Willem B. Hoogendam, David O. Jones, Christopher J. Storfer+26 more
AstronomerPhotometric and spectroscopic follow-up of the strongly lensed, hydrogen-poor SLSN 2025wny at z = 2.0155 shows reasonable agreement with lower-redshift SLSNe. Keck-II/KCWI rest-frame UV spectra cover 11–61 days after maximum light, show virtually no iron-group line blanketing, and contain absorption features matching previously identified SLSN-I features from abundance tomography. Pan-STARRS photometry constrains the brightest image’s magnification to 19.4 ± 1.6, approximately 2–4 times the mass-modeling estimates. A MOSFiT magnetar-injection model including nickel-56 decay reproduces the near-maximum light curve with parameters typical of local SLSNe-I: a spin period of 4.1 ms (+0.7/−1.0) and a magnetic field of 2.4 × 10^14 G (+1.1/−0.8 × 10^14 G). This fit does not establish the power source, and the late-time plateau suggests an additional source. Narrow interstellar lines indicate sub-solar host metallicity; host-galaxy UV-to-optical lines yield estimated outflow velocities of about 575 km/s and an exceptionally high Lyman-alpha escape fraction of 0.23 ± 0.03. Additional high-redshift discoveries expected from LSST and Roman will test population-level consistency of SLSNe-I in the early universe.
PublicAstronomers studied SN 2025wny, an exceptionally bright stellar explosion with little hydrogen, whose light is magnified by gravitational lensing. Its measured redshift is 2.0155. Brightness measurements suggest that the brightest lensed image is magnified about 19 times—roughly 2–4 times more than estimates from lens mass models. A model powered by a rapidly spinning, strongly magnetic stellar remnant, together with radioactive nickel decay, can explain the brightness near its peak, but this is not proof of that explanation. A later leveling-off in brightness suggests another energy source may also contribute. The ultraviolet spectra show almost none of the light suppression associated with iron-group elements. Spectral lines indicate that the host galaxy has fewer heavy elements than the Sun, fast gas outflows, and an unusually high escape fraction for Lyman-alpha light. Overall, this distant explosion resembles closer examples reasonably well; future surveys are expected to test whether that similarity holds for larger samples.
Young explorerAstronomers watched a very bright star explosion far away. Gravity acted like a magnifying glass, making its light look brighter. It looked quite like some explosions closer to us. A model says a tiny, fast-spinning leftover star might help power its light, but that is not certain. The explosion stayed bright later on, so something else might be helping too.
Ferdinand, Murray Brightman, Jean-Marie Hameury+9 more
AstronomerThe authors report the discovery and X-ray characterization of M31 ULX-3, a transient, off-nuclear ultraluminous X-ray source first detected serendipitously on 2021 June 9. Its peak unabsorbed 0.3–10 keV luminosity was approximately 10^39 erg s^-1. Spectral evolution suggests increasing advection at later epochs, contrary to the expected transition from a super-Eddington slim disk to a standard thin disk as the outburst decays. The Hameury–Lasota disk-instability model can reproduce the observed light curve with characteristic timescales of approximately 41–61 days; this fit does not establish the model uniquely. The inferred accretion rate would be super-Eddington for a 1.4-solar-mass neutron star but approximately Eddington for a 10-solar-mass black hole, leaving the compact object's identity unresolved. Comparison of nearby Hubble Source Catalog objects with stellar isochrones suggests a possible giant donor with log10(age/yr) approximately 8.5 and mass approximately 3.2 solar masses, assuming A_V = 1.58; the donor association is tentative. The estimated M31 transient-ULX occurrence rate is 0.18 ± 0.10 per year, lower than rates reported for other galaxies. The discovery adds to M31's small known transient-ULX population and motivates regular X-ray monitoring.
PublicAstronomers discovered a temporary, exceptionally bright X-ray source in M31, called M31 ULX-3. First spotted on June 9, 2021, it reached a peak X-ray luminosity of about 10^39 ergs per second. Its changing X-ray spectrum suggests that more heat was being carried inward through the surrounding disk at later stages—opposite to the expected trend as such an outburst fades. A model involving an unstable disk can reproduce the observed changes in brightness, with characteristic timescales of about 41–61 days, but this is a possible explanation rather than a confirmed mechanism. The inferred rate of incoming matter would exceed the usual Eddington benchmark for a neutron star of the assumed mass, but would be near that benchmark for a more massive stellar black hole; the study does not settle which object is present. Nearby optical sources suggest a possible giant companion supplying matter, although that identification depends on assumptions about dust dimming and stellar evolution. The estimated rate of these transient sources in M31 is 0.18 ± 0.10 per year, lower than previous estimates for other galaxies. Regular X-ray observations could help uncover more.
Young explorerAstronomers found something in a galaxy called M31 that became very bright in X-rays for a while. It may be a neutron star or a black hole taking in material, but they do not know which. Its X-rays changed in a surprising way as it faded. A model of a changing disk of material can explain how its brightness rose and fell, but that does not prove what happened. A nearby big star might be feeding it, though that is not certain either. The astronomers say we should keep watching nearby galaxies for more temporary bright spots like this.
Samantha Creech, Francesca Civano, Daniel Wik+13 more
AstronomerThis study presents the first spectral modeling of 52 NuSTAR sources discovered in the latter half of the NEP-TDF campaign and a spectroscopic variability analysis of the full 112-source catalog, identifying seven variable candidates. Simultaneous NuSTAR and XMM-Newton observations, supplemented by 1.8 Ms of Chandra monitoring, provide the broad-band coverage needed to distinguish intrinsic coronal brightness changes from changes in obscuring column density. The authors find that detecting variability requires roughly 1,000 or more total counts distributed across roughly 10 or more epochs. Comparisons with survey sensitivity are intended to inform population synthesis models of how variability affects faint-AGN detectability. Significant column-density variability is slightly more common on timescales longer than 100 days, suggesting only a slight dominance of the torus as the driver of obscuration variability in faint AGN, rather than establishing it as the principal source.
PublicAstronomers studied how X-rays change over time in a catalog of 112 sources, using observations from NuSTAR, XMM-Newton, and Chandra. They identified seven candidates for variability. For active galactic nuclei, these changes can arise either because the hot corona near a supermassive black hole changes brightness or because the amount of material blocking our view changes. Observations spanning a broad range of X-ray energies help separate these explanations. The study finds that detecting changes requires roughly 1,000 or more recorded X-ray counts spread across roughly 10 or more observing visits. It also examines how changing brightness or obscuration could affect whether faint active galaxies are detected. Changes in the blocking material were slightly more common over periods longer than 100 days. This hints that the surrounding structure called the torus may contribute slightly more than other obscuring regions, but the evidence does not establish strong dominance.
Young explorerScientists watched X-rays from faraway places where giant black holes are surrounded by material. Out of 112 sources, they found seven that might be changing. Sometimes the hot stuff near a black hole gets brighter or dimmer. Sometimes more or less stuff gets in the way, like a curtain. The scientists needed lots of X-rays collected over many visits to spot changes. Changes in the curtain were a little more common over longer stretches of time. That gives a clue about where the curtain is, but it does not tell them for sure.
Eliza Neights, Eric Burns, Nicolò Parmiggiani+21 more
AstronomerCOSI, a soft gamma-ray telescope scheduled to launch in 2027, will use an onboard transient-trigger algorithm and promptly distribute alerts with localizations to support afterglow follow-up and associations with other instruments’ transients. The authors simulate short gamma-ray burst observations, process them with the planned onboard algorithm to estimate sensitivity, and combine that sensitivity with a simulated intrinsic sGRB population. They predict approximately 47–89 sGRB triggers per year, including approximately 7–10 per year localized to within 2.5°. Assuming the gravitational-wave sensitivity anticipated for O5, they predict 0–3 joint detections. These are simulation-based forecasts, not observed detection rates.
PublicThe Compton Spectrometer and Imager (COSI), scheduled to launch in 2027, will watch for brief flashes of gamma rays and quickly alert astronomers to where they occurred. Those alerts could help other telescopes study the fading light and connect events detected by different instruments. Using simulated bursts and COSI’s planned detection software, researchers estimate that it will detect about 47–89 short gamma-ray bursts each year, with about 7–10 located to within 2.5 degrees on the sky. They also predict 0–3 bursts detected jointly with gravitational waves, assuming the sensitivity expected during the O5 gravitational-wave observing run. These numbers are predictions from simulations, not measurements from the telescope.
Young explorerScientists plan to send a telescope called COSI into space in 2027 to look for quick flashes called gamma-ray bursts. It will send messages telling other scientists where to look, so they can try to see what happens after a flash. The team used pretend flashes in a computer to guess how many COSI might find. They think it could find dozens each year and give a more exact place for a few of them. They also think zero to three flashes might be noticed along with ripples called gravitational waves, depending on how well the wave detectors work. These are guesses from computer tests, not flashes COSI has already seen.
Samuel Gómez Gómez, Xisco Jimenez Forteza, Carlos Palenzuela+1 more
AstronomerLittle Red Dots are compact, broad-line sources interpreted as accreting black holes embedded in dense gas. This study computes inspirals of 10–30-solar-mass black holes in proposed LRD interiors and uses a waveform mismatch criterion to assess distinguishability from vacuum and between models. Bondi-like free-fall cavities and radiative envelopes predict measurable environmental signatures in essentially every detectable event. Convective quasi-star signatures are measurable for central black hole masses below roughly 100,000 solar masses and redshifts below roughly 0.6; a co-rotating disc produces no measurable imprint. Favorable cases also allow discrimination between interior models. These are modeled prospects, not gravitational-wave detections. With a 10-solar-mass companion, none of the 14 JWST LRDs at redshift above 3.9 would be detectable, whereas 30 of 31 LRDs below redshift 0.9 would be detectable if their central black holes were about 100 times less massive than their virial estimates; many would show measurable interior signatures. For the population out to redshift 6, a four-year LISA mission is predicted to yield 0.08–0.8 detectable events for 100,000-solar-mass hosts and 10-solar-mass companions, or 1.5–15 for 30-solar-mass companions, assuming inspiral rates like those of ordinary galactic nuclei. In dense clusters where captures become plunges, the predicted yield falls to at most about 0.0001.
PublicLittle Red Dots are compact astronomical sources that appear to contain black holes feeding on dense gas. Scientists have proposed several very different explanations for the gas surrounding those black holes. This study calculates how a smaller black hole spiraling into the central one would generate gravitational waves, and whether the gas would leave a recognizable signature. The calculations predict strong signatures for some dense-gas models, signatures only under certain conditions for another, and no measurable signature for a disc rotating with the orbit. In favorable cases, the waves could distinguish competing explanations. No such detections are reported here. Detectability depends strongly on black hole mass and distance: many nearby LRDs could be detectable only if their black holes are about 100 times less massive than existing virial estimates. Predicted event numbers for a four-year LISA mission range from less than one to several, depending on the companion mass and assumed inspiral rate. If captures instead produce direct plunges in dense clusters, the expected number becomes extremely small.
Young explorerSome tiny red dots in space seem to hide black holes wrapped in gas. Scientists used calculations to ask what would happen if a smaller black hole circled inward toward a bigger one. The gas might change the ripples they make in space, giving clues about what is inside the red dots. This has not been seen yet, and there might be very few chances to catch it.
Nathan Walker, Davide Lazzati, Tyler Parsotan+4 more
AstronomerThe study investigates gamma-ray bursts from the deaths of massive Population III stars as an alternative to direct stellar detection through gravitational lensing. Using source-frame mock observables, it finds substantial overlap between Pop III and Pop I GRBs, but identifies potential discriminants in light-curve timescales, isotropic-equivalent energies, peak energies, and positions in empirical prompt-emission correlations. These properties depend sensitively on progenitor mass and explosion energy; the modeled Pop III bursts tend toward longer characteristic timescales and higher isotropic-equivalent peak energies. The authors propose Pop III GRBs as a possible origin of the soft X-ray prompt-emission population recently detected by Einstein Probe. This is a model-based interpretation, not a confirmed detection of Pop III stars or their GRBs.
PublicThe Universe’s first generation of stars has not been directly detected. This study explores whether gamma-ray bursts produced when massive first-generation stars die could help identify them. Simulated signals suggest that these bursts might last longer and have higher peak energies than bursts from Population I stars, although the two groups share many properties. The differences depend strongly on the stars’ masses and explosion energies. The researchers also suggest that such bursts could explain a population of soft X-ray flashes recently detected by Einstein Probe, but that connection remains unconfirmed.
Young explorerThe very first stars are hard to find. Scientists used computer models to explore bright flashes that might happen when big first stars die. Their pretend flashes often lasted longer than flashes from another kind of star. Some real X-ray flashes might come from those first stars, but scientists do not know yet.
A. Papitto, A. Di Marco, M.C. Baglio+22 more
AstronomerIXPE significantly detected linear polarisation in 2–8 keV X-rays from the 2.5 ms accreting millisecond pulsar SAX J1808.4-3658 during the decay of its 2025 outburst. The average polarisation degree was 2.9% ± 0.5%, with an angle of 46° ± 5°, broadly consistent with the optical direction and a degree similar to that of the only other targeted AMSP. An IXPE–NuSTAR pulse-phase timing solution confirmed the long-term spin and orbital evolution; no significant pulse-phase variability in the Stokes parameters was found. Interpreting the polarised emission as arising from surface hot spots places those spots nearly along the neutron star’s spin axis. At the peak of a type-I thermonuclear burst, the authors also found tentative evidence for 2–6 keV polarisation of 16% ± 6%, with an angle nearly orthogonal to the persistent emission. If confirmed, this burst polarisation would exceed expectations for reflection from a thin accretion disc. The geometry inferred from polarisation can inform pulse-profile modelling used to constrain neutron-star masses and radii.
PublicThe IXPE observatory detected a preferred orientation, called polarisation, in X-rays from SAX J1808.4-3658, a neutron star spinning once every 2.5 milliseconds and drawing in matter. During the fading stage of its 2025 outburst, the measured polarisation was 2.9% ± 0.5%, with an orientation broadly matching that seen in optical light. The researchers found no significant change in polarisation as the star rotated. If the polarised X-rays come from hot spots on the star’s surface, the measurements suggest those spots lie close to its spin axis. Such clues about geometry help researchers interpret X-ray pulses to constrain neutron-star masses and sizes. During a thermonuclear burst, there was also a tentative sign of stronger polarisation, 16% ± 6%, oriented almost at right angles to the steady emission. That finding needs confirmation; if real, it would be stronger than expected from X-rays reflected by a thin disc of infalling matter.
Young explorerScientists watched a tiny star that spins very fast and pulls in matter. They found that some of its X-ray light had a favorite direction, a bit like little arrows pointing the same way. If that light comes from hot spots on the star, the spots seem to be near the line it spins around. These clues can help scientists work out how big and heavy the star is. During a sudden burst, they also saw a hint that more of the light lined up, in a different direction. They need to check that hint before they can be sure.
Yu-Heng Liu, He Liu, Hong-Ming Liu+3 more
AstronomerThis theoretical study examines axion effects on hybrid stars using a Maxwell construction for the hadron–quark transition, an ImMDI hadronic equation of state, and a three-flavor NJL quark model with an axion-modified KMT interaction. The calculations show that the axion field a/f_a slightly stiffens quark matter but substantially lowers the baryon density of the phase transition. These competing effects can soften the hybrid-matter equation of state, unlike the effect of vector coupling. The predicted maximum stellar mass changes only weakly, whereas the quark-core mass and radius increase significantly, particularly at weak vector coupling. Within this modeling framework, the principal axion effect is an earlier transition and a larger quark core; these are theoretical results, not observational detections.
PublicThe researchers used theoretical models to explore how an axion field might affect hybrid stars, whose interiors could contain a core of quark matter. Their calculations suggest that the field allows ordinary nuclear matter to turn into quark matter at lower densities. Although it makes quark matter slightly harder to compress, the earlier transition can make the star’s matter overall easier to compress. In the model, the largest possible stellar mass changes little, but the quark core becomes substantially larger and more massive, especially when the modeled vector interaction is weak. These findings depend on the chosen description of matter and its transition; they do not establish that axions or quark cores have been observed in stars.
Young explorerScientists used a math model to imagine a very dense star with a special kind of matter called quark matter in its middle. They asked what might happen if something called an axion field were there. In their model, quark matter could form before the star’s matter got quite as squeezed, making the middle bigger. The biggest mass the star could have changed only a little. This is an idea worked out with math, not something they saw happen in a real star.
Wen-Yuan Yu, Wen-Long Zhang, Hou-Jun Lü
AstronomerA systematic search for gamma-ray emission simultaneous with X-ray flares identifies 50 pulse–flare pairs in 38 GRBs, with 19 reported to have measured redshifts. Joint temporal and spectral analyses cover the overlapping emission intervals; the paired spectra are well described by absorbed power-law, power-law plus blackbody, cutoff power-law, and Band models. Self-organized criticality analysis finds similar power-law distributions for the temporal parameters of the gamma-ray pulses and simultaneous X-ray flares. The largest absolute difference in distribution slopes is approximately 0.36 for waiting time, versus at most approximately 0.12 for rise time, peak time, decay time, and duration. The isotropic-energy distributions in the redshift subsample differ more, with a slope difference of approximately 0.54. These statistical similarities support, but do not establish, a shared physical origin, potentially involving central-engine activity. The study addresses simultaneous pairs; comparable studies of non-simultaneous emission remain incomplete.
PublicThe researchers searched gamma-ray bursts for gamma-ray pulses occurring at the same time as X-ray flares, finding 50 paired events across 38 bursts. They compared the timing and spectra of the two kinds of emission. Across the sample, the statistical patterns describing how the pulses and flares rise, peak, fade, and last were closely similar. The patterns in the gaps between events differed somewhat more, and the energy distributions differed more still in the subset with measured redshifts. These findings suggest that the gamma-ray pulses and X-ray flares may come from the same underlying process, possibly activity in the burst's central engine. They do not prove that explanation, and the study focuses on emission observed simultaneously.
Young explorerSome bursts in space make flashes of gamma rays and X-rays at the same time. Scientists found that these two kinds of flashes have similar patterns in how they brighten and fade. That is a clue that the same thing might make both kinds of flashes, but scientists are not sure yet.
Li-ming Zhuo, Hou-Jun Lü, Xiao-Xuan Liu+2 more
AstronomerThis simulation study examines the still-uncertain relative contributions of binary neutron star (BNS) and black hole–neutron star (BH-NS) mergers to Galactic r-process enrichment. It combines COMPAS population synthesis, SkyNet nucleosynthesis, and stochastic multi-zone Galactic chemical evolution (GCE), considering five neutron-star equations of state and different black-hole spins. The averaged abundances appear not to depend significantly on these choices within the explored models. For given equations of state, simulated BNS abundances exceed BH-NS abundances below the second peak near mass number A≈130, whereas the ordering reverses above A=130. In the simulations, disk winds predominantly produce lighter r-process elements (A<130), while dynamical ejecta mainly produce heavier ones (A>130). Despite the heavier-element abundance comparison, BNS mergers dominate late-stage GCE production of lanthanides such as europium; BH-NS mergers contribute only a small amount to the heavy r-process enrichment represented by Milky Way Eu/Fe tracks. These are model findings, not a direct observational determination of the merger contributions.
PublicHow much do two merging neutron stars, versus a neutron star merging with a black hole, contribute to the Milky Way’s heavy elements? That remains an open question. Researchers linked computer simulations of stellar populations, element production through rapid neutron capture, and the Galaxy’s chemical evolution. Across the neutron-star matter models and black-hole spins tested, average element abundances appeared to change little. The simulations associate lighter r-process elements mainly with winds from disks around the mergers, and heavier ones mainly with material thrown out during the collisions. Although the modeled black-hole–neutron-star mergers have higher abundances above a particular atomic mass, neutron-star pairs dominate the later Galactic production of elements such as europium. Black-hole–neutron-star mergers contribute only a little to the modeled europium-to-iron history. These conclusions come from simulations, rather than direct measurements of each merger type’s contribution.
Young explorerWhen two tiny, super-dense stars crash together, or one crashes with a black hole, they can help make heavy ingredients for our galaxy. Scientists used computer models to study both kinds of crashes. Their models suggest that crashing star pairs make most of an ingredient called europium later in the galaxy’s life. The black-hole crashes add only a little in these models. Scientists are still figuring out how much each kind really makes.
Yui Kuboike, Toshiki Sato, Kai Matsunaga
AstronomerDeep Chandra observations of Cassiopeia A reveal a compositional sequence in its O-rich ejecta, from Ne-rich through NeSi-rich to O/Si-rich material. Principal component analysis of narrow-band images identifies this sequence, and spatially resolved spectroscopy of 20 representative regions confirms systematic Ne and Mg depletion toward the O/Si-rich component. The O/Si-rich composition across elements from O to Ca is well reproduced by O-layer material in one-dimensional presupernova models of 17–20 solar masses that underwent strong shell-merger-induced burning and mixing. Ne-rich ejecta instead resemble less strongly processed O-shell material. These components are segregated on remnant-wide scales: Ne-rich ejecta are preferentially northern, while O/Si-rich ejecta are more prominent in the southeast. The observations and model comparison suggest spatially heterogeneous late-stage burning and mixing in the progenitor, with some asymmetric presupernova structure possibly surviving the explosion; this survival remains an interpretation rather than a direct demonstration.
PublicChandra X-ray observations show that oxygen-rich debris in the supernova remnant Cassiopeia A has different chemical compositions in different places. Neon-rich debris is concentrated mainly toward the north, while debris rich in oxygen and silicon is more prominent in the southeast and contains less neon and magnesium. The researchers compared these observations with one-dimensional models of stars before they explode. Models in which neighboring internal layers merged, burned, and mixed strongly reproduce the oxygen-and-silicon-rich material’s composition across several elements. The neon-rich material resembles a less heavily processed layer. These findings suggest that burning and mixing varied from place to place inside the original star, and that some of this uneven structure may have survived its explosion. The model agreement supports that interpretation but does not prove it.
Young explorerCassiopeia A is the leftover material from a star that exploded. Scientists used X-ray pictures to see that its pieces contain different mixes of ingredients in different places. They compared those mixes with computer models of stars. The clues suggest that some layers inside the star may have mixed more than others before it exploded. Some signs of that uneven mixing may still be there, but scientists are not sure.
Sébastien Le Bihan, Daniel Grošelj, Martin Lemoine
AstronomerIf confirmed, IceCube’s TeV-neutrino detections from nearby Seyfert galaxies imply substantial reprocessing of accompanying gamma rays into the MeV band through electromagnetic cascades. The authors combine radiative kinetic simulations of magnetized coronal turbulence with predictions for hadronically induced cascades to separate electron-powered and hadronic emission. For NGC 4151, their model predicts that leptonic emission dominates the MeV band and remains comparable to the hadronic cascade up to roughly 0.1 GeV, provided the nonthermal electron tail contains at least about 5% of the electron energy. The leptonic component may be detectable by the upcoming COSI mission, while the predicted hadronic component lies below its sensitivity. The model’s nonthermal electrons can also account for the 0.1–1 MeV cosmic X-ray background excess, generally attributed to AGNs, and Cygnus X-1’s hard-state MeV tail. These observational comparisons support the model but do not establish a unique emission interpretation.
PublicGamma rays from the hot regions around black holes could come from energetic electrons or from processes that also produce neutrinos. If IceCube’s reported neutrinos from nearby Seyfert galaxies are confirmed, the accompanying gamma rays must largely be converted into lower-energy radiation. Combining computer simulations with predictions for this conversion, the researchers model the galaxy NGC 4151. They predict that electrons supply most of its MeV gamma rays if sufficiently energetic electrons carry at least about 5% of the total electron energy. The upcoming COSI mission might detect this electron-powered signal, but the predicted component associated with neutrino production is too faint for it. The model can also explain two existing observations: an excess in the cosmic X-ray background and a gamma-ray tail from Cygnus X-1. Those comparisons offer support, rather than proof, for the model.
Young explorerHot stuff around a black hole can make light in different ways. The scientists used computer models to work out which way might make most of one kind of light from a galaxy called NGC 4151. Their model says speedy little particles called electrons could do most of the work, if enough energy is in them. A future space mission might see that light. This is a prediction, not something the mission has seen yet.
Fabio Antonini, Aleksandra Olejak, Isobel Romero-Shaw+1 more
AstronomerThe authors argue that dynamical assembly in star clusters predicts ordered pairing rather than necessarily near-equal masses: two black-hole masses are drawn independently from a common one-body spectrum and then ordered. Within this framework, the primary-mass distribution determines the conditional secondary-mass distribution. Cluster simulations reproduce the mass-pairing morphology, including ridges at nearly constant secondary mass inherited from the underlying spectrum. Along these ridges, q = m2/m1 decreases as primary mass increases. Dynamical pairing predicts fixed-secondary-mass ridges with amplitudes tied to primary-spectrum peaks, whereas isolated binary evolution more naturally produces fixed-q structures, offering a formation-channel diagnostic. A non-parametric reconstruction of the gravitational-wave population shows a tentative enhancement near a secondary mass of 30 solar masses for primary masses of approximately 40 solar masses or more, broadly compatible with ordered pairing. The authors also find that dynamical formation naturally explains the rapid decline above roughly 30 solar masses in the secondary-mass distribution recently reported by the LIGO–Virgo–KAGRA Collaboration; this interpretation does not establish a unique formation channel.
PublicBlack holes that become partners through encounters in star clusters are often expected to have similar masses. This study argues that a broader prediction is to select two masses independently from the same distribution and then label the heavier black hole as the primary. Under this model, knowing how primary masses are distributed determines the expected distribution of companion masses. Star-cluster simulations support this picture: a common companion mass can appear across a range of heavier partners, so their mass ratio decreases as the heavier partner gets heavier. Such patterns could help distinguish cluster formation from isolated binary evolution, which more naturally produces patterns at a constant mass ratio. A reconstruction of the gravitational-wave population contains a tentative excess of companions near 30 times the Sun's mass paired with primaries of about 40 solar masses or more. This is broadly consistent with the model, not conclusive evidence. The authors also argue that dynamical formation naturally explains the recently reported sharp drop in companions above roughly 30 solar masses.
Young explorerTwo black holes can become partners in a crowded group of stars, and they do not have to weigh almost the same. The scientists describe a rule like picking two weights separately from the same bag, then calling the heavier one the big partner. Their computer models make patterns that fit this rule: a smaller partner can keep about the same weight while its bigger partner gets heavier. A study of gravitational-wave signals gives a possible hint of smaller partners weighing about 30 Suns with bigger partners weighing about 40 Suns or more. That hint is not certain. Scientists have also reported that smaller partners weighing more than about 30 Suns become much less common. The authors say their star-group idea can explain that drop, but this does not prove how every pair formed.
Probit J Kalita, Bharat Kumar, H C Das
AstronomerThis study computes composition g-modes and fundamental f-modes in full general relativity for neutron stars containing fermionic dark matter coupled to nucleons only through gravity, rather than in chemical equilibrium as assumed in earlier one-fluid proposals. Inference from NICER and GW170817 data, using a prior comprising 63 nucleonic equations of state (EOSs), does not favor dark matter and yields 95% upper bounds on its mass fraction ranging from 0.12 to 0.26 for particle masses of 0.5–2 GeV. In the calculations, a dark core containing 10% of the stellar mass raises the fundamental g-mode frequency by 10–15% at fixed EOS, several times less than in the one-fluid picture. The authors identify a larger indirect effect: accommodating a dark core requires a stiffer nucleonic EOS, so the g-mode primarily reflects the required density dependence of the symmetry energy rather than the dark matter content itself. At fixed radius and symmetry energy, a 10%-mass dark core is equivalent to a 9–12 MeV change in the symmetry-energy slope L. The calculated f-mode instead follows mean density; a dark core shifts its relation with tidal deformability by about 1%, well outside the posterior spread for nucleonic stars. This is a modeled distinction, not an observed dark-matter signature.
PublicCould the vibrations of neutron stars reveal dark matter inside them? The researchers calculated these vibrations for stars in which dark matter interacts with ordinary matter only through gravity. Their analysis of NICER and GW170817 data finds no preference for dark matter. Within the models considered, the 95% upper limits allow dark matter to account for at most about 12–26% of a star’s mass, depending on the assumed dark-matter particle mass. The calculations show that one proposed vibration signal is less directly sensitive to dark matter than earlier models suggested. A dark core containing 10% of the star’s mass increases that vibration’s frequency by 10–15% when the description of ordinary matter is held fixed. A larger influence comes from changing how stiff the ordinary matter must be to accommodate the core, making the signal difficult to interpret as a direct dark-matter indicator. Another type of vibration shows a roughly 1% shift in its relationship with how easily the star is deformed by tides. That shift is a theoretical result, not a detection of dark matter.
Young explorerA neutron star is a very tightly packed star that can wiggle. Scientists did calculations to ask what those wiggles might be like if mysterious dark matter were hiding inside. Some wiggles changed only a little because of the dark matter itself. They depended more on how stiff the star’s ordinary stuff was. Another kind of wiggle changed in a different way that might offer a clue. But these were calculations: the information from real stars did not show that dark matter was needed.
Joheen Chakraborty, Andrew Mummery, Eliot Quataert+3 more
AstronomerThe authors present a joint spectral-timing framework for quasi-periodic eruptions (QPEs), interpreted as repeated collisions between a stellar-mass orbiter and an SMBH accretion disk in an extreme mass-ratio inspiral (EMRI). An analytic timing model using Kerr geodesic frequencies and warped disk geometry is coupled to a self-irradiated disk SED model, with shared SMBH mass, spin, and disk parameters. Applied to GSN 069 and eRO-QPE2, the framework simultaneously reproduces eruption timings and quiescent spectra, offering circumstantial—not definitive—support for the EMRI interpretation and warped disks. Sparse timing data prevent a unique solution in either source; eRO-QPE2 has six physical solution modes with comparable timing and SED fits. Denser timing coverage is needed to distinguish these modes and address sampling aliases before realizing the framework's potential for precision constraints on the SMBHs, disks, and companions.
PublicRepeating X-ray outbursts from the centers of galaxies may occur when a small orbiting companion repeatedly passes through the disk of material around a supermassive black hole. The researchers tested this explanation by jointly modeling when the outbursts arrive and how the disk emits light between them. Their model includes a warped disk and the effects of the black hole's gravity on the companion's orbit. It can reproduce both kinds of observations for GSN 069 and eRO-QPE2, which lends indirect support to the proposed explanation but does not prove it. Too few outburst timings are available to pin down a single solution for either source. For eRO-QPE2, six different physical solutions fit comparably well. More frequent observations could help distinguish them and make these outbursts a more precise tool for studying black holes and their surroundings.
Young explorerSome galaxy centers make X-ray flashes again and again. Scientists think a small companion might be going around a huge black hole and bumping through a disk of material, making the flashes. They made a model that can match both the flash times and the light seen between flashes in two galaxy centers. But that does not prove their idea is right. They have not seen enough flash times to choose just one answer. Watching more flashes could help them work out what is happening.
Yerong Xu, Xiurui Zhao, Elena Bertola+14 more
AstronomerThe XMM-Newton spectrum of the quasar WISEA J094835.95+432302.6 at z=1.893 contains two candidate redshifted absorption features at rest-frame energies of approximately 4.65 and 5.75 keV. Monte Carlo simulations accounting for the look-elsewhere effect estimate confidence levels of 99.3% and 94.1%, respectively. The features can be interpreted as Fe XXV/XXVI K-shell absorption from a single ultra-fast inflow with an apparent velocity of 0.37(+0.02/−0.01)c; this identification remains unconfirmed. Confirmation through follow-up XMM-Newton observations would extend reported ultra-fast inflow candidates from the local Universe to cosmic noon, the peak epoch of cosmic star formation and black hole accretion.
PublicAstronomers report two possible absorption features in the X-ray spectrum of a distant quasar, seen during the era when star formation and black hole growth were at their peak. The features could be caused by iron in material rushing toward the black hole at an apparent speed of about 37% of the speed of light. Simulations that account for searching across the spectrum give the features confidence levels of 99.3% and 94.1%, but the inflow interpretation still needs confirmation. Follow-up observations with XMM-Newton could provide a rare opportunity to study how black holes gathered material during this busy period of cosmic history.
Young explorerScientists used an X-ray telescope to look at a bright object far away in space. They found two places where some X-ray light seems to be missing. That might mean material is rushing very fast toward a black hole. But they are not sure yet and need to look again. If they are right, it could help us learn how black holes grew long ago.
G. Grolleron, C. Plard, M. Dell'aiera+5 more
AstronomerThis work evaluates GammaLearn, a deep-learning framework for Imaging Atmospheric Cherenkov Telescope analysis, against the standard LST-1 analysis by producing sensitivity curves and applying it to real LST-1 observations. Deep-learning reconstruction of particle energy, arrival direction, and type has shown promise on simulated data, exploiting full temporal and charge information rather than simplified image-shape parameters, particularly near the approximately 20 GeV energies accessible to LST-1. The abstract reports no quantitative comparison or specific observational result. LST-1 is operating in La Palma as CTAO's first prototype; the stated sensitivity improvement of up to tenfold concerns CTAO relative to current instruments, not a demonstrated GammaLearn gain. The scientific motivation includes distant active galactic nuclei and their use in probing fundamental physics and cosmology.
PublicResearchers are testing GammaLearn, a deep-learning program, to interpret observations from the operating LST-1 telescope in La Palma, Spain. Such programs have shown promise in simulated data for estimating particles' energy, incoming direction, and type. They use detailed timing and charge information instead of relying on simplified image shapes, with particular promise at low energies. This study compares GammaLearn with the telescope's standard analysis using sensitivity curves and applies it to real observations, but the abstract does not say how much better, if at all, it performs on those observations. The work could help studies of distant active galaxies, which are useful for investigating fundamental physics and the universe.
Young explorerScientists are testing a computer program that learns to help them understand what a telescope sees. It tries to work out how much energy a tiny particle has, where it came from, and what kind it is. Programs like this have looked promising with pretend data made by computers. Now the scientists are comparing this program with their usual method and trying it on real telescope data. They have not said here whether it works better on the real data. They hope this kind of work will help them study faraway galaxies.
Sofia V. Sosa Fiscella, Michael T. Lam, Olivia West+49 more
AstronomerFrequency-dependent pulse-profile evolution introduces systematic TOA delays, but the FD log-polynomial model used by NANOGrav can absorb other chromatic contributions, including interstellar dispersion, inflating inferred profile evolution and producing dataset-dependent coefficients. The authors introduce monomial (IFD) and Legendre (LIFD) expansions and test them using observations of 11 pulsars from the NANOGrav 15-year dataset and simulations, with comparisons to frequency-resolved templates. Legendre-based models generally recover profile-evolution delays more faithfully; in simulations, they reduce the residual offset relative to FD by as much as 85%. The simulations also demonstrate dispersion-model bias: FD overestimates the injected DM by 0.013 pc cm^-3, compared with 0.0002 pc cm^-3 for LIFD. These findings support Legendre bases for mitigating covariance among chromatic effects and improving targeted timing studies and noise modeling for nanohertz gravitational-wave detection.
PublicPulsars emit repeating radio pulses whose shapes change with radio frequency, complicating measurements of when the pulses arrive. The mathematical model commonly used by NANOGrav can confuse these shape changes with delays caused by material between the pulsar and Earth. Researchers tested two alternative models on observations of 11 pulsars and on simulated data, also comparing them with frequency-specific pulse templates. The model based on Legendre polynomials generally represented the shape-related delays more accurately. In simulations, it reduced the remaining timing offset by up to 85% relative to the standard model and produced much less bias in estimates of interstellar dispersion. The results support using this approach to better separate different sources of timing delay and improve noise modeling for searches for very low-frequency gravitational waves; they do not report a new gravitational-wave detection.
Young explorerPulsars are stars that send us repeating radio flashes, a bit like lighthouses. The flashes can look different when we listen at different radio frequencies. That makes it tricky to tell exactly when they arrived, because stuff between the stars and Earth can slow the signals too. Scientists tried new math using signals from 11 pulsars and pretend signals made for testing. One kind of math was generally better at telling the different effects apart. In the pretend tests, it made fewer timing mistakes. This could help scientists search for tiny ripples in space.
A. Tortosa, L. Zappacosta, E. Piconcelli+51 more
AstronomerThe study tests whether the steep X-ray spectra previously reported for HYPERION quasars reflect unusually efficient long-term SMBH growth or a broader property of luminous early quasars. It analyses 28 luminous QSOs at z ≃ 5.85–7.56, with 26 included in the correlation analysis, extending the sample mainly toward lower growth efficiencies and incorporating new XMM-Newton observations. Black hole masses and growth indicators were re-derived homogeneously using the latest JWST-based spectroscopy. No statistically significant correlation was found between coronal spectral parameters and black hole growth indicators. The luminous z ≳ 6 quasars systematically exhibit steep X-ray continua, with high photon indices and/or low high-energy cutoffs, consistent with cold coronae and possibly linked to rapid accretion. If such slopes are common among early AGN, they could lower future survey count rates at fixed intrinsic luminosity and bias the inferred early AGN census.
PublicBright quasars in the early universe contain black holes with masses around a billion times that of the Sun, assembled within the universe’s first billion years. Their X-rays reveal conditions close to the growing black holes. Researchers studied 28 luminous quasars and used 26 to test whether their X-ray properties track indicators of how efficiently the black holes grew. They found no statistically significant relationship, unlike the link suggested by an earlier sample focused on the most efficiently grown black holes. The quasars generally have X-ray emission that drops steeply toward higher energies. This is consistent with relatively cool X-ray-emitting gas near the black holes, possibly associated with rapid feeding, but that explanation is not established. If this pattern is widespread among early active galaxies, future X-ray surveys could detect fewer photons from them at the same intrinsic brightness, making some harder to find.
Young explorerScientists looked at light called X-rays from 28 very bright places around giant black holes when the universe was young. The light had fewer high-energy X-rays, which could mean the gas making it was cooler than expected. They checked whether the X-rays were linked to how well the black holes had grown, but did not find a clear link. Fast feeding might help explain the light, but scientists are not sure. If many early black holes make light this way, future X-ray searches might have a harder time spotting them.
Jose M. Ladino, Carlos E. Romero-Figueroa, Hernando Quevedo
AstronomerThis theoretical study applies shadow thermodynamics and geometrothermodynamics to the Reissner–Nordström black hole with a cosmological constant parameterized by a curvature radius. The authors derive explicit shadow-radius expressions in terms of the horizon, photon-sphere, and observer radii. The calculated phase structure depends strongly on the curvature radius, admitting configurations with zero, one, or two phase transitions. Thermodynamic geometry and geometrothermodynamics yield different descriptions of the microscopic structure, with the differences attributed to the curvature radius. The authors impose quasi-homogeneity of the thermodynamic system to ensure consistency of the geometrothermodynamic treatment. These are theoretical results, not observational measurements.
PublicThe researchers use mathematical models to study how a black hole’s shadow relates to its thermodynamic behavior. Their model includes a cosmological constant, represented by a curvature scale. They calculate the shadow’s size from the black hole’s horizon, the region where photons can orbit, and the observer’s location. Depending on the curvature scale, the model allows no phase transitions, one, or two. Two geometric methods also give different interpretations of the black hole’s microscopic structure. The researchers attribute these differences to the curvature scale and impose a mathematical scaling condition to keep one method consistent. The study does not report observations of an actual black hole.
Young explorerScientists used math to study a black hole and its shadow. In their model, changing how space curves can change how the black hole behaves, a little like how water can change into ice. The math allows no such changes, one, or two. Two ways of doing the math also give different ideas about what might be happening on a tiny scale. These are ideas from calculations, not things the scientists watched happen.
Aasim Jan, Sophia Nicolella, Aaron Zimmerman+4 more
AstronomerA multi-family waveform reanalysis of GW190521, including a model with both eccentricity and spin precession, finds evidence for high eccentricity: 0.81 with uncertainties of +0.05 and −0.01 at 5 Hz. The authors attribute non-eccentric solutions to failure to explore the high-likelihood region at large eccentricity. Including eccentricity removes indications of spin precession, suggesting that apparent precession in quasicircular analyses is at least partly an eccentricity–precession degeneracy. All models favor comparable masses, although one permits a secondary solution with more asymmetric masses. The inferred probability that the primary occupies the approximately 60–130 solar-mass pair-instability supernova mass gap is at least 97%; the secondary’s gap membership is model-dependent. Simulated GW190521-like injections suggest that unmodeled eccentricity could explain the observed waveform systematics, while a similar quasicircular, precessing injection shows no significant model dependence. Interpretation remains challenging because the high total mass yields few observable cycles. Crucially, the inferred eccentricity exceeds current models’ calibration range; the authors test robustness using highly eccentric numerical-relativity waveforms, but the abstract does not state the outcome of that test.
PublicA new analysis of the gravitational-wave event GW190521 favors two black holes approaching merger on a strongly elongated orbit rather than a nearly circular one. When the researchers allow this elongated motion in their models, they find no indication of spin-related wobbling, suggesting that earlier signs of such wobbling may partly reflect confusion between these effects. The models generally favor black holes of similar mass. They assign at least a 97% probability that the heavier black hole falls in the roughly 60–130 solar-mass range called the pair-instability supernova mass gap; conclusions about the lighter black hole depend on the model. Tests with simulated signals suggest that omitted orbital elongation could explain some differences between models. These are inferences, not a uniquely established picture: the signal contains few observable cycles, and the inferred elongation exceeds the range for which current models are calibrated. The abstract mentions an additional simulation-based robustness test without reporting its outcome.
Young explorerScientists studied a short signal from two black holes coming together. Their new calculations suggest the black holes moved around each other on a very stretched-out path, not a nearly round one. That stretched path might explain something that looked like wobbling before. But the signal is short, and the scientists’ tools have not been fully checked for paths this stretched, so the answer is not settled.
Ethan McKeever, Victor Guedes, Shu Yan Lau+1 more
AstronomerThe authors derive a phenomenological anisotropic-fluid model for spherically symmetric massive boson stars, extending the effective perfect-fluid treatment beyond the strong-coupling limit. They supply fits for the anisotropy profile and effective equation of state in terms of the central scalar-field amplitude and the self-interaction coupling divided by the squared scalar-field mass. Numerical validation using a standard neutron-star construction method yields masses and radii in excellent agreement with full boson-star calculations, with computational cost reduced by about a factor of 10. The framework applies over a broad range of model parameters, but remains a phenomenological description restricted here to spherical symmetry. A ready-to-use Python Tolman-Oppenheimer-Volkoff solver is provided. These are theoretical and computational results, not observational evidence for boson stars.
PublicBoson stars are hypothetical compact objects that could resemble black holes. Calculating their structure is often difficult and computationally expensive. This study develops a simpler description that treats them like a fluid whose pressure can differ with direction, extending earlier fluid descriptions beyond the strong-interaction limit. In computer calculations, the new method produces masses and radii in excellent agreement with the full boson-star calculations while costing about one-tenth as much computationally. The authors also provide Python software for using the method. The results concern spherical theoretical models across a broad range of parameters; they do not establish that boson stars have been observed.
Young explorerScientists are studying a possible kind of space object called a boson star, which might look like a black hole. They made a simpler computer recipe to work out how heavy and how big a round boson star would be. Its answers matched the harder calculations very well, and it took about one-tenth as much computer work. This is a way to study imagined stars on computers, not a report that someone has found one in space.
Bakhromzod Rizoi
AstronomerThis historical review examines Soviet contributions to high-energy neutrino astrophysics, rather than reporting new neutrino observations. It distinguishes four strands: Cherenkov radiation and cosmic-ray applications; proposals for large underground and natural-water detectors; atmospheric, cosmogenic, and astrophysical neutrino theory; and underground, underwater, radio, and in-ice detection techniques. The article argues that Markov’s 1960 proposal primarily targeted atmospheric neutrinos through Cherenkov detection of charged secondary particles in water. It distinguishes early Soviet radio-detection concepts for Antarctic ice from the optical deep-polar-ice concept formulated by Halzen and Learned in 1988. Separate discussions cover the Pamir cosmic-ray school, Zatsepin, Kuzmin, and Berezinsky’s theoretical work, Baksan, Soviet participation in DUMAND, and the Lake Baikal program. Connections to IceCube vary: some are conceptual and citation-based, others methodological or institutional. In particular, Pamir provides historical context, not evidence of a direct experimental lineage to IceCube.
PublicThis article explores the Soviet role in the history of neutrino astronomy and how different ideas and research programs relate to IceCube. It is a historical account, not a report of a new discovery. A key distinction concerns proposals for detectors: Markov’s 1960 water-based idea focused mainly on neutrinos produced in the atmosphere and on detecting light from the charged particles they produce. Early Soviet ideas for using Antarctic ice involved radio detection; Halzen and Learned proposed an optical detector in deep polar ice in 1988. The article also reviews theoretical work and several experimental programs. Its central caution is that shared ideas, methods, and institutions do not all establish the same kind of historical connection. The Pamir cosmic-ray work, for example, should not be treated as a direct experimental ancestor of IceCube.
Young explorerThis article tells a story about how scientists developed ideas for finding particles called neutrinos. Some suggested looking for light in water, while others explored radio signals in ice. Later, scientists proposed looking for light deep in polar ice. The article explains how Soviet scientists helped this history grow. But not every earlier experiment led straight to IceCube, and this is a history story, not a new discovery.
Abhishek Rout
AstronomerThis theoretical study treats low-frequency gravitational and pseudoscalar scattering by a non-rotating black hole in dynamical Chern-Simons gravity. The axial gravitational sector couples irreducibly to the pseudoscalar, whereas the polar sector remains general relativistic. At first order in the dimensionless coupling zeta = (ell_CS/M)^4, matched asymptotic expansions yield an exact quadrupole conversion result, d_2 = 3(pi^2-9)^2/8, and a high-precision reconstruction of the absorption-asymmetry quantity, kappa_2 = (21/80)pi^4 + (27/8)pi^2 - 89833/1536, within an analytically controlled transcendental basis. These expressions contain only pi^4, pi^2, and rational terms in that basis. In contrast, the transmission phase includes an analytically derived static integral involving the Riemann zeta value zeta(3)-9/8, with its overall matching prefactor identified numerically. The leading reflection-phase asymmetry vanishes, implying no leading-order low-frequency polarization rotation of the reflected wave, while a subleading O(omega zeta) transmitted-phase asymmetry remains. Numerically, normalized flux asymmetries are consistent with a 1/(M omega)^2 falloff in the geometric-optics limit, where conversion loss is the leading remaining flux effect. Direct two-channel integration checks the matched-asymptotic results. These calculations provide analytic targets connecting parity-violating absorption and conversion to axial/polar quasinormal-mode splitting; they are not observational detections.
PublicThe researchers calculate how gravitational waves and a second kind of wave, called a pseudoscalar wave, scatter from a non-spinning black hole in an alternative theory of gravity called dynamical Chern-Simons gravity. In this theory, one gravitational-wave sector can exchange energy with the pseudoscalar field, while the other behaves as in general relativity. For low-frequency waves and to first order in the theory's coupling strength, the study obtains an exact conversion expression and reconstructs an absorption difference with high numerical precision. Direct numerical calculations check the low-frequency results. The reflected wave has no polarization rotation at leading low-frequency order, although a smaller phase difference remains in the transmitted wave. At high frequencies, numerical results are consistent with the relative flux differences shrinking as the inverse square of frequency, with conversion into the other wave type providing the main remaining flux effect. These are theoretical calculations, not observations of black holes, and offer benchmarks for relating wave absorption and conversion to differences in black-hole ringing modes.
Young explorerImagine waves meeting a black hole that does not spin. Scientists used math to explore a special gravity theory in which one kind of gravity wave can turn partly into another kind of wave. For slowly wiggling waves, they worked out how this could happen and checked their math with computer calculations. In their simplest low-frequency result, the wave bouncing back does not get its wiggle direction turned. This is a prediction from a theory, not something they watched happen in space.
Hui-Ming Zhang, Su-Jie Lin, Jie Feng+4 more
AstronomerThe authors develop a unified charge-dependent solar modulation model by solving the three-dimensional Parker transport equation with a realistic wavy heliospheric current sheet and self-consistent drift effects. They adopt a GALPROP local interstellar spectrum constrained by Voyager data and fit time-resolved AMS-02 proton and antiproton fluxes from May 2011 to June 2022, excluding the HMF polarity-reversal epoch from mid-2012 to early 2015. Neural-network surrogate models accelerate computation of propagation and modulation matrices for parameter scans. The model simultaneously describes the measured proton and antiproton fluxes with physically reasonable parameters; its reported agreement does not cover the excluded reversal epoch.
PublicThe Sun’s magnetic environment affects positively charged protons and negatively charged antiprotons differently as they travel through the solar system. Researchers built a three-dimensional model of these effects and fitted it to measurements from the Alpha Magnetic Spectrometer-02 collected between May 2011 and June 2022. Their model accounts for both particle types with physically reasonable settings, while neural-network tools make calculations faster. The analysis leaves out mid-2012 to early 2015, when the Sun’s surrounding magnetic field was reversing direction, so the reported success does not establish how well the model works during that interval.
Young explorerTiny particles called protons and antiprotons have opposite electric charges. The Sun’s magnetic field changes how they travel. Scientists made a computer model that could explain measurements of both kinds of particles. But they left out a time when the Sun’s magnetic field was flipping, so this study does not show whether the model works then.
Guoying Zhao, Duo-Le Cao, Rong-Feng Shen+29 more
AstronomerThe multi-wavelength study of EP250416a, also designated GRB 250416C, combines gamma-ray, X-ray, and optical observations following triggers by Einstein Probe, SVOM, and Konus-Wind. The burst lasted 30 s in X-rays and 17.7 s in gamma rays. Joint spectral fitting over 0.5–5000 keV gives E_peak = 342 keV, with uncertainties of −232/+90 keV. Gemini South/GMOS afterglow spectroscopy measured z = 0.963. The inferred isotropic-equivalent energies are E_X,iso = 2.7 × 10^50 erg (−0.5/+0.9 × 10^50 erg) and E_gamma,iso = 7.34 × 10^51 erg (−2.1/+5.1 × 10^51 erg), consistent with the long-GRB Amati relation. A 25–50 keV to 50–100 keV fluence ratio of 0.78 (−0.12/+0.10) supports classification as an X-ray-rich GRB. The X-ray afterglow evolves from shallow decay, alpha ≈ −0.5, to a canonical phase, alpha ≈ −1. A very late break at approximately 1.5 × 10^6 s is interpreted as a jet break, implying a jet half-opening angle of 10.6 degrees (−1.8/+1.9 degrees). Despite a faint optical detection at r = 24.16 ± 0.13 mag, the low optical-to-X-ray spectral index, beta_OX = 0.3, identifies the burst as optically dark. Host-galaxy extinction is a possible explanation; the extinction-curve model requires A_V,host = 2.7 ± 0.3 mag, rather than establishing extinction as the cause.
PublicAstronomers studied a brief cosmic flash called EP250416a, or GRB 250416C, using gamma rays, X-rays, and visible light. It lasted 30 seconds in X-rays and 17.7 seconds in gamma rays. Its measured spectrum places it among X-ray-rich gamma-ray bursts, and its estimated energy is consistent with a known relationship for long gamma-ray bursts. Visible-light spectroscopy measured a redshift of 0.963. After the initial flash, the X-ray glow faded slowly and then more quickly. The researchers interpret a much later change in that fading as a sign of a jet, estimating its half-opening angle at about 11 degrees. The visible afterglow was detected but was unusually faint compared with the X-rays, leading to an 'optically dark' classification—not meaning that no visible light was seen. Dust in the burst's host galaxy could explain this faintness, but that explanation depends on an extinction model and is not established as the cause.
Young explorerAstronomers watched a quick flash in space using different kinds of light. After the flash, its glow slowly faded. They could see only a tiny bit of ordinary light, even though their tools saw X-rays much more clearly. Dust in the galaxy where the flash happened might have hidden some of that ordinary light, but the astronomers are not sure.
Elizabeth Flanagan, Fabio Antonini, Thomas Callister+4 more
AstronomerUsing GWTC-5 binary black hole mergers, the authors apply hierarchical Bayesian inference with flexible Gaussian-process population models to infer mass-ratio and effective-spin distributions as functions of primary mass. They identify four mass regions with sharp changes in both properties. Below approximately 15 solar masses, equal-mass systems are strongly favored and χ_eff is narrowly distributed around a positive peak. At 18–30 solar masses, the mass-ratio distribution is substantially flatter, while χ_eff broadens and peaks consistently with zero; positive skewness is tentative and not statistically required. Around the feature near 35 solar masses, equal-mass binaries are again strongly favored, with a narrow χ_eff distribution consistent with symmetry about zero. Above approximately 45 solar masses, both distributions broaden significantly. The inferred spin-distribution support approaches that expected for binaries containing previous merger remnants, making this region consistent with hierarchical mergers in star clusters, rather than establishing that origin uniquely. The coincident mass-ratio and spin transitions suggest distinct formation channels: the authors interpret isolated binary or triple evolution as likely dominant at lower masses, with dynamical assembly increasingly important at higher masses.
PublicThe researchers studied a gravitational-wave catalog to ask whether merging black holes have different properties depending on the mass of the heavier member. Their statistical analysis identifies four groups. Below about 15 times the Sun’s mass, partners tend to have similar masses, and their combined spin measure clusters around a positive value. Between 18 and 30 solar masses, the partners’ mass ratios are more varied and the spin measure has a wider spread, peaking near zero. A possible preference toward positive spin values is not statistically required. Near 35 solar masses, similar-mass partners become common again, with a narrow spin distribution centered near zero. Above about 45 solar masses, both properties become much more varied. The highest-mass group is compatible with black holes that formed in earlier mergers and then merged again in star clusters, but this is not proof of that history. The authors suggest that different mass groups reflect different ways of bringing black holes together, with interactions among objects becoming more important at higher masses.
Young explorerScientists studied pairs of black holes joining together. They found clues that the pairs differ depending on how heavy the bigger black hole is. In some groups, the two black holes usually have nearly the same weight. In other groups, their weights and spinning are more varied. The heaviest group could include black holes made when other black holes joined together before. That is a possible story, not something the scientists have proved.
Uri Keshet
AstronomerThe study cross-correlates 16.3 years of high-latitude Fermi-LAT data with the western Galactic hemisphere eROSITA map to search for velocity-dependent, p-wave WIMP annihilation associated with galaxy clusters. A blind composite matched-filter search for the γγ, γZ, and γh line triad yields candidate WIMP rest energies near 71.9 and 67.5 GeV. Each has local significance near 3σ but only 1.6σ after pixel-shuffle trial correction; Monte Carlo and analytic estimates give 1.8–2.1σ. A nine-line search for two cross-annihilating WIMPs gives masses of 66.4 and 71.9 GeV, with a weak cross-annihilation triad corresponding to 69.2 GeV, at 2.3σ. Interpreting a previously reported approximately 43.2 GeV line in three nearby clusters as γZ fixes a WIMP mass near 72 GeV: at this externally fixed mass, the triad reaches 3.0σ, or 5.1σ when combined with the reported line, dropping to 3.9σ under alternative assumptions. The triad is insensitive to tested detrending, masks, and filters, appears in different Galactic sectors, and is absent from the X-ray-uncorrelated spectrum. It strengthens with positive rather than negative redshift broadening and peaks near Δz = 0.05, interpreted as consistent with expectations; its two non-43 GeV channels alone reach 2.3σ. Reported intrinsic cross sections are a few 10^-19 cm^3 s^-1, not loss-corrected and conditional on WIMPs tracing the X-ray gas. These are candidate annihilation signatures, not an established dark-matter detection.
PublicResearchers compared gamma-ray observations from Fermi-LAT with an X-ray map from eROSITA, looking for sets of three narrow gamma-ray features that might come from dark-matter particles annihilating in galaxy clusters. Their broad search found two possible sets, but the statistical evidence was weak after accounting for how many possibilities were tested. The leading candidate corresponds to a particle rest energy near 72 GeV. It also matches the mass inferred if a previously reported gamma-ray line in three nearby clusters is interpreted as one of the predicted annihilation signals. Using that externally specified mass strengthens the evidence; combining the new set with the earlier line gives a reported significance of 5.1σ, or 3.9σ under alternative assumptions. The features appear in several sky regions and respond to redshift broadening in a way the authors consider consistent with expectations. These clues are suggestive, but they do not establish that dark matter produced the signals.
Young explorerScientists looked at two kinds of light from space to search for clues about dark matter, something they are trying to understand. They found a few patterns that might fit what happens when dark-matter particles meet and turn into light. One pattern also fits a clue reported before. But the patterns could be misleading, so scientists have not proved that they found dark matter.
Akihiro Suzuki, Keiichi Maeda, Toshikazu Shigeyama
AstronomerThe authors model the Einstein Probe X-ray transient EP260321a as shock breakout from supernova ejecta interacting with dense, wind-like circumstellar material (CSM). Their semi-analytic treatment uses a thin-shell approximation with relativistic effects and a mildly relativistic outer envelope. The observed X-ray properties are well explained within this model by a high-velocity envelope with kinetic energy approximately 3.5 × 10^49 erg, excluding the supernova ejecta, and a wind mass-loss rate of approximately 1.2 × 10^-3 (v_w / 1000 km s^-1) solar masses per year, where v_w is the wind velocity. Within the model, the observed burst duration requires the dense CSM to extend to approximately 350 solar radii, corresponding to approximately 10^-5 solar masses. These are model-dependent inferences rather than direct measurements of the envelope or CSM. The authors interpret the results as evidence that shock-breakout observations can sensitively probe mass loss from stripped-envelope supernova progenitors shortly before core collapse.
PublicEinstein Probe detected a brief X-ray event called EP260321a. The researchers tested whether it could be explained by a shock from an exploding star breaking out through dense gas shed by the star. Their model, which includes effects important for material moving at a substantial fraction of the speed of light, explains the observed X-ray properties well. It points to a fast outer layer carrying about 3.5 × 10^49 ergs of kinetic energy and a dense stellar wind. To account for the burst's duration, the model requires surrounding gas extending to about 350 times the Sun's radius, with a total mass about one hundred-thousandth of the Sun's. These estimates depend on the model; they are not direct measurements of the gas. The study suggests that such X-ray flashes can reveal how stars that have lost their outer envelopes shed material shortly before their cores collapse.
Young explorerA space mission called Einstein Probe spotted a quick flash of X-rays. The scientists made a model to see whether an exploding star could make that flash by pushing a fast wave through thick gas around it. Their model fits the flash well. It suggests the star had blown gas into space before it exploded. The scientists did not measure that gas directly, so this is an explanation that fits what they saw, not proof of exactly what happened.
Mauricio González-Servín, Emilio Tejeda, Susana Lizano+2 more
AstronomerRestricted three-body and SPH simulations explore tidal separation of a solar-like star–white dwarf binary approaching a 10^6-solar-mass supermassive black hole on a parabolic orbit. The binary orbital phase controls which component becomes tightly bound and which is ejected as a hypervelocity object, providing a simulated pathway to non-parabolic TDEs. Elliptical and hyperbolic TDEs occur with equal probability in the modeled encounters. Approximately 88% of orientations yield clean disruption without white dwarf accretion; the remaining 12%, concentrated in two narrow phase windows, produce a white dwarf with a captured debris envelope. Direct white dwarf–solar-like star collisions near pericenter occur for about 4% of orientations, with fallback peaking up to five times earlier and twenty times higher than in the single-star comparison. For the innermost approximately 1.5% of orientations, the combined white dwarf and envelope mass exceeds 1.4 solar masses, but the degenerate core does not: the captured material is non-degenerate. Nova-like events and peculiar red giant-like objects are suggested outcomes, not established results. Depending on phase, the mechanism may also produce repeating partial TDEs and quasi-periodic eruptions. These simulations support binary separation as a channel for diverse TDE behavior rather than reporting observational confirmation of these outcomes.
PublicA star torn apart by a supermassive black hole is often modeled as arriving alone. This study instead simulates a pair—a Sun-like star and a white dwarf—approaching a black hole with a million times the Sun’s mass. The black hole can split the pair, capturing one member and ejecting the other at very high speed. In the models, this produces stellar disruptions on both bound and unbound paths, with equal probability. About 88% of the modeled orientations leave the white dwarf without captured material, while about 12% give it an envelope of stellar debris. In roughly 4%, the stars collide, and disrupted material returns toward the black hole with a peak up to five times earlier and twenty times higher than for a lone star. Some debris-covered white dwarfs exceed 1.4 solar masses in total, but their dense cores do not exceed that mass. The authors suggest possible nova-like outbursts, unusual giant-like objects, or repeated flares; these are potential consequences, not confirmed observations.
Young explorerScientists used computer models to see what could happen when two stars travel together near a huge black hole. The black hole can pull the pair apart, keeping one star nearby and throwing the other far away. Sometimes a star gets torn up, and the smaller star catches some of the pieces like a coat. The scientists think this might also make repeated flashes, but the models do not prove those flashes happen in space.
Tieguang Zi, Shailesh Kumar, Genliang Li+3 more
AstronomerThis theoretical study models eccentric, equatorial extreme mass-ratio inspirals around Kerr black holes in the presence of a massive scalar field, assuming the inspiralling object carries scalar charge. The authors solve the massive scalar perturbation equation in the frequency domain, calculate scalar energy fluxes at the horizon and infinity, and incorporate them into an adiabatic inspiral model. Comparisons with general relativity and the massless scalar limit use accumulated GW phase differences and waveform mismatches. The calculations show that massive scalar radiation can cause significant GW dephasing, with stronger effects for more eccentric orbits. Larger scalar field masses suppress the scalar flux because fewer harmonics meet the propagation condition at infinity. Fisher-information forecasts and Bayesian parameter estimation yield consistent projected constraints on scalar charge and field mass for the Laser Interferometer Space Antenna. These are model-based prospects for testing massive scalar fields and scalar-tensor gravity, not observational detections.
PublicWhen a much smaller object spirals around a rotating black hole, it produces gravitational waves. This study asks how those waves would change if an additional, hypothetical field existed and the smaller object carried a charge that allowed it to emit radiation into that field. The researchers calculated the resulting orbital motion and gravitational-wave signals rather than reporting an observation. Their model predicts potentially substantial changes in the waves’ timing, especially for more elongated orbits. A larger mass for the hypothetical field reduces its radiation because fewer components can propagate to infinity. Two methods of estimating what the future Laser Interferometer Space Antenna could measure gave consistent expectations for limits on the field’s mass and the object’s charge. The findings suggest these systems could help test alternatives to general relativity, but do not establish that the field exists.
Young explorerImagine a little object going around a giant black hole on an oval path, slowly moving closer. It makes tiny ripples in space. Scientists used a model to ask what would happen if an extra, invisible field were there too. In their model, the extra field could change the timing of the ripples, especially when the path is more stretched out. A future space detector might use those changes to look for clues about the field. The scientists have not found the field; they are working out how to search for it.
Loïc Fernandez, Jean-Loïc Kneur, Marcus Benghi Pinto+3 more
AstronomerThis theoretical study extends the RGOPT-resummed NNLO perturbative QCD pressure of cold, dense symmetric matter to beta equilibrium and charge neutrality. The underlying resummed pressure has reduced renormalization-scale sensitivity relative to the NNLO perturbative QCD pressure. The authors provide a compact equation-of-state fit for N_f = 2+1 massive quarks at different values of X, where the renormalization scale is X times the baryon chemical potential divided by 3. Their pure quark-star models are compatible with astrophysical observations for X = 2.71–3.30; X = 3.84 is required if the secondary component of GW190814 is interpreted as a neutron star. Hybrid-star models combine the quark equation of state with three representative relativistic mean-field hadronic models spanning soft and stiff equations of state. Stable hybrid configurations compatible with the mass of PSR J0740+6620 are obtained for X of roughly 2–2.71. The largest scale produces modeled quark-core radii of 2–8 km, while the smallest produces a small central quark core. These are model-based compatibility results, not observational detections of quark stars or quark cores.
PublicThe researchers calculated how extremely dense quark matter could behave inside compact stars. Their theoretical method reduces sensitivity to a scale choice used in the calculation, and they provide a convenient formula describing the matter’s pressure. They then model stars made entirely of quark matter and stars with quark cores surrounded by ordinary hadronic matter. Some models agree with existing astronomical constraints, including the mass of the heavy pulsar PSR J0740+6620. Depending on the calculation’s scale choice, modeled quark cores can be small or have radii of 2–8 kilometers. A separate constraint depends on whether the smaller object in GW190814 was a neutron star. The study does not establish that these observed objects contain quark matter.
Young explorerScientists used math to imagine what might be inside very tightly packed stars. They tried stars made of tiny bits called quarks, and stars with quarks only in the middle. Some of their pretend stars fit what astronomers know about real stars. Changing a choice in the math changes how big the quark middle can be. But this does not show that real stars have quarks in their centers.
