Only one white dwarf star has ever been caught eating an asteroid. Recently, however, astronomers may have found another that just finished its meal.

Eating Asteroids

Although stars like our Sun don’t explode in violent supernovae like their massive counterparts, they don’t slink quietly into a peaceful old age either. When a solar-mass star reaches the end of its main sequence life, it first swells dramatically (the Sun may eventually grow so large that it consumes Earth and the device you’re reading this on), then shrinks down to a tiny but incredibly hot ember known as a white dwarf.

As one might imagine, this process is not kind to any planets or asteroids that were previously circling the star. While some might survive, others are sent spiraling inwards where they break apart and are accreted onto their hosts. Due to the extreme temperatures and surface gravity of white dwarfs, whatever falls on their surfaces is vaporized, sorted by weight, and quickly dragged out of sight. Since heavy elements cannot last long in a white dwarf’s atmosphere, whenever astronomers see their stains in the star’s spectrum, they know that the star must have recently consumed the rocky remains of their former asteroids and planets.

However, although researchers have found these stains in over a quarter of white dwarfs and consequently have reasoned that asteroid snacking must be common, they’ve only ever caught one star mid-meal. Recently, Ben Zuckerman (University of California, Los Angeles) and a team of collaborators may have found another, though it may have just finished dining.

Leftover Crumbs

This new star, called WD J0234-0406, shares some characteristics with the “iconic” WD 1145+017 that was first spotted mid-meal, but it also differs in an interesting way. High-resolution spectroscopy reveals that both stars have gaseous material orbiting around them along highly non-circular paths. These have been interpreted as “precessing rings of high velocity gas” that previously belonged to parent asteroids. However, while WD 1145+017 appears to flicker as bits of disintegrating asteroids pass between it and our line of sight, WD J0234-0406 is rock steady. Neither TESS nor the Zwicky Transient Facility have detected any dips in light from the star despite the evidence that solid material must have recently drizzled into the star’s atmosphere.

The researchers suggest that this relative quiet is a matter of timing. While asteroids are actively breaking up around WD 1145+017, the parent bodies that supplied the gas and dust around WD J0234-0406 may have shattered long ago and have already been either vaporized or ground down into smaller particles. All that is left over are the crumbs slowly spiraling toward the star.

Although WD J0234-0406’s meal may not be as dramatic as WD 1145+017’s feast, it’s still exciting to expand the sample of known white dwarf-asteroid interactions. And, with the upcoming release of data from the DESI survey poised to reveal the spectra of tens of thousands of white dwarfs, the sample is likely to grow again soon.

Citation

“High-velocity Circumstellar Gas Orbiting a White Dwarf Star,” B. Zuckerman et al 2026 ApJ 1004 254. doi:10.3847/1538-4357/ae23c4

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The camera that checked JWST’s clock is losing its funding.

White dwarfs often show signs of metals in their spectra, providing evidence that these evolved stars have accreted planetary material. Could white dwarf spectra also provide evidence for technological activity in these star systems?

A Record of Planets Past

When a Sun-like star reaches the end of its hydrogen-burning lifetime, it first puffs up into a red giant before exposing its white-hot core, which evolves into a white dwarf. This dramatic transition shakes up any planets that happened to be orbiting the star, and some close-in planets may end up crumbling apart, their rubbly remains peppering the surface of the white dwarf.

So far, astronomers have found hundreds of white dwarfs that appear to be polluted with heavy elements from their destroyed planets. These observations provide a valuable look into the bulk compositions of planetary materials outside our solar system. They may also provide a way to detect patterns of chemical abundances that are not natural, resulting from technological processes like industrial refining or the creation of alloys — in other words, a technosignature that is evidence of not just life, but technologically advanced life.

Seeking Signs of Technology

A team led by Bo-Lun Huang (黄博伦) from Beijing Normal University recently investigated whether there is evidence for chemical technosignatures in the current sample of polluted white dwarfs. Huang and collaborators began their investigation with a catalog containing 697 measurements of white dwarfs with metals in their spectra. They applied Bayesian statistical methods to weigh the hypothesis that the chemical makeup of these white dwarfs is entirely natural against the possibility that they contain a blend of natural and technologically altered material.

The team used thousands of chemical abundance measurements from meteorites as a reference for the natural bulk composition of planetary material. For the mixture of natural and processed material, they combined the meteorite reference material with a template that is metal-rich and silicate-poor, with enhanced amounts of iron, nickel, chromium, and manganese.

No Strong Evidence, but a Path Forward

Ultimately, Huang’s team found that strong statistical support for the existence of technological processes was uncommon, though there were certain measurements in their sample of white dwarfs that were difficult to reconcile with a solely natural model.

Perhaps unsurprisingly, the team also found that the quality of the chemical abundance measurements affected the constraining power of the observation; some white dwarfs had upper limits for just a few elements, while others had definitive detections of many elements. They found that the most discerning observations recorded iron, magnesium, chromium, and titanium, plus either nickel, silicon, or sodium.

While this work didn’t dredge up firm evidence for technological activity, it provides a jumping-off point for future searches. The handful of white dwarfs in this sample that were fit poorly by a purely natural model could be compared against other technosignature models or targeted with high-resolution spectroscopy. Future measurements of iron and magnesium in polluted white dwarfs may be useful as a preliminary screening tool, helping to pick out intriguing targets for follow-up observations.

Citation

“A Calibrated Bayesian Search for Potential Chemical Technosignatures in Polluted White Dwarfs,” Bo-Lun Huang et al 2026 ApJ 1006 9. doi:10.3847/1538-4357/ae742c

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What’s the story behind the longest gamma-ray burst ever observed? Researchers explore how repeated interactions between a white dwarf and an intermediate-mass black hole could explain GRB 250702B’s unusual properties.

An Exceptional Gamma-Ray Burst

In 2025, the Fermi Gamma-ray Space Telescope spotted an intense flash of gamma rays from a distant, dusty galaxy, and a fleet of spacefaring and earthbound telescopes soon revealed the remarkable characteristics of the event. GRB 250702B featured multiple bursts spanning several hours, individual flares lasting roughly 100 seconds, and X-ray emission in the 24 hours leading up to the gamma-ray activity — something never seen before in a gamma-ray burst.

These characteristics have been challenging to explain with typical models of long gamma-ray burst formation, such as collapsing massive stars, but researchers have developed numerous promising alternatives. In a new research article, astronomers have shown how GRB 250702B’s behavior might be explained by repeated close encounters between a white dwarf and an intermediate-mass black hole.

Eccentric Close Encounters

Yuri Sato (Tohoku University) and collaborators modeled the source of GRB 250702B as a white dwarf that has been captured into orbit around an intermediate-mass black hole. In their model, the white dwarf travels on an extremely eccentric orbit, drawing close to the black hole roughly once an hour. Each time the white dwarf ventures close, the black hole’s tidal forces strip away part of the star until, after about 40 such encounters, the white dwarf is completely destroyed.

When the black hole peels material away from the white dwarf, some material swirls into an accretion disk, and some is cast off into space. Accretion from the disk powers a narrow relativistic jet: the source of the event’s powerful gamma-ray flares. This should mean that there is one jet produced each time the white dwarf is partially disrupted — 40 times — yet astronomers detected only a handful of flares from GRB 250702B.

Jet Precession and Model Predictions

The discrepancy can be resolved if the angle between the jet and the black hole’s spin axis precesses over time so that only some of the jets are pointed toward us. This can occur if the accretion disk is misaligned relative to the black hole’s spin. As an alternative, disk instabilities or other processes could keep all but a few of the expected jets from being launched.

Sato and coauthors found that these two scenarios have different long-term outcomes, providing a potential way to ascertain what’s going on at the source; in the jet precession scenario, the jets that are launched away from our line of sight produce an order of magnitude more radio emission at late times.

This work by Sato and collaborators demonstrates how the repeated partial tidal disruption of a white dwarf by an intermediate-mass black hole can match the properties of one of the most remarkable recent transient sources — one that has pushed astronomers to consider new ways of producing gamma-ray bursts.

Citation

“Successive Partial Disruptions with Orbital Precession in a White Dwarf–Black Hole System for Repeating GRB 250702B,” Yuri Sato et al 2026 ApJL 1003 L44. doi:10.3847/2041-8213/ae6a8f

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

Title: Fast Radio Bursts from White Dwarf Binary Mergers: Isolated and Triple-Induced Channels
Authors: Cheyanne Shariat et al.
First Author’s Institution: California Institute of Technology
Status: Published in ApJL

The History of Fast Radio Bursts

Since the discovery of the Lorimer Burst in 2007, astronomers have studied fast radio bursts (FRBs) in extreme detail. However, these extragalactic millisecond-duration radio transients have remained an enigma. Like many astrophysical phenomena, their discovery was serendipitous. The most prolific FRB-discovery instrument, CHIME, was not originally built to study them; the acronym stands for “Canadian Hydrogen Intensity Mapping Experiment,” reflecting its original (and ongoing) mission to map the cosmological distribution of hydrogen in the primordial universe. Since its construction, CHIME has discovered several thousand FRBs and even identified a smaller fraction that are known to repeat, some with consistent periods and others that are sporadic and seemingly random. (Check out their live catalog of repeating sources.)

Despite having thousands of sources to study, the only thing we know fairly confidently about FRBs is that many of them are extragalactic, and some others are even at cosmological distances. If we don’t understand how FRBs are produced, how can we know their distance? FRBs display a unique signature in their radio spectra, where higher frequencies arrive at the telescope first and lower frequencies arrive later, delayed by an inverse frequency-squared relationship. In a “dynamic spectrum,” this makes the pulse actually appear like a sweep from high to low frequency that follows the shape of a parabola; for example, the brightest pixels in Figure 1 of this Bite display this sweeping shape. This effect results from the FRB propagating through an ionized plasma with a specific density. Since the FRB is ultimately an electromagnetic wave, this slows down the speed of the FRB as a function of frequency. Measuring this effect, called dispersion, allows us to infer that the FRB signal passed through more plasma than can be accounted for within our own Milky Way galaxy, indicating that the FRB must have originated from much farther away. So far, there is only one example of an FRB from within our own galaxy, which was identified as originating from a magnetar, a highly magnetic pulsar.

FRB Progenitor Candidates

Although we know that most FRBs are located at extragalactic or even cosmological distances, it’s still not clear what objects that can generate them. Since magnetars and other compact objects are often considered reliable progenitors of FRBs, understanding their populations and comparing them with observed FRBs may reveal the origin of FRBs. Candidate FRB progenitor systems are usually divided into “prompt” channels — like the collapse of a star into a magnetar during a core-collapse supernova — and “delayed” channels where the FRB engine is formed on longer timescales, like accretion-induced collapse of white dwarfs or compact-object mergers. Figure 1 displays several of these channels, particularly those considered in today’s article, in which stellar evolution results in the transfer of material from one star to another (accretion-induced collapse) or gravitational radiation allows two objects to inspiral and merge. These events could create highly magnetized white dwarfs or magnetars that may produce FRBs.

Simulating Hierarchical Triples

In today’s article, we’re considering the role of hierarchical triple star systems in producing FRB-emitting objects. A hierarchical triple consists of an inner binary and a distant, tertiary star; see the first panel of Figure 1. These systems may play an important role because many stars that become white dwarfs of at least 0.8 solar mass exist in hierarchical triples: 35% of 2-solar-mass stars and 50% of 8-solar-mass stars are in triples. Stars of both masses will end their lives as white dwarfs.

The tertiary star plays an essential role in increasing the likelihood of the inner binary interacting: the eccentric Kozai–Lidov (EKL) mechanism causes the inner orbit to oscillate between highly inclined (with respect to the orbit of the tertiary star) and highly eccentric. Unlike isolated binaries that aren’t excited in this way, the eccentric orbit phase causes the inner stars to pass much closer to each other, increasing the likelihood of interaction or even a merger that could produce an FRB-emitting remnant.

The authors of today’s article produced a realistic population of triple systems by sampling from empirically measured distributions of masses, periods, and orbital eccentricities. These distributions were derived from observations collected by the Gaia satellite, an all-sky optical telescope that has now observed more than one billion stars in the Milky Way. The authors also created a “control” sample of isolated binaries by removing the tertiary star from the same sample of systems. The systems were then evolved for an age randomly selected between 0 and 12.5 billion years to simulate “constant” star formation similar to that in the Milky Way. Finally, they reapply these simulations at three different “metallicities” — the fraction of elements other than hydrogen or helium relative to that of the Sun.

Figure 2 displays these two populations: the isolated binaries are shown as filled histograms, and the hierarchical triples are shown as histograms with dashed lines. Each column represents the three different progenitor classes considered in Figure 1. At solar metallicity, the delays to merging are greater in triples than in secular binaries, leading to more mergers overall (top left panel). At lower metallicities, there are fewer mergers in all progenitor pathways in triples than in isolated binaries due to changes in stellar evolution attributed to weaker winds and larger pre-white dwarf masses.

A Cosmic Population of FRBs

Since we can’t realistically track individual star systems from their formation to the end, we need to convert the delay-time distributions shown in Figure 2 to an observable. To do this, the authors combine the results of their simulations with measurements of the cosmic star formation rate — how many stars form per unit time as a function of the universe’s age — and the evolution of the universe’s metallicity as stars fuse hydrogen into heavier elements and return this material to the interstellar medium as these stars end their lives in shedding red giants or supernovae. This analysis produces the number of FRBs that should be observed as a function of distance or lookback time into the universe’s history, which is displayed in Figure 3.

This analysis reveals key measurable differences between lone binaries and hierarchical triples: most notably, binary white dwarf mergers peak later in the universe (redshift of z ~ 1), while single binaries peak earlier (redshift of z ~ 2). These results highlight the importance of including triples in FRB progenitors because they are more likely to contribute to populations at later times — making them closer and more easily detectable — in the total population of FRBs. Future instruments like CHIME with the new outriggers and the Deep Synoptic Array will expand the sample of FRBs to reach farther cosmological distances, with better localizations, enabling more statistically motivated tests of different formation pathways.

Original astrobite edited by Catherine Slaughter.

About the author, Will Golay:

I am a graduate student in the Department of Astronomy at Harvard University and the Center for Astrophysics | Harvard & Smithsonian, advised by Edo Berger. I study radio emission from transient astrophysical objects like tidal disruption events.

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Roughly 25–50% of the white dwarfs in the solar neighborhood are “polluted,” showing signs of accretion of metal-rich planetary material. New JWST observations reveal the contents of the debris disk surrounding one of the most polluted white dwarfs in the solar neighborhood.

Heavy-Metal Pollution

White dwarfs are the remnants of low- to intermediate-mass stars that have ceased core fusion and evolved off the main sequence. The presence of metals in white dwarf atmospheres shows that it’s common for white dwarfs to accrete rocky materials from tidally disrupted bodies in their surroundings, allowing for a post-mortem investigation of the composition of rocky worlds in far-off planetary systems.

One of the most impressively metal-polluted white dwarfs known is GD 362, which is surrounded by a dusty debris disk and shows evidence for at least 16 accreted elements. GD 362 is a helium-atmosphere white dwarf, but previous observations have also shown that it has an unusually large amount of hydrogen in its atmosphere — a possible sign that the star has consumed one or more bodies containing water or ice.

Disk Investigation

Now, a team led by William Reach (Space Science Institute) has obtained JWST spectra of GD 362 to examine the material in its disk directly. Using both the Near-Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI), the team collected spectra of the white dwarf from 0.6 to 17 microns, with additional photometric measurements at 18, 21, and 25.5 microns. The JWST spectra show bright emission from the white dwarf at wavelengths shorter than 2.5 microns, with a clear signature of disk material at longer wavelengths, including a strong emission feature at 9–11 microns.

Reach’s team modeled the JWST spectra to constrain the mineralogy of the disk and its physical attributes. They found that the disk likely stretches from 140 to 1,400 times the white dwarf’s radius and contains both silicates and carbon, with the prominent emission feature pointing to olivine and pyroxene silicate minerals. The elements seen in the white dwarf’s atmosphere are generally similar to those observed in the disk, strengthening the connection between accretion from the disk and the metals present in the white dwarf’s spectrum.

Hydrogen Mismatch

The new JWST data furthered the investigation of GD 362’s atmospheric hydrogen and the possibility that it’s accreting water- or ice-rich material. Though water molecules have spectral features in the range studied, none of these features appeared in the JWST spectra of GD 362. This isn’t necessarily a surprise; the team showed that water molecules in the disk would quickly be split apart by GD 362’s high-energy radiation.

Curiously, though, Reach’s team found little evidence for hydrogen-rich material within the disk that could be the source of the white dwarf’s atmospheric hydrogen. Because accreted hydrogen would remain in the star’s atmosphere indefinitely, the presence of atmospheric hydrogen could be evidence that the white dwarf accreted water-rich material from its debris disk in the past, though the materials currently present in the disk are dry.

In addition to investigating GD 362’s disk, Reach and collaborators searched for planets orbiting the white dwarf. Though they found none, they were able to rule out the presence of companions with masses greater than 25 times the mass of Jupiter.

Citation

“Composition of Planetary Debris Around the White Dwarf GD 362,” William T. Reach et al 2025 ApJ 994 195. doi:10.3847/1538-4357/ae11a9

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Astronomers have discovered the most compact cataclysmic variable system containing a strongly magnetized white dwarf. The extreme closeness of the system suggests that the companion may be a metal-poor star — the first time such a star has been paired with a strongly magnetized white dwarf.

Meet the Cataclysmic Variable

Cataclysmic variables are binary star systems that contain a white dwarf and a companion star in uncomfortably close quarters. In these systems, the companion star transfers gas to the white dwarf, resulting in sudden, irregular, and often repeated outbursts as the stolen gas ignites on the scorching surface of the white dwarf.

These bound-together stars typically orbit one another on orbits ranging from about 80 minutes to 10 hours. Though theorists place the minimum orbital period around 76 minutes, a handful of cataclysmic variable systems have cropped up with periods below this limit. The systems that have limboed under the limit are thought to have stellar companions that are more compact than typical main-sequence stars, allowing the white dwarf to nestle in closer.

Exploring Below the Limit

Discovered in 2019 by the Gaia spacecraft, Gaia19bxc is a cataclysmic variable that fluctuates with a period of 64.42 minutes. If this variability is linked to the orbital period of the system, that would place it well below the theoretical minimum period. Adding to the intrigue, early observations also hinted that Gaia19bxc’s white dwarf is strongly magnetic, making the system what’s called a polar. In polar systems, the white dwarf’s magnetic field diverts the accreted matter toward the white dwarf’s poles as it is collected, rather than into a disk around the white dwarf’s equator.

Now, Ilkham Galiullin (Kazan Federal University) and collaborators have analyzed photometry and spectra of Gaia19bxc from the Zwicky Transient Facility, the Hale Telescope, and the Keck I telescope to investigate the nature of this unusual system.

The team’s analysis confirmed that the stars of Gaia19bxc orbit one another every 64.42 minutes, cementing the system’s place below the period minimum for typical cataclysmic variables. The system’s double-peaked light curves and evidence for an accretion stream — rather than an accretion disk — confirm the system’s polar nature, implying a magnetic field strength greater than 10 million Gauss. This makes Gaia19bxc the most closely orbiting system to contain a strongly magnetized white dwarf.

A Sign of Discoveries to Come

These observations illuminate the nature of the white dwarf — but what about the companion star?

Galiullin and coauthors saw no evidence for metal lines in Gaia19bxc’s spectrum, nor did they see spectral features arising from a hot companion star. These findings suggest that the companion is an old, cool, compact, metal-poor star, which would make Gaia19bxc the first known polar to contain a metal-poor star. It’s also one of only a handful of cataclysmic variables to contain a metal-poor star and be below the theoretical period minimum.

Though Gaia19bxc is currently in a class of its own, it may not be for long; with the start of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time rapidly approaching, many more cataclysmic variable systems as faint as or fainter than Gaia19bxc may soon be discovered.

Citation

“Optical Spectroscopy of the Most Compact Accreting Binary Harboring a Magnetic White Dwarf and a Hydrogen-Rich Donor,” Ilkham Galiullin et al 2025 ApJL 990 L57. doi:10.3847/2041-8213/adff82

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Flashing on and fading quickly, recurrent novae are captivating astronomical phenomena. A recent study identifies one system that challenges our current understanding.

Rapid Recurrent Novae

When a white dwarf — the white-hot remnant of a dead star — has a close binary companion, the white dwarf can pull material from the companion star onto its boiling surface. Ignited in a bright flash, the accreted material is blown out from the white dwarf in a nova explosion that gradually expands and fades over time. Some novae, known as recurrent novae, repeat on observable timescales, creating a “new” star in the sky on periods ranging from one to one hundred years.

Our nearest galactic neighbor, Andromeda, hosts the most rapid recurrent novae observed to date, including the shortest-period known recurrent nova, M31N 2008-12a. M31N 2008-12a has erupted once a year for millions of years and will eventually meet its fate in a supernova explosion. 

Discovered in 2017, the second-shortest-period nova M31N 2017-01e has an outburst about every 2.5 years. This nova has sparked intrigue among researchers due to its low-amplitude outbursts and rapid evolution compared to other recurrent novae. While M31N 2017-01e exhibits some emission features typical for recurrent novae, recent studies have suggested that the system’s companion star may be a moderately young, blue B-type star. Most novae occur in systems where the white dwarf’s companion is a late-type main-sequence, subgiant, or giant star, making M31N 2017-01e an unusual case requiring further investigation. 

Dialing In on M31N 2017-01e

Aiming to constrain the nature and companion star of the nova, Shatakshi Chamoli (Indian Institute of Astrophysics and Pondicherry University) and collaborators performed a multiwavelength analysis using ultraviolet and optical observations of M31N 2017-01e.

In monitoring the nova during and in between outbursts, the authors identified a source at the reported location of M31N 2017-01e that exhibited variability and color consistent with previous observations of the system. Through a detailed photometric analysis, the authors found that the color and emission properties of the source are consistent with a hot, early-type star as was previously suggested. Though all the observational signs point toward a B-type companion, there’s one glaring obstacle to that scenario: such a massive star would typically be unable to transfer the amount of mass necessary to fuel the nova’s frequent eruptions without the accretion becoming unstable.

Be a Companion

What else, then, could the companion be? The authors considered another stellar companion known as a Be star — a rapidly rotating, early-type star that occasionally hosts a disk of loose stellar material. With a blue color and spectral features similar to B-type stars, a Be star could match the observational properties of the nova’s companion while solving the problem of its accretion. Outbursts of M31N 2017-01e likely arise due to the white dwarf lying very near or within the Be star’s circumstellar disk, siphoning material and adequately fueling the system’s recurring eruptions. To confirm this hypothesis, researchers will need to perform follow-up infrared observations to search for the tell-tale signs of a dusty disk around the companion star. 

This system is rare and challenges the assumed properties of recurrent novae. From this study, it is clear that nova progenitors are potentially quite diverse and require further multiwavelength observational programs to identify more systems like M31N 2017-01e.

Citation

“Challenging Classical Paradigms: Recurrent Nova M31N 2017-01e, a BeWD System in M31?” Shatakshi Chamoli et al 2025 ApJ 991 174. doi:10.3847/1538-4357/adf843

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Do neutron stars form solely through core-collapse supernovae, or is there another way? New research explores theorized processes in which a white dwarf shrinks down to become a neutron star.

Alternate Pathways

Neutron stars are known to form when high-mass stars explode in core-collapse supernovae. Theory suggests these stars can also form through accretion-induced collapse and merger-induced collapse. These scenarios involve a white dwarf, the remnant core of a low- to intermediate-mass star. If a white dwarf becomes too massive to support itself, either by accreting gas from a companion or colliding with another white dwarf, it could, under certain conditions, collapse into a neutron star.

So far, researchers have yet to definitively associate any transient signal with the creation of a neutron star from a collapsing white dwarf, though there are several candidates. To advance the search for these signals, researchers must understand the details of the collapse and predict its electromagnetic signature.

Collapsing Further

Eirini Batziou (Max Planck Institute for Astrophysics and Technical University of Munich) and collaborators investigated the burst of nucleosynthesis that might follow a white dwarf’s collapse, potentially powering an electromagnetic transient. The team performed two-dimensional hydrodynamic simulations of six white dwarfs on the cusp of collapsing into neutron stars. Each simulation run varied the mass, central density, rotation rate, and angular momentum profile of the white dwarf. Two of the modeled white dwarfs had masses very close to the Chandrasekhar limit, the mass above which a white dwarf can hypothetically no longer support itself through electron degeneracy pressure. The remaining synthetic stars had higher masses that were bolstered by rapid rotation.

Each of the modeled white dwarfs began to collapse when the crushing pressure of gravity forced the star’s sea of electrons to invade atomic nuclei, removing the support of electron degeneracy pressure. The white dwarfs’ cores shrank and condensed into protoneutron stars, while their outer layers fell inward and rebounded.

Setting the Stage for Element Creation

The simulations show that rotating and non-rotating white dwarfs have different outcomes when they collapse. Non-rotating white dwarfs cast off material in all directions, while rapidly rotating white dwarfs tend to lose material through wide outflows at their poles. The equator of the rapidly rotating white dwarf is ringed by a torus of material that feeds the neutron star as it forms.

These divergent outcomes affect the amount of ejected material and the production of neutrinos. Ultimately, these differences result in opposite behavior: in the non-rotating case, the ejected material is initially rich in neutrons before transitioning to a proton-rich outflow, while the rotating case starts out with proton-rich ejecta that transitions to a neutron-rich outflow. This suggests that elements created through the rapid capture of neutrons, like gold, can form when white dwarfs collapse into neutron stars, potentially powering an observable electromagnetic signal.

These simulations by Batziou and coauthors are the first to extend substantially beyond the moment the outer layers of the collapsing white dwarf bounce off the central protoneutron star, illuminating the ejection of material, production of neutrinos, and nucleosynthesis. Future work will dive deeper into the details of element creation, predict the luminosity of these events, and explore the role of magnetic fields.

Citation

“Nucleosynthesis Conditions in Outflows of White Dwarfs Collapsing to Neutron Stars,” Eirini Batziou et al 2025 ApJ 984 197. doi:10.3847/1538-4357/adc300

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Using JWST, researchers have spotted a freezing cold 5.2-Jupiter-mass exoplanet orbiting an old white dwarf at a distance of just 0.02 au. With a temperature of 186K (−125℉/−87℃), this is the coldest exoplanet whose light has been directly detected.

The Fate of Sun-Like Stars

Low- to intermediate-mass stars eventually evolve into red giants and then white dwarfs: crystallized, superheated stellar cores that slowly cool and fade over millennia. What happens to the planets around stars that evolve into white dwarfs is an open question, one that can be answered by detecting and characterizing the planets that remain in these systems.

Planets orbiting at radii beyond 2 au are expected to weather their host star’s transition to a red giant, and dedicated searches for white-dwarf exoplanets have revealed a small number of planets at this safe distance. Observations have also begun to hint at planets orbiting white dwarfs more closely — within the “forbidden zone” thought to be scoured out by the host star’s transformation into a red giant — and researchers have now confirmed the presence of a planet eking out an existence extremely close to its white dwarf host.

Companion Detection

The white dwarf WD 1856+534 is located roughly 82 light-years away. In 2020, researchers using data from the Transiting Exoplanet Survey Satellite and a handful of ground-based telescopes detected a Jupiter-sized object orbiting WD 1856+534 every 1.4 days at a distance of just 0.02 au — nearly 30 times closer than Mercury is to the Sun.

The original observations couldn’t discern whether the object, cataloged as WD 1856+534b, was a massive exoplanet or a low-mass brown dwarf. Now, a team led by Mary Anne Limbach (University of Michigan) has performed follow-up observations of the system. Using JWST’s Mid-Infrared Instrument (MIRI), Limbach’s team detected WD 1856+534b by subtracting a detailed model of the white dwarf’s flux from the observed flux. The object’s faint thermal glow was detected with an overall statistical significance of 5.7 sigma.

Brown Dwarf or Planet?

By modeling this thermal emission, Limbach and collaborators definitively showed that WD 1856+534b is a planet. Its mass is likely around 5.2 Jupiter masses, though masses between 0.84 and 5.9 Jupiter masses are possible. With an exceedingly chilly temperature of just 186K — only 60K warmer than Jupiter — WD 1856+534b is the coldest exoplanet whose emission has been directly detected.

Because WD 1856+534b couldn’t have survived its host star’s transformation into a red giant at its current position, it must have migrated inward from a more distant orbit. The cause of this migration isn’t yet clear, though common-envelope evolution or gravitational nudges from another planet or star may have played a role. Upcoming JWST observations that probe WD 1856+534b’s atmosphere and search for other planets in the system could provide answers.

Citation

“Thermal Emission and Confirmation of the Frigid White Dwarf Exoplanet WD 1856+534 b,” Mary Anne Limbach et al 2025 ApJL 984 L28. doi:10.3847/2041-8213/adc9ad

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