Friday, November 13, 2026

Astronomers Discover Nāpōwawāʻenakaulua, the Oldest Compact Quasar Pair in the Universe



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Artist’s impression of Nāpōwawāʻenakaulua above Maunakea

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Artist’s impression of Nāpōwawāʻenakaulua above Maunakea (annotated)

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Galaxy of Dreams



The Gemini North telescope on Maunakea and James Webb Space Telescope observed the pair of rapidly feeding supermassive black holes just 900 million years after the Big Bang

The oldest pair of compact quasars ever observed has been found only 900 million years after the Big Bang. Scientists say there is no theoretical explanation for how the pair of actively feeding black holes grew so massive at such an early time in the history of the Universe. The pair of quasars has been given the Hawaiian nickname Nāpōwawāʻenakaulua.

An international team of astronomers has discovered J1602+4228AB, nicknamed Nāpōwawāʻenakaulua, the most distant, and thus oldest, compact pair of quasars ever found in the Universe. Their close separation also makes them the most compact pair of quasars found in the early-Universe era known as cosmic dawn. While astronomers theorize that quasar pairs are common, actually finding and characterizing these energetic objects is rare. Even rarer — finding them this early in the history of the Universe.

Nāpōwawāʻenakaulua’s surprising nature was revealed through observations with the Gemini North telescope, located on the dormant volcano Maunakea in Hawai‘i, and the James Webb Space Telescope (JWST). Silvia Onorato, a postdoctoral research associate at NSF NOIRLab, led the study. The results are presented in a paper published in The Astrophysical Journal Letters.

Gemini North is one half of the International Gemini Observatory, an international collaboration led by the U.S. National Science Foundation, in partnership with Canada, Chile, Brazil, Argentina, and the Republic of Korea, and operated by NSF NOIRLab.

The first billion years of cosmic time were a period of furious assembly: dark matter halos collapsed, galaxies ignited their first generation of stars, and massive galaxies formed the very first supermassive black holes at their centers. As galaxies interacted, collided, and in some cases merged completely, their supermassive black holes were fed with large quantities of gas and stars. A fraction of this “accreted mass” from feeding was converted into energy, causing the black holes to become so bright as to outshine all the stars in their host galaxy. These are what astronomers call quasars.

Scientists have established that galaxy interactions and mergers are common in the Universe. Therefore, they expect to find an abundance of pairs of quasars with a separation less than the typical size of a galaxy. However, this has proven difficult for a few reasons: 1) a supermassive black hole’s “quasar phase” is relatively short; 2) these objects are very far away, so they are faint and hard to detect with ground-based telescopes; 3) at such small separation scales, the individual members of a quasar pair are hard to resolve.

Enter Nāpōwawāʻenakaulua, which is not only the third known quasar pair found at cosmic dawn, but it was found so early in the history of the Universe that scientists cannot explain how it came into existence. The nature of Nāpōwawāʻenakaulua is captured in its name, which translates to “Two celestial bodies of fathomless powerful darkness in the brilliance of heat reincarnating energy into the Universe,” as created by the A Hua He Inoa program at the ʻImiloa Astronomy Center of Hawaiʻi and the University of Hawai‘i’s Ka Haka ʻUla O Keʻelikōlani (Hawaiian Language College) [1].

The pair is separated by a distance of approximately 18,100 light-years, or roughly one-fifth the diameter of the Milky Way Galaxy. They have masses of 1.5 billion and 400 million times that of the Sun, respectively. Their distance from us places them at only 900 million years after the Big Bang. During this period, the Universe’s first stars, galaxies, and black holes were still relatively young. The extreme mass of Nāpōwawāʻenakaulua at this time therefore challenges our current understanding of how large-scale cosmic structures are formed.

“There is no definitive theoretical explanation for how a single one of these giant quasars exists so early in the age of our Universe, much less two,” says Onorato. “We observed Nāpōwawāʻenakaulua at a time when the Universe was only a thirteenth of its age and astonishingly, its supermassive black holes are just as massive as those we see today.”

Nāpōwawāʻenakaulua was uncovered in data from the Aether survey, a JWST program led by Emanuele Paolo Farina, Associate Scientist at NSF NOIRLab/Gemini, aimed at compiling a census of objects in the early Universe. Using JWST’s Near-Infrared Spectrograph Integral Field Unit, the survey collected a sample of 200 quasars, representing 43% of all known quasars at this stage of cosmic history. It was during visual inspections of the Aether dataset that the team made the exciting discovery that quasar J1602+4228A had a companion.

Follow-up observations with Gemini North’s Gemini Near-Infrared Spectrograph (GNIRS) allowed the team to resolve the two quasars as individuals. J1602+4228A and B are so close together, and J1602+4228B is so faint, that observing it from the ground should have been nearly impossible. However, perfect timing and perfect weather conditions on Maunakea allowed the team to accomplish this scientific feat. “The sky over Maunakea was so clean and sharp that we managed to collect the data in only two nights,” says Onorato. Additional observations with the Gemini Multi-Object Spectrograph (GMOS) further constrained the properties of the quasar pair [2].

While the complete origin story of Nāpōwawāʻenakaulua remains a mystery, the team proposes that this rare quasar pair may serve as a signpost of an extreme peak in the matter density field of the early Universe, where galactic interactions simultaneously fed star formation and the rapid growth of the black holes.

“Nāpōwawāʻenakaulua is a really unique environment,” says Onorato. “It’s a laboratory for astronomers to study how the very first massive galaxies and their central black holes assembled together through direct galaxy interactions during these early times.”




Notes

[1] The A Hua He Inoa (AHHI) program utilizes traditional naming practices, and often works with students, teachers, and community members who are fluent in ‘Ōlelo Hawaiʻi, the indigenous language of Hawaiʻi. Nāpōwawāʻenakaulua was created by Larry Kimura, a professor at Ka Haka ʻUla O Keʻelikōlani. It combines Nā (plural indicator), Pō (fathomless powerful darkness) to represent the supermassive black holes, Wawā (reincarnation or procreation as referenced from hānau wawā in Pukui-Elbert (1986) dictionary), ʻEna (brilliance of heat) to represent the bright radiation emitted from the matter accreting onto the central black holes, and Kaulua (double or pair) to represent the two quasars. Nāpōwawāʻenakaulua also harkens back to two previously named objects from AHHI: Pōwehi, the first image of a black hole in 2019, and Pōniuāʻena, the furthest quasar discovered at the time in 2020.

[2] GMOS was used to investigate whether a gravitational lens positioned in front of the quasar pair was creating the appearance of the second, fainter quasar. Differences in the shape of each quasar's spectra led the team to favor that this is a real physical pair; however, a lens model is needed to definitively rule out gravitational lensing.



More information

This research is presented in a paper titled “Nāpōwawā‘enakaulua: a close quasar pair at cosmic dawn in the Aether survey” appearing in The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/aeb11f

The team is composed of S. Onorato (NSF NOIRLab/International Gemini Observatory [Gemini], USA), E. P. Farina (NSF NOIRLab/Gemini, USA/Italian National Institute for Astrophysics [INAF], ITA), R. Decarli (INAF, ITA), K. Protušová (Heidelberg University, DEU), E. Pizzati (Center for Astrophysics | Harvard & Smithsonian, USA), D. Pelliccia (UC Santa Cruz, USA), D. S. Chu (University of Hawai‘i, USA), L. L. Kimura (Ka Haka ‘Ula O Ke‘elikōlani/College of Hawaiian Language, USA), L. Lozi (NSF NOIRLab/Gemini, USA), E. Peavy (NSF NOIRLab/Gemini, USA), F. Arrigoni–Battaia (Max Planck Institute for Astrophysics [MPA], DEU), E. Bañados (Max Planck Institute for Astronomy [MPIA], DEU), A. J. Barth (University of California, Irvine, USA), S. Belladitta (MPA, DEU/INAF, ITA), M. Bischetti (University of Pisa/INAF, ITA), S. E. I. Bosman (Heidelberg University/MPIA, DEU), H. Choi (University of Michigan [U-M], USA), T. Costa (Newcastle University, GBR), A. Eilers (Massachusetts Institute of Technology, USA), X. Fan (University of Arizona [UA], USA), S. Gallerani (Scuola Normale Superiore, ITA), T. R. Geballe (NSF NOIRLab/Gemini, USA), A. J. Gloudemans (NSF NOIRLab/Gemini, USA), E. Kim (NSF NOIRLab/Gemini, USA), B. C. Lemaux (NSF NOIRLab/Gemini, USA), W. Liu (UA, USA), Y. Matsuoka (Ehime University, JPN), C. Mazzucchelli (Universidad Diego Portales, CHL), A. Nitta (NSF NOIRLab/Gemini, USA), J. Schindler (University of Hamburg, DEU), A. W. Stephens (NSF NOIRLab/Gemini, USA), H. Suh (NSF NOIRLab/Gemini, USA), F. Walter (MPIA, DEU), F. Wang (U-M, USA), and J. Yang (U-M, USA).>

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

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



Links



Contacts:

Silvia Onorato
Postdoctoral Research Associate
International Gemini Observatory/NSF NOIRLab
Email:
silvia.onorato@noirlab.edu

Emanuele Paolo Farina
Associate Scientist
International Gemini Observatory/NSF NOIRLab
Email:
emanuele.farina@noirlab.edu

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


Thursday, November 12, 2026

A constant companion: surprisingly stable neutron star accretion

A scientist's diagram illustrating the layout of a BeXRB system, showing the decretion disk around the Be star and a neutron star on an eccentric (highly elliptical) orbit around it, but still maintaining steady accretion despite being far away from the material of the disk. Image credit: P. Thalhammer/Remeis Observatory. Download Image

During the past week, NuSTAR observed IGR J06074+2205, the latest in a series of observations of a sample of Be X-ray binaries (BeXRBs) — binary systems with a neutron star orbiting and accreting matter from its Be star companion, a type of massive star characterized by unique equatorial outflows. BeXRBs display occasional but exceptionally bright outbursts, partly resulting from their eccentric orbits, and are well-studied during these bright states. Their behaviour when the neutron star is farther away from the Be star has been a longstanding question. A handful of BeXRBs — the most well-known of them — have already been confirmed to accrete steadily at low luminosities, challenging previous models. The current observations, by targeting those systems that have not yet been observed at low luminosities, aim to complement our understanding of BeXRBs by performing an unbiased hard X-ray survey to probe the universality of prolonged stable accretion outside of outbursts in these systems, and to identify exceptions to what is becoming the prevalent scenario. The data obtained will not only shed light on the properties of individual accreting neutron stars, such as their magnetic fields and spin periods, but will also contribute towards sharpening constraints on the X-ray luminosity function of High Mass X-ray Binaries, which are crucial to understanding the star formation history of our Galaxy.

Author: Aafia Ansar Mohideen (Research Scientist, Dr. Karl Remeis Sternwarte Astronomical Institute, Germany)



Wednesday, November 11, 2026

Astronomers Find Hints of Star Population That Failed to Explode

These pictures taken by NASA's Hubble Space Telescope in 2007 and 2015 show an example of a star thought to have died via a failed supernova. A giant star N6946-BH1 is seen before and after it vanished out of sight, likely after imploding to form a black hole. Credit: NASA/ESA/C. Kochanek (OSU)

This chart shows the rates of mergers between black hole pairs (y-axis) plotted against the mass of the heavier black hole in the pair (x-axis), as inferred from gravitational-wave data. It compares two models—both show a peak at 10 solar masses—but they differ in whether they have a gap in masses between 12 and 16 solar masses (blue line) or not (yellow line). The blue model is a prediction for a population of black holes that formed via failed supernovae—the rate is of mergers is much lower between 12 and 16 solar masses, implying that merging black holes are not efficiently formed in that mass range. The LIGO-Virgo-KAGRA gravitational-wave data favor the failed supernovae model. Credit: University of Illinois Urbana-Champaign/Isaac Legred

Katerina Chatziioannou

Isaac Legred



LIGO–Virgo–KAGRA observations find evidence for black holes that may have formed after quietly imploding

When the most massive stars in the universe die, they often detonate in fiery supernovae, dramatically blasting most of their matter into space. The remaining stellar cores collapse into neutron stars and, sometimes, black holes. However, theories suggest that some massive stars might die without a bang, instead directly collapsing inward to become neutron stars or black holes.

Now, a new Caltech-led study using data from the LIGO–Virgo–KAGRA network of gravitational-wave observatories finds hints of a distinct population of black holes that may have formed from such failed supernovae. While the study did not find direct evidence for failed supernovae, it does show that previous gravitational-wave observations match what theorists had predicted for such a population.

LIGO, the National Science Foundation (NSF)-funded Laser Interferometer Gravitational-wave Observatory, which consists of detectors in Louisiana and Washington, made history in 2015 with the first direct detection of gravitational waves, or ripples in space-time, from a pair of colliding black holes. Since then, the Virgo detector in Italy and the Kamioka Gravitational-wave Detector (KAGRA) in Japan, have joined together in one network that has spotted more than 300 black hole collisions.

"A vast majority of the merging black holes in the universe are about 10 times the mass of our Sun," says LIGO team member Katerina Chatziioannou, a professor of physics at Caltech and a William H. Hurt Scholar. "Our data are showing that this group of black holes may have a common origin—they may be a distinct subpopulation that failed to go supernova. These results represent a connection between the gravitational-wave data and underlying astrophysics we are trying to extract."

Chatziioannou led the new research, which has been published in the journal Physical Review D. The lead author is Isaac Legred (PhD '25), a postdoc at the University of Illinois Urbana-Champaign who performed the research while at Caltech. Former Chatziioannou lab member Jacob Golomb (PhD '25), now at Asari AI, is also an author.

Earlier studies had revealed that merging black holes often have a mass of about 10 times the mass of our Sun, and theorists had proposed that this large population may represent failed supernovae. That means that when the black holes merge, either the most massive black hole of the pair, or both of them, may have originated from a star that imploded rather than exploded. The goal of the Caltech-led team was to see if this idea was consistent with the gravitational-wave data.

In the study, the researchers looked at the distribution of the masses of 257 black hole mergers detected by the LIGO–Virgo–KAGRA network over the past 10 years. The data revealed a dramatic peak of black holes at 10 solar masses—three-quarters of the entire sample of mergers. And for the first time, the team found a distinct lack of black holes in the 12 to 16 solar-mass range.

"We see 10 solar-mass black holes merging all the time," Legred says. "But why are, say, 14 solar-mass black holes so rare? The gap we see in the distribution of masses indicates there may be a special cocktail of internal physics that goes into forming the abundance of 10 solar-mass black holes."

The scientists also looked at the distribution of the rates at which those black holes spin (the spins are also influenced by how the black holes formed). This revealed that the population of 10 solar-mass black holes fell into a narrower range of spin rates than the overall sample of black holes. Together, the findings support the idea that the 10 solar-mass black holes are distinct from the overall population, and thus likely have a common origin—possibly the result of the quiet implosion of massive stars.

"We can look up at the sky and try to study historical records of massive stars that failed to explode, but it's challenging because they just vanish without exploding, leaving a dark patch of sky," Legred says. "With this study, we show the gravitational-wave data are consistent with most binary black holes forming from a very special kind of failed supernova, but more research is needed. Black holes are born in some of the most extreme environments in the universe, so the prospect of better understanding their formation is very exciting."

The study titled "Low-mass failed supernovae and the 10 peak in the merging black hole mass distribution," was funded by the National Science Foundation, the U.S. Department of Energy, and the Simons Foundation. LIGO is operated by Caltech and MIT.

Written by Whitney Clavin

Source: Caltech/News



Contact:

Whitney Clavin
(626) 395‑1944

wclavin@caltech.edu


Tuesday, November 10, 2026

ASA's Chandra Finds Source of Star's Mysterious Outbursts

AT 2016blu in NGC 4559 (Labeled)
Credit: X-ray: NASA/CXC/Univ. of Virgina/M. Aghakhanloo et al.; Optical: SDSS;
Image Processing: NASA/CXC/SAO/P. Edmonds


JPEG (772 kb) - Large JPEG (6.9 MB) - Tiff (95.4 MB) - More Images

A Tour of AT 2016blu - More Videos



  • Researchers using Chandra have uncovered the source of large, repeating flares of light from a giant star.

  • The Chandra data revealed the presence of a black hole or neutron star in an oval-shaped orbit with the unstable star.

  • After monitoring the star, AT 2016blu, with optical telescopes, the team asked Chandra to observe it at a specific time.

  • During their closest approach the black hole or neutron star pulls material from the unstable star, which is heated and produces X-rays.



Astronomers have discovered what is triggering repeated outbursts from a giant, unstable star using NASA’s Chandra X-ray Observatory, as described in our latest press release. This volatile star, known as AT 2016blu, is located in the spiral galaxy NGC 4559 that is about 37 million light-years from Earth.

For about 15 years, astronomers have watched as AT 2016blu has repeatedly grown extremely bright in optical light only to dim back down again. AT 2016blu is a type of luminous blue variable (LBV), which are hot massive stars characterized by changes in brightness (Eta Carinae is the most famous LBV).

This change in brightness was so dramatic that it rivaled the light output of a supernova explosion, which was ruled out as an explanation since the star repeated this behavior many times. (Some have referred to this star as a “supernova imposter”.) To solve this puzzle, a team of astronomers turned to Chandra and found that during an optical outburst in March 2026, the object also glowed brightly in X-rays.

AT 2016blu in Quiescence and Outburst in X-ray & Optical Light.
Credit: X-ray: NASA/CXC/Univ. of Virgina/M. Aghakhanloo et al; Optical: NSF/KAIT

This increase in X-ray brightness Chandra provided the answer: a previously hidden companion object keeps pulling material away from the massive star every 113 days as they orbit one another. This partner is either a stellar-mass black hole or a neutron star (the dense collapsed core of a massive star). When the star gets to its closest approach to the neutron star or black hole in their oval-shaped orbit, some of its material is pulled away and gets captured by the black hole or neutron star. The material then orbits at very high speeds close to the speed of light, getting so hot that it shines brightly in X-rays.

This composite image shows AT 2016blu in X-rays from Chandra (magenta) along with its host galaxy, NGC 4559, in optical light from the Sloan Digital Sky Survey (red, green, and blue). The colors of the optical image blend to appear white in many regions. The Chandra data from March 2026 show X-ray sources in the field, some of them associated with NGC 4559, and the Sloan data shows the galaxy and foreground and background objects. The LBV AT 2016blu is in the middle of the small square and is seen in both the Chandra and Sloan data. The much brighter X-ray source within the square is unrelated to AT 2016blu.

The Chandra data from March 2026 revealed that AT 2016blu was at least 100 times brighter in X-rays than in Chandra data from 2001 to 2002, which is before the outbursts began. AT 2016blu is bright enough in X-rays to be classified as a candidate ultra-luminous X-ray source (ULX). These are rare, bright X-ray sources found with telescopes like Chandra that astronomers have yet to fully understand. The current thinking is that some of them contain neutron stars, and others have black holes.

A paper describing these results, led by Mojgan Aghakhanloo (University of Virginia), is being published in The Astrophysical Journal on November 9, 2026; it is available at https://iopscience.iop.org/article/10.3847/1538-4357/ae9a86.

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.





Visual Description:

This release features a composite image of a spiral galaxy with a giant, unstable star at its outer edge. Using Chandra, astronomers have discovered the star's previously hidden companion, which triggers luminous outbursts every 113 days.

The spiral galaxy is NGC 4559. Shown at a sharp angle in the composite image, its flat pink and milky blue face tilts toward our upper left. Sitting near the outer edge of the dense spiral, near the center of the frame, is a small group of pink and blue dots. This group is outlined with a white square, enlarged and annotated in supporting images.

The smallest pink dot in the square is AT 2016blu, a massive star some 33 times the size of our Sun. For over 15 years astronomers have been watching this star get bright and then dim again in optical light on a regular basis. Chandra's X-ray observations suggest that a hidden companion object, either a stellar mass black hole or a neutron star, is pulling material from AT 2016blu every 113 days as they orbit one another. This captured material gets so hot that it shines brightly in X-rays.

Other pink and blue specks within the white square and enlargement are unresolved stars or star clusters, too distant to be related to the movement of material between AT 2016blu and its hidden but influential neighbor.



Fast Facts for AT 2016blu in NGC 4559:

Credit: X-ray: NASA/CXC/Univ. of Virgina/M. Aghakhanloo et al.; Optical: SDSS; Image Processing: NASA/CXC/SAO/P. Edmonds
Release Date: November 9, 2026
Scale: Image is about 12 arcmin (130,000 light-years) across.
Category: Black Holes, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 12h 35m 52.2s | Dec +27° 55´ 55.9"
Constellation: Coma Berenices
Observation Dates: 5 observations during Mar 2026 Observation Time: 26 hours 30 minutes (1 days 2 hours 30 minutes)
Obs. ID: 31041, 32254-32257
Instrument:
ACIS
References: Aghakhanloo, M, et al, 2026, ApJ, Published.
Color Code: X-ray: magenta; Infrared: red, green, and blue;
Distance Estimate: About 37 million light-years from Earth (z=0.00261)



Monday, November 09, 2026

A Mighty Wind Blew Away Gas and Made Early Galaxies Brighter

The JWST found an overabundance of bright galaxies in the early Universe, only a few hundred million years after the Big Bang, as shown in this artist's illustration. According to our understanding, they should've been much rarer. Something must have blown the obscuring gas away. Image Credit: Matt Twombly for Simons Foundation

Only a few hundred million years after the Big Bang, during the Cosmic Dawn, bright galaxies populated the Universe in numbers higher than expected. The JWST showed that these galaxies formed very dense, compact clusters of stars. Why their star formation was concentrated in such dense clusters is a puzzle, as is the brightness of their host galaxies.

A pair of researchers may have figured it out. Their work is titled "Lyα Radiation Pressure in Dense Star Clusters: Implications for Star Formation and Winds at Cosmic Dawn," and it's published in The Astrophysical Journal. The authors are Shyam H. Menon and Aaron Smith. Lead author Menon is a research fellow at the Flatiron Institute’s Center for Computational Astrophysics, and co-author Smith is an assistant professor of physics at the University of Texas at Dallas. The Lyman-Alpha (Lyα) radiation in the paper's title is a very important factor in astrophysics. It's produced when an electron in a hydrogen atom transitions from excited to ground state. Since hydrogen is by far the most abundant element in the Universe, Lyα is a fundamental way to probe the Universe's earliest galaxies, including the interstellar medium (ISM) and the intergalactic medium (IGM).

"Observations with the JWST in lensed fields have revealed that galaxies at cosmic dawn may concentrate their star formation in highly dense, compact, star clusters," the authors write. "The high columns and low metallicities encountered in their birth environments suggest that Lyα radiation pressure may be crucial to their formation and evolution."

These panels show some of the bright and dense star clusters the JWST found in the early Universe, only about 460 million years after the Big. The panel on the right shows their location in SPT0615-JD1, a strongly-lensed galaxy. Image Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration


“Our results show Lyman-alpha radiation can push low-density gas and dust away really, really fast,” lead author Menon said. “It can sort of clear the ‘fog,’ allowing us to see stars in the early universe much more clearly than we would otherwise.”

Lyα's utility as a diagnostic tool also explains its powerful ability to push dust and gas away so quickly. Lyα radiation is different than others. Typically, when an atom absorbs energy, it re-emits it at a different wavelength. But hydrogen atoms absorb Lyα and then re-emit it again almost instantaneously, where it interacts with more hydrogen. This absorption-emission cycle makes it a powerful diagnostic tool, and it also gives Lyα the ability to bully hydrogen gas.

Astrophysicists knew this, but understanding its effect on a large scale was difficult.

“We’ve known for a very long time that Lyman-alpha radiation could be important because it carries a lot of force,” Menon says. “But we’ve never actually been able to estimate how important it is in a realistic environment because of how challenging it is to model.”

Researchers have tried to incorporate it into models, but Lyman-alpha resists those attempts. Some haven't even tried to include it. "The oversight is related to its high dimensionality and complexity, as well as the inherently demanding computational requirements for modeling it self-consistently," the authors write.

The reason it's difficult to model is precisely because of its repeating cycle of absorption and emission. But difficult isn't synonymous with impossible.

Menon and Smith didn't try to simulate it. Instead, they took snapshots from existing simulations and got busy calculating the force necessary to explain the snapshots. "In this study, we address this question by postprocessing snapshots from radiation-hydrodynamic simulations of dense star-cluster-forming clouds with a range of dust abundances using the COLT Monte Carlo code," they explain. COLT stands for Cosmic Lyman-alpha Transfer. Study co-author Aaron Smith is COLT's original creator, and he wrote it to "simulate the production and escape of Lyα from hydrodynamical simulations," according to the COLT website.

In short, they examined simulation snapshots of star-forming regions in the early Universe, and calculated the amount of Lyα necessary to explain what they saw.

These are multiple views of a 2.5-million-year simulation visualizing a gas cloud as it is cleared away and the formation of stars. From left to right, the views show the gas density, ionization and temperature. Credit: Shyam Menon (Flatiron Institute) and Aaron Smith (UT Dallas).


The results showed that Lyman-alpha radiation wasn't strong enough to blow away the gas in the dense star-forming regions found by the JWST. The gravity from the dense gas in those filaments was too strong for Lyman-alpha to overcome. But beyond those dense filaments, it was powerful enough to blow away the more diffuse gas and the dust.

This graphic shows how Lyman-Alpha was able to blow away gas and dust that obscured early galaxies and their dense star clusters. Image Credit: Lucy Reading-Ikkanda/Simons Foundation

The authors outline two simple conclusions in their paper: "Lyα radiation pressure is unlikely to preclude efficient star formation," and "Lyα radiation pressure can drive dynamically significant winds once star formation saturates."

"Therefore, our results suggest that the SFE is likely to remain high in the dense star clusters forming at high-z. On the other hand, a significant fraction of the volume-filling gas can be ejected by Lyα radiation pressure, suggesting implications for the visibility of light from the cluster, ionizing photon escape, and launching outflows from the galaxy," the researchers write in their paper.

So once star formation had proceeded far enough in these dense clusters, Lyman-alpha made them visible by blowing away the rest of the gas.

“When the density is low enough, the Lyman-alpha radiation can push the gas to really high speeds, launching explosive winds that can shoot material clear out of the galaxy,” Menon says. "That cleared away the gas obscuring the dense clusters, making them visible."

By Evan Gough




Evan Gough is a science-loving guy with no formal education who loves Earth, forests, hiking, and heavy music. He's guided by Carl Sagan's quote: "Understanding is a kind of ecstasy."


Sunday, November 08, 2026

European orbiter detects hints of volcanic activity on Mars

This image shows the northern flanks of the Alba Mons volcano on Mars in wider context. The white icon shows the location of the close-up image featured in this story. Credits: MEx/HRSC global colour mosaic, ESA/DLR/FU Berlin, G. Michael. Inset: Blended MOLA-HRSC digital elevation model, Fergason et al 2018. Credits: Mars Express & HRSC. License: CC BY-SA 3.0 IGO or ESA Standard Licence

New evidence from gas seeping above volcanic rifts suggests Mars is not geologically dead deep inside, but merely sleeping.

Fresh fissures along the Alba Mons region hint at active spots under the surface, where gases from inside the planet may be making their way up to the surface.

An international research team led by Alexander Trokhimovskiy suggests that the release of hydrogen chloride comes from hot magma beneath the surface – a sign of dormant volcanism.

The ExoMars Trace Gas Orbiter (TGO) first reported hydrogen chloride gas in the martian atmosphere back in 2021. This gas is commonly found escaping from magmatic vents on Earth, leading researchers to wonder whether the same was happening on Mars.

“Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently, and possibly still does,” says Daniel Mège, Professor at the Space Research Centre of the Polish Academy of Sciences and co-lead author of a paper published in Science Advances yesterday.

Magmatic gas release on Mars

Rising gas

It was early summer in the northern hemisphere of Mars when a team of researchers noticed spikes of hydrogen chloride where it shouldn’t have been, and during an odd season.

Then a close look at the Alba Mons region using TGO’s CaSSIS camera showed fresh and narrow fissures, in some cases hundreds of metres long, associated with colour changes on the surface.

The team of researchers relied on geological intuition to make the link between the gas and the rifts. “Looking at the spatial distribution of the seeping, it became instantly obvious to me that there was something volcanic behind it, but it had to be demonstrated,” concedes Daniel.

“A huge part of the work consisted of examining all the possible chemical processes going on in the martian atmosphere. We needed to be rigorous, critical and creative to explain the presence of hydrogen chloride. The data were complex, but also excellent brain food,” adds Daniel.

The team suggests that the seepage is connected to a dormant magma chamber, a sort of volcanic plumbing system under the martian surface.

Niches for life

Magmatic gases like hydrogen chloride could have been more abundant in the past, contributing to a thicker atmosphere and warmer climate and allowing liquid water to cover much of the martian surface. If lava rising through the crust meets groundwater, this could lead to warm habitable niches.

“Looking for martian life in the seeping fissures of the Alba Mons region would make a lot of sense. If hydrothermal systems are active, they could contain the ingredients and energy needed for microorganisms to develop, and shield microorganisms from the hostile and changing environment above the surface,” ponders Daniel.

“These findings may prove to be TG’s greatest success yet,” highlights Colin Wilson, ESA’s project scientist for the ExoMars Trace Gas Orbiter.

Paper published in Science Advances on 4 November 2026, “Enigmatic HCl detections as a potential signature of igneous activity on Mars.”
“The Trace Gas Orbiter was able to find the smoking gun. It was like looking for a needle in a haystack. It’s truly amazing that it spotted a handful of molecules from a perhaps intermittent source, whilst moving continuously along its orbit to monitor the whole martian atmosphere,” explains Daniel.

Scientists sug gest magmatic gases might be rising through these fissures, like some fumaroles on Earth. Blocked by ice during winter’s freezing temperatures, down to -120°C, the fissures would channel the release of chloride as the ice sublimates in early summer.

The discolouration around the fissures could come from deposits left behind by gases escaping from Mars’s interior, as around fumaroles (volcanic gas vents) on Earth.

This gas varies seasonally on Mars, reaching its maximum in northern hemisphere winter, then mostly disappearing in the summer. Most of this variability appears to be linked with Mars’ dust and water cycles. Yet there was one exception to this pattern, always in the same season and at the same place – above volcanic fissures on the flanks of the Alba Mons volcano, in early summer.

Mars is not dead, just dormant

Mars has the largest volcanoes in the Solar System, but it is not known how active they are. Orbital imagery shows that some volcanoes appear to have been active within the last few million years, and seismometers have detected marsquakes – the earthquakes of Mars. Both facts point to the possibility of Mars being volcanically active.

However, no new lava flows or eruptions have ever been observed.
This image shows a region of Mars lying on the northern flanks of the Alba Mons volcano. The white spots may be caused by deposition around vents where magmatic gases may be escaping from Mars’s interior. The image, taken on 3 February 2023, is approximately 20 km by 20km in size and is centred at approximately 64.6°N/274.4°E. Credits: ESA/TGO/CaSSIS. License: CC BY-SA 3.0 IGO or ESA Standard Licence

Fissures and seasonal gases

The finding is the result of combined atmospheric and geological analysis. First came the detection of hydrogen chloride strongly localised in space and at a time just after the frosts of winter sublimate. The infrared spectrometers from TGO’s Atmospheric Chemistry Suite were on the case.

Then a close look at the Alba Mons region using TGO’s CaSSIS camera showed fresh and narrow fissures, in some cases hundreds of metres long, associated with colour changes on the surface.

“The Trace Gas Orbiter was able to find the smoking gun. It was like looking for a needle in a haystack. It’s truly amazing that it spotted a handful of molecules from a perhaps intermittent source, whilst moving continuously along its orbit to monitor the whole martian atmosphere,” explains Daniel.

Scientists suggest magmatic gases might be rising through these fissures, like some fumaroles on Earth. Blocked by ice during winter’s freezing temperatures, down to -120°C, the fissures would channel the release of chloride as the ice sublimates in early summer.

The discolouration around the fissures could come from deposits left behind by gases escaping from Mars’s interior, as around fumaroles (volcanic gas vents) on Earth.

The team of researchers relied on geological intuition to make the link between the gas and the rifts. “Looking at the spatial distribution of the seeping, it became instantly obvious to me that there was something volcanic behind it, but it had to be demonstrated,” concedes Daniel.

“A huge part of the work consisted of examining all the possible chemical processes going on in the martian atmosphere. We needed to be rigorous, critical and creative to explain the presence of hydrogen chloride. The data were complex, but also excellent brain food,” adds Daniel.

The team suggests that the seepage is connected to a dormant magma chamber, a sort of volcanic plumbing system under the martian surface.

The ExoMars Trace Gas Orbiter (TGO) studies water vapour and its components as it rises through the atmosphere and out into space. By looking specifically at the ratio of hydrogen to its heavier counterpart deuterium, the evolution of water loss over time can be traced. TGO uses two primary occultation techniques—solar occultation and mutual radio occultation—to probe the martian atmosphere and ionosphere. Credits: ESA. License: ESA Standard Licence

Niches for life

Magmatic gases like hydrogen chloride could have been more abundant in the past, contributing to a thicker atmosphere and warmer climate and allowing liquid water to cover much of the martian surface. If lava rising through the crust meets groundwater, this could lead to warm habitable niches.

“Looking for martian life in the seeping fissures of the Alba Mons region would make a lot of sense. If hydrothermal systems are active, they could contain the ingredients and energy needed for microorganisms to develop, and shield microorganisms from the hostile and changing environment above the surface,” ponders Daniel.

“These findings may prove to be TGO’s greatest success yet,” highlights Colin Wilson, ESA’s project scientist for the ExoMars Trace Gas Orbiter.

Paper published in Science Advances on 4 November 2026, “Enigmatic HCl detections as a potential signature of igneous activity on Mars.”

Source: ESA/News


Saturday, November 07, 2026

First Detection of a Rocky Exoplanet’s Secondary Eclipse by Hubble

Ilustration of a lava world exoplanet orbiting close to its host star.
Credit: ESO/L. Calçada;
CC BY 4.0

The Hubble Space Telescope has detected the secondary eclipse of a rocky exoplanet for the first time. These observations place constraints on the possible atmosphere of the lava world TOI-2431b.

Valuable Eclipses

Thousands of exoplanets have been discovered via the transit method, which captures the temporary dimming of a star’s light caused by a planet passing in front of a star from our perspective. Far fewer planets have been spotted passing behind their stars — what’s known as a secondary eclipse — creating a much subtler dip in the combined light from the star and the planet.

A planet’s secondary eclipse encodes valuable information about its dayside temperature, the reflectivity of its surface, and the properties of its atmosphere. Recently, Sebastian Zieba (Center for Astrophysics | Harvard & Smithsonian) and collaborators reported on Hubble Space Telescope observations of the extreme exoplanet TOI-2431b, marking the first time that Hubble has detected the secondary eclipse of a rocky exoplanet.


The combined light from TOI-2431b and its host star over all orbital phases. The secondary eclipse is located at 0.00.
Adapted from Zieba et al. 2026

TOI-2431b (purple star) stands out from other lava worlds in terms of its dayside brightness temperature. The light purple star shows the estimated dayside temperature for an arbitrary nonzero albedo. Credit: Zieba et al. 2026

A First for Hubble

TOI-2431b orbits its K-type host star every 5.4 hours, making it the shortest-period planet with a measured mass (6.2 Earth masses) and radius (1.54 Earth radii). It’s expected to be a lava world: a rocky planet with such a high temperature that all or part of its surface is molten.

These planets orbit their host stars so closely that searing radiation and stellar winds have long since stripped away their primordial atmospheres, but observations have demonstrated that these planets can have atmospheres — albeit deeply un-Earth-like ones composed of superheated rock vapor.

Zieba and coauthors used Hubble to observe TOI-2431b and combined these near-infrared observations with visible-light data from the Transiting Exoplanet Survey Satellite (TESS), which first detected TOI-2431b in 2019. The planet’s secondary eclipse suggests a dayside brightness temperature of 2524K — hot enough to melt many types of rocks — and this temperature is roughly equal to expectations for a world that absorbs all incident energy and redistributes none of it. This interpretation would make TOI-2431b an outlier among the lava worlds observed so far, which generally appear to have a mechanism — a reflective surface, a cloudy atmosphere, or a way to transport heat efficiently from day to night — acting to lower their dayside temperatures.

Modeled optical-to-infrared emission spectrum of TOI-2431b. The no-atmosphere and rock-vapor atmosphere models are indistinguishable with current Hubble and TESS data (red and blue circles) but may be distinguishable with JWST (simulated observation plotted with a green diamond). Click to enlarge. Credit: Zieba et al. 2026

Atmosphere or Not?

These observations don’t definitively rule out an atmosphere or a somewhat reflective surface, since at the near-infrared and visible wavelengths to which Hubble and TESS are sensitive, it’s not possible to disentangle the thermal emission from the planet and the starlight reflected by the planet. Zieba and collaborators modeled a possible rock-vapor atmosphere for TOI-2431b, which showed that the planet’s emission with and without an atmosphere is similar at the wavelengths probed by Hubble and TESS.

While the current data are consistent with TOI-2431b having no atmosphere, JWST will push our observations into the wavelength realm in which a possible rock-vapor atmosphere could be detected. This work represents an exciting first for Hubble, demonstrating its ability to place constraints on hot rocky planets and setting the stage for further insights from JWST.

Zieba and coauthors used Hubble to observe TOI-2431b and combined these near-infrared observations with visible-light data from the Transiting Exoplanet Survey Satellite (TESS), which first detected TOI-2431b in 2019. The planet’s secondary eclipse suggests a dayside brightness temperature of 2524K — hot enough to melt many types of rocks — and this temperature is roughly equal to expectations for a world that absorbs all incident energy and redistributes none of it. This interpretation would make TOI-2431b an outlier among the lava worlds observed so far, which generally appear to have a mechanism — a reflective surface, a cloudy atmosphere, or a way to transport heat efficiently from day to night — acting to lower their dayside temperatures.

By Kerry Hensley

Citation

“The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: The 5.4 hr Planet TOI-2431 b,” Sebastian Zieba et al 2026 ApJL 1011 L32. doi:10.3847/2041-8213/aeb4ab



Friday, November 06, 2026

Lessons from a stellar instructor

A star cluster seen up close, filling the view with thousands of stars. They are clearly divided between blue ones, which are scattered around the outskirts of the image but more towards the centre and are the majority in the bright core of the cluster, and yellow stars, which are present in the core but make up most of the cluster outside of that. A few orange stars are closer to us and appear noticeably larger.



Today’s ESA/Hubble Picture of the Month gives us a lesson in galactic history. This sparkling collection of stars is named Messier 30 (M30) after Charles Messier, the French astronomer who catalogued M30 and other diffuse objects that might be mistaken for comets. M30 lies about 27 500 light-years away in the constellation Capricornus.

M30 is a globular cluster: a roughly spherical star cluster containing anywhere from tens of thousands to millions of stars. These clusters generally reside on the outskirts of galaxies, orbiting within a vast, diffuse region called the halo like a swarm of moths around a lightbulb. Our Milky Way galaxy has at least 150 globular clusters, the nearest of which is about 6000 light-years away. These clusters are impressively ancient: astronomers have estimated their ages at 11.5 to 13.5 billion years, making certain globular clusters nearly as old as the Universe itself.

Globular clusters have long played an important role in helping us learn about our galaxy. More than a century ago, astronomer Harlow Shapley used observations of a particular type of variable star to measure the locations of and distances to dozens of globular clusters within our galaxy. This work showed that the Sun is not in the centre of our galaxy, and that the galactic centre lies instead toward the constellation Sagittarius. (His distance measurements were incorrect, however, and he concluded that our galaxy is about twice as large as it really is.)

Today, astronomers continue to learn about our galaxy by observing globular clusters. Because globular clusters are so ancient, they can give us clues about how our galaxy was assembled long ago. Globular clusters that formed within our galaxy can act as time capsules, preserving the original chemistry of our young galaxy.

However, it’s possible that not all globular clusters that orbit within our galaxy today formed there. Researchers have discovered that M30 and many other globular clusters orbit in the direction opposite from the way our galaxy spins. This may mean that these clusters did not form within our galaxy at all, but may instead have been captured by the Milky Way galaxy in the distant past!

Hubble has observed M30 multiple times, A previously released image of M30 featured data from Hubble’s Advanced Camera for Surveys. These data came from an observing programme (#10775; PI: Sarajedini) that surveyed dozens of Milky Way globular clusters, observing red and near-infrared light that revealed stars down to just 20% of the mass of the Sun. A more recent programme (#13297; PI: Piotto) returned to M30 and other globular clusters in our galaxy, this time observing the clusters with Hubble’s Wide Field Camera 3 and using three filters that captured bluer light. This programme collected data that was critical for studying exotic objects like blue straggler stars as well as for investigating the multiple populations of stars that can inhabit a single globular cluster.

Most recently, Hubble viewed many of these globular clusters once more, aiming to detect how the stars in these clusters had moved over 15 years. This programme (#16298, PI: Libralato) allowed astronomers to study how different populations of stars in globular clusters move — a feat only possible due to Hubble’s longevity and ability to discern fantastically small details in distant objects.



Stars on demand

NGC 3227
Credit: ESO/A. Berdeu



Nothing is being attacked with space lasers in this Picture of the Week, although it may look like those four bright yellow streaks are menacing the galaxies to the right of the image. These streaks are, in fact, four artificial stars. As starlight passes through our restless atmosphere it gets blurred, distorting astronomical images. Artificial stars allow us to correct for this, but why do the ones in this picture look elongated rather than point sources, and how are they generated?

The artificial stars you see in this image were created by laser beams rising from ESO’s Very Large Telescope (VLT) in Chile. Each beam comes from one of the VLT’s four Unit Telescopes. The beams themselves show faintly at the lower left, scattering off the air on their way up. As they travel upwards, the atmosphere becomes less dense, and the beams appear progressively fainter. But when they reach 90 km above the ground they encounter a layer rich in sodium atoms that glow brightly as they are excited by the lasers.

Because these atoms are spread across a layer about 5-10 km thick, they appear as streaks when photographed from an angle, like in this picture taken 2.5 km away from the telescopes. But they look like point sources when seen from the telescopes where the lasers are coming from. An adaptive optics system monitors how these artificial points twinkle, and controls a thin flexible mirror that reshapes itself hundreds of times per second. This in turn unblurs the incoming light from the astronomical target one is observing.

The target in this case is the supermassive black hole at the centre of NGC 3227, one of the galaxies to the right of the image. It is what astronomers call an active galaxy, whose centre shines brightly as the black hole pulls in the gas around it. ESO astronomer James Leftley is studying several such galaxies with the GRAVITY and MATISSE instruments at the VLT Interferometer (VLTI), which links all four Unit Telescopes so that they work together like a single giant telescope up to 130 metres across. The facility was recently upgraded through the GRAVITY+ project, which saw lasers added to VLT telescopes. With these lasers, the VLTI and its instruments can unblur incoming light almost anywhere in the southern sky, creating stars on demand wherever they are needed.

Source: ESO/potm


Thursday, November 05, 2026

South is south, and north is north in the X-ray map of the Milky Way


Fig.1: Left: X-ray (top) and radio (bottom) images of the sky in galactic coordinates, showing prominent features corresponding to the horizontal galactic disk and vertical extensions above and below the disk. Right: zoomed images, showing the central part of the galaxy. The northern side, dominated by the North Polar Spur, appears much brighter and has a more complicated morphology than the shell-like southern bubble. Credit: X-ray: Predehl et al. 2020, Sunyaev et al. 2020; Radio: Haslam et al. 1982


The largest features visible in the sky are from our home galaxy, the Milky Way. In the optical spectrum, this is the disc of our galaxy, which is prominent across the entire electromagnetic spectrum, from radio waves to ultra-high-energy gamma rays. In the X-ray sky, the second-largest feature is the so-called 'eROSITA bubbles', giant structures above and below the galactic disk that span almost half the sky. These were mapped by the eROSITA X-ray telescope on board the SRG Observatory. Recent studies suggest that these 'bubbles' consist of overlapping heterogeneous structures (different in the north and south), which are partly driven by the release of energy at the centre of our galaxy and partly powered by outflows from star-forming regions in the disk. Although separating these structures is difficult, it is well worth the effort: we can learn about transient outbursts in our galactic centre and measure the properties of low-density gas far from the disk.

The eROSITA bubbles are arc-like structures above the disc of the galaxy that are visible in eROSITA images in the general direction of the galactic centre (see Fig. 1 and these press releases from 2020 and 2021). Direct measurements of the distance to these structures are problematic, but the hypothesis that they are associated with the centre of the Milky Way is attractive, placing the bubbles some 30 thousand light-years away from us. According to this hypothesis, the energy required to create the bubbles originates from a powerful energy release in the galactic centre, possibly from the supermassive black hole Sgr A* or an outburst of star formation in close proximity to the Galactic Centre. A similar hypothesis was first proposed decades ago to explain a bright feature in the radio band (the North Polar Spur, or NPS), and was later extended to include hourglass-shaped structures visible in gamma rays (the Fermi Bubbles).

The eROSITA bubbles fit into this picture as the outer edge of a shock wave propagating through the gas of our galaxy, compressing and heating it (see Press Release 2021). However, the Northern and Southern bubbles differ in morphology and brightness, suggesting the presence of additional effects affecting their appearance.

North is North

Two recent studies argue that, in addition to the shock wave, plumes of hot, metal-enriched gas rise buoyantly from the most active star-forming regions in the galactic disk and contribute to X-ray emission in the northern hemisphere. This makes the northern eROSITA bubble much more prominent than the southern one.

The physics of plume formation is well understood in principle. Supernova explosions from the most massive stars in a star-forming region release energy and produce hot, metal-enriched gas. Initially confined by dense, cold ambient matter, the hot gas breaks through and forms a plume that rises into the galactic atmosphere, away from the disk. As the break is more likely to occur on one side of the region (above or below the galactic disk), a one-sided plume is expected. The differential rotation of the gas above the disk gives the plume a shape reminiscent of smoke rising from a steam locomotive. This plume is hypothesised to account for the remarkable brightness and complex structures of the Northern Bubble. The W43 complex, one of the most active star-forming regions in the Milky Way, lies directly beneath the NPS. In this model, it is the most plausible source of the plume.

Fig. 2: Detailed image of the northern and southern eROSITA bubbles in the 0.7–1.05 keV band (in stereographic projection). At these energies, nearby hot gas contributes little, providing a clearer view of the eROSITA bubbles, which consist of denser, hotter gas. The bottom-right plot shows the X-ray brightness profile across the southern eROSITA bubble radial profile compared with the shell model. The top-right compares the observed X-ray spectrum of the southern bubble shell with predictions from an expanding spherical shock (red line). These data provide us with information on the density, temperature, and heavy element abundance in the gas some 30 000 light years away from the Sun. Adopted from Churazov et al. (2026) .

Fig. 3: On the left, the simplest geometrical model of the shells associated with propagating shocks. From the Sun's position, only a small portion of the putative spherical shell can be seen; the rest is obscured and contaminated by emission from the galactic disk. The green box marks the Sun's position. Right: the X-ray map of the entire sky from the MAXI telescope, with regions affected by the propagating shock in the current scenario delineated. In the simplest model, similar shell-like structures should appear below and above the disk. Recent models postulate that a 'metal-rich plume' rises buoyantly from a star-forming region in the disc, sitting atop these structures. This plume corresponds to NPS in the radio maps and a bright X-ray arc. The plume dominates the northern sky, with the 'proper' northern eROSITA bubble (similar to the southern bubble) barely visible as a faint extension to the left of the plume. Adopted from Churazov et al. (2026) - MAXI .

In contrast, the southern eROSITA bubble, with its much simpler morphology, appears to be consistent with a shockwave driven by a transient energy release at the centre of the Milky Way. Its shell-like appearance (Fig. 2) is reminiscent of a supernova remnant, albeit 100–1000 times larger, and consistent with expectations for a shock driven by a 5–10 Myr-old explosion that has already reached distances of the order of 20,000 light-years from the galactic centre. This makes its boundary appear almost at zenith in the galactic coordinate system. This hypothesis can be further tested by measuring the X-ray spectrum of the southern bubble shell, which reasonably supports the shock scenario.

Interpreting the southern eROSITA bubble as a shock wave propagating through tenuous gas high above the galactic plane is an attractive way to measure its density, temperature, and metal abundance. This is usually challenging because it is difficult to separate the emission from this gas from the contributions of much closer, denser gas. However, the shock compresses and heats this gas, making it suddenly 'visible' (see Fig. 3) as a brighter shell surrounded by a dimmer background. The density and metal abundance can be determined through X-ray spectral analysis.

The gas through which the shockwave is propagating is around 200 times hotter than the interstellar medium in the disk, has a density that is several thousand times lower, and has a 5–10 times lower abundance of heavy elements, such as oxygen and iron. Thus, the eROSITA bubbles provide an in situ probe of Galactic gas located far from us (see Fig. 3).

If the southern eROSITA bubble is indeed a 'proper' shock, there may be a similar structure in the northern sky. Unlike the plume discussed above, which can be highly asymmetric, the massive energy release in the galactic centre should produce comparable bubbles above and below the disk. Such structures can be identified in the northern bubble, just outside the much brighter NPS plume (Figures 1 and 3). It is comparable in size and brightness to the southern bubble, but the bright plume outshines it in the overlapping regions.

In future, high-resolution X-ray spectroscopy could provide the most direct probe of our current understanding of the properties and origin of the eROSITA bubbles by measuring line velocities and broadening at different positions across the bubbles with sensitive X-ray microcalorimeters. This could be achieved by combining a large grasp with high spectral resolution, such as the recently proposed Line Emission Mapper mission. In particular, a double-horn profile of emission lines with a separation of approximately 2 eV would strongly suggest the presence of an expanding shell in the southern bubble. This would place tight constraints on the age and energetics of the past energy release in the galactic centre.




Authors:

Eugene Churazo
Scientific Staff
Tel.:
2219
Email: echurazov@mpa-garching.mpg.de

Ildar Khabibullin
Guest

Email: ildar@MPA-Garching.MPG.DE

Rashid Sunyaev
Emeritus Director
Tel.:
2244
Email: rsunyaev@mpa-garching.mpg.de



Original publications:

1. Churazov E., Khabibullin I. I., Bykov A. M., Chugai N. N., Sunyaev R. A., Utrobin V. P., Zinchenko I. I.
Southern eROSITA bubble as a forward shock and the low-metallicity CGM. South-east side story
A&A (2026)

DOI

2. Churazov E., Khabibullin I. I., Bykov A. M., Chugai N. N., Sunyaev R. A., Utrobin V. P., Zinchenko I. I.
North Polar Spur: Gaseous plume(s) from star-forming regions ∼3─5 kpc from the Galactic Center?
A&A (2024)


DOI

3. Kraft R., et al.
(2022)

Source

4. Khabibullin, I., et al.
LEM All-Sky Survey: Soft X-ray Sky at Microcalorimeter Resolution
(2023)


Source