Saturday, September 05, 2026

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

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Nā ʻUhane Māhoe Huki Pū i ke Ola

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Project Hōkūlani Interns Summer 2026

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Project Hōkūlani Galaxy Presentation

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Project Hōkūlani Stargazing on Maunakea

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Project Hōkūlani Interns Fall 2025

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Project Hōkūlani Interns Shadow Nighttime Operations



Videos

Pan on NGC 7253
PR Video noirlab2621a
Pan on NGC 7253

Zooming into NGC 7253
PR Video noirlab2621b
Zooming into NGC 7253



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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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




More information

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

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



Links



Contacts:

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

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


Friday, September 04, 2026

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

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

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

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



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

Seeing Active Black Holes in a Different Light

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

From the Nucleus to the Outskirts

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

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

A Bridge Between AGN Modes

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

What's missing?

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




Authors:

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

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



Original publication

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

DOI


Thursday, September 03, 2026

A Busy Month in the Galactic Center

A deep X-ray image of the Galactic center taken with the Chandra observatory, with low-, intermediate-, and high-energy X-rays colored in red, green, and blue respectively. It shows thousands of point sources, all powered by accreting white dwarfs, neutron stars, or black holes, embedded in large clouds of hot gas. Sources from this enormous population will frequently go into outburst, prompting astronomers to trigger target-of-opportunity observations to track their evolution. Image credit: NASA/CXC/UMass/D. Wang et al. Download Image



It has been a busy month for the NuSTAR observatory. NuSTAR has in the past performed on average six Target of Opportunity (ToO) observations each month, but the numbers have been steadily increasing over the summer, in part because the Sun has moved away from the position on the sky of the Galactic center, a particularly active part of the sky. So far this month there have been 22 ToO submissions to NuSTAR, five of which were ToO proposals from the Guest Observer (GO) program, and a further five approved Director's Discretionary Time proposals—a new record for time-domain observation requests! More than half of these have been requests to observe transient sources within 5 degrees of the Galactic center, including observations for three GO programs of a bright, previously unknown transient X-ray source, MAXI J1750-327, coordinated with NASA's IXPE mission. Other ToO requests have taken advantage of the new policy allowing short NuSTAR exposures, either splitting up GO observations to increase the number of visits or performing brief monitoring visits to well-known X-ray binaries to keep track of their behavior and to alert the community when an expected outburst begins. Up until recently, the Swift mission has performed the majority of this kind of monitoring. The increase in NuSTAR time domain observations will help to cover some of this lost capability, but it will not be able to replace the key role Swift has played in the X-ray astronomy ecosystem. We salute the Swift team for their extraordinary work over the past decades and the great teamwork the Swift and NuSTAR observatories have been able to achieve together, and wish them the best in their final months of operations.

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



Wednesday, September 02, 2026

Do black holes pretend to have large masses?

A closer look at the gravitational-wave event GW231123
© Simulation: I. Markin (University of Potsdam), H. Pfeiffer (Max Planck Institute for Gravitational Physics), T. Dietrich (University of Potsdam and Max Planck Institute for Gravitational Physics); Collage: B. Knispel, M. Zumalacárregui (Max Planck Institute for Gravitational Physics)



To the point
  • The signal: On 23 November 2023, both LIGO observatories in the US detected gravitational waves from the most massive black hole merger to date.

  • The mystery: According to previous studies, the two black holes had masses approximately 100 and 140 times that of our Sun, respectively. However, according to standard models of stellar evolution, black holes of these masses are difficult to form. How they could have evolved remains a mystery.

  • A possible solution: Scientists at the Max Planck Institute for Gravitational Physics in Potsdam have now proposed an explanation for these unusual masses. The signal may have been magnified by a galaxy and diffracted by an object within it, making the black holes appear more massive than they really are.



A potential explanation for a mysterious gravitational wave signal.

The gravitational-wave signal GW231123, detected by the two LIGO detectors in the US on 23 November 2023 from the merger of two black holes, continues to puzzle scientists. Given their large masses, the existence of these black holes cannot be explained with the standard understanding of stellar evolution. However, they are not only very massive, but also spin very quickly. This makes interpreting the signal particularly challenging and suggests an unusual formation history for the binary system.

In a new study, a research team at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI) in the Potsdam Science Park investigated whether the measured masses and spins appeared larger than they actually were due to the effect of a gravitational lens.

Light on Curved Paths and Distorted Gravitational Waves

Light traveling through the universe is deflected by massive objects, resulting sometimes in multiple images of the same astrophysical source. This gravitational lensing effect needs to be accounted for to correctly interpret observations. Lensing is routinely observed on electromagnetic sources such as stars and galaxies, and expected to occur in a fraction of gravitational-wave sources.

“Like light, gravitational waves can also be deflected, magnified and split into multiple signals by massive objects,” says Miguel Zumalacárregui, group leader in the Astrophysical and Cosmological Relativity Department at the AEI. “For gravitational waves, diffraction and interference effects give us an additional way to identify and study lensed signals.”

Detecting these subtle lensing diffraction effects requires sensitive detectors and novel data-analysis methods. To make this analysis possible, the team developed a mathematical description of gravitational-wave lensing and software fast enough to analyze the data.

“If we assume that GW231123 was deflected and distorted by a compact object of about 190 to 850 solar masses—or by an extended structure such as a globular cluster—we can understand the observed high masses,” says Srashti Goyal, co-lead author and postdoc at the AEI Potsdam when working on the topic. “Moreover, the lensing interpretation does not require unusually high spins.” Taking these effects into account, the total mass of the source would be around 140 solar masses rather than about 230 solar masses. The system would then be much less extreme and easier to accommodate within known black-hole formation scenarios.

Across the Universe

The study’s title, “Across the Universe”, is a nod to the Beatles — but here the journey really does change how the source appears. As gravitational waves travel through the expanding Universe, their wavelengths are stretched and their frequencies lowered (an effect known as cosmological redshift) — the equivalent of lowering a sound’s pitch. Just as a cello played back at a lower pitch might be mistaken for a double bass, a distant black-hole binary can appear more massive than it really is. Gravitational magnification adds to the illusion by making the distant source appear closer.

“Our analysis also suggests that the compact lens was embedded in a larger gravitational field, such as that of the galaxy hosting it,” adds Héctor Villarrubia-Rojo, co-leading author of the study and a postdoctoral scholar at the Universidad Complutense in Madrid, Spain. “By including this external potential, we can describe the small-scale diffraction and the large-scale magnification within a single framework.”

New insights from lensed gravitational waves

So far, researchers have not unambiguously detected any signals affected by gravitational lensing in the data from gravitational-wave detectors. According to the new study, GW231123 is a promising candidate for such an event.

“The nature of the lens remains a major mystery in our analysis, as individual compact lenses with 100–1,000 solar masses should be exceedingly rare,” adds Zumalacárregui. “Future work will need to establish whether such lenses can form, or whether an ensemble of lighter objects, including stars, can explain this event.”

Current data do not yet allow an unambiguous claim of gravitational lensing. Following further upgrades to the detectors, however, the scientists expect to be able to detect and interpret lensed gravitational waves using new data analysis methods.

The detection — or lack thereof — of gravitational waves deflected by the gravity of other objects will provide new insights into gravitational-wave astronomy: Gravitational magnification may reveal black-hole mergers beyond the distance current detectors can normally reach, while diffraction can probe compact objects and dark-matter structures along the line of sight. Consequently, these deflected gravitational waves could become a new method for exploring the universe.




Media contact:

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

Science contacts:

Dr. Srashti Goyal
Postdoc
Email:
srashti.goyal@iucaa.in
Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India

Dr. Héctor Villarrubia-Rojo
Postdoctoral scholar
Email:
hectorvi@ucm.es
Universidad Complutense, Madrid, Spain

Dr. Miguel Zumalacarregui
Group Leader
Tel:
+49 331 567-7322
Fax: +49 331 567-7298
Email: miguel.zumalacarregui@aei.mpg.de



Publication

Goyal, S.; Villarrubia-Rojo, H.; Zumalacarregui, M.
Across the Universe: GW231123 as a magnified and diffracted black hole merger. The Astrophysical Journal Letters 1008, L12 (2026)


MPG.PuRe - DOI - pre-print



Related information

1. Homepage of the “Astrophysical and Cosmological Relativity” department

2. YouTube video: The Next Frontier: Lensing of Gravitational Waves


Tuesday, September 01, 2026

A Pulsar in a Nebula in a Supernova Remnant

Featured Image: A Pulsar in a Nebula in a Supernova Remnant

When a massive star collapses, the subsequent supernova can leave behind the star’s condensed core in the form of a neutron star. Some neutron stars are also pulsars, which rotate at incredible speeds, emit beamed radio emission, and expel winds of charged particles. A pulsar’s relativistic charged-particle winds billow around the pulsar as it travels through space — often at a few hundreds of kilometers per second or faster, having received a “kick” when its progenitor star exploded. When these winds interact with the surrounding supernova ejecta or the interstellar medium, the interaction creates a detectable pulsar wind nebula. The image above combines data from the Australian Square Kilometre Array Pathfinder (orange) and Wide-field Infrared Survey Explorer (cyan) to show a pulsar wind nebula, indicated with a white rectangle, within a larger supernova remnant. Sanja Lazarević (Western Sydney University) and collaborators discovered this pulsar wind nebula, which they’ve named “Thunder” in a nod to the supernova remnant’s moniker, “Nimbus.” The cometary shape of the pulsar wind nebula suggests that the pulsar is moving quickly, traveling outward from the center of the explosion that occurred some 30,000–45,000 years ago. To learn more about the discovery and characterizati,bron of this pulsar wind nebula, check out the article linked below.

Citation

“EMU Discovery of Thunder: A Bow-Shock PWN Powered by PSR J1631–4722 Escaping the Nimbus SNR (G336.7+0.5),” S. Lazarević et al 2026 ApJ 1007 159. doi:10.3847/1538-4357/ae7f11


Monday, August 31, 2026

Thermal Anomaly Discovered Below Mars's South Pole

Artist concept of Mars's warm southern interior
Credit: Artist concept: NASA / Theophilus Britt Griswold



Researchers have discovered a thermal asymmetry deep beneath the surface throughout Mars's southern hemisphere.

Based on gravitational measurements that give clues to the Red Planet's interior structure, Mars's interior southern hemisphere is around 200 to 400 degrees Celsius warmer than the northern half of the planet and partially molten. The surprising finding adds additional context to Martian history and the periods of time in which it may have hosted conditions favorable for life.

The research was led by Caltech alumnus Alexander Berne (PhD '26), who is now a postdoctoral associate at the University of Arizona. The findings are reported in a paper appearing in the journal Nature on August 27.

During his graduate studies at Caltech, Berne developed a model that uses variations in gravitational data to infer the structure of a planetary body's interior. Berne and his collaborators then aimed to apply his model to understanding Mars's interior. Using data collected over decades from three different Mars missions—Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter—the team measured tiny variations in these spacecrafts' velocities and used them to reconstruct the gravitational field around Mars. The gravitational forces exerted by the Sun on Mars vary over seasonal timescales as a result of Mars's slightly elliptical orbit and its tilted rotation axis. A technique called tidal tomography measures how those gravitational signatures vary over time and results in a model of the planet's interior.

"Scientists usually assume that the interiors of planetary bodies are generally spherically symmetric, but this is not necessarily true," Berne says. "As we get more gravity data, we can determine the three-dimensional intricacies of a planet's interior structure. These inferences in turn give us a blueprint for designing future missions and scientific exploration of these worlds. Understanding the interior structure of planetary bodies helps us unravel the processes that shaped their formation and evolution."

On the surface, Mars is a geologically asymmetrical planet: Its southern hemisphere contains towering mountains and deep craters, whereas the northern hemisphere is composed of low flat lands. In the new study, the team was surprised to discover that Mars's interior is also thermally asymmetric—the southern hemisphere is hundreds of degrees hotter than the north.

The new observation also happens to suggest explanations for other phenomena observed on Mars, such as magnetic anomalies found in iron minerals in the south. A thermal anomaly in the southern mantle could mean that a magnetic field existed strong enough to cause magnetic differences between the north and south. Additionally, NASA's InSight mission had previously discovered that seismic waves dissipate more quickly in the south, which could be explained if the region were hotter.

"The dichotomy that we see between north and south is important to understand because it gives information about processes that may have influenced the hydrology of Mars, including the formation of basins that may have held water," says Amirhossein Bagheri, a postdoctoral scholar at Caltech and co-author on the paper. Bagheri is also a former member of the InSight team.

It is still unclear what created the thermal anomaly, and there are several hypotheses for its origins, including a giant impact releasing heat from the north, past spontaneous convection in the Martian southern mantle, and thick geological features trapping excess heat from escaping.

The paper is titled "Tidal Tomography Reveals a Thermal Anomaly Beneath Mars's Crustal Dichotomy." In addition to Berne and Bagheri, co-authors are Nicholas Wagner and Harriet Lau of Brown University, Isamu Matsuyama and Angela Marusiak of the University of Arizona, Sander Goossens of NASA Goddard Space Flight Center, Karwai Cheng of the Institute of Astronomy and Astrophysics at Academia Sinica in Taiwan, Antonio Genova of the University of Rome in Italy, Marc Rovira-Navarro of the Delft University of Technology in the Netherlands, Chuan Qin of UCLA, Douglas Hemingway of the University of Texas at Austin, Shijie Zhong of the University of Colorado Boulder, and Francis Nimmo of UC Santa Cruz. Funding was provided by NASA.

Source: Caltech/News



Contact:

Caltech Media Relations

mr@caltech.edu


Sunday, August 30, 2026

Lenticular Galaxy NGC 4996

NGC 4996
Credit: NAOJ; Image provided by Masayuki Tanaka

Detail: Low Res. (46 KB) / Mid. Res. (860 KB) / High Res. (8.7 MB)

A lenticular galaxy, which means "lens-shaped," occupies an intermediate position between elliptical and spiral galaxies in the Hubble Classification scheme. These galaxies exhibit little or no ongoing star formation and lack the prominent spiral arms that characterize spiral galaxies. Instead, many lenticular galaxies feature a bright central bar and, in some cases, a faint outer ring, both of which are visible in this galaxy.

Astronomers believe that lenticular galaxies have lost much of the gas necessary for forming new stars. As star formation ceased, their spiral arms may have gradually faded from view. The bar and ring structures observed today are thought to be remnants of the galaxy’s former disk. Galaxies slowly change their appearance over time, and this lenticular galaxy may provide us with a glimpse of one stage in that evolutionary transition.

Distance from Earth: 260 million light-years
Instrument: Hyper Suprime-Cam (HSC)



Saturday, August 29, 2026

Calculating black hole scattering for any mass ratio

Gravitational two-body scattering event with gravitational waves.



State-of-the-art predictions can now be used to create waveform models for next-generation gravitational-wave detectors.

An international team, including researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in the Potsdam Science Park, has calculated with record precision how two black holes deflect each other's paths when they fly past one another under the influence of their mutual gravitational attraction. This novel result covers any mass ratio.

Gravitational-wave observatories routinely detect ripples in spacetime from colliding black holes. Decoding these signals requires predictions of black-hole motion, and these predictions must be accurate enough to keep pace with ever more sensitive detectors. Recently, methods borrowed from particle physics — treating gravity with the tools of quantum field theory developed for colliders — have driven rapid progress.

Using their worldline quantum field theory approach and high-performance computers, the researchers computed the energy-conserving part of the deflection angle at the fifth order of approximation in the strength of gravity. The key advance is completing the mass dependence at this order, where earlier results applied only to highly unequal pairs. The explicit analytic answer involves exotic mathematical functions related to higher-dimensional generalizations of torii, and a subtle infinity at one special fly-by speed cancels in their refined definition of energy-conserving effects. This state-of-the-art prediction may now be used for the waveform models required for next-generation gravitational wave detectors.

Paper abstract

Using the worldline quantum field theory formalism, we compute conservative contributions to the scattering angle and impulse for classical black hole scattering at fifth post-Minkowskian (5PM) and second self-force (2SF) order. This four-loop calculation involves non-planar Feynman integrals and requires advanced integration-by-parts reduction, novel differential-equation strategies, and efficient boundary-integral algorithms to solve a system of hundreds of master integrals in four integral families on high-performance computing systems. The resulting function space includes multiple polylogarithms as well as iterated integrals with a K3 period, which generate a spurious velocity divergence at v/c = √8/3, γ = 3. This divergence is present in the potential region and must be canceled by contributions from the radiative memory region, while its dimensional-regularisation pole should cancel against the radiative tail region. As the standard use of Feynman propagators fails to ensure this cancellation, we instead propose a “(γ-3)” conservative prescription that realises both cancellations, leading to a physically sensible answer. All available low-velocity checks of our result against the post-Newtonian literature are satisfied.




Contacts:

Media contact:


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



Publication Driesse, M.; Jakobsen, G. U.; Mogull, G.; Nega, C.; Plefka, J.; Sauer, B.; Usovitsch, J.
Conservative Black Hole Scattering at Fifth Post-Minkowskian and Second Self-Force Order. Physical Review Letters 137, 081402 (2026)

MPG.PuRe - DOI - pre-print


Friday, August 28, 2026

One-sided spiral

A spiral galaxy. It has a prominent spiral arm on one side (lower left) and a wide, glowing core. Dark brown filaments of dust swirl through its disc, while blue clusters of stars are found mostly going out to its arm. On the opposite side to the arm (upper right), gas trails off from the disc, out of the view in this image. A matching spiral arm is not visible on this side. The galaxy lies on a dark background. Credit: ESA/Hubble & NASA, D. Thilker, J. Lee and the PHANGS-HST Team



The subject of this ESA/Hubble Picture of the Month is a spiral galaxy struggling against some of the titanic forces that appear on galactic scales in space. This is NGC 4654, an intermediate spiral galaxy in the constellation Virgo (the Maiden). “Intermediate” means that it lies between the spiral galaxies that have a bar across the centre and those that don’t, with a weak bar structure in its centre. It is situated 72 million light-years from Earth in the Virgo Cluster, a particularly massive and populous galaxy cluster.

NGC 4654 is particularly asymmetric, with a rounded and clearly-defined edge on one side and a long tail of gas stretching out from the opposite side — beyond Hubble’s view in this image. The cause of this gaseous tail is the same as for many of the other galaxies jostling in the crowded Virgo Cluster: namely, ram pressure stripping. NGC 4654 moves with such high velocity through space that it sweeps up and rams through the intracluster medium, the hot, rarefied gas filling the space between the Virgo Cluster’s galaxies. The intracluster medium in turn exerts a “ram pressure” on the galaxy, compressing the galaxy’s leading edge and tugging at its gas, creating the elongated tail.

It’s not just the galaxy’s gas that is unevenly distributed: its stars are too, and this is more unusual for a spiral galaxy. While the spiral arm on its leading edge is rich with stars and gas, the opposite arm noticeably lacks stars, influencing the galaxy’s lopsided spiral shape. It’s thought that ram pressure alone is unlikely to have had this effect. Rather, NGC 4654 has also been subjected to the gravitational force of the fellow Virgo Cluster galaxy NGC 4639. While the two galaxies are far apart now, it’s thought that a fly-by interaction between them around 500 million years ago ripped away NGC 4654’s gas along one side, limiting star formation there and creating the asymmetry in its shape.

Many galaxies that undergo ram pressure stripping suffer reduced star formation rates as the cold gas that collapses to form their stars is pulled away and lost. NGC 4654, however, is still forming nearly two Suns’ worth of stars every year, a rate comparable to other galaxies of similar size. The active star formation can be seen in the latest Hubble data used in this image, which picks up on a wavelength of red light that’s emitted by the clouds of energised gas where newborn stars lurk. The bright pink bubbles appear all across NGC 4654, from its forward spiral arm, to around its weak bar, and out to the edge of its disc.

The data used for this image come from two observing programmes (#15654, #17502) that have the aim of linking gas in galaxies with star formation. By observing many prominent galaxies in the vicinity of our own, researchers hope to better understand how gas moves around in galaxies, where and when it collapses to form stars and star clusters, and what effect those new stars have on the gas around them.




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Thursday, August 27, 2026

Striking star clusters and irregular clumps

An irregular galaxy, appearing like a broad band of tiny stars. It is denser on one side, with a faint cloud of gas among the stars. Clumps of brighter points are newly formed stars, with the largest lights being star clusters, and with many surrounded in glowing blue gas clouds. Plumes of red dust surround the galaxy. A foreground star appears very large and bright. A few distant alaxies appear in the background. Credit: ESA/Webb, NASA & CSA, A. Leroy



The latest ESA/Webb Picture of the Month is a new, infrared look into the strange final phase of a galactic merger. Arp 263, an irregular galaxy, lies in the constellation Leo at a relatively nearby distance of around 25 million light-years.

Originally discovered in 1784 and also catalogued as NGC 3239, this galaxy was included in American astronomer Halton Arp’s Atlas of Peculiar Galaxies in 1966, as possibly one of the most remarkable and strange galaxies in the sample. Arp categorised it with the galaxies featuring “irregular clumps”. In 2023, the galaxy was featured in an image from the NASA/ESA Hubble Space Telescope, where these clumps are revealed to be bright nebulae between the galaxy’s dense clouds of gas, where stars are forming.

Arp 263 is believed to result from a past galactic merger. Apart from its unusual distorted shape, astronomers have noticed a few features that point to this. It has two short, curved tails of stars, beyond the field of view of this Webb image, which are a feature that’s associated with gravitational interactions. However, there are no nearby galaxies that Arp 263 could be interacting with now. The stars in the galaxy are oriented differently to its hydrogen gas, where they would normally be symmetric, and parts of that gas are moving at different velocities to each other. And, of course, the widespread formation of new stars across Arp 263 is typical of a galaxy whose gas has been seriously shaken up.

Although Arp 263 clearly hasn’t yet settled into a more regular shape after its gravitational tug-of-war, its former companion galaxy is now nowhere to be found. It’s possible that this was a dwarf galaxy small enough to have been already completely dissolved into the larger Arp 263 — or that its companion was simply much more heavy than it was bright, making it difficult to spot as a remnant.

This new image from Webb’s Near-Infrared Camera (NIRCam) reveals an entirely different view of Arp 263, taking us inside the thick gas crowding the galaxy to see the many stars scattered there. These old stars contrast with the several areas of star birth, where multitudes of new stars are forming in numerous clusters. Dust spread throughout the galaxy glows with the light, here shown in red, emitted by complex molecules; around the star-forming regions we also see — in blue colours — hydrogen gas, ionised by starlight and emitting its own light in turn. The most intense area of star formation features a curved chain of compact star clusters, leading to the largest and brightest star-forming nebula. Webb allows us to peek into this stellar nursery and see the stars that have formed within.

The brightest of the bright spots in Arp 263 is a shining star, named BD+17 2217. It appears so large and bright, with long diffraction spikes created by the telescope’s optics, because it is part of our own galaxy. The galaxies that appear in the background are much more distant, most hundreds of millions of light-years away from both us and Arp 263. A few of these galaxies are identifiable as spiral galaxies, but Webb’s NIRCam reveals the hundreds of much more distant galaxies lurking in the background as orange dots.Arp 263

This image was made with data from observing programme #3707 (PI: Leroy), a survey of the nearby, large, star-forming galaxies in the southern sky. These galaxies are close enough that Webb’s sharp vision can deliver a detailed picture of the stars, star clusters and interstellar dust within the galaxy. The observations will be used to better understand the cycle of star formation and how it plays out across galaxies; Arp 263, with its disturbed disc of gas and its chaotic star formation, presents a unique and fascinating target for these investigations.



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Wednesday, August 26, 2026

Subaru Telescope Archive Data Reveal Unexpected Surface Properties of a Comet

Figure 1: Comet 28P/Neujmin captured by the Subaru Telescope's Hyper Suprime-Cam (HSC) (white box and enlarged inset). The image shown is from one of HSC's 104 CCD detectors. In addition to the comet, the image contains more than 2,000 stars and galaxies. View the original images here (CCD image
, Enlarged image). (Credit: NAOJ)

Comets are natural "time capsules," preserving ice and dust from the birth of the Solar System 4.6 billion years ago. Yet the solid nucleus of a comet is rarely observed directly, because it is normally hidden by a cloud of gas and dust known as a coma.

A research team including scientists from the University of Occupational and Environmental Health, Kyoto Sangyo University, and the National Astronomical Observatory of Japan discovered a nearly dormant, coma-free comet in publicly available archival data from the Subaru Telescope's Hyper Suprime-Cam (HSC). These observations enabled the first precise ground-based measurement of the reflectance properties of a cometary nucleus, providing new insights into how comets differ from asteroids and how they have evolved over time.

Why Are Cometary Nuclei Important?

Comets are small bodies composed primarily of ice and dust. They are thought to have formed in the outer Solar System and remained largely unchanged since the early days of the Solar System. Asteroids, by contrast, are rocky bodies found mainly between the orbits of Mars and Jupiter.

Comets and asteroids were once regarded as completely different types of objects. However, recent observations have blurred the distinction, with the discovery of water-bearing asteroids and cometary nuclei containing minerals similar to those found on asteroids.

Determining whether the surfaces of cometary nuclei are truly similar to those of asteroids—or fundamentally different—is an important step toward understanding how the bodies in our Solar System formed and how they have evolved over billions of years.

Why Are Cometary Nuclei Difficult to Observe?

Studying cometary nuclei directly is, however, extremely challenging. A cometary nucleus can be observed directly only when the comet is far enough from the Sun that its ice remains frozen and no coma forms. At such distances, comets are extremely faint—only very large-aperture telescopes can detect them.

In addition, investigating the surface properties of a cometary nucleus requires observations made under a special viewing geometry known as opposition, in which the observer views the comet with the Sun almost directly behind them (Figure 2).

Near opposition, the object appears brighter than usual, and the way its brightness changes provides clues to the properties of the particles covering its surface (Note 1). Opportunities to observe a comet under such favorable conditions are extremely rare.

Figure 2: Schematic illustration of opposition geometry.
Credit: NAOJ

A Chance Discovery in the Subaru Telescope Archive

The research team has been conducting a systematic search of publicly available archival data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP) to identify Solar System objects serendipitously captured in the images.

During this search, they discovered Comet 28P/Neujmin at a distance of more than 10 astronomical units from the Sun—farther than from the Sun to Saturn—in a dormant state with no visible coma (Figure 1). Remarkably, the comet had been observed under nearly ideal conditions, close to opposition, where the Sun, the comet, and the Earth were almost perfectly aligned. This enabled the team to make the first clear ground-based detection of the opposition brightening of a cometary nucleus (Figure 3, left).

The discovery was made possible by the Subaru Telescope's 8.2-meter primary mirror, capable of detecting such a faint and distant cometary nucleus, together with HSC's exceptionally wide field of view, which allowed the comet to appear serendipitously in observations taken for a different scientific purpose.

A Comet That Looks Like an Asteroid—But Behaves Differently

The analysis showed that the surface color of Comet 28P/Neujmin closely resembles that of dark, reddish asteroids. These asteroids have very low reflectance and are thought to be rich in water-bearing materials. This result is consistent with previous studies.

However, when the researchers examined how the comet's brightness changed near opposition, they found an unexpected difference. These dark asteroids generally exhibit only a modest increase in brightness when viewed near opposition. In contrast, Comet 28P/Neujmin showed a much stronger brightening, comparable to that of high-reflectance asteroid types (Figure 3, right).

Figure 3: Brightening of Comet 28P/Neujmin near opposition (left) and comparison with different asteroid types (right). The left panel shows that the data point obtained at a Sun–comet–Earth phase angle of 0.33° (black circle), corresponding to an almost face-on viewing geometry, is significantly brighter than observations made at larger phase angles. Such a sharp increase in brightness is not seen in dark, low-reflectance asteroid types (D-, C-, and P-type; right panel). Instead, the brightening observed for Comet 28P/Neujmin is comparable to that of high-reflectance asteroid types (E-, S-, and M-type). (Credit: NAOJ)


These findings provide important clues about the fine-scale structure of the comet's surface, including the size of the surface grains, the amount of empty space between them, and the way the grains are packed together. The results suggest that although the nucleus of Comet 28P/Neujmin resembles low-reflectance asteroids in terms of its color and overall reflectance, its surface microstructure may be fundamentally different.

As comets repeatedly approach the Sun, their surface ice sublimates. This ongoing activity may have gradually produced a surface structure unlike that found on asteroids.

The Scientific Value of Archival Data

This study demonstrates how the combination of the Subaru Telescope's large aperture, HSC's wide field of view, and the publicly available HSC-SSP data archive can lead to unexpected discoveries, even for Solar System objects that were not the original targets of the observations.

Dr. Takafumi Ootsubo (University of Occupational and Environmental Health), lead author of the paper, comments, "The same archive likely contains many more Solar System objects waiting to be found. By applying the same observational approach to many more comets in the future, we hope to uncover how the surface structures of cometary nuclei have evolved over time, ultimately providing new insights into how Solar System bodies formed and evolved into the objects we see today."

This study was published in the Publications of the Astronomical Society of Japan (PASJ) on August 25, 2026 (Ootsubo et al., "Opposition effect of comet 28P/Neujmin observed with Subaru Hyper Suprime-Cam").

This research is based on data obtained with the Subaru Telescope and retrieved from the Hyper Suprime-Cam (HSC) data archive system operated by the Astronomy Data Center and the Subaru Telescope of the National Astronomical Observatory of Japan (NAOJ).

This work was supported by JSPS KAKENHI Grants (Nos. 23H01234, 23K25930, 24H00271, 23H01217, 23K25913, 23K22557, 24K00684, 25K24630, and 25K07393), in cooperation with the NEDO project "Technology Development of Next-Generation Computing for AI Chips Enabling High-Efficiency and High-Speed Processing," under the research program "Ultra-Large-Scale Data Analysis: Application to e-Science."

(Note 1) When an airless body is viewed almost directly from the direction of the Sun, shadows cast by surface particles become nearly invisible, making the surface appear brighter than usual. In addition, light scattered multiple times between the particles tends to be redirected back toward the observer, sometimes producing a sharp increase in brightness. This phenomenon is known as the opposition effect. By measuring the opposition effect, astronomers can infer physical properties of the surface, such as the size of the particles and how densely they are packed.




About the Subaru Telescope

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


Tuesday, August 25, 2026

ALMA Reveals Long-Lived Hotspots on Betelgeuse’s Bubbling Surface

A Bubbling Betelgeuse - This ALMA image shows the submillimeter surface of Betelgeuse, revealing its irregular shape and regions of hotter gas. The brightest hotspot, toward the northeast of the star, appears at nearly the same location in ALMA observations separated by more than seven years, suggesting that some structures in Betelgeuse’s atmosphere can survive considerably longer than predicted by current models of stellar convection. Credit: ALMA (ESO/NAOJ/NRAO)/W. Dent et al.



A remarkably detailed image obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) reveals the uneven surface of Betelgeuse, the famous red supergiant in the constellation Orion. The observations show bright hotspots and an irregular, corrugated outline shaped by the enormous motions taking place within the star.

Located roughly 600 light-years from Earth, Betelgeuse is one of the closest red supergiants and has a radius about 800 times that of the Sun. Its immense size makes it possible for ALMA to resolve structures across its atmosphere that would remain hidden in most other stars.

The new observations were obtained in 2023 using ALMA in its longest-baseline configuration, achieving a resolution as fine as about seven milliarcseconds. They reveal an atmosphere with an average temperature of around 2300 K and at least two hotter regions, to the northeast and southwest of the stellar disk. The brightest hotspot is up to about 800 K hotter than the surrounding gas.

These structures are thought to be linked to enormous convective motions inside Betelgeuse. Hot gas rising from deeper layers can generate shocks as it reaches the star’s outer atmosphere, producing the bright and uneven features detected by ALMA.

One finding particularly surprised the researchers. When they compared the 2023 observations with similar ALMA data obtained in 2015, the prominent northeastern hotspot appeared in almost the same location and with a similar intensity. This suggests that the feature has persisted for at least seven years — considerably longer than the lifetimes of large convective structures predicted by current models.

The surface itself is also far from spherical. ALMA measured variations of up to about six percent in its apparent radius, while fainter emission extends several stellar radii into Betelgeuse’s atmosphere. Observations of molecules including silicon monoxide (SiO) and carbon monoxide (CO) reveal an even more irregular and clumpy environment surrounding the star.

The orientation of the long-lived hotspots is also intriguing in light of recent evidence for a close companion to Betelgeuse, although the observations do not establish a direct connection. Continued high-resolution observations with ALMA could reveal whether the hotspots remain fixed and how they relate to convection, mass loss, and the structure of the star’s extended atmosphere.

Betelgeuse is approaching the final stages of its evolution and will eventually explode as a supernova. “Its eventual fate as a supernova makes it fascinating to know what it actually looks like now,” says lead author Bill Dent, an astronomer at ESO.




Additional Information

This post is based on the original published by the European Southern Observatory (ESO), an ALMA partner on behalf of Europe.

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

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



Contacts:

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

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


Monday, August 24, 2026

Stellar spin may explain why repeated black hole flares grow dimmer


A hydrodynamical simulation of a star being ripped apart by the tidal forces of a supermassive black hole.
Credit: NASA/ S. Gezari (JHU)/ J. Guillochon (UCSC)



At the center of most galaxies lies a supermassive black hole, with a mass millions to billions of times that of our sun and some of the most extreme gravity in the universe.

Some stars that venture too close to such black holes live to tell the tale. Rather than being completely destroyed, they survive to make repeated close passes, producing a new flare of light each time.

These repeating partial tidal disruption events (rpTDEs) give astronomers the opportunity to watch the same star and black hole interaction unfold again and again, thanks to wide-field time-domain surveys that repeatedly scan large areas of the sky for objects that change in brightness.

But in several cases, researchers have noticed a puzzling pattern: The successive flares grow progressively dimmer. For years, theoretical models couldn't explain why.

Now, a team of astrophysicists at Syracuse University has shown that the answer may lie in a previously overlooked factor—the star's spin.

The study, published in The Astrophysical Journal, was led by doctoral student Ananya Bandopadhyay, working with postdoctoral researcher Benjamin Amend and associate professor Eric Coughlin—all in the Department of Physics—as well as colleagues at other institutions.

When stars meet black holes

In a typical tidal disruption event (TDE), a black hole's tidal force—the difference in gravitational pull across a nearby star—tears the star completely apart.

As the disrupted stellar debris falls toward, or "accretes" onto, the black hole, it loses energy that is emitted in the form of light over the course of days to months.

While black holes themselves emit no light, TDEs provide a short-lived supply of fuel that lights up the surrounding region, allowing astronomers to study these otherwise invisible objects indirectly.

If a star orbiting a black hole does not come close enough to be completely ripped apart, it can, however, lose a fraction of its mass, resulting in a partial TDE. In a repeating partial TDE, the surviving core continues orbiting the black hole, losing more material with each new close pass, a few months to several years apart.

The dimming mystery

How much material a star loses during repeated encounters depends partly on its internal structure. Bandopadhyay compares a low-mass star to a fluffy meringue, which can become increasingly vulnerable to the black hole's tidal forces.

By contrast, a higher-mass star has a more centrally concentrated, onion-like structure and can shed its outer layers while its dense core remains relatively unaffected, losing decreasing amounts of mass over time.

Those differences can help explain why rpTDEs don't all behave the same way. But one pattern in particular has mystified researchers. Of the roughly 10 repeating systems identified to date, four have produced flares that grow progressively dimmer.

Decreasing mass loss might seem like an obvious explanation. But previous hydrodynamical simulations showed that, surprisingly, even as the material lost decreased with each encounter, the predicted flares retained roughly the same brightness.

"We were puzzled by this for two years," Bandopadhyay says.

Their previous work had revealed another effect of the black hole's tidal forces. In addition to stripping material from the star, they exert a torque that causes the star to spin faster with each close encounter. As a result, although less material falls back toward the black hole, it returns over a shorter period of time, helping to keep the predicted flare at roughly the same brightness.

To reproduce the dimming astronomers were actually observing, the researchers needed what Bandopadhyay called "a new ingredient"—a star that was already spinning rapidly before its first encounter with the black hole.

The new study found that this initial rotation prevents the star from being significantly spun up during each passage. Without that additional spin-up, the timescale over which the stripped material falls back remains relatively constant. As the star loses less material with each encounter, the peak fallback rate—and the predicted brightness of the flare—can finally decline.

Tracing the star's past

But why would the star already be spinning so rapidly?

"It is also extremely difficult to 'bind' a star to a supermassive black hole so tightly that it orbits the black hole in a matter of months, and yet they seem to do so in rpTDEs," Coughlin says.

The so-called Hills mechanism may explain both. Under this scenario, a pair of closely orbiting stars passes near a supermassive black hole, which tears the binary apart, ejecting one star and capturing the other.

In a close binary, the stars can become tidally locked, causing each to rotate on its axis at the same rate that the pair orbits each other. The tighter the binary, the shorter that orbital period and the faster a tidally locked star spins. The binaries capable of leaving a captured star on the short orbit observed in rpTDEs would have to be extremely tight—also leaving a tidally locked star spinning rapidly before its capture.

"Ananya's work demonstrates that each of these peculiarities can be explained by the same underlying phenomenon: the tidal destruction of a binary system and the capture of one of the stars," Coughlin says. "From a theoretical standpoint, this is a major step forward in our understanding of the physics at play in these systems."

Zooming out, Coughlin notes that Hills capture may also have produced some of the stars orbiting Sagittarius A*, the supermassive black hole at the center of the Milky Way. The new findings could therefore help explain some of the properties of stars in what he calls "our own cosmological backyard."

by Olivia Hall, Syracuse University

edited by Sadie Harley, reviewed by Robert Egan

Source: Phys.org



Publication details

Ananya Bandopadhyay et al, The Role of Stellar Spin in Repeating Partial Tidal Disruption Events, The Astrophysical Journal (2026). DOI: 10.3847/1538-4357/ae8f31

Journal information: Astrophysical Journal



Provided by Syracuse University


Sunday, August 23, 2026

Strange Signals Called Long-period Radio Transits Come From Cataclysmic Variables

This iullustration shows a white dwarf star accreting material from its companion. New research says that this can explain at least one of the puzzling Long Period Radio Transients, mysterious radio signals that repeat with periods ranging from a few minutes to a few hours. Image Credit: Carl Knox (OzGrav, Swinburne University of Technology) and Joshua Preston Pritchard (CSIRO).


Long period radio transients (LPTs) are mysterious signals coming from objects inside our galaxy. They're highly polarized, coherent radio bursts that repeat regularly, with periods ranging from a few minutes to a few hours. Scientists detected hints of the first LPT in 2005, and now they know of many more of them.

So far, an explanation has lagged behind their detections, but new research has an explanation for at least one of them. The research is titled "Periodic radio and X-ray emission from an accreting white dwarf binary," and it's published in Nature Astronomy. The lead author is Kovi Rose, a PhD student from the University of Sydney’s School of Physics and CSIRO.

"Little is known about the physical origins of these systems," the authors write. "Astronomers have proposed magnetars that rotate slowly and white dwarfs that rapidly orbit with a companion star as potential explanations."

Recent examples of LPTs support the idea that white dwarfs with a companion are responsible for LPTs. But the actual mechanism that creates them has remained unclear.

In this work, the researchers present the discovery, and explanation, of a new LPT named LPT ASKAP J174508.9-505149. The new LPT, referred to as J17 in this article, has a 1.3 hour orbit, and "exhibits orbitally modulated X-ray emission and radio bursts," the authors write. "These elliptically polarized radio bursts drift in emission frequency, potentially due to a longer beat period, and turn off for several hours at a time."

J17's radio signal switches off for hours at a time, a wrinkle that's a clue to the mechanism behind the LPT. The pulse frequencies also drift up and down over a longer beat period. "ASKAP J1745-5051 exhibits pulse properties not previously observed in LPTs, providing valuable insights into the progenitor system," the authors write. J17's signal is dynamic in other ways, too.

The researchers say that the LPT is coming from a magnetic cataclysmic variable (CV), a binary star where one is a highly magnetized white dwarf, and the other is a donor star.

“For the first time we have pinpointed the origin of these signals, confirming the source to be a ‘cataclysmic variable’, or an accreting white dwarf star,” lead author Rose said in a press release. “Long-period radio transients have puzzled astronomers for years,” Rose added. “We’ve only found about a dozen, and their origins have been unclear. Now, we’ve been able to show that the source for one of these transients comes from a white dwarf actively pulling material from a companion star.”

Binary stars where one is a white dwarf drawing material from a donor star are responsible for Type 1a supernova explosions. In those cases, the white dwarf accumulates so much material from its partner that it eventually explodes, obliterating the star.

But in cataclysmic variables, things play out differently. And while LPTs might seem similar to pulsars, they're distinctly different.

"The pulsing that we see is not coming from a spin. We think it’s coming from an orbit,” said study co-author David Kaplan, Professor of Physics and Astrophysics at the University of Wisconsin Milwaukee . “In order for (these binary stars) to orbit once every 80 minutes, they have to be both very small and very close together. In fact, they’re probably so small and so close together that some material from one star is spilling out onto the other star, and that gives rise to a particular signature that we saw in some observations that really ties it to this class of cataclysmic variables (which have been widely studied for the past hundred years).”

The CV in this work includes a white dwarf about the size of Earth, but with a mass about the same as the Sun. The companion star is a red dwarf with about 1/10th of the Sun's mass. The pair orbit very close to one another, completing an orbit in a little more than an hour.

There's an x-ray component to J17, and that comes from donor star material that gathers on the white dwarf's surface and heats up, emitting x-rays. But the radio bursts don't emanate from that. Instead, they're generated by the stars' interacting magnetic fields.

“These emissions are all tied to the orbital motion of the system,” Rose said. “But interestingly, the radio and X-ray signals don’t peak at the same time, which tells us they’re being produced in different regions of the system.”

This figure from the research shows some of the signals received from ASKAP J1745−5051. There's a lot her for non-scientists to decipher, but the main takeaway is that it correlates emissions with phases in the cataclysmic variable. ATCA, MKT, and ASKAP are all radio telescope arrays. The y-axis shows radial velocity, and it's always zero during phase 2 and phase 4, a clue to the nature of the emissions. Image Credit: Rose et al. 2026. NatAstr.


J17's intermittent signals and pulses arise from the system's plasma and magnetic fields. "Varying conditions in the local plasma density and magnetic field interaction may explain the intermittency and unique pulse morphologies in the observed radio pulsations from ASKAP J1745-5051," the authors write. "Our observations of ASKAP J1745-5051 demonstrate that magnetically driven accretion plays a key role in the generation of emission across the electromagnetic spectrum in magnetic CVs, including coherent radio pulses and variable X-ray emission."


There have been hints that binary stars are behind LPTs, but this study presents the best evidence yet. The authors say that J17's modulated radio and x-ray emissions are associated with its orbital period, and that it "clearly establishes that accreting CVs make up at least part of the population of LPTs."

“Some similar objects had been linked to binary systems before, but this is the first one where we can clearly see both stars and the accretion process in action,” said co-author Tara Murphy, Professor in the University of Sydney's School of Physics. J17 can be an important reference point in the study of LPTs, according to the researchers. “This system gives us a way to decode these signals. It could help us determine whether other long-period transients are more like pulsars or like white dwarf systems, acting like a stellar Rosetta stone,” lead author Rose said.

J17 is also important in another way, one that it shares with other high-energy astrophysical objects. “These systems are natural laboratories,” Mr Rose said. “They allow us to test our understanding of how matter behaves in strong magnetic fields and under intense gravitational forces.”

The question now is, can these cataclysmic variables explain the entire class of LPTs, or are their multiple sources?

"Determining if these processes can explain the properties of the entire emerging class of LPTs will require detailed simulations and modelling, as well as the discovery and investigation of new LPTs," the authors conclude.

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."