–6 million years ago. Using this information and the recent mapping of stellar associations in the Local Bubble, Caitlyn Nojiri (University of California, Santa Cruz) and collaborators modeled the necessary supernova input to produce the level of radioactive material present on Earth. From their modeling, they estimate that the iron peak ~2.5 million years ago can be attributed to a single supernova explosion from either the Upper Centaurus Lupus or Tucana Horologium stellar associations. The iron peak 5–6 million years ago, the authors suggest, arises from the solar system passing through the enriched outer shell of the Local Bubble.

Given the amount of radioactive iron deposited on Earth, the authors predict a powerful supernova progenitor capable of releasing some of the highest-energy cosmic rays in the universe. Through knowing the approximate location of the supernova and modeling its energy output, the authors estimate the amount of cosmic radiation Earth was exposed to from the time the supernova exploded to now. In their model, cosmic-ray radiation varies over time as the supernova evolves, meaning the Earth received a much higher volume of cosmic rays for the first 100,000 years after the explosion.

Cosmic-ray spectra (top panel) and the amount of cosmic radiation received at various depths on Earth (bottom panel) for the modeled supernova in the Upper Centaurus Lupus stellar association. Modified from Nojiri et al 2025

Impacts on Life

What does this cosmic-ray exposure mean for life on Earth? Though the exact effects of this radiation are not certain, biological studies have shown that radiation exposure can cause DNA to break, which can accelerate the rate at which genetic mutations and evolutionary changes occur. The authors note a prior study that showed the rate of virus diversification in Lake Tanganyika in Africa accelerated 2–3 million years ago. Though this cannot be definitively attributed to the supernova, the overlapping timeframes are suggestive of cosmic radiation playing a role in the evolution of life on our planet.

This study underscores the importance of considering cosmic radiation when it comes to understanding the environmental factors that drove biological evolution on Earth. Further studies must be performed in order to constrain the threshold at which this radiation goes from driving species diversification to becoming detrimental to life and its evolution. The Local Bubble has left imprints on the solar system and on Earth in ways that astronomers and biologists will continue to uncover.

By Lexi Gault

Citation

“Life in the Bubble: How a Nearby Supernova Left Ephemeral Footprints on the Cosmic-Ray Spectrum and Indelible Imprints on Life,” Caitlyn Nojiri et al 2025 ApJL 979 L18. doi: 10.3847/2041-8213/ada27a

Source: American Astronomical Society/AAS-Nova

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DESI Uncovers 300 New Intermediate-Mass Black Holes Plus 2500 New Active Black Holes in Dwarf Galaxies

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Artist’s illustration of dwarf galaxy with active galactic nucleus

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Dwarf Galaxy AGN Candidates

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Intermediate Black Hole Candidates

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Dwarf AGN Candidates Scatter Plot

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Videos


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Cosmoview Episode 94: DESI Uncovers 300 New Intermediate-Mass Black Holes Plus 2500 New Active Black Holes in Dwarf Galaxies

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Cosmoview Episodio 94: DESI descubre un tesoro de 300 nuevos agujeros negros de masa intermedia y 2.500 agujeros negros activos en galaxias enanasin English only

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Pan across dwarf AGN illustration


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Pan across Dwarf AGN candidates


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Pan across IMBH candidates

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The Dark Energy Spectroscopic Instrument discovers a treasure trove of active black holes in dwarf galaxies and reveals that surprisingly few are of intermediate mass

Within the Dark Energy Spectroscopic Instrument’s early data, scientists have uncovered the largest samples ever of intermediate-mass black holes and dwarf galaxies hosting an active black hole, more than tripling the existing census of both. These large statistical samples will allow for more in-depth studies of the dynamics between dwarf galaxy evolution and black hole growth, and open up vast discovery potential surrounding the evolution of the Universe’s earliest black holes.

Using early data from the Dark Energy Spectroscopic Instrument (DESI), a team of scientists have compiled the largest sample ever of dwarf galaxies that host an actively feeding black hole, as well as the most extensive collection of intermediate-mass black hole candidates to date. This dual achievement not only expands scientists’ understanding of the black hole population in the Universe, but also sets the stage for further explorations regarding the formation of the first black holes to form in the Universe and their role in galaxy evolution.

DESI is a state-of-the-art instrument that can capture light from 5000 galaxies simultaneously. It was constructed, and is operated, with funding from the Department of Energy (DOE) Office of Science. DESI is mounted on the U.S. National Science Foundation (NSF) Nicholas U. Mayall 4-meter Telescope at the NSF Kitt Peak National Observatory, a Program of NSF NOIRLab. The program is now in its fourth of five years surveying the sky and is set to observe roughly 40 million galaxies and quasars by the time the project ends.

The DESI project is an international collaboration of more than 900 researchers from over 70 institutions around the world and is managed by DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab).

With DESI’s early data [1], which include survey validation and 20% of the first year of operations, the team, led by University of Utah postdoctoral researcher Ragadeepika Pucha, was able to obtain an unprecedented dataset that includes the spectra of 410,000 galaxies [2], including roughly 115,000 dwarf galaxies — small, diffuse galaxies containing thousands to several billions of stars and very little gas. This extensive set would allow Pucha and her team to explore the complex interplay between black hole evolution and dwarf galaxy evolution.

While astrophysicists are fairly confident that all massive galaxies, like our Milky Way, host black holes at their centers, the picture becomes unclear as you move toward the low-mass end of the spectrum. Finding black holes is a challenge in itself, but identifying them in dwarf galaxies is even more difficult, owing to their small sizes and the limited ability of our current instruments to resolve the regions close to these objects. An actively feeding black hole, however, is easier to spot.

“When a black hole at the center of a galaxy starts feeding, it unleashes a tremendous amount of energy into its surroundings, transforming into what we call an active galactic nucleus,” says Pucha. “This dramatic activity serves as a beacon, allowing us to identify hidden black holes in these small galaxies.”

From their search the team identified an astonishing 2500 candidate dwarf galaxies hosting an active galactic nucleus (AGN) — the largest sample ever discovered. The significantly higher fraction of dwarf galaxies hosting an AGN (2%) relative to previous studies (about 0.5%) is an exciting result and suggests scientists have been missing a substantial number of low-mass, undiscovered black holes.

In a separate search through the DESI data, the team identified 300 intermediate-mass black hole candidates — the most extensive collection to date. Most black holes are either lightweight (less than 100 times the mass of our Sun) or supermassive (more than one million times the mass of our Sun). The black holes in between the two extremes are poorly understood, but are theorized to be the relics of the very first black holes formed in the early Universe, and the seeds of the supermassive black holes that lie at the center of large galaxies today. Yet they remain elusive, with only around 100–150 intermediate-mass black hole candidates known until now. With the large population discovered by DESI, scientists now have a powerful new dataset to use to study these cosmic enigmas.

“The technological design of DESI was important for this project, particularly its small fiber size, which allowed us to better zoom in on the center of galaxies and identify the subtle signatures of active black holes,” says Stephanie Juneau, associate astronomer at NSF NOIRLab and co-author of the paper. “With other fiber spectrographs with larger fibers, more starlight from the galaxy's outskirts comes in and dilutes the signals we’re searching for. This explains why we managed to find a higher fraction of active black holes in this work relative to previous efforts.”

Typically, black holes found in dwarf galaxies are expected to be within the intermediate-mass regime. But intriguingly, only 70 of the newly discovered intermediate-mass black hole candidates overlap with dwarf AGN candidates. This adds another layer of excitement to the findings and raises questions about black hole formation and evolution within galaxies.

“For example, is there any relationship between the mechanisms of black hole formation and the types of galaxies they inhabit?” Pucha said. “Our wealth of new candidates will help us delve deeper into these mysteries, enriching our understanding of black holes and their pivotal role in galaxy evolution.

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

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Notes

[1] DESI early data is available as files via the DESI collaboration and as searchable databases of catalogs and spectra via the Astro Data Lab and SPARCL at the Community Science and Data Center, a Program of NSF NOIRLab.

[2] DESI's early data contain nearly 3.5 million unique galaxy spectra. The sample used in this work was selected based on redshift (distance) and accurate detection of emission lines.

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More information

This research was presented in a paper titled “Tripling the Census of Dwarf AGN Candidates Using DESI Early Data” to appear in The Astrophysical Journal. DOI: 10.3847/1538-4357/adb1dd. The study can be found ahead of publication here.

The team is composed of Ragadeepika Pucha (University of Utah, University of Arizona), S. Juneau (NSF NOIRLab), Arjun Dey (NSF NOIRLab), M. Siudek (Institute of Space Sciences (ICE-CSIC), Instituto de Astrof´ısica de Canarias), M. Mezcua (ICE-CSIC, Institut d’Estudis Espacials de Catalunya (IEEC)), J. Moustakas (Siena College), S. BenZvi (University of Rochester), K. Hailine (University of Arizona), R. Hviding (Max Planck Institute for Astronomy, University of Arizona), Yao-Yuan Mao (University of Utah), D. M. Alexander (Durham University), R. Alfarsy (University of Portsmouth), C. Circosta (European Space Agency (ESA), University College London), Wei-Jian Guo (National Astronomical Observatories, Chinese Academy of Sciences), V. Manwadkar (Stanford University, SLAC National Accelerator Laboratory), P. Martini (The Ohio State University), B. A. Weaver (NSF NOIRLab), J. Aguilar (Lawrence Berkeley National Laboratory), S. Ahlen (Boston University), D. Bianchi (Università degli Studi di Milano), D. Brooks (University College London), R. Canning (University of Portsmouth), T. Claybaugh (Lawrence Berkeley National Laboratory) K. Dawson (University of Utah), A. de la Macorra (Universidad Nacional Autónoma de México), Biprateep Dey (University of Toronto, University of Pittsburgh), P. Doel (University College London), A. Font-Ribera (University College London, The Barcelona Institute of Science and Technology), J. E. Forero-Romero (Universidad de los Andes), E. Gaztañaga (IEEC, University of Portsmouth, ICE-CSIC), S. Gontcho A Gontcho (Lawrence Berkeley National Laboratory), G. Gutierrez (Fermi National Accelerator Laboratory), K. Honscheid (The Ohio State University), R. Kehoe (Southern Methodist University), S. E. Koposov (University of Edinburgh, University of Cambridge), A. Lambert (Lawrence Berkeley National Laboratory), M. Landriau (Lawrence Berkeley National Laboratory), L. Le Guillou (Sorbonne Université, CNRS/IN2P3), A. Meisner (NSF NOIRLab), R. Miquel (Institució Catalana de Recerca i Estudis Avançats, The Barcelona Institute of Science and Technology), F. Prada (Instituto de Astrofísica de Andalucía (CSIC)), G. Rossi (Sejong University), E. Sanchez (CIEMAT), D. Schlegel (Lawrence Berkeley National Laboratory) M. Schubnell (University of Michigan), H. Seo (Ohio University), D. Sprayberry (NSF NOIRLab), G. Tarlé (University of Michigan), and H. Zou (National Astronomical Observatories, Chinese Academy of Sciences).

This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Humanities, Science and Technology of Mexico (CONAHCYT); the Ministry of Science, Innovation and Universities of Spain (MICIU/AEI/10.13039/501100011033), and by the DESI Member Institutions. The authors are honored to be permitted to conduct scientific research on I’oligam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.

Current DESI Member Institutions include: Aix-Marseille University; Argonne National Laboratory; Barcelona-Madrid Regional Participation Group; Brookhaven National Laboratory; Boston University; Brazil Regional Participation Group; Carnegie Mellon University; CEA-IRFU, Saclay; China Participation Group; Cornell University; Durham University; École Polytechnique Fédérale de Lausanne; Eidgenössische Technische Hochschule, Zürich; Fermi National Accelerator Laboratory; Granada-Madrid-Tenerife Regional Participation Group; Harvard University; Kansas State University; Korea Astronomy and Space Science Institute; Korea Institute for Advanced Study; Lawrence Berkeley National Laboratory; Laboratoire de Physique Nucléaire et de Hautes Energies; Ludwig Maximilians University; Max Planck Institute; Mexico Regional Participation Group; National Taiwan University; New York University; NSF’s National Optical-Infrared Astronomy Research Laboratory; Ohio University; Perimeter Institute; Shanghai Jiao Tong University; Siena College; SLAC National Accelerator Laboratory; Southern Methodist University; Swinburne University; The Ohio State University; Universidad de los Andes; University of Arizona; University of Barcelona; University of California, Berkeley; University of California, Irvine; University of California, Santa Cruz; University College London; University of Florida; University of Michigan at Ann Arbor; University of Pennsylvania; University of Pittsburgh; University of Portsmouth; University of Queensland; University of Rochester; University of Toronto; University of Utah; University of Waterloo; University of Wyoming; University of Zurich; UK Regional Participation Group; Yale University. For more information, visit desi.lbl.gov.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit http://www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag (Kitt Peak) to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

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

Established in 2007 by Mark Heising and Elizabeth Simons, the Heising-Simons Foundation (www.heisingsimons.org) is dedicated to advancing sustainable solutions in the environment, supporting groundbreaking research in science, and enhancing the education of children.

The Gordon and Betty Moore Foundation, established in 2000, seeks to advance environmental conservation, patient care and scientific research. The Foundation’s Science Program aims to make a significant impact on the development of provocative, transformative scientific research, and increase knowledge in emerging fields. For more information, visit www.moore.org.

The Science and Technology Facilities Council (STFC) of the United Kingdom coordinates research on some of the most significant challenges facing society, such as future energy needs, monitoring and understanding climate change, and global security. It offers grants and support in particle physics, astronomy and nuclear physics, visit www.stfc.ac.uk.

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Links

• Read the paper: Tripling the Census of Dwarf AGN Candidates Using DESI Early Data
• Press release by University of Utah
• Press release by University of Portsmouth
• Press release by ICE-CSIC
• Interview with Ragadeepika Pucha on DESI Blog
• Visit the Dark Energy Spectroscopic Instrument webpage
• Images of DESI
• Videos of DESI
• Images of Nicholas U. Mayall 4-meter telescope
• Videos of Nicholas U. Mayall 4-meter telescope
• Check out other NOIRLab Science Releases

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Contacts

Ragadeepika Pucha
University of Utah
Postdoctoral Researcher
Email: dr.raga.pucha@gmail.com

Stephanie Juneau
Associate Astronomer
NSF NOIRLab
Email: stephanie.juneau@noirlab.edu

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

Webb Reveals Rapid-Fire Light Show From Milky Way's Central Black Hole

Flaring Disk Around Milky Way's Black Hole (Artist's Concept)
Credits/Illustration: NASA, ESA, CSA, Ralf Crawford (STScI)

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Videos

Infrared Flickers and Flares from Sagittarius A*
Credits/Video: NASA, ESA, CSA, Farhad Yusef-Zadeh (Northwestern), Howard Bushouse (STScI), Alyssa Pagan (STScI)

Observations and Light Curve of Sagittarius A*
Credits/Video: NASA, ESA, CSA, Farhad Yusef-Zadeh (Northwestern), Howard Bushouse (STScI), Alyssa Pagan (STScI)

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The supermassive black hole at the center of the Milky Way appears to be having a party, complete with a disco ball-style light show. Using NASA’s James Webb Space Telescope, a team of astrophysicists has gained the longest, most detailed glimpse yet of the “void” that lurks in the middle of our galaxy.

They found that the swirling disk of gas and dust (or accretion disk) orbiting the central supermassive black hole, called Sagittarius A*, is emitting a constant stream of flares with no periods of rest. The level of activity occurs over a wide range of time — from short interludes to long stretches. While some flares are faint flickers, lasting mere seconds, other flares are blindingly bright eruptions, which spew daily. There also are even fainter changes that surge over months.

The new findings could help physicists better understand the fundamental nature of black holes, how they get fed from their surrounding environments, and the dynamics and evolution of our own galaxy.

The study published in the Feb. 18 issue of The Astrophysical Journal Letters.

“In our data, we saw constantly changing, bubbling brightness,” said Farhad Yusef-Zadeh of Northwestern University in Illinois, who led the study. “And then boom! A big burst of brightness suddenly popped up. Then, it calmed down again. We couldn’t find a pattern in this activity. It appears to be random. The activity profile of this black hole was new and exciting every time that we looked at it.”

Random Fireworks

To conduct the study, Yusef-Zadeh and his team used Webb’s NIRCam (Near-Infrared Camera) to observe Sagittarius A* for a total of 48 hours in 8- to 10-hour increments across one year. This enabled them to track how the black hole changed over time.

While the team expected to see flares, Sagittarius A* was more active than they anticipated. The observations revealed ongoing fireworks of various brightnesses and durations. The accretion disk surrounding the black hole generated five to six big flares per day and several small sub-flares or bursts in between.

Two Separate Processes at Play

Although astrophysicists do not yet fully understand the processes at play, Yusef-Zadeh suspects two separate processes are responsible for the short bursts and longer flares. He posits that minor disturbances within the accretion disk likely generate the faint flickers. Specifically, turbulent fluctuations within the disk can compress plasma (a hot, electrically charged gas) to cause a temporary burst of radiation. Yusef-Zadeh likens these events to solar flares.

“It’s similar to how the Sun’s magnetic field gathers together, compresses, and then erupts a solar flare,” he explained. “Of course, the processes are more dramatic because the environment around a black hole is much more energetic and much more extreme. But the Sun’s surface also bubbles with activity.”

Yusef-Zadeh attributes the big, bright flares to occasional magnetic reconnection events — a process where two magnetic fields collide, releasing energy in the form of accelerated particles. Traveling at velocities near the speed of light, these particles emit bright bursts of radiation.

“A magnetic reconnection event is like a spark of static electricity, which, in a sense, also is an ‘electric reconnection,’” Yusef-Zadeh said.

Dual ‘Vision’

Because Webb’s NIRCam can observe two separate wavelengths at the same time (2.1 and 4.8 microns in the case of these observations), Yusef-Zadeh and his collaborators were able to compare how the flares’ brightness changed with each wavelength. Yet again, the researchers were met with a surprise. They discovered events observed at the shorter wavelength changed brightness slightly before the longer-wavelength events.

“This is the first time we have seen a time delay in measurements at these wavelengths,” Yusef-Zadeh said. “We observed these wavelengths simultaneously with NIRCam and noticed the longer wavelength lags behind the shorter one by a very small amount — maybe a few seconds to 40 seconds.”

This time delay provided more clues about the physical processes occurring around the black hole. One explanation is that the particles lose energy over the course of the flare — losing energy quicker at shorter wavelengths than at longer wavelengths. Such changes are expected for particles spiraling around magnetic field lines.

Aiming for an Uninterrupted Look

To further explore these questions, Yusef-Zadeh and his team hope to use Webb to observe Sagittarius A* for a longer period of time, such as 24 uninterrupted hours, to help reduce noise and enable the researchers to see even finer details

“When you are looking at such weak flaring events, you have to compete with noise,” Yusef-Zadeh said. “If we can observe for 24 hours, then we can reduce the noise to see features that we were unable to see before. That would be amazing. We also can see if these flares repeat themselves or if they are truly random.”

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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About This Release

Credits:

Media Contact:

Amanda Morris
Northwestern University, Evanston, Illinois

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Farhad Yusef-Zadeh (Northwestern)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Northwestern University Press Release

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“Out of science fiction”: First 3D observations of an exoplanet’s atmosphere reveal a unique climate

PR Image eso2504a
The 3D structure of the atmosphere of the exoplanet Tylos

PR Image eso2504b
The 3D structure of the atmosphere of the exoplanet Tylos (labeled)

PR Image eso2504c
Structure and motion of the atmosphere of the exoplanet Tylos

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Videos

PR Video eso2504a
ESO News | First 3D observations of an exoplanet’s atmosphere

PR Video eso2504b
The different layers of the atmosphere on WASP-121b

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Astronomers have peered through the atmosphere of a planet beyond the Solar System, mapping its 3D structure for the first time. By combining all four telescope units of the European Southern Observatory’s Very Large Telescope (ESO’s VLT), they found powerful winds carrying chemical elements like iron and titanium, creating intricate weather patterns across the planet’s atmosphere. The discovery opens the door for detailed studies of the chemical makeup and weather of other alien worlds.

“This planet’s atmosphere behaves in ways that challenge our understanding of how weather works — not just on Earth, but on all planets. It feels like something out of science fiction,” says Julia Victoria Seidel, a researcher at the European Southern Observatory (ESO) in Chile and lead author of the study, published today in Nature.

The planet, WASP-121b (also known as Tylos), is some 900 light-years away in the constellation Puppis. It’s an ultra-hot Jupiter, a gas giant orbiting its host star so closely that a year there lasts only about 30 Earth hours. Moreover, one side of the planet is scorching, as it is always facing the star, while the other side is much cooler.

The team has now probed deep inside Tylos’s atmosphere and revealed distinct winds in separate layers, forming a map of the atmosphere’s 3D structure. It’s the first time astronomers have been able to study the atmosphere of a planet outside our Solar System in such depth and detail.

“What we found was surprising: a jet stream rotates material around the planet’s equator, while a separate flow at lower levels of the atmosphere moves gas from the hot side to the cooler side. This kind of climate has never been seen before on any planet,” says Seidel, who is also a researcher at the Lagrange Laboratory, part of the Observatoire de la Côte d'Azur, in France. The observed jet stream spans half of the planet, gaining speed and violently churning the atmosphere high up in the sky as it crosses the hot side of Tylos. “Even the strongest hurricanes in the Solar System seem calm in comparison,” she adds.

To uncover the 3D structure of the exoplanet's atmosphere, the team used the ESPRESSO instrument on ESO’s VLT to combine the light of its four large telescope units into a single signal. This combined mode of the VLT collects four times as much light as an individual telescope unit, revealing fainter details. By observing the planet for one full transit in front of its host star, ESPRESSO was able to detect signatures of multiple chemical elements, probing different layers of the atmosphere as a result.

“The VLT enabled us to probe three different layers of the exoplanet’s atmosphere in one fell swoop,” says study co-author Leonardo A. dos Santos, an assistant astronomer at the Space Telescope Science Institute in Baltimore, United States. The team tracked the movements of iron, sodium and hydrogen, which allowed them to trace winds in the deep, mid and shallow layers of the planet’s atmosphere, respectively. “It’s the kind of observation that is very challenging to do with space telescopes, highlighting the importance of ground-based observations of exoplanets,” he adds.

Interestingly, the observations also revealed the presence of titanium just below the jet stream, as highlighted in a companion study published in Astronomy and Astrophysics. This was another surprise since previous observations of the planet had shown this element to be absent, possibly because it’s hidden deep in the atmosphere.

“It’s truly mind-blowing that we’re able to study details like the chemical makeup and weather patterns of a planet at such a vast distance,” says Bibiana Prinoth, a PhD student at Lund University, Sweden, and ESO, who led the companion study and is a co-author of the Nature paper.

To uncover the atmosphere of smaller, Earth-like planets, though, larger telescopes will be needed. They will include ESO’s Extremely Large Telescope (ELT), which is currently under construction in Chile’s Atacama Desert, and its ANDES instrument. “The ELT will be a game-changer for studying exoplanet atmospheres,” says Prinoth. “This experience makes me feel like we’re on the verge of uncovering incredible things we can only dream about now.”

Source: ESO/News

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More information

This research was presented in a paper published in the journal Nature titled “Vertical structure of an exoplanet’s atmospheric jet stream” (doi:10.1038/s41586-025-08664-1).

The team is composed of: Julia V. Seidel (European Southern Observatory, Santiago, Chile [ESO Chile]; Laboratoire Lagrange, Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Nice, France [Lagrange]), Bibiana Prinoth (ESO Chile and Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Lund, Sweden [ULund]), Lorenzo Pino (INAF-Osservatorio Astrofisico di Arcetri, Florence, Italy), Leonardo A. dos Santos (Space Telescope Science Institute, Baltimore, USA, Johns Hopkins University, Baltimore, USA), Hritam Chakraborty (Observatoire de Genève, Département d’Astronomie, Université de Genève, Versoix, Switzerland [UNIGE]), Vivien Parmentier (Lagrange), Elyar Sedaghati (ESO Chile), Joost P. Wardenier (Département de Physique, Trottier Institute for Research on Exoplanets [IREx], Université de Montréal, Canada), Casper Farret Jentink (UNIGE), Maria Rosa Zapatero Osorio (Centro de Astrobiología, CSIC-INTA, Madrid, Spain), Romain Allart (IREx), David Ehrenreich (UNIGE), Monika Lendl (UNIGE), Giulia Roccetti (European Southern Observatory, Garching bei München, Germany; Meteorologisches Institut, Ludwig-Maximilians-Universität München, Munich, Germany), Yuri Damasceno (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Porto, Portugal [IA-CAUP], Departamento de Fisica e Astronomia, Faculdade de Ciências, Universidade do Porto, Porto, Portugal [FCUP]; ESO Chile), Vincent Bourrier (UNIGE), Jorge Lillo-Box (Centro de Astrobiología (CAB); CSIC-INTA, Madrid, Spain), H. Jens Hoeijmakers (ULund), Enric Pallé (Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain [IAC]; Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Tenerife, Spain [IAC-ULL]), Nuno Santos (IA-CAUP and FCUP), Alejandro Suàrez Mascareño (IAC and IAC-ULL), Sergio G. Sousa (IA-CAUP), Hugo M. Tabernero (Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Universidad Complutense de Madrid, Spain), and Francesco A. Pepe (UNIGE).

The companion research, uncovering the presence of titanium, was published in the journal Astronomy & Astrophysics in a paper titled “Titanium chemistry of WASP-121 b with ESPRESSO in 4-UT mode” (doi: 10.1051/0004-6361/202452405)

The team behind this paper is composed of: Bibiana Prinoth (European Southern Observatory, Santiago, Chile [ESO Chile] and Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Lund, Sweden [ULund]), Julia V. Seidel (ESO Chile; Laboratoire Lagrange, Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Nice, France [Lagrange]), H. Jens Hoeijmakers (ULund), Brett M. Morris (Space Telescope Science Institute, Baltimore, USA), Martina Baratella (ESO Chile), Nicholas W. Borsato (ULund, School of Mathematical and physical Sciences, Macquarie University, Sydney, Australia), Yuri Damasceno (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Porto, Portugal [IA-CAUP], Departamento de Fisica e Astronomia, Faculdade de Ciências, Universidade do Porto, Porto, Portugal [FCUP]; ESO Chile), Vivien Parmentier (Lagrange), Daniel Kitzmann (University of Bern, Physics Institute, Division of Space Research & Planetary Sciences, Bern, Switzerland), Elyar Sedaghati (ESO Chile), Lorenzo Pino (INAF-Osservatorio Astrofisico di Arcetri, Florence, Italy), Francesco Borsa (INAF-Osservatorio Astronomico di Brera, Merate, Italy), Romain Allart (Département de Physique, Trottier Institute for Research on Exoplanets [IREx], Université de Montréal, Canada), Nuno Santos (IA-CAUP and FCUP), Michal Steiner (Observatoire de l'Université de Genève, Versoix, Switzerland), Alejandro Suàrez Mascareño (Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Tenerife, Spain), Hugo M. Tabernero (Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Universidad Complutense de Madrid, Spain) and Maria Rosa Zapatero Osorio (Centro de Astrobiologia, CSIC-INTA, Madrid, Spain).

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.

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Links

• Research paper (Nature)
• Research paper (A&A)
• Photos of the VLT
• Find out more about ESO's Extremely Large Telescope on our dedicated website and press kit
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• World's darkest and clearest skies at risk from industrial megaproject

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Contacts:

Julia Victoria Seidel
European Southern Observatory (ESO) and Lagrange Laboratory, Observatoire de la Côte d'Azur
Santiago, Chile and Nice, France
Tel: +33 743 32 79 73
Email: jseidel@oca.eu

Bibiana Prinoth
Lund University
Lund, Sweden
Tel: +46 72 442 03 69
Email: bibiana.prinoth@fysik.lu.se

Leonardo A. dos Santos
Space Telescope Science Institute
Baltimore, USA
Tel: +1 (410) 338-4395
Email: ldsantos@stsci.edu

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: press@eso.org

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Mystery of 'remarkable' cosmic explosion that lay hidden for years

The "remarkable" XRT 200515 cosmic explosion observed by NASA's Chandra X-ray Observatory. Credit: Steven Dillmann Licence type: Attribution (CC BY 4.0)

The "needle in the haystack" discovery of a powerful explosion from a mysterious unknown object outside our galaxy has excited astronomers.

It went unnoticed for years within a vast, two decade-long archive of observations by NASA's Chandra X-ray Observatory, before being unearthed by a new paper published in Monthly Notices of the Royal Astronomical Society.

Astronomers led by Stanford University and Harvard believe the "remarkable" cosmic explosion could either be the first X-ray burster ever discovered in the Large Magellanic Cloud (LMC), a rare flare from a magnetar – one of the most mysterious objects in the universe – or something entirely new and unheard of.

"Have you ever flipped through old photo albums and suddenly found something fascinating hidden in the background of a picture, no one had ever noticed before? Now imagine doing that on a cosmic scale," said lead researcher Steven Dillmann, a PhD student at Stanford University.

"Using a novel machine learning approach, we looked back through over 20 years of archived observations from NASA's Chandra X-ray Observatory and discovered a remarkable, powerful X-ray flash from an unknown object outside our own galaxy that had gone unnoticed for years within the vast Chandra archive – a true needle in the haystack event."

In 15 May 2020, while Chandra was observing the remains of an exploded star in the LMC (a small galaxy neighbouring our Milky Way), it accidentally captured a bright and extremely fast X-ray flash from an unknown origin.

This flash appeared and disappeared within a few seconds, went unnoticed during the initial observation, and so was stored in the large Chandra archive.

The field of view Chandra was observing when XRT 200515 occurred. The XRT 200515 label in yellow points to the burst. Credit: Steven Dillmann

Licence type: Attribution (CC BY 4.0)

Unlike traditional approaches, the novel machine learning method used in the new study managed to uncover the so-called extragalactic fast X-ray transient (FXT), which the researchers named XRT 200515 in reference to the day it was detected by Chandra.

"The cosmic flash is particularly interesting because of its unusual characteristics that are different to any of the other extragalactic FXTs that have previously been detected by Chandra," said Mr Dillmann.

"It produced an incredibly energetic initial burst that lasted for only 10s, whereas others lasted for minutes or hours. This was followed by a longer, less energetic afterglow lasting for a few minutes."

As neither Chandra nor any other telescope has ever recorded the source before or since this burst, its true nature remains a puzzle.

The researchers believe one explanation is that it could be the first X-ray burster ever discovered in the LMC. These are systems involving two stars: one small and super-dense dead star (called a neutron star) and a normal companion star that orbits around it.

The neutron star is like a cosmic vacuum cleaner – its powerful gravity pulls gas off its companion star. When enough gas builds up on the neutron star's surface, it triggers a massive thermonuclear explosion that releases an intense burst of X-ray radiation.

An image of the lightcurve (amount of photons received from the burst location over time) of XRT 200515, which shows how strong and fast the burst is. Credit: Steven Dillmann

Licence type: Attribution (CC BY 4.0)

Another theory is that it could be a rare, giant flare from a distant magnetar – neutron stars with extremely strong magnetic fields. These flares are some of the most explosive events in the cosmos, releasing a huge amount of gamma rays in a very short time.

If XRT 200515 is an X-ray counterpart to such an event, it would be the first giant magnetar flare observed at these X-ray energy levels.

The final explanation the researchers put forward is that it might be a previously unknown type of cosmic explosion that could reveal new insights about the universe.

"This discovery reminds us that space is dynamic and ever-changing, with exciting phenomena occurring constantly," said Mr Dillmann.

"It also demonstrates the value of using artificial intelligence for scientific discovery in archived astronomical data – there might be countless other discoveries waiting to be found in observations we've already made."

The researchers are now fine-tuning their method to search for signs of planets outside the Milky Way, building on previous breakthrough work led by co-author Rosanne di Stefano, which identified the first potential extragalactic planet candidate.

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

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
press@ras.ac.uk

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Scientific contacts:

Steven Dillmann
Stanford University
stevendi@stanford.edu

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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 and review 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 peer review, in which fellow experts on the editorial boards accept the paper as worth considering. 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 X, Facebook, LinkedIn and YouTube.

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A spiral hiding an impostor

UGC 5460

A spiral galaxy seen close to face-on. The centre of its disc is a bright, pale yellowish oval shape. Spiral arms extend from either side of the oval through the disc on irregular paths. They are marked throughout by bright bluish-white patches of stars. Distant background galaxies appear as small orangish blobs around the spiral galaxy. In the top-left corner a nearby star shines brightly, spikes radiating from it. Credit: ESA/Hubble & NASA, W. Jacobson-Galán, A. Filippenko, J. Mauerhan

The sparkling spiral galaxy gracing this NASA/ESA Hubble Space Telescope Picture of the Week is UGC 5460, which sits about 60 million light-years away in the constellation Ursa Major. This image combines four different wavelengths of light to reveal UGC 5460’s central bar of stars, winding spiral arms and bright blue star clusters. Also captured in the upper left-hand corner of this image is a far closer object: a star just 577 light-years away in our own galaxy.

UGC 5460 has hosted two recent supernovae named SN 2011ht and SN 2015as. It’s because of these two stellar explosions that Hubble targeted this galaxy, collecting data for three observing programmes that aim to study various kinds of supernovae.

SN 2015as was what’s known as a core-collapse supernova: a cataclysmic explosion that happens when the core of a star far more massive than the Sun runs out of fuel and collapses under its own gravity, initiating a rebound of material outside the core. Hubble observations of SN 2015as will help researchers understand what happens when the expanding shockwave of a supernova collides with the gas that surrounds the exploded star.
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SN 2011ht might have been a core-collapse supernova as well, but it could also be an impostor called a luminous blue variable. Luminous blue variables are rare stars that experience eruptions so large that they can mimic supernovae. Crucially, luminous blue variables emerge from these eruptions unscathed, while stars that go supernova do not. Hubble will search for a stellar survivor at SN 2011ht’s location, and the explosion’s identity may be revealed at last.

Source: ESA/Hubble/potw

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