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cataclysmic variable system

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.

Light curves of Gaia19bxc

Phase-folded light curves for Gaia19bxc from the Caltech HIgh-speed Multi-colour camERA (CHIMERA) on the Hale Telescope. The double-peaked light curve is evidence for cyclotron beaming, which occurs in strongly magnetized white dwarfs. [Adapted from Galiullin et al. 2025]

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

histogram of cataclysmic variable orbital periods

Gaia19bxc’s orbital period compared to known polar cataclysmic variables (gray) as well as the theorized minimum periods for systems containing a metal-poor (Pop II) companion (cyan) and an evolved companion (blue). [Galiullin et al. 2025]

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

A glowing orange sphere set against a background image of the Milky Way's disk of stars.

Isolated brown dwarfs are some of the rarest and hardest to study objects in our stellar neighborhood. Recently, astronomers revealed that one of the most famous isolated brown dwarfs, W1935, is not actually one brown dwarf but two.

Challenging but Fascinating

Astronomers know of only 50 free-floating brown dwarfs within the nearest 200 light-years or so, and even the ones we know about are poorly understood. Since brown dwarfs are frigid compared to their stellar cousins, they consequently shine much less brightly and at longer wavelengths of light. Even taking a picture of these ~500K objects requires long stares with specialized telescopes, and these facilities already have their schedules full supporting a wide range of other areas of research from distant galaxies to exploding supernovae.

A color photograph of Jupiter showing its red bands, great red spot, and a bright spiraling blue aurora near the north pole.

An image of Jupiter and its prominent aurora taken with the Hubble Space Telescope. [NASA, ESA, and J. Nichols (University of Leicester); Acknowledgment: A. Simon (NASA/GSFC) and the OPAL team]

So, when an in-demand telescope like JWST spends time on brown dwarf science, each byte of data it sends back is both precious and likely to contain a new discovery. This has already happened several times: back in 2023, research published in the AAS journals (and summarized on AAS Nova) described JWST’s discovery of the first-ever Y+Y binary system, and in 2024, astronomers at the 243rd meeting of the AAS presented the first detection of methane emission on a brown dwarf — a sign of auroral activity.

Recently, JWST continued its pattern of discovery: the telescope took another look at the brown dwarf W1935, where methane emission was detected for the first time, and again found something surprising.

A New Binary

When JWST first took a look at this brown dwarf, it used its Near Infrared Spectrograph (NIRSpec) to record a spectrum of the object. These data revealed a large spike near 3 microns that perfectly lined up with methane emission from an aurora, similar to what we observe on Jupiter in the solar system. This was a thrilling find, since it hinted at an exciting possibility: Jupiter’s aurora is powered by its nearby moon Io, so the researchers cautiously wondered if W1935’s aurora could be evidence of a companion satellite as well.

A multi-panel figure with noisy (real) images in the left column, smooth models in the middle column, and pixelated residuals in the rightmost column. The models are in good agreement with the data.

Images of W1935 taken with MIRI (left column), the author’s model for those images (center column), and the residuals (right column). The model includes two nearby point sources that are so close together they appear as one slightly elongated source. Click to enlarge. [De Furio et al. 2025]

Soon after these observations, JWST once again turned to W1935, but this time used its Mid-Infrared Instrument (MIRI) to take images of the object at long wavelengths. A team of researchers led by Matthew de Furio, University of Texas at Austin, recently analyzed these images and noticed something interesting: W1935 isn’t just one brown dwarf, but rather two roughly equal-mass brown dwarfs packed close together on 16–28 year orbits.

Doubly Interesting

This makes W1935 just the second-ever known Y+Y dwarf binary and cements its status as one of the most interesting brown dwarf systems discovered to date. So far, it’s not clear which object is responsible for the auroral signal since the objects are so close together that their images blur together without careful modeling and image processing.

De Furio’s team pointed out that JWST has yet another instrument that could prove useful here: its Integral Field Unit spectrometer within NIRSpec. Should JWST revisit this fascinating system, it could study the aurora’s variability over time, pin it to one specific object within the binary, and hopefully shed some light on whether any moons play a role in the methane emission. Given all we have learned each time JWST has turned to these strange worlds, we can only hope that it will do so again soon.

Citation

“Discovery of the Second Y+Y Dwarf Binary System: CWISEP J193518.59-154620.3,” Matthew De Furio et al 2025 ApJL 990 L63. doi:10.3847/2041-8213/adfee1

Illustration of a tidal disruption event

Catastrophic encounters between stars and massive black holes usually take place in the nuclei of galaxies, but not always. Researchers recently reported on the brightest-ever radio emission from an off-nuclear tidal disruption event caused by a wandering or recoiling black hole.

Signature of a Roaming Black Hole

Tidal disruption events occur when a star ventures too close to a massive black hole. The tidal forces of the black hole stretch the star until it’s partially or entirely disrupted, sometimes causing jets or outflows to spray from the shredded star. One thing that often distinguishes a tidal disruption event from the sea of other possible transients is the location, close to the nucleus of a galaxy.

But not all tidal disruption events happen in the center of a galaxy. In rare cases, a massive black hole roaming elsewhere in a galaxy may encounter a star, sending out a tell-tale signal in an unexpected location.

radio images of AT 2025tvd

Radio observations of AT 2024tvd on two dates after its optical discovery. The tidal disruption event was not detected at 88 days post-discovery (left) and outshone the center of its host galaxy on 160 days post-discovery (right). Click to enlarge. [Sfaradi et al. 2025]

One such event is AT 2024tvd, which was discovered at optical wavelengths by the Zwicky Transient Facility. Though the initial identification placed it at the center of its host galaxy, follow-up observations suggested that it was in fact 2,600 light years from the center. What can radio observations tell us about this rare off-center event?

Radio Reconnaissance

Less than three months after AT 2024tvd was discovered, Itai Sfaradi (University of California, Berkeley) and collaborators launched a months-long radio-wavelength observing campaign using the Very Large Array, the Atacama Large Millimeter/submillimeter Array, the Arcminute Microkelvin Imager Large Array, the Allen Telescope Array, and the Submillimeter Array. Radio observations are critical for investigating jets and outflows from tidal disruption events.

The observations, which spanned centimeter and millimeter wavelengths, revealed two emission peaks from the tidal disruption event. The first peak occurred roughly 131 days after the event was discovered, and the second followed at day 194.

Radio emission from AT 2024tvd compared to other radio-bright tidal disruption events

Demonstration of the fast evolution of AT 2024tvd’s radio emission (red and orange stars) compared to other radio-bright tidal disruption events (other symbols). [Sfaradi et al. 2025]

About 40% of the tidal disruption events that have been identified at optical wavelengths show this kind of delayed brightening at radio wavelengths, but AT 2024tvd stands out as having the fastest radio evolution ever seen. Even among fairly fast-evolving flares, AT 2024tvd is unusual, having a brighter second peak than peer events.

Prompt or Delayed, Outflow or Jet?

To understand the origin of the fast-evolving, extremely bright radio emission from AT 2024tvd, Sfaradi’s team modeled the emission that would arise from outflows and jets. For both wide-angle outflows and narrow jets, the team considered both prompt — arising simultaneously with the event’s optical detection — and delayed sources.

The team’s modeling highlighted several possible scenarios. In the first, both bright radio peaks arose from a single outflow that was launched about 84 days after the star met its doom. The double-peaked behavior is due to the outflow interacting with a complex distribution of material surrounding the black hole. It’s also possible for the two peaks to arise from separate outflows or jets, one launched around 84 days and the other around either 170 or 190 days, depending on whether the second source is a mildly relativistic outflow or a relativistic jet.

Sfaradi and collaborators posited that AT 2024tvd’s unusual radio behavior could be due to its off-nuclear location, but they acknowledged that this event might simply occupy a region of tidal disruption event parameter space that had yet to be explored. Sensitive interferometric or polarimetric observations may reveal more about how AT 2024tvd interacts with its environment, helping to illuminate the nature of this rare event.

Citation

“The First Radio-Bright Off-Nuclear TDE 2024tvd Reveals the Fastest-Evolving Double-Peaked Radio Emission,” Itai Sfaradi et al 2025 ApJL 992 L18. doi:10.3847/2041-8213/ae0a26

nova

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.

M31N 2017-01e light curves

Two light curves of M31N 2017-01e outbursts from 2024 (top) and 2019 (bottom) showing how the light evolves over time. Click to enlarge. [Chamoli et al 2025]

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. 

M31N 2017-01e Progenitor search

Optical image showing the location of sources near the location of M31N 2017-01e. The yellow circle corresponds to a radius of 5 arcseconds and is centered on the nova. Labeled S0, the source coincides with the location of the nova with sub-arcsecond resolution. Click to enlarge. [Modified from Chamoli et al 2025]

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

WISPIT 2b

Have you ever eaten a meal so quickly that you started to glow? Although this behavior likely isn’t relatable for most humans, astronomers are beginning to find more and more baby planets doing just that.

Planetary Glow Up

Planets are, famously, quite large. But astronomers know that they don’t start out that way, and that instead, stars and planetary systems start as wispy collections of dust and gas. This raw material eventually compresses itself into stars and planets and life capable of contemplating such things, but how exactly that happens is not perfectly understood.

A colored-pencil drawing of gas flowing around a planet, with arrows noting the direction of the flow at various points.

A schematic of some of the processes involved during giant planet formation. Click to enlarge. [Batygin 2018]

Astronomers have the broad contours sketched out at least. Protoplanets destined to become gas giants like Jupiter and Saturn start by gobbling up all the material around them and eventually clear out gaps in the disks in which they are born. What little material flows into these gaps gets sucked onto the planet in a process called accretion, though exactly where this material lands and how gravity and magnetic fields interact is up for debate.

A number of different mechanisms predict that during this process, the protoplanet should emit light at a certain frequency associated with electrons jumping between energy levels in hydrogen atoms — what astronomers call Hα emission. In other words, they should glow at that specific wavelength only when they are accreting, though how strongly and consistently will depend on exactly what is happening around the planet.

These ideas existed only on paper until 2019, when a team first observed two glowing, growing planets around the star PDS 70. Recently, however, a powerful new instrument has begun collecting data, and astronomers just announced it has found another similar protoplanet: WISPIT-2b.

A New Discovery

A team of researchers led by Laird Close (University of Arizona) announced the discovery of this new world after analyzing images taken with the powerful new MagAO-X instrument on one of the 6.5-meter Magellan telescopes in Chile. The team outfitted the camera with a narrow filter that only admitted the Hα emission associated with accretion, then collected thousands of images over about two hours in April 2025. After stacking and post-processing their data, a faint dot jumped out beside the central star, right in the gap between two bright rings in the star’s disk.

A bright dot beside fainter rings of material.

A follow-up image of WISPIT-2b taken with a broader filter. [Laird et al. 2025]

This protoplanet, which the authors name WISPIT-2b in honor of their Wide Separation Planets in Time (WISPIT) survey, is likely about five times the mass of Jupiter and only 5 million years old, making it a baby on astronomical timescales. Based on how strongly it’s glowing, the team estimates that it’s accreting the equivalent of about 100 times the mass of Phobos, Mars’s largest moon, each year. This process won’t continue forever, as eventually the remains of the star’s disk will disperse and the planet will have to go hungry.

This remarkable find is only the third protoplanet unambiguously found to be embedded within a disk, and the first to be found in the gap between rings in a disk. With MagAO-X collecting data and the WISPIT survey underway, we’re likely in store for many other discoveries in the coming years. With enough observations and examples of these growing worlds, astronomers will fill in their models of how exactly giant planets as we know them are formed.

Citation

“Wide Separation Planets in Time (WISPIT): Discovery of a Gap Hα Protoplanet WISPIT 2b with MagAO-X,” Laird M. Close et al 2025 ApJL 990 L9. doi:10.3847/2041-8213/adf7a5

ultracompact dwarf galaxy

With very small stellar masses and tiny radii, ultracompact dwarf galaxies raise questions about the dividing line between the highest-mass star clusters and the lowest-mass galaxies. A recently published article leverages JWST’s high resolution to target one tiny galaxy and investigate its origins.

UCD 736

Location of UCD 736 in the Virgo Cluster with the other ultracompact dwarf galaxies with supermassive black hole detections labeled. Click to enlarge. [Taylor et al 2025]

Origins of Ultracompact Dwarf Galaxies

How tiny can a galaxy get? Discovered 20 years ago among the dense environments of the Virgo and Fornax clusters, ultracompact dwarf galaxies walk the line between the largest globular clusters and the smallest galaxies. Determining if these dwarfs are stellar in nature or actually of galactic origin is complex, but one sure way to get at this question is to determine if an ultracompact dwarf galaxy houses a supermassive central black hole. 

While astronomers have identified hundreds of these tiny dense galaxies, supermassive black holes have been detected in only five. Hoping to extend this sample, Matthew Taylor (University of Calgary) and collaborators targeted UCD 736, an ultracompact dwarf galaxy located in the Virgo galaxy cluster. If a massive black hole is found in this galaxy, it will be the smallest and least luminous ultracompact dwarf to have such a detection. Exploring galaxies at such small sizes will allow researchers to determine what fraction of ultracompact dwarfs have galactic or star cluster origins, which can provide insights into massive black hole seeding mechanisms in the early universe.

Modeling Black Hole Mass

Model results

Summary of results for the three black hole modeling methods for UCD 736, indicating the quality of the models and how the observed velocity dispersion and spatial distribution of the galaxy fit with the models. Click to enlarge. [Taylor et al 2025]

In order to search for a central black hole in UCD 736, Taylor and team obtained high-resolution spectroscopy from JWST and supplemental imaging from the Hubble Space Telescope. The authors used the stellar kinematics and light profile of the galaxy to estimate the mass of its central black hole with three independent modeling methods. Based on the expected impacts of a massive black hole on galaxy dynamics and the estimated stellar population of the galaxy, the authors found that UCD 736 likely hosts a central supermassive black hole with mass ~2.1 million times the mass of the Sun. 

However, the authors noted that the three models do not provide equivalent confidence levels in this estimate — while one model confidently rules out the possibility of no central black hole at 3σ significance, the other two models were less constraining, ruling out the possibility of there not being a black hole to only 1σ. Despite these differences, all three models agree on the central black hole mass within the first confidence interval, indicating a positive detection of a black hole in UCD 736.

Progenitor of UCD 736

From their observations and modeling, the authors presented the fifth positive detection of an ultracompact dwarf galaxy with a central supermassive black hole within the Virgo Cluster. Given the presence of this black hole, UCD 736 likely originated as a more massive galaxy that was tidally stripped as it interacted with other nearby cluster galaxies. Interestingly, though, other ultracompact dwarf galaxies with black hole detections in the Virgo Cluster are much closer to the massive galaxy that likely stripped them. UCD 736 sits about 160,000 light-years outside of the nearest giant galaxy Messier 59’s tidal radius, which does not rule out interactions but could indicate that Messier 59 is particularly good at stripping material from smaller galaxies. 

Continued searches for black holes in ultracompact dwarfs will further probe the differences between the highest-mass globular clusters and the lowest-mass galaxies. Revealing more within this parameter space will allow astronomers to test black hole seeding and galaxy formation theories.

Citation

“A Supermassive Black Hole in a Diminutive Ultracompact Dwarf Galaxy Discovered with JWST/NIRSpec+IFU,” Matthew A. Taylor et al 2025 ApJ 991 L24. doi:10.3847/2041-8213/ae028e

A blue/white star with lines representing magnetic fields sprouting from the poles against a black background.

Neutron stars don’t stick around for long after they’re born. Recent research has now uncovered just how fast they flee.

They Grow Up So Fast

Human beings require many years of care and support from their parents before they’re able to venture forth into the world. This is an embarrassingly long process compared to the standard for animals like deer and horses, whose offspring are ready to walk mere minutes after birth. However, baby neutron stars, some of the densest objects in the known universe, put all life on Earth to shame with their immediate self-reliance: after a fiery birth from a supernova explosion, these stars flee the site of their creation at hundreds of kilometers per second.

Crab Nebula supernova remnant

Hubble Space Telescope and Herschel Space Observatory image of the Crab Nebula, which is the remnant of a supernova explosion. [ESA/Herschel/PACS/MESS Key Programme Supernova Remnant Team; NASA, ESA and Allison Loll/Jeff Hester (Arizona State University)]

These “natal kicks,” as they’re called in research literature and in recent work by Paul Disberg and Ilya Mandel (Monash University and OzGrav) are a natural consequence of neutron star formation. When a massive star burns through the last of its fuel and surrenders to its own gravity, it collapses inward and compresses its core into a neutron star before rebounding in an explosion. This collapse is never perfectly symmetric, however, and the slight imbalance gives the resulting neutron star a shove.

By measuring the characteristic speeds of these “kicks,” astronomers can deduce how asymmetric the preceding collapse must have been, along with other information about the earliest moments of the supernova. Though measuring the speed of something so small from the other side of the galaxy is no easy task, Disberg and Mandel’s recent publication in The Astrophysical Journal Letters takes on the challenge.

Quantifying the Kicks

The pair first began by examining measurements of neutron stars known to be less than 10 million years old, which is extremely young in an astronomical context. Since these objects haven’t had time to be slowed down or altered from their course by passing stars or the galactic tide, their present-day speeds should be the same as their natal kicks. The researchers found that while every neutron star had its own unique kick velocity, the distribution of all the velocities followed a log-normal pattern with a peak near 150–200 km/s.

Measured kick velocities and fit distributions

Measured kick velocities (histograms) and fit distributions (curves) for different subsamples. Click to enlarge. [Disberg & Mandel 2025]

Next, Disberg and Mandel examined the distribution of velocities from older neutron stars. These, which had to be measured via a different method, turned out to be very similar to the distribution assigned to the younger stars. Finally, they re-examined previous studies that attempted their own models of the kick distribution. Though several of these studies conflicted with one another, the team found that these discrepancies could be explained by different sample sizes and mistaken statistical interpretations. On the whole, the team’s distribution fit all the available data well and the most succinctly of any alternative framework.

Going forward, other astronomers focused on modeling supernovae, orbits within the galaxy, and binary-star evolution can use this distribution either to sanity check their models or as inputs to other simulations. Through slow accumulation of studies like this, each with its own quantified measurement of some property in the galaxy, we come to understand our universe more fully and unlock our ability to make ever more models and predictions.

Citation

“The Kick Velocity Distribution of Isolated Neutron Stars,” Paul Disberg and Ilya Mandel 2025 ApJL 989 L8. doi:10.3847/2041-8213/adf286

A photograph of a large radio dish taken during the day from above.

To measure properties of a pulsar accurately, astronomers have to stack many individual observations together to boost the signal above the noise. But what if there was a more clever, more effective way to add observations than simple stacking?

Weak Cosmic Lighthouses

Pulsars, or rapidly spinning neutron stars that emit narrow cones of radio waves, are often referred to as the galaxy’s lighthouses. Just like a sailor looking to shore might see a periodic flash when a lighthouse’s beacon sweeps over their ship, so too would radio telescopes aimed at a pulsar detect a “pulse” when its beam sweeps across Earth. However, although this comparison to lighthouses is a powerful analogy, it starts to break down when considering the speed and strength of these flashes.

A time series showing a Gaussian-like spike.

An example of one noisy individual pulse. Click to enlarge. [Sosa Fiscella et al. 2025]

While lighthouses may take several seconds to rotate their lens and lamp once around, pulsars do the same in just a few milliseconds. What’s more, while lighthouses are designed to be bright enough that sailors can notice every individual flash, pulsars are comparatively dim. To confidently measure the “pulse profile,” or how a pulsar’s radio intensity changes as a function of its rotation phase, astronomers need to stack those hundreds of thousands of pulses together into one artificial super-bright pulse. Only then can they measure the quantities they care about, like the precise spin period and average pulse arrival time.

This practice rests of the subtle assertion that every individual pulse is just a noisy variation of the same unchanging pulse profile. But is that safe to assume? And can we improve the precision of our measurements by doing something more complex than simple stacking? These are the questions recently tackled by a team of astronomers led by Sofia V. Sosa Fiscella (Rochester Institute of Technology) in research published in The Astrophysical Journal.

Squeezing the Data

The researchers focused on one particularly bright source named PSR J2145−0750 that was observed by the Green Bank Telescope for two hours in 2017. This pulsar is so bright that it’s possible to measure quantities like the pulse width, height, center, and total energy of individual pulses, not just the final stack. The team did just that for each of the more than 200,000 pulses in their dataset and assigned each one a vector of four numbers. When they next sorted the pulses into distinct groups, they found that there were indeed correlations among these variables: for example, pulses with higher maximum heights tended to arrive earlier and be narrower than the overall average.

A 3D plot across different measured pulse characteristics where each point is colored according to its cluster.

A visual representation of the different pulse clusters. Each point corresponds to one pulse. Click to enlarge. [Sosa Fiscella et al. 2025]

To take advantage of this structure, they created a stacked pulse profile for each cluster, measured the center in each of them, then averaged all the cluster-specific times together into a final answer. While the standard method of stacking all of the data into one pulse profile resulted in a timing precision of 0.066 microsecond, this new method shrank the uncertainty to 0.057 microsecond, a meaningful improvement.

Though the team cautions that this new method will likely only be relevant for the pulsars for which we can measure individual pulses, they also point out that as better telescopes come online, we’ll be able to do that for more pulsars. In the meantime, astronomers can take comfort in the fact that as our technological abilities improve, so do our abilities to squeeze as much from our data as possible.

Citation

“Improving Pulsar Timing Precision with Single Pulse Fluence Clustering,” Sofia V. Sosa Fiscella et al 2025 ApJ 984 111. doi:10.3847/1538-4357/adc1c2

Pulsar diagram

Pulsars, the best timekeepers in the universe, are key to many fields within astronomy. A new survey searching for pulsars has come online and is already making discoveries.

Searching for Pulsars

Pulsars, the extremely dense cores left over from some massive stars’ deaths, act as astronomical lighthouses — spinning fast and emitting jets of light from their magnetic poles, they send steady pulses of light to observers on Earth. Pulsars are particularly intriguing sources, providing insights into multiple areas of astrophysics like gravitational waves, general relativity, and high-density matter properties. While more than 3,700 pulsars have been discovered to date, increasing this number will enable further exciting science. 

Multiple pulsar surveys have utilized single-dish radio telescopes to cover portions of the sky, and to date, these surveys have primarily focused on finding pulsars near the dense stellar population in the Milky Way’s galactic plane. While these surveys have detected many pulsars, they are limited by their small fields of view, taking longer to cover large portions of the sky, and they miss the population of pulsars that must lie within globular clusters orbiting in the galactic halo. Some low-frequency detectors address these limitations but require intense computational resources to sift through the raw data to find pulsars. How can we search for pulsars efficiently across the sky?

Introducing CHAMPSS

CHAMPSS pointing map

CHAMPSS pointing map showing the survey’s planned sky coverage. The orange stars correspond to the newly discovered pulsar, and the pink points denote known pulsars within the commissioning surveys. Click to enlarge. [Andrade et al 2025]

Hoping to cover the gaps in pulsar surveys thus far, researchers turned to the Canadian Hydrogen Intensity Mapping Experiment (CHIME). CHIME is a unique instrument that utilizes a set of cylindrical antennas to monitor large portions of the sky for radio sources from 400 to 800 MHz. This instrument has already made great strides in detecting transient radio events and has discovered more than 80 pulsars since its first light in 2017. 

With a clear opportunity to advance the pulsar search, a group of scientists developed the CHIME All-sky Multiday Pulsar Stacking Search (CHAMPSS) — a radio pulsar survey that covers the full northern sky daily and uses long-term data stacking to detect irregular and faint sources. Through stacking observations across multiple days, CHAMPSS builds up signals to find faint sources that would otherwise go undetected. The data processing pipeline searches in real time for strong peaks that signify a transient radio event, and follow-up analysis determines if the event is a pulsar candidate. A strong candidate then moves through further stages to confirm it as a pulsar and determine its properties. 

Pulsar discoveries

The 11 pulsars discovered with CHAMPSS. Click to enlarge. [Andrade et al 2025]

First Discoveries and Looking Forward

What has CHAMPSS uncovered thus far? In testing the system through multiple commissioning surveys on a small subset of the sky, the CHAMPSS collaboration has discovered 11 new pulsars with periods ranging from 0.2 to 1.5 seconds. Additionally, the collaboration tested the sensitivity of their survey by searching for known pulsars within the observed area, and they found that their predicted and detected signal-to-noise ratios for known pulsars agree well. This confirmation allows the team to advance to the next phase of the survey, and it will soon be in full swing.

CHAMPSS complements and expands upon other radio pulsar searches, discovering faint and irregular sources that are missed without repeated observations. The future of pulsar astronomy is promising, and with the advent of this survey, a new collection of pulsars will be discovered. 

Citation

“CHIME All-sky Multiday Pulsar Stacking Search (CHAMPSS): System Overview and First Discoveries,” Christopher Andrade et al 2025 ApJ 990 50. doi:10.3847/1538-4357/adeb51

A spiral of bright material circling a black core.

Simulations suggest that there should be a million stars in our galaxy that once wandered so close to a supermassive black hole that they were nearly destroyed. What are the long-term effects of this encounter, and could astronomers observe the scars of these near-death experiences?

Moths to a Flame

center of the Milky Way

This infrared and X-ray image of the Milky Way’s center shows a swirl of hot gas surrounding Sagittarius A*, our galaxy’s central supermassive black hole. [NASA, ESA, SSC, CXC, STScI]

The center of our galaxy is a dangerous place to be a star. Like mosquitoes drawn to a light, millions of stars swarm around the supermassive black hole named Sagittarius A*, packing themselves in tight and kicking one another onto wild, eccentric, and ever-changing orbits. Every 100,000 years or so, one of these stars gets an unlucky push and finally gives in to the black hole’s irresistible pull. A nudge from a neighbor will send it hurtling beyond the point of safety, and in one intense flyby, it’ll be ripped apart by Sagittarius A*’s immense gravitational field.

Simulations suggest that most of the time, these hapless stars are not completely destroyed by their close encounters with the black hole. In principle, then, there should be about a million “survivor” stars wandering near the center of our galaxy. But, what would these survivors look like? And with careful measurements, could we tell them apart from their regular, unscathed counterparts?

Simulating a Star’s Worst Day

Recently, a team of astronomers led by Rewa Clark Bush (University of California Santa Cruz, Cabrillo College, Wesleyan University) tackled this question. First, the team needed to simulate a terrible day for a hypothetical star: the day it passes closest to the black hole. To compute what happens to the star in those intense couple of hours, they used an open-source hydrodynamic code called FLASH to track the state of the star in granular detail.

An 8-panel figure showing complex, asymmetric patterns of gas around a dense core.

Temperatures (top row) and diffusion timescales (bottom row) of four stars soon after their closest approach to the black hole. Click to enlarge. [Bush et al. 2025]

Then, once the star (or what was left of it) managed to flee back to safety, the team froze the simulations and took stock. They found that depending on the initial size of the star and the distance of its closest approach, the black hole stripped away anywhere from a few percent to almost two thirds of the star’s mass. The researchers then fed the stars into another code called MESA to simulate how the disturbed stars would settle into a new equilibrium and evolve over billions of years.

Back on Track

Plot comparing disturbed and undisturbed stars

Comparison of the original undisturbed stars (filled circles), the stars after a black hole encounter (open symbols), and other stars with different initial masses (black points). Click to enlarge. [Bush et al. 2025].

The team found that although these unlucky stars likely glow tens to hundreds of times brighter than usual after their flyby, this period of enhanced brightness lasts less than 100,000 years. For our galaxy, this translates to 1–10 stars currently in the galactic center that have been brightened by an encounter with a supermassive black hole.

Eventually, though, these stars pretty much return to a new normal. Though these stars would have had slightly different colors and luminosities had they not encountered the black hole, they end up looking similar to undisturbed stars with the same final mass.

Although detailed spectroscopic measurements of these remnants might reveal a strange composition thanks to all the stirring that happened during the flyby, it’d be hard to tell anything happened to these stars otherwise. Ultimately, life goes on, even for stars that were nearly destroyed by the most massive creature in the galaxy.

Citation

“Black Hole Survival Guide: Searching for Stars in the Galactic Center that Endure Partial Tidal Disruption,” Rewa Clark Bush et al 2025 ApJL 990 L7. doi:10.3847/2041-8213/adefde

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