Kosuke Nishiwaki, Claudio Gheller, Gianfranco Brunetti+1 more
AstronomerThe authors present a GPU-accelerated C/C++ Fokker–Planck solver for post-processing cosmological MHD simulations, evolving cosmic-ray proton and electron spectra along Lagrangian tracer trajectories. The solver treats cooling, re-acceleration, and secondary-particle production. A Chang–Cooper discretization yields independent tridiagonal systems, solved on NVIDIA GPUs with CUDA parallel cyclic reduction. Adaptive sub-stepping is constrained by cooling or re-acceleration timescales, while batching groups tracers with similar sub-stepping patterns. Performance tests on CINECA’s Leonardo Booster system show approximately tenfold higher per-node throughput with GPU acceleration. This is a computational performance result, not an observational finding; comparisons with next-generation radio data and future radio, gamma-ray, and high-energy neutrino applications are intended uses.
PublicResearchers have developed faster software to model how high-energy particles evolve in simulated galaxy clusters and the filaments of the cosmic web. The software follows simulated protons and electrons, accounting for energy losses, renewed acceleration, and the production of secondary particles. It processes outputs from simulations of cosmic gas and magnetic fields, using graphics processors and grouping similar calculations to work efficiently. Tests on the Leonardo Booster computing system found that GPU acceleration increased the amount of work completed per computing node by about a factor of ten. The advance is in simulation software, rather than a new observation of space. It is intended to support future comparisons with radio observations and studies combining radio, gamma-ray, and high-energy neutrino signals.
Young explorerScientists made a faster computer tool to follow tiny, speedy particles in pretend versions of space. It works out how the particles lose energy, speed up again, and make other particles. On one big computer system, special chips helped it do about ten times as much work in the same time. This is a better way to do computer experiments, not a new discovery seen in the sky. Scientists hope to use it to help compare their pretend space with future observations of real space.
Ashwin Devaraj, Rahul Sharma, Ketan Rikame+1 more
AstronomerAnalysis of a 148 ks NuSTAR observation and archival RXTE/PCA data detects coherent pulsations in the intermediate SFXT IGR J16418-4532 at 1208.67 ± 0.04 s and 1209.4178 ± 0.0084 s, respectively. Optimising epoch-folding detections over trial orbital corrections gives projected neutron-star semi-major axes of 55.1 ± 3.5 and 51.3 ± 2.6 light-seconds. The corrections fully remove the orbital delays visible in sliding-window pulse profiles. The inferred orbital parameters constrain the companion to approximately 12–18 solar masses and 13–16 solar radii; the authors report the first SFXT binary mass-function constraint obtained from neutron-star orbital motion. Phase-averaged spectroscopy finds a robust absorption feature near 50 keV across the tested continuum models, interpreted as a cyclotron line implying a magnetic field of approximately 5 × 10^12 G. Optimising pulse significance over orbital corrections is proposed as a route to dynamical mass measurements in other SFXTs with variable pulse profiles; the underlying accretion processes remain poorly understood.
PublicAstronomers studied IGR J16418-4532, a binary system whose X-ray brightness varies dramatically. NuSTAR and archival RXTE observations reveal regular pulses about every 20 minutes from its neutron star. By testing corrections for the neutron star’s orbital motion, the researchers strengthened the pulse signal and removed timing shifts caused by the orbit. The inferred orbit constrains the companion star to roughly 12–18 times the Sun’s mass and 13–16 times its radius. They also found a robust absorption feature near 50 keV, interpreted as evidence for a magnetic field of about five trillion gauss. The authors propose that this timing approach could help measure masses in similar systems, although the processes driving their extreme X-ray variability remain poorly understood.
Young explorerScientists watched a tiny star that sends out X-ray flashes like a lighthouse, about once every 20 minutes. It travels around with a much bigger star, and that trip changes when its flashes reach us. Working out those changes helped scientists estimate how big and heavy its companion is. A mark in the X-ray light also suggests the tiny star has a very strong magnetic field. Scientists still do not fully understand why this system’s X-ray brightness changes so much.
Marion Guelfand, Valentin Decoene, Olivier Martineau+3 more
AstronomerThe authors present a radio-based reconstruction method for extensive air showers with zenith angles above 60°, motivated by cosmic-ray and neutrino studies above 10^17 eV. It combines a point-source-like wavefront description with an Angular Distribution Function modeling electric-field amplitudes at 50–200 MHz. Realistic cosmic-ray simulations yield arrival-direction resolution better than 0.07° and primary-energy resolution of about 15%; these are simulated performance figures, not measured resolutions for detected events. Direct application to voltage traces enables efficient cosmic-ray selection, accurate direction reconstruction, and first-order energy estimation. The method is illustrated using the first cosmic-ray candidates detected by GRANDProto300, supporting the detection principle. Applicability to upward-going neutrino-induced showers remains an in-principle extension, not a reported neutrino detection.
PublicThe study presents a way to use radio signals from particle showers traveling at shallow angles through the atmosphere to estimate the direction and energy of the incoming particle. Such showers could help researchers study extremely energetic cosmic rays and neutrinos. The method models both the shape of the radio wavefront and how signal strength varies with angle. In realistic cosmic-ray simulations, it reconstructed directions to better than 0.07 degrees and energies to about 15%. Those accuracy figures come from simulations rather than measurements of the detected candidates. The researchers also demonstrate the method on the first cosmic-ray candidates recorded by the GRANDProto300 prototype, supporting its detection approach. The method could in principle also work for upward-moving showers caused by neutrinos, but the abstract reports no neutrino detection.
Young explorerA very energetic particle can make a shower of tiny particles in the air, and that shower can send out radio signals. Scientists made a way to use those signals to work out where the particle came from and how much energy it had. It worked well in computer tests, and they also showed it using signals that might be from real cosmic rays. They hope it can help find particles called neutrinos too, but this study does not say they found any.
Harry Ho-Yin Ng, Jiabao Liu, Arthur Offermans+3 more
AstronomerThis simulation study examines fast and collisional flavor instabilities in long-lived binary neutron-star merger remnants using axisymmetric general-relativistic three-flavor Boltzmann transport with muons and muonic interactions, initialized from 3D grey moment-based simulations. The transport largely reproduces the parent simulations, including trapped weak equilibrium in the core, muonic non-equilibrium associated with prolonged disk demuonization, and cold weak equilibrium in transparent regions. Linear stability analysis finds strong, widespread collisional flavor instability in all three flavor sectors, with narrow resonance-like structures. Muonic interactions shift the electron–tau fast flavor instability toward denser disk regions relative to the extended instability outside the disk in the two-flavor model. Disk demuonization creates a muon-neutrino excess and one-sided muon-lepton-number angular distributions that suppress fast instability in the electron–muon and muon–tau sectors. Local three-flavor quantum kinetic calculations show nonlinear coupling that excites coherence even in an initially stable sector. Diagonal collisional repopulation strongly affects nonlinear evolution and asymptotic populations; omitting it overestimates flavor equilibration. These results support three-flavor transport and consistent inclusion of collisional repopulation in future subgrid models, but are based on simulations, linear analysis, and local quantum kinetic calculations rather than observations.
PublicWhen two neutron stars merge, neutrinos can affect the glowing debris and the elements it produces. This study uses computer simulations to explore how neutrinos change among three types, or flavors, in long-lived merger remnants. Unlike the common two-flavor approximation, the calculations distinguish muon and tau neutrinos and include interactions involving muons. The researchers find that these interactions change where rapid flavor changes can become unstable, moving one instability toward denser parts of the debris disk while suppressing it in two other flavor pairings. Their mathematical stability analysis also finds widespread instabilities linked to collisions. Separate local calculations show that flavor pairings influence one another, so a pairing that initially appears stable can develop quantum coherence. Collisions that replenish the flavor populations are crucial: leaving them out makes the populations appear more equal than the calculations with replenishment predict. The work argues for treating all three flavors and their collisions consistently in future merger models; it does not report observed flavor changes or calculate a resulting change in the merger’s light or element production.
Young explorerWhen two neutron stars crash together, they leave hot stuff that sends out tiny particles called neutrinos. Neutrinos come in three kinds and can change from one kind to another. Scientists used computer models to study these changes, rather than watching a real crash. Their models show that keeping track of all three kinds matters: what happens to one pair can affect another pair. Bumps between particles also matter. If the model leaves out how those bumps refill the different kinds, it makes them look too evenly mixed.
A. C. S. Readhead, M. F. Aller, R. D. Blandford+16 more
AstronomerThe authors report evidence for 2:1 harmonic periodicities in the radio light curves of the SMBHB candidates PKS J0805-0111 and PKS 2131-021 from OVRO and UMRAO monitoring, following an earlier detection in J1309+1154. If confirmed, these patterns would favor a physical origin for strong blazar periodicities with 2:1 commensurabilities. Differences among the three sources may reflect differences in their central engines. The analysis emphasizes careful dissection of light curves to identify coherent behavior amid correlated random variability: the observed periods so far exceed two years, and periodic signals can disappear for long intervals. Four proposed models account for 2:1 commensurabilities and differ in whether shorter-period SMBHB candidates should emerge in future observations. The periodicities remain contested, and neither their reality nor the binary interpretation is established.
PublicRadio monitoring has revealed possible repeating patterns in two blazars, PKS J0805-0111 and PKS 2131-021, each suspected of hosting a pair of supermassive black holes. The patterns have periods in a two-to-one ratio: one cycle takes twice as long as the other. A similar pattern was previously detected in a third candidate, J1309+1154. If confirmed, this shared timing relationship could help show that the repetitions have a physical cause rather than being chance features of random brightness changes. Confirmation is difficult because the observed cycles all last more than two years and can vanish for long stretches. The authors propose four explanations that differ in whether shorter cycles should eventually be found. They also discuss arguments against the patterns being real; the evidence does not yet establish that these objects contain black hole pairs.
Young explorerScientists watched how bright some faraway objects called blazars look in radio waves. In two of them, they found hints of repeating changes: one repeat takes twice as long as another. They had seen a similar pattern in a third object before. They wonder whether pairs of huge black holes could be involved, but they do not know yet. The objects also change in messy ways, and the repeating patterns can hide for a long time. The scientists have four possible explanations, and more watching could help tell them apart.
Sophie Aerdker, Xingwei Gong, Martin Lemoine+1 more
AstronomerThis theoretical and Monte Carlo study develops a covariant microscopic description of relativistic shear acceleration, using stochastic differential equations for angular scattering in the locally comoving frame. Unlike standard Fokker–Planck treatments that assume small momentum gains per scattering, it can probe the transition to non-gradual acceleration when the mean free path approaches the shear scale. For an idealized infinite layer linear in flow four-velocity, the modeled shear rate peaks in the mildly relativistic region, while Lorentz aberration suppresses transverse particle motion in relativistic regions. Particles leaving the central layer consequently encounter power-law-tailed waiting times, producing subdiffusive momentum evolution and acceleration times that can substantially exceed local estimates. A two-state continuous-time random walk with Lévy-distributed waiting times reproduces the Monte Carlo energy distributions. A momentum-dependent mean free path can also introduce spectral breaks. The authors discuss finite jet profiles and argue that these effects merit inclusion in jet acceleration models; these are modeling results, not astronomical detections.
PublicFast jets from powerful cosmic sources may accelerate particles to extremely high energies when neighboring parts of the flow move at different speeds. This study develops a mathematical model and runs particle simulations to examine that process beyond a common assumption that each scattering changes a particle’s momentum only slightly. In an idealized, infinitely extended flow, particles that leave the central region can spend unusually long periods away from it, slowing their overall acceleration substantially compared with local estimates. A statistical model that includes these long waits reproduces the simulated energy distributions. The calculations also show that allowing the distance between scatterings to depend on particle momentum can create changes in the shape of the energy distribution. These are theoretical findings, not observations of a jet, and the authors also discuss more limited jet profiles.
Young explorerSome space jets have parts moving at different speeds, which might help tiny particles gain energy. Scientists used math and computer experiments to study this. In their pretend jet, particles sometimes wandered away from the middle and waited a very long time before gaining more energy. That could make the process slower than a simpler calculation suggests. They have not watched this happen in a real space jet.
Ruediger Staubert, Konstantin Postnov, Vladislav Revnivtsev+1 more
AstronomerThe study compiles Her X-1 Turn-On times across 55 years through 2026, combining published historical work with observations from five monitoring instruments. These rapid transitions from the off-state to Main-On serve as timing markers for the irregular approximately 35-day flux cycle, which includes Main-On and a weaker Short-On and has a relatively stable mean period near 34.85 days. Turn-Ons preferentially occur at orbital phases 0.25 and 0.75. Cycle lengths cluster near 20.0, 20.5, and 21.0 orbital periods, with 57% at 20.5. The O-C diagram shows two long-term sections separated by the prolonged Anomalous Low AL3; each can be modeled with a parabola representing smooth period evolution. Superposed variations on hundreds-of-days timescales are partly quasi-periodic, while straight rising and falling O-C segments indicate relatively rapid period changes. Anomalous Lows, during which at least the soft X-ray emission essentially shuts off, show an apparent underlying recurrence period of 5.4 years rather than an established strict periodicity.
PublicHercules X-1 is a binary X-ray pulsar whose brightness follows an uneven cycle of roughly 35 days, with a strong bright interval and a weaker one. Researchers assembled 55 years of records through 2026 to track the rapid brightening that starts the stronger interval. These events tend to occur at two particular points in the system's 1.7-day orbit. The brightness cycles most often last 20.5 orbits, but also cluster around 20 and 21 orbits. The timing record reveals both gradual changes over decades and faster changes over hundreds of days. Two long stretches of the record, separated by an unusually prolonged faint episode, can be described by smooth mathematical curves. Other exceptionally faint episodes, when at least the soft X-rays essentially disappear, suggest a possible 5.4-year pattern, but the researchers do not establish a perfectly repeating schedule.
Young explorerHercules X-1 is a space system that sends us X-rays. It gets brighter and dimmer in a pattern that takes about 35 days, but it is not a perfect clock. Scientists collected 55 years of records and checked when it suddenly became bright. Some cycles were longer and some were shorter. Sometimes it became very faint. Those faint times might follow a pattern too, but scientists are not sure it repeats regularly.
Z. Lucas Uhm
AstronomerThis theoretical study revisits the electron spectrum below the minimum acceleration energy, gamma_m, in fast-cooling sources such as GRBs and blazars. The familiar gamma_e^-2 spectrum assumes a steady-state electron population; the authors argue that generally evolving, non-steady-state populations can depart substantially from it. They analytically derive a new spectrum, f_U, for radiative cooling through synchrotron emission and inverse Compton scattering, and for combined radiative and adiabatic cooling. They also show that f_U solves a Fokker–Planck equation throughout the energy range below gamma_m and derive generalized expressions for both cooling cases. Comparison with a detailed numerical calculation of a blazar electron spectrum yields excellent agreement across that range. This is an analytical and numerical result, rather than an observational detection; broader applications to high-energy sources remain prospective.
PublicFast-moving electrons in powerful cosmic sources, including gamma-ray bursts and blazars, can rapidly lose energy by emitting light and transferring energy to photons. A commonly used rule describes how many electrons remain at different energies, but it assumes a population that stays steady over time. This study develops a new mathematical description for the cooled electrons when that population is changing. The researchers consider radiation losses alone and radiation combined with another process called adiabatic cooling. Their formula agrees very well with a detailed computer calculation for a blazar across the low-energy range studied. The work provides a theoretical tool, not a new observation, and its possible usefulness for other energetic cosmic phenomena remains to be explored.
Young explorerTiny particles called electrons can lose energy very quickly in powerful places in space. An old math rule describes them when their crowd stays steady, but the crowd can change. Scientists made a new math rule for those changing, cooled-down particles. It matched a detailed computer calculation very well. This was a math-and-computer study, not a new sighting in the sky.
L.E. Rodríguez, M. Cruces, G. Voisin+2 more
AstronomerThe authors explore gravitational self-lensing of neutron-star radio pulses by a black-hole companion as a possible channel for repeating FRBs. Their simple circular NS–BH binary model includes Lense–Thirring precession, pulse splitting, and image delays. Purely Keplerian orbits yield activity windows several orders of magnitude shorter than those observed in periodic FRBs, whereas precessing orbits can produce windows lasting a few to tens of days. In the model, lensing converts an intrinsic log-normal pulse-energy distribution into one with a high-energy power-law tail spanning up to four orders of magnitude. If observed millisecond inter-burst waiting times are interpreted as lensing-induced image delays, the inferred BH masses are 10^3–10^4 solar masses; this is a conditional inference, not a detection of such companions. Crucially, the modeled amplification cannot bridge the energy gap between Galactic magnetar radio pulses and FRBs. The authors also interpret the non-detection of NS–intermediate-mass-BH systems as suggesting low abundance, making this a likely rare channel.
PublicFast radio bursts are bright flashes from beyond our galaxy whose origin remains uncertain. This study tests a proposed explanation in which a neutron star orbits a black hole, whose gravity magnifies the star’s radio pulses. In the authors’ model, an orbit that slowly changes orientation can create active periods lasting a few to tens of days, while a simpler orbit produces periods far too short to match periodic bursts. The modeled magnification also creates a tail of unusually energetic pulses. If the observed millisecond gaps between some consecutive bursts are delays between lensed copies of one pulse, the black hole would have a mass of 1,000–10,000 Suns. That interpretation is not evidence that these companions have been found. The model still cannot make Galactic magnetar radio pulses bright enough to explain FRBs, and the lack of detected neutron-star–black-hole pairs of this kind suggests the proposed route is probably rare.
Young explorerScientists see very bright flashes of radio waves from faraway space, but they do not know for sure what makes them. They tried a model where a small star goes around a black hole. The black hole’s gravity could act like a magnifying glass, making the star’s flashes look brighter and sending copies to us at slightly different times. The model can make some patterns like the ones scientists see, but it does not make the flashes bright enough. No star-and-black-hole pairs of this kind have been found, so this idea is not a proven answer and may happen only rarely.
Zhihao Ouyang, Hubing Xiao, Shangchun Xie+7 more
AstronomerThis systematic study analyzes 85 TeV-detected blazars using archival Swift-XRT and NuSTAR observations available through May 2024. Spectral fitting yields unabsorbed X-ray fluxes and photon indices. Fractional-variability analysis identifies 78 sources as variable in soft X-rays and 14 in hard X-rays. For well-sampled soft X-ray light curves, flux distributions generally favor log-normal forms. Power spectral density slopes, defined by P(f) ∝ f^−β, span β = 0.1–1.6, with most between 1.0 and 1.6. Positive TeV–X-ray luminosity correlations support, but do not establish, a leptonic emission scenario. X-ray luminosity also correlates with disk luminosity, while no significant correlation with black hole mass is found.
PublicResearchers studied archival X-ray observations of 85 blazars—active galaxies with jets directed toward us—that have also been detected at very high gamma-ray energies. Using Swift-XRT and NuSTAR data available through May 2024, they identified brightness variations in 78 sources at lower X-ray energies and 14 at higher X-ray energies. For sources with well-sampled lower-energy observations, the brightness patterns generally followed a log-normal distribution. Blazars with greater very-high-energy gamma-ray luminosity also tended to have greater X-ray luminosity. This supports, without proving, an explanation in which electrons and related particles produce the radiation. X-ray luminosity also tracked the luminosity of the disk around the black hole, but showed no statistically significant relationship with black hole mass.
Young explorerScientists looked at old X-ray observations of 85 bright things in space called blazars. Many changed how brightly they shone: 78 changed in one kind of X-ray light, and 14 changed in a higher-energy kind. Blazars that gave off more very energetic gamma-ray light also tended to give off more X-ray light. That is a clue about how tiny particles might make the light, but it is not proof. The scientists also found that brighter disks around the black holes went with brighter X-rays. They did not find a clear link between X-ray brightness and how heavy the black holes were.
Jasmine Parsons, Lorenzo Sironi, Anatoly Spitkovsky+1 more
AstronomerThe authors present the first 3D particle-in-cell study of coherent wave generation by flux-rope mergers in relativistic reconnection, using outflow boundaries and guide-field ratios Bg/B0 = 0, 0.1, and 0.3. The simulated efficiency of converting inflowing magnetic energy into escaping coherent waves is about 7 × 10^-4 without a guide field, a factor of a few below 2D results, and about (1–2) × 10^-3 at moderate guide fields, comparable to 2D without a guide field. They propose that transport of reconnected field away from diffusion regions explains the comparable efficiencies. The simulated escaping waves are linearly polarized along a direction set by the upstream field; with a guide field, opposite-side polarization angles differ by approximately 2 arctan(Bg/B0). These simulation results support, but do not establish, reconnection as the source of coherent radio emission in Crab-like pulsars and as a possible fast-radio-burst mechanism.
PublicComputer simulations show that merging magnetic structures can produce organized electromagnetic waves even in three dimensions, extending earlier two-dimensional work. Only a small fraction of the incoming magnetic energy escapes as these waves, but adding a magnetic-field component along the structures raises the efficiency to roughly the level found in earlier two-dimensional simulations without that component. The simulated waves also have a definite polarization direction that depends on the surrounding magnetic field. The findings strengthen the idea that this process could power radio emission from Crab-like pulsars and perhaps fast radio bursts; they are not observations proving that either source uses this mechanism.
Young explorerScientists used a computer to pretend that rope-like bundles of magnetic field were joining together in space. In their three-dimensional pretend world, the bundles made waves that carried away a little energy. This could help explain radio signals from some stars, and maybe some very quick radio flashes from space. But the computer test does not prove that real stars make their signals this way.
Ajith Balu, Kinjal Roy, Biswajit Paul
AstronomerThis study analyzes quiescent Be X-ray binaries using eROSITA's first all-sky survey, eRASS1, to investigate emission at low mass-accretion rates. Detected systems generally have X-ray luminosities of about 10^33–10^36 erg s^-1, with spectra well fitted by either absorbed power-law or blackbody models. Under the blackbody interpretation, the emission appears to originate from only a fraction of the neutron-star surface; the spectral fits do not uniquely establish that interpretation. Luminosity upper limits are reported for undetected systems. The quiescent luminosities are used to assess low-rate accretion scenarios, including the propeller regime and cold-disc accretion, without the abstract identifying a preferred model. The study also compares the eRASS1 detection space with luminosities previously reported by other X-ray observatories.
PublicBe X-ray binaries are pairs of stars that usually contain a neutron star and a Be star. Although these systems spend most of their time in a quiet state, they are often studied during bright outbursts. This study instead used eROSITA's first all-sky survey to examine their quiet X-ray emission and investigate what happens when little matter is being accreted. The detected systems mostly emitted about 10^33–10^36 ergs per second in X-rays. Two different models described their X-ray spectra well, so the fits alone do not give a unique physical explanation. One model suggests that the emission comes from only part of the neutron star's surface. For systems not detected, the researchers reported upper limits on luminosity. They used the quiet-state luminosities to assess competing explanations for accretion at low rates and compared the survey's detection range with earlier X-ray observations.
Young explorerSome pairs of stars give off X-rays, a kind of light our eyes cannot see. These pairs usually include a tiny, very dense star called a neutron star. Scientists used a space telescope to study the pairs while they were quiet, rather than having bright outbursts. They found that two different descriptions could explain the X-ray light they saw. One suggests that only a small part of the neutron star's surface is shining, but they are not sure that is the right explanation. Studying these quiet times helps scientists explore how a little bit of matter might fall onto the neutron star.
Saptashwa Bhattacharyya, Giacomo Principe, Dmitry Malyshev+5 more
AstronomerThe authors extend AutoSource-ID from optical to gamma-ray data, using U-Net segmentation for detection and dedicated deep neural networks for localization, flux estimation, and genuine-versus-spurious classification. Training uses Monte Carlo simulations based on 10 years of Fermi-LAT observations. Applied to the observational data, the pipeline produces 1FDL, presented as the first deep-learning-derived Fermi-LAT all-sky source list, with more than 3800 sources, estimated positions and fluxes, and probability scores for detection reliability. Tests varying the interstellar emission model find performance comparable to or better than standard likelihood-based catalog methods under those background variations. The list is broadly consistent with 4FGL-DR2 over the same observational period, and a few new sources are confirmed in the later 16-year FL16Y list. The results support the potential of deep learning for gamma-ray source analysis, while explicitly assessing sensitivity to background modeling and allowing for spurious detections.
PublicResearchers have used deep learning to build an all-sky list of more than 3800 gamma-ray sources from 10 years of Fermi-LAT observations. They trained the software on simulated data, then used it to find sources, estimate their positions and brightnesses, and score how likely each detection is to be real rather than a false signal. A key challenge is separating sources from gamma-ray emission spread across the sky. When the researchers varied their model of this background emission, the method performed as well as or better than the standard catalog approach in those tests. The new list largely agrees with an existing catalog covering the same decade, and a few newly identified sources were confirmed in a later 16-year source list. The findings suggest that deep learning is promising for this work, but not every detection is necessarily genuine.
Young explorerScientists taught a computer to look for places in the sky that send out a kind of light called gamma rays. First, it practiced on pretend sky pictures made by a computer. Then it searched real sky data and made a list of more than 3800 possible sources. Some spots might be false alarms, so it also gave each one a score for how likely it is to be real. The scientists checked how well it worked when they changed their picture of the background glow. It did about as well as, or better than, their usual method in those tests. Its list mostly matched an earlier list, and a few new spots were confirmed in a later one.
Zahoor Malik, B. van Soelen, Sikandar Akbar+1 more
AstronomerUsing 17.9 years of Fermi-LAT light curves at 3-, 7- and 30-day cadence, the study tests whether changing-look blazars (CLBs) show gamma-ray evidence for accretion-regime changes rather than optical broad-line dilution by a variable jet continuum. At 30-day cadence, CLBs and identically selected and analysed FSRQ controls have statistically indistinguishable fractional variability: medians of 0.483 and 0.437, respectively (p = 0.94), versus 0.262 for BL Lacs (p = 1.4 × 10^-4). The result persists with low-synchrotron-peaked controls and flux and sampling matching. Other diagnostics and Eddington-scaled disc luminosity also associate CLBs with FSRQs. CLBs show no excess of bimodal gamma-ray flux distributions, and optical transition direction does not predict gamma-ray spectral evolution. They reach hard, BL Lac-like spectra more often than FSRQs, but these episodes do not last longer than expected by chance. Only in this spectral behaviour and their spectral response to brightening are CLBs intermediate. The weak gamma-ray imprint of optical classification changes favours variable jet dilution over accretion-regime switching, without establishing it conclusively.
PublicChanging-look blazars switch between two optical classifications. This could mean their black-hole feeding flow changes state, or simply that a brightening jet overwhelms the broad emission lines used to classify them. To distinguish these explanations, researchers examined 17.9 years of gamma-ray observations from Fermi-LAT rather than relying on long-term averages that can hide changing states. The changing-look objects varied much like flat-spectrum radio quasars, one of the two classes, and more strongly than BL Lac objects, the other class. This finding held after checks for differences in source selection, brightness and observation sampling. The researchers found no excess of two-state gamma-ray brightness patterns, and the direction of an optical classification change did not predict how the gamma-ray spectrum changed. Although changing-look objects more often reached BL Lac-like spectra than quasars did, those episodes were no longer than chance would allow. Overall, the evidence favours a variable jet hiding the optical lines rather than a change in the feeding flow, but does not prove that explanation.
Young explorerThese faraway objects can look like two different kinds of space beacons. Maybe the way their black holes eat changes, or maybe a bright jet just hides some clues in their light. Scientists watched a very energetic kind of light from them for almost 18 years. Even when their usual-light look changed, this energetic light mostly behaved like that of one kind of beacon. That makes the bright-jet hiding idea seem more likely, but scientists are not certain.
Andrea Sabatucci, Armen Sedrakian
AstronomerThis theoretical study tests the robustness of neutrino-trapping effects in hot hybrid-star models against uncertainties in the hadronic and quark equations of state and the phase-transition construction. Isentropic models combine finite-temperature covariant density functionals with a three-flavor NJL quark model including repulsive vector interactions and two-flavor color superconductivity; a phenomenological pressure shift locates deconfinement because NJL lacks confinement. Across the parameter range explored, trapped electron neutrinos shift deconfinement to higher density and reduce sensitivity to the nuclear symmetry-energy slope by increasing the proton fraction and hence isospin symmetry. Stronger vector coupling stiffens quark matter and moderately increases the maximum mass for the couplings studied. Stronger diquark pairing and RG-consistent regularization affect pairing gaps, phase boundaries, and quark-core composition more than the qualitative mass–radius trends. Global and local electron-lepton-number conservation yield similar mass–radius relations but substantially different interiors, with a considerably more extended mixed phase under global conservation. These are model results, not observational findings.
PublicThe researchers used theoretical models to explore how trapped neutrinos affect hot stars that may contain both ordinary nuclear matter and quark matter. In every set of conditions they examined, trapping electron neutrinos pushed the transition to quark matter to higher density. It also made the predictions less sensitive to one uncertainty in how nuclear matter behaves. Stronger repulsion between quarks increased the maximum mass the models could support, though only moderately over the range studied. Other changes to the quark model affected the predicted interior more strongly than the overall mass–radius pattern. Two ways of imposing conservation of electron-lepton number gave similar masses and radii but different internal structures: allowing conservation across the coexisting phases produced a much broader region where nuclear and quark matter mix. These calculations explore uncertain descriptions of dense matter; they are not observations of stellar interiors.
Young explorerScientists used math to imagine a very hot star whose middle might contain tiny building blocks called quarks. They asked what happens if tiny particles called neutrinos stay trapped inside. In the models they tried, the star’s matter needed to be squeezed more tightly before it changed into quark matter. Different rules could also make the pretend stars look much alike on the outside but have very different insides. These are ideas tested with math, not things the scientists saw inside a real star.
P.S. Koliogiannis, N. Paar
AstronomerThis modeling study uses measured electric dipole polarizabilities of neutron-rich nuclei to constrain equation-of-state predictions for uniformly rotating neutron stars in general relativity. The authors compare a family of relativistic energy-density-functional equations of state with systematically varied symmetry energy against the subset consistent with those measurements. At the transition where the innermost stable circular orbit meets the stellar surface, the constraint reduces the predicted spread in mass and equatorial radius by factors of about seven to ten across the spin frequencies considered. Along that transition, the predicted disk-inner-edge orbital frequency occupies a band narrower than 20 Hz at each spin. The authors further propose that a measured spin and a kilohertz quasi-periodic oscillation, if interpreted as disk orbital motion, could restrict the mass–radius region; an independent mass estimate could then test the symmetry-energy constraint. These are model-dependent constraints and a proposed observational application, not direct measurements of neutron-star masses or radii.
PublicMeasurements of how neutron-rich atomic nuclei respond to an electric field can help narrow predictions about rapidly spinning neutron stars. The researchers calculated models with different descriptions of matter inside these stars, then retained those compatible with the nuclear measurements. They studied the boundary between disks that extend to the star’s surface and disks whose inner edge is set by unstable orbits. In their models, the nuclear measurements narrowed the range of stellar masses and radii at this boundary by factors of about seven to ten. They also narrowed the predicted orbital frequency at the disk’s inner edge to a range less than 20 hertz wide for each stellar spin considered. The team suggests combining a measured stellar spin with a rapid brightness oscillation to further constrain mass and radius, but this requires interpreting that oscillation as the motion of orbiting disk material. These findings narrow model predictions rather than directly measure a star’s size or mass.
Young explorerA neutron star is a very tightly packed star that can spin fast, with material circling around it. Scientists made computer models to explore where that circling material can stay safely in orbit. They used measurements of tiny atomic centers to choose which models fit better. That made the models agree more closely about how heavy and wide the star would be when the closest safe orbit touches its surface. The scientists also suggest that a star’s spin and quick flickers of light might help check these ideas, if the flickers really come from material going around the star.
Michael W. Healy-Kalesh, Sara Saeedi, Manami Sasaki+5 more
AstronomerAn eROSITA search identified an extended X-ray shell coincident with the Galactic recurrent nova V745 Scorpii. The authors propose that it is a nova super-remnant (NSR), a structure excavated from the surrounding interstellar medium by repeated nova eruptions. Supporting evidence includes its alignment with the nova, a size consistent with known NSRs, a radial emission profile resembling that of the confirmed NSR around M31N 2008-12a, a corresponding infrared cavity, agreement with the radial profile of a synthetic X-ray ring from an NSR model, and the reported absence of alternative sources capable of producing the structure. Simulations predict NSRs around all novae, while shocks between ejecta and the shell, and among ejecta, are predicted to produce extended X-ray emission. The identification remains a proposal; if confirmed, this would be the first NSR identified through its X-ray emission.
PublicAstronomers have found a shell of X-ray emission at the location of V745 Scorpii, a nova that erupts repeatedly. They propose that the shell is a nova super-remnant: a vast structure formed as repeated eruptions push aside surrounding interstellar gas. Its position, size, brightness pattern and matching infrared cavity support this interpretation, as does comparison with a simulated shell. The researchers also report no other source capable of creating such a large structure. Models predict that collisions involving material expelled by the nova can make these shells shine in X-rays. The interpretation is not yet confirmed, but this could be the first nova super-remnant identified by its X-ray glow.
Young explorerSome stars have big outbursts again and again, pushing away gas around them. Scientists found a shell glowing in X-rays near one of these stars. They think the outbursts may have made it. Its shape and a gap in the nearby gas are clues, and a computer model looks similar. But they still need to check whether their idea is right.
Miranda Pikus, Abigail Polin, Dillon Hasenour+1 more
AstronomerThis first parameter survey of double detonations at such low white-dwarf masses predicts faint, rapidly evolving transients from systems with total masses around 0.6 solar masses and accreted helium shells up to 0.3 solar masses. Nuclear hydrodynamics calculations with Cattails and radiation transport with Sedona produce a continuum of core-powered and shell-powered events, with at most 0.03 solar masses of radioactive nickel in the core or shell material, respectively. Model light curves peak near absolute magnitude -17 within 5–10 days. Ejecta dominated by intermediate-mass elements and unburnt core material produce noticeable spectral features. These are theoretical predictions, not reported detections; the authors propose that such explosions could constitute a historically missed supernova population that large sky surveys might identify.
PublicComputer simulations suggest that relatively low-mass white dwarfs could produce a population of faint, fast supernovae that past searches may have missed. In the proposed double-detonation process, an explosion in an accumulated helium layer triggers another explosion in the star’s carbon-oxygen core. The researchers modeled systems with total masses around 0.6 times the Sun’s mass. Their predicted explosions reach peak brightness within 5–10 days and are relatively dim, with distinctive spectral features from the expelled material. The study does not report finding these events: its predictions could help large sky surveys search for them.
Young explorerA white dwarf is a kind of star that can explode. Scientists used computers to explore what might happen if a small white dwarf had one explosion in its outside layer that set off another inside. Their pretend stars made quick, faint flashes. The scientists have not found these flashes in this study, but their computer work could help people look for them in the sky.
Yuma Takeichi, Daichi Tsuna, Daichi Hiramatsu+2 more
AstronomerThe progenitors of intermediate-luminosity red transients (ILRTs), which occupy the luminosity gap between novae and supernovae, remain debated. This study constructs a semi-analytical framework combining predicted electron-capture supernova (ECSN) light curves with dust attenuation and re-emission in super-AGB progenitor winds. Although dust could reduce the tension between theoretically bright ECSNe and fainter ILRTs, varying wind mass-loss rates and ECSN model parameters still makes it challenging to reproduce both ILRT light curves and color evolution simultaneously. This modeling result potentially challenges standard ECSN explanations, rather than excluding ECSNe altogether. The authors propose either an ECSN population with substantially lower explosion energies, approximately 10^48–10^49 erg, and dimmer plateaus, or alternative models producing similarly low explosion energies.
PublicIntermediate-luminosity red transients are stellar outbursts brighter than novae but fainter than supernovae, and their origins remain uncertain. One proposed explanation is an electron-capture supernova from a super-AGB star, but theoretical models predict explosions brighter than these transients. The researchers modeled whether dust in the star’s wind could hide enough light, while also accounting for light re-emitted by the dust. Across the model variations they explored, they found it difficult to match both how the transients brighten and fade and how their colors change. This raises questions about standard electron-capture supernova models as an explanation, but does not rule them out. The authors suggest weaker electron-capture explosions, or another kind of explosion with similarly low energy, as possibilities rather than established answers.
Young explorerSome stars make red flashes, and scientists are not sure what causes them. One idea is a kind of exploding star, but models say it should shine too brightly. The researchers used calculations to ask whether dust around the star could hide some light. It was still hard to match both the flashes’ changing brightness and their changing colors. Maybe the explosions are weaker than expected, or maybe something else makes the flashes. Scientists do not know yet.
Ignacio Magaña Hernandez, Antonella Palmese
AstronomerThis study forecasts LISA binary-black-hole detections using population constraints from GWTC-5.0 and the O3 intermediate-mass binary search; these are not LISA observations. The released GWTC-5.0 population posterior yields 6.6 expected detections in four years at signal-to-noise ratio >8, with a 90% credible interval of 4.4–12.1. Alternative models use a broken power law plus two or three Gaussian peaks for either primary masses or a common component-mass distribution. In the three-peak common-distribution model, extrapolating from 300 to 1000 solar masses roughly doubles the median forecast to about 14, while the upper 90% credible bound rises from tens to thousands; approximations may compromise the most extreme counts. For the reference population, 39% (+22/−11 percentage points) of LISA-detectable binaries are predicted to merge during the mission or within ten years afterward. Essentially all these mergers would be detectable by the reference Cosmic Explorer configuration if operating at merger. The forecasts highlight sensitivity to the high-mass population and its implications for multiband observations.
PublicResearchers used ground-based gravitational-wave observations to forecast how many pairs of black holes LISA could detect. Their reference population model predicts about seven detections over four years, with a 90% credible range of roughly four to twelve. The forecast depends strongly on how common very massive black holes are. Extending one alternative model to higher masses roughly doubles its typical prediction to about fourteen, but also allows extremely large counts whose reliability may be limited by the calculations’ approximations. In the reference model, about 39% of LISA-detectable pairs would merge during the mission or within ten years afterward, with substantial uncertainty. Nearly all those mergers could also be detected by a reference Cosmic Explorer design, provided it is operating when they merge. These are predictions, not detections by LISA.
Young explorerTwo black holes going around each other can make ripples in space. Scientists used clues from ripples already measured to guess how many black-hole pairs LISA might notice. Their usual model says about seven in four years, but the number is uncertain, especially because they do not know how many very big black holes there are. Some pairs might later join together, and another detector could catch that part too, if it is running. These are guesses based on models, not things LISA has already seen.
Dario Rossi, Leonardo Gualtieri, Thomas P. Sotiriou
AstronomerThe authors introduce a semi-agnostic framework for modeling black hole binary inspirals beyond general relativity, fixing the field content without choosing a specific theory. They expand in post-Newtonian order and in l/L, the ratio of the length scale controlling deviations from general relativity to the system’s characteristic length scale. For a massless scalar field coupled to the metric at leading post-Newtonian order, accounting for the l/L scaling of both interactions and source-characterizing quantities yields an inspiral description with a small number of universal parameters. The parametrization is intended to support combined bounds from multiple sources and searches for specific fields; the abstract reports a theoretical framework, not observational constraints.
PublicThis theoretical study presents a way to describe pairs of black holes spiraling toward one another when gravity may differ from general relativity. Rather than choosing one alternative theory, the authors specify the types of fields involved and focus on a massless scalar field coupled to spacetime geometry. Within their leading-order approximation, they find that a small set of shared parameters can describe the inspiral. The framework could help researchers combine information from multiple black hole pairs to constrain departures from general relativity and search for particular fields. No observational detection or measured limits are reported.
Young explorerTwo black holes can circle each other and spiral closer together. Scientists made a new math recipe to explore how this might happen if gravity works a little differently from our usual description. In the version they studied, just a few numbers are needed to describe the spiral. The recipe could help scientists check ideas about gravity using many black hole pairs, but this study does not show that gravity really is different.
Selma Vangstein, Christopher J. Moore
AstronomerThe Letter examines the model dependence of gravitational-wave tests of the horizon area law: although these offer a striking consistency check of general relativity, their underlying models assume GR. In a specific example using simulations of merging boson stars, horizonless exotic compact objects can mimic black-hole mergers and pass an area-law test at a confidence as high as approximately 92%. This simulated counterexample cautions against interpreting a passed test as independent evidence for event horizons or GR.
PublicGravitational-wave tests of the horizon area law check whether a merger behaves as general relativity says black holes should. But the models used in these tests already assume that theory, which limits what a successful test establishes. In simulations, the researchers found that merging boson stars—exotic compact objects without event horizons—could imitate merging black holes and pass the test with confidence as high as about 92%. This is a simulated example, not an observation of boson stars, showing that passing the test need not mean the merging objects had event horizons.
Young explorerScientists use ripples in space to check a rule about black holes. But the check uses models that already follow Einstein’s theory of gravity. In a computer pretend-world, scientists made special objects called boson stars merge. These objects had no black-hole boundaries, called event horizons, but they could still look like merging black holes and pass the check. So passing this check alone does not prove that the objects were black holes.
Toru Kojo
AstronomerThis theoretical study uses a simple constituent-quark model of electrically neutral ddu baryons, including neutron- and Δ⁰-like states, to investigate how magnetic fields shift the onset of quark saturation and thus the limit of a purely baryonic description. Calculated baryon wave functions and spectra show spin-flavor polarization, transverse spatial compression, and strong suppression of transverse kinetic energy. Single-quark distributions derived from the one-body reduced density matrix are used to calculate occupation probabilities in an ideal baryon gas. For a field directed along +z, the spin-down d quark in the lowest Landau level saturates first. The calculated saturation density decreases at weak fields but increases at stronger fields. The authors interpret this nonmonotonic behavior as competition between polarization, which promotes saturation, and transverse squeezing, which broadens transverse quark momenta and delays saturation. These are model results, not observational measurements.
PublicA theoretical calculation explores how magnetic fields change the density at which quarks inside neutral particles such as neutrons begin to fill their available quantum states. That saturation marks a limit to describing the matter purely in terms of baryons, the particles made of quarks. In a simplified quark model and an ideal gas of baryons, magnetic fields change the quarks’ spin arrangement and squeeze their sideways spatial distribution. The calculated saturation density falls for weak fields but rises for stronger fields. The explanation is a competition: rearranging spins favors earlier saturation, while squeezing the quarks spreads their sideways momenta and delays saturation. These findings come from a model, rather than observations.
Young explorerNeutrons have tiny parts called quarks inside them. Scientists used a simplified math model to ask what happens when a magnetic field acts on these parts. Their model says the field changes how the quarks line up and squeezes them sideways. It also changes how much matter can be packed together before certain places allowed by quantum rules become full. A weak field makes those places fill sooner, but a stronger field makes them fill later. This is what the model says, not something the scientists watched happen.
Yogesh Kumar, Mihir Arora, Manas Lohani+3 more
AstronomerThis theoretical study models spin-polarized strange quark matter and strange quark star structure using a thermodynamically self-consistent quasiparticle framework. A dynamic bag constant is coupled to the medium-dependent reduction of effective quark masses, enforcing internal thermodynamic consistency. The model yields non-monotonic sound-speed behavior and a significantly stiffer high-density equation of state, predicting maximum stable gravitational masses up to 2.19 solar masses. The authors interpret hot, magnetized strange quark matter as a viable explanation for massive pulsars such as PSR J0740 6620 and PSR J0952 0607 without unrealistic thermal or structural assumptions. These are model predictions, not observational evidence that either pulsar is a strange quark star.
PublicThe researchers developed a theoretical model of stars made from strange quark matter. Their model links changes in the quarks’ effective masses to a changing quantity called the bag constant, keeping the description thermodynamically consistent. It predicts that the matter becomes more resistant to compression at high densities, allowing stable stars with gravitational masses up to 2.19 times the Sun’s mass. The authors suggest that hot, magnetized strange quark matter could explain massive pulsars such as PSR J0740 6620 and PSR J0952 0607 without unrealistic assumptions about their heat or structure. The study does not establish that those pulsars are actually made of strange quark matter.
Young explorerScientists used math to imagine a very heavy star made of tiny bits called quarks. In their model, hot, magnetic quark matter becomes harder to squeeze when packed very tightly. That could help a star hold itself up even if it has more than twice as much mass as the Sun. The scientists think this might explain some very heavy stars, but they have not shown that those stars really have quark matter inside.
Alessandro Rizzo, Nicolò Parmiggiani, Andrea Bulgarelli+12 more
AstronomerThe authors reformulate maximum-likelihood gamma-ray source detection and localization as a Quadratic Unconstrained Binary Optimization (QUBO) problem suitable for quantum annealing. They test the formulation on AGILE GRID observations generated with AGILEpy in the 30 MeV–50 GeV band, using simulated quantum annealing rather than quantum hardware. The method reproduces classical flux and position estimates within their statistical uncertainties and selects the correct grid node among candidate positions in 97% of the maps. These tests support the approach's feasibility for this optimization problem and motivate future deployment on actual quantum annealers; they do not demonstrate performance on quantum hardware.
PublicFinding gamma-ray sources and measuring their brightness requires solving a complicated mathematical search problem. The researchers recast this problem into a form designed for quantum annealing, a computing approach that seeks the best solution by representing possible answers as energy states. They tested it using simulated quantum annealing on AGILE observation maps generated with the AGILEpy software. The brightness and position estimates agreed with conventional results within statistical uncertainty, and the method chose the correct candidate location in 97% of the maps. The results are promising, but testing on actual quantum annealing hardware remains a future step.
Young explorerScientists want to find where gamma rays, a kind of light, come from in the sky. They tried a new computer puzzle on practice sky maps. It picked the right spot from a list in 97 out of every 100 maps, and its answers about position and brightness were close to those from the usual method. The computer was imitating a method called quantum annealing; trying it on a real quantum machine comes next.
Sergey Troitsky
AstronomerThis review surveys astrophysical tests of particle-physics models: stellar structure and evolution constrain extra energy-loss and transport channels; high-energy photon propagation probes mixing with new particles and modified electron–positron pair production; and large-volume neutrino telescopes search for magnetic monopoles, neutrinos from superheavy dark-matter decay, and non-standard neutrino propagation. Applications include the tip of the red-giant branch, gamma-ray burst 221009A, and Baikal-GVD and IceCube data. Parameter inference relies on forward models incorporating the response to new physics, propagation, detection, and nuisance parameters. The abstract reports no specific numerical constraints or detections of new physics.
PublicThis review explains how stars, high-energy light, and neutrino detectors can test ideas about particles and their interactions. Researchers examine how stars lose or move energy, how energetic light travels through space, and whether neutrino detectors contain signs of hypothetical particles or unusual neutrino behavior. Examples involve red-giant stars, gamma-ray burst 221009A, and the Baikal-GVD and IceCube experiments. These tests compare observations with models that account for possible new physics, travel through space, detector effects, and other factors affecting the inference. The abstract does not announce a discovery of new particles or give numerical limits.
Young explorerStars and tiny bits of light can help scientists look for clues about what the universe is made of. Scientists study how stars use energy, how light travels, and what special detectors catch. They compare what they see with calculations of what might happen if unfamiliar particles or rules exist. This paper explains some of those tests; it does not say that a new particle has been found.
Antonio Gómez-Bañón, Pantelis Pnigouras, José A. Pons
AstronomerThis theoretical study computes the nonradial l=2 oscillation spectrum of neutron stars containing an axion condensate in light QCD axion models, using the relativistic Cowling approximation with fully coupled, dynamical fluid and axion perturbations. Changes to the equilibrium structure raise f- and p-mode frequencies by up to about 20%, but dynamical axion coupling partially offsets this increase, almost completely for the f-mode. Modes above the axion-mass propagation threshold can damp through axion emission. The f-mode stays below this threshold in all condensate-supporting configurations studied, whereas p-mode damping times can reach about 10 ms, shorter than their gravitational-wave damping times, except near certain axion masses where the outgoing axion amplitude nearly vanishes. The calculated spectrum also includes strongly damped axion-dominated quasinormal modes with imaginary parts of order kHz and gravitationally bound axion states analogous to gravitational atom levels. Below threshold, bound p-modes exhibit avoided crossings with these states and exchange fluid- and axion-dominated character. These are model results, not observational detections.
PublicThe researchers theoretically explore how hypothetical particles called axions could change the vibrations of neutron stars. In the models considered, dense matter can produce an axion field inside the star. Its effect on the star’s structure raises some vibration frequencies by as much as about 20%, but interaction between the vibrating matter and the axion field counteracts that change, nearly cancelling it for one main type of vibration. Some higher-frequency vibrations could also lose energy by emitting axions, fading in as little as about 10 milliseconds—faster than they lose energy through gravitational waves—although this emission becomes very weak for certain axion masses. The calculations also reveal rapidly fading axion-dominated vibrations and axion states held by the star’s gravity, which can mix with the star’s matter vibrations. These findings come from an approximate theoretical calculation; they are not evidence that axions have been observed in neutron stars.
Young explorerImagine a neutron star ringing like a bell. Scientists used math to ask what would happen if tiny particles called axions made a field inside it. In their model, that field can change how the star rings and can carry energy away, making some vibrations fade quickly. It can also have its own vibrations that mix with the star’s. This is an idea they calculated, not something they have seen happen.
Semra Gurtas Dogan, Hassan Hassanabadi, Abdullah Guvendi
AstronomerThis theoretical study computes scalar and electromagnetic quasinormal modes of a Schwarzschild black hole surrounded by a King-profile dark matter halo. Sixth-order WKB and Padé-improved calculations agree with time-domain fundamental frequencies to within 0.2% for the configurations examined; rewriting the lapse using the inverse hyperbolic sine mitigates cancellation in high-order derivatives. The halo lowers both oscillation frequency and damping rate. In the enclosed-mass metric, the real-frequency shift is almost entirely explained by halo mass within the photon sphere, while the additional damping-rate decrease follows the circular null orbit’s Lyapunov-exponent-to-angular-frequency ratio. Because that metric places some halo material inside the horizon, the authors also construct an exterior halo using an Einstein cluster. Frequency reductions are similar, but the real part then follows the Schwarzschild frequency multiplied by the halo’s gravitational redshift factor. An inner-edge density discontinuity scatters waves and changes damping rates by up to about 9%. For continuous profiles, deviations from the redshift relation stay below about 1.5% at an inner radius of 3M and below about 0.5% for the examined cases with inner radii at least 4M. No unstable modes are found in the perturbation sectors and parameter configurations tested.
PublicCalculations—not observations—explore how a dark matter halo changes the way disturbances around a nonrotating black hole oscillate and fade. For the scalar and electromagnetic disturbances studied, the halo makes the oscillations slower and their fading more gradual. Two numerical approaches agree on the fundamental frequencies to within 0.2% in the tested cases. The researchers also compare two halo models because the first places some dark matter inside the black hole’s horizon. When the halo is entirely outside, its gravitational redshift largely explains the slower oscillations. A sharp density boundary can scatter the disturbances and alter how quickly they fade; smoother boundaries give closer agreement with the redshift description. No growing, unstable modes were found, but only the specified disturbances and model configurations were tested.
Young explorerScientists used math to imagine a black hole with dark matter around it. In their models, little wiggles around the black hole wiggle more slowly and take longer to fade when the dark matter is there. A sharp edge in the dark matter can also scatter the wiggles. These are calculation results, not something they watched in the sky.
K. Folias, Ch.C. Moustakidis
AstronomerThis work investigates how short-range nucleon–nucleon correlations modify the momentum distribution underlying quarkyonic matter models and affect quantities including energy density, pressure, and sound speed. The correlations populate momenta above the Fermi momentum, producing a high-momentum tail. The abstract cites experimental and theoretical support for an approximately 1/k^4 tail at high densities, but reports no quantitative changes to quarkyonic-matter properties. The authors argue that incorporating these correlations is important for a complete model and suggest that heavy-ion collisions may probe quarkyonic matter; this is a proposed possibility, not a reported detection.
PublicThe researchers examine how close-range interactions between nuclear particles could affect a proposed form of very dense matter called quarkyonic matter. These interactions give some particles unusually high momentum, changing the distribution of particle motion used in the model. The authors cite experiments and theory supporting a particular pattern in this high-momentum population and investigate its implications for energy density, pressure, and the speed of sound. The abstract does not report how much these properties change. It also suggests that collisions between heavy atomic nuclei might help probe quarkyonic matter, without claiming that such matter has been detected.
Young explorerImagine tiny particles packed very close together. When they interact up close, some can get an extra-fast kick. Scientists are studying how those speedy particles might change an idea for a special kind of tightly packed matter. Experiments support the pattern of speedy particles, but this summary does not say exactly how they change the special matter. The scientists also think smashing heavy atomic centers together might help them look for it; they have not said they found it.
Dipak Debnath, Hsiang-Kuang Chang
AstronomerThe Galactic black hole candidate MAXI J1834-021 showed approximately 10 months of faint outburst activity after its discovery on February 5, 2023. NICER observations from March 7 to October 4 trace its spectral and timing evolution. The outburst profile and QPO properties suggest rebrightening after the primary episode, during which low-frequency QPOs decreased monotonically in frequency. Fits with both diskbb plus powerlaw and the Two Component Advective Flow (TCAF) model indicate that the source remained in harder spectral states throughout the observed epoch, with emission dominated by a hot, nonthermal Compton cloud. The authors classify the activity as a failed outburst because no softer spectral states were observed. TCAF spectral fitting yields a model-dependent mass estimate of 12.4 ± 1.7 solar masses.
PublicMAXI J1834-021, a suspected black hole in our Galaxy, underwent a faint outburst lasting about 10 months after its discovery in February 2023. Researchers used NICER observations covering March through October to follow changes in its X-ray brightness, spectrum, and repeating fluctuations. The fluctuations slowed during the main episode, and the observations suggest that the source brightened again afterward. Spectral models indicate that emission from a hot cloud dominated throughout the observations, without a transition to a softer X-ray state. This missing transition led the researchers to call it a failed outburst—not an absence of activity. One physical model estimates the object's mass at 12.4 ± 1.7 times the Sun's mass; that estimate depends on the model.
Young explorerScientists watched X-rays from something that might be a black hole. It had a long, faint burst of activity and may have brightened again afterward. Its X-ray flickers slowed down during the main burst. The X-rays never changed into a softer kind during the observations, so scientists call this a “failed outburst.” That does not mean nothing happened!
Nicholas Earl, K. Decker French, Jason T. Hinkle+5 more
AstronomerFEADME is a GPU-accelerated Python framework using JAX and NumPyro for differentiable forward modeling and Bayesian inference of broad Balmer-line profiles with relativistic elliptical accretion disks. The authors fit three model families per spectrum for 237 double-peaked emitters and five tidal disruption events (TDEs), selecting preferred models with WAIC. Posterior-quality filtering leaves 165 disk-bearing AGN and 27 usable TDE epochs. Under the common elliptical-disk prescription, AGN span a broad, continuous distribution of fitted geometries and kinematics, summarized by five phenomenological Gaussian-mixture morphology bins. TDE and AGN parameters overlap in radial scale, local broadening, and emissivity slope, while TDE epochs tend toward lower fitted eccentricities and broader non-disk Gaussian components. Comparison with published circular-disk plus spiral-arm fits to the same AGN spectra yields substantially different parameter distributions, showing strong dependence on the asymmetry prescription. Most sources favor a disk plus an additional broad-line component, consistent with, but not establishing, coexistence of disk emission and more isotropic or wind-driven gas.
PublicThe researchers introduce FEADME, software that models the shapes of broad hydrogen emission lines to investigate gas disks around black holes. They applied it to 237 objects with double-peaked emission lines and five events in which a star is torn apart by a black hole. After quality checks, their analysis retained 165 active galactic nuclei and 27 observations of the stellar-disruption events. In their elliptical-disk model, the active galaxies show a continuous variety of disk properties. The disruption events overlap with them in several fitted properties but tend to have less elongated disks and broader emission attributed to a separate gas component. These are model-dependent inferences: a different approach to explaining asymmetry in the same active-galaxy spectra gives substantially different disk properties. Most objects favor models with both a disk and another broad emission component, suggesting that other gas, possibly in a wind or moving in a wider range of directions, also contributes.
Young explorerGas swirling around black holes gives off light. Scientists made a computer tool to use patterns in that light to work out what the swirling gas might look like. They studied active galaxies and events where a black hole tears a star apart. Their models suggest that the gas disks come in many shapes, and that other gas often adds light too. But they cannot simply see these shapes: different ways of modeling the same light can give different answers.
Shining Yang, Jianbo Lu, Mou Xu+1 more
AstronomerThis study models charged-particle dynamics in magnetized Simpson–Visser (SV) black-bounce spacetime, whose regularization parameter a allows Schwarzschild, regular-black-hole, and traversable-wormhole geometries. A chi-squared analysis uses observed high-frequency quasi-periodic oscillations (HFQPOs) from GRS 1915+105, XTE 1550-564, and GRO 1655-40 to constrain spacetime and magnetic-field parameters. Within the model, the magnetic field significantly changes the charged-particle innermost stable circular orbit and epicyclic-frequency distribution, allowing additional resonance-model variants. AIC comparisons strongly favor ER_8, give moderate support to ER_3, substantially less support to ER_6 and ER_7, and essentially none to the remaining tested resonance models; BIC and Bayes-factor results are broadly consistent. For the better-supported models, the reported range is 0 ≤ a/M < 0.736 at 68% confidence. The authors interpret this as compatibility with a magnetized regular black hole, not a detection of that geometry. Their suggested connection between a small regularization parameter and quantum effects remains an interpretation rather than observational evidence for quantum effects.
PublicThe researchers tested a theoretical description that can represent ordinary black holes, regular black holes, or traversable wormholes, depending on one parameter. They compared models of rapid, nearly repeating signals observed from three microquasars with predictions involving charged particles moving near a black hole in a magnetic field. Their calculations show that the magnetic field changes the particles’ stable orbits and oscillation frequencies. Among the tested explanations for the signals, one resonance model, ER_8, received the strongest statistical support, while most alternatives received little or none. For the better-supported models, the fitted parameter range is compatible with a regular black hole. This does not establish that such a black hole exists in these systems. The authors also suggest a possible link to quantum effects, but the analysis does not demonstrate those effects.
Young explorerScientists studied fast, almost-repeating signals from three places in space. They tested different math ideas about tiny charged particles moving near black holes with magnetic fields. One idea matched the signals better than the others they tried. Their math allows a special kind of black hole, but it does not prove that this kind is really there.
Kratika Mazde, Angelo Ricarte, George N. Wong
AstronomerAn observed correlation among millimeter luminosity, X-ray luminosity, and mass in active galactic nuclei suggests a common emission source. The authors ray-trace five general relativistic magnetohydrodynamic simulations with dynamically important magnetic fields, including synchrotron emission, bremsstrahlung, and Compton scattering. Models with Eddington ratios comparable to those of the observed sample reproduce the correlation without tuning; lower-Eddington-ratio models depart from it, which the authors attribute tentatively to observational bias against extremely low accretion rates. Inverse Compton scattering dominates X-ray production in almost all models and in every model consistent with the observed correlation. The modeled relationship depends only modestly on spin. These results support a compact, hot, strongly magnetized accretion flow as an explanation for the millimeter and X-ray properties of low-luminosity active galactic nuclei. The effects of non-thermal electrons, weaker magnetic fields, and radiative cooling remain for future work.
PublicObservations of active galactic nuclei show a connection between their millimeter-wave brightness, X-ray brightness, and mass, suggesting that the two kinds of light share a source. Researchers tested this idea using five computer simulations of hot gas flowing toward a black hole, with magnetic fields strong enough to affect the gas motion. Models with relative feeding rates comparable to those in the observed sample reproduced the relationship without fine-tuning. Models with lower relative feeding rates did not; the authors suggest this may reflect how difficult such weakly feeding systems are to include in observations. In all models matching the observed relationship, X-rays came mainly from light gaining energy by scattering off electrons, rather than from bremsstrahlung radiation. Black-hole spin had only a modest effect on the modeled relationship. The study supports—but does not uniquely establish—a compact, hot, magnetized gas flow as the shared source. Other electron populations, weaker magnetic fields, and cooling still need investigation.
Young explorerAstronomers see a pattern in two kinds of invisible light coming from places where gas falls toward black holes. They made five computer pretend-worlds to see whether hot gas and strong magnetic fields could explain it. Some matched the pattern without special adjustments. In those models, tiny particles called electrons gave light extra energy to make X-rays. Models where the black hole was fed much more slowly did not match, perhaps because real places like those are hard to spot. The models make this explanation look promising, but there is more to test.
Georgios Dimopoulos, Claudio Ricci, Stéphane Paltani
AstronomerThe authors use RefleX ray tracing to construct two publicly available X-ray spectral table models with more realistic circumnuclear geometries than simplified slab or torus configurations. RXToPo includes an X-ray source, a dusty torus, and a hollow polar cone; RXagn1 additionally includes the accretion disk and broad line region. Both models span a wide X-ray energy range and were applied to the spectrum of NGC 424, demonstrating their potential for studying AGN dominated by reprocessed emission. The abstract does not report quantitative fit results or establish superiority over existing models.
PublicX-rays can help astronomers investigate material around growing supermassive black holes, but models that reproduce the observations often use simplified shapes. This study presents two publicly available computer models that calculate X-ray spectra using more realistic arrangements of surrounding material. Both include a dusty ring and a hollow cone extending toward the poles; one also includes the disk feeding the black hole and a region associated with broad emission lines. Applying the models to NGC 424 illustrates their promise for studying sources whose observed X-rays are dominated by radiation altered by surrounding material, rather than establishing that either model uniquely describes the source.
Young explorerScientists want to learn what is around giant black holes by studying a kind of light called X-rays. They made two computer models with shapes like a dusty ring and a hollow cone to work out how nearby stuff changes that light. They tried both models on a galaxy called NGC 424. The models look useful, but that does not mean scientists now know exactly how everything around its black hole is arranged.
Giuseppe Arrò, Vladimir Zhdankin, Fabio Bacchini
AstronomerThe authors introduce a pulsating-box setup for studying particle acceleration in high-beta plasmas undergoing compression–expansion cycles. Fully kinetic simulations show efficient acceleration by magnetic pumping, producing nonthermal energy distributions with power-law tails. The numerical results agree closely with a derived generalized maximum-entropy model that links the power-law index to the injected energy. These simulation and theoretical results may help explain high-energy particles in some high-beta space and astrophysical plasmas; the abstract reports no observational test.
PublicComputer simulations suggest that repeated compression and expansion can efficiently give particles more energy through a process called magnetic pumping. The simulated particle energies develop a high-energy tail described by a power law. A mathematical model developed by the researchers closely matches the simulations and connects the shape of that tail to the energy put into the system. This work could help explain energetic particles in some plasmas in space, but it does not establish that this process produces those particles in nature.
Young explorerScientists used a computer to model what happens when a material called plasma is squeezed and allowed to expand again and again. In their model, a magnetic process gave particles more energy, and some gained much more than others. Their math matched the computer results very well. This might help explain very energetic particles in space, but they have not shown that it happens there.
Floor S. Broekgaarden, Ana Lam, Sasha Levina+14 more
AstronomerThis study systematically compares formation-channel predictions from more than 200 isolated-binary population-synthesis simulations using a unified hierarchical taxonomy. For merging BBH and BHNS systems, predicted channel fractions span nearly the full 0–100% range from common-envelope (CE)-dominated to without-CE-dominated evolution, often with similar merger rates. Thus, merger rates alone cannot uniquely identify the underlying evolutionary pathways. In contrast, the simulations predict that more than 90%, and in some cases 100%, of BNS formation involves at least one CE phase, suggesting a qualitatively different role for CE evolution in these systems. Channel fractions depend primarily on prescriptions for mass-transfer stability, angular-momentum loss, CE efficiency, and supernova physics; their nonlinear, correlated effects limit the transferability of one-at-a-time parameter trends across frameworks. The authors call for transparent channel definitions, reproducible pipelines, systematic cross-code comparisons, and observational constraints beyond merger rates.
PublicMerging black holes and neutron stars could help astronomers reconstruct how massive stars formed and evolved, but that reconstruction depends on computer models. This study compares more than 200 simulations of pairs of stars evolving in isolation. For pairs that become two black holes or a black hole and a neutron star, models can predict similar merger rates while disagreeing sharply about how the pairs got close enough to merge. In particular, they disagree about whether the stars needed a common-envelope phase, when both share an envelope of gas. For pairs that become two neutron stars, however, the simulations predict that more than 90% go through at least one such phase. These are model predictions, not direct observations of the stars’ histories. The comparison shows why merger rates alone cannot settle which evolutionary routes occur, and why clearer model comparisons and other observational constraints are needed.
Young explorerScientists use computer models to imagine how two stars can change and eventually crash together as black holes or tiny stars called neutron stars. They compared more than 200 simulations. For pairs with a black hole, different models can predict about the same number of crashes even when the stars take very different paths. Some paths have both stars sharing a blanket of gas, and others do not. For two neutron stars, the models say almost all pairs share that blanket at least once. These are computer predictions, so scientists need more clues than just how often crashes happen to learn which paths real stars take.
Zhengyan Liu, Zelin Xu, Ji-an Jiang+20 more
AstronomerAn optical search with WFST targeted S251112cm, a GW candidate with possible subsolar-mass components, beginning 20.2 hours after the trigger. Three nights of observations covered about 780 square degrees and 51% of the updated localization probability. Four newly emerging, off-nuclear transients had host distances broadly consistent with the GW distance, but all evolved substantially more slowly than AT 2017gfo, ruling out AT 2017gfo-like behavior and disfavoring association as rapidly evolving kilonova counterparts. Combined WFST and DECam observations covered approximately 67% of the localization probability. Conditional on the counterpart lying within that footprint, a binary-neutron-star kilonova model grid disfavors dynamical ejecta masses of roughly 0.01 solar masses or greater, or wind ejecta masses of roughly 0.05 solar masses or greater, over most of the covered GW probability for viewing angles below 60 degrees and other parameters fixed to the AT 2017gfo best fit. A phenomenological analysis constrains rapidly evolving transients with half-rise times of at most two days to peak absolute magnitudes fainter than approximately -13. The authors describe these as the strongest northern-sky optical constraints to date for possible rapidly evolving counterparts to this emerging class of GW candidates.
PublicAstronomers searched for an optical flash associated with S251112cm, a gravitational-wave candidate that may involve objects less massive than the Sun. WFST began observing 20.2 hours after the alert and searched for three nights. It found four possible flashes at broadly compatible distances, but all changed too slowly to resemble the reference kilonova AT 2017gfo, making them unlikely rapidly evolving counterparts. Combining WFST and DECam observations covered regions containing about 67% of the estimated probability for the source's location. If the counterpart was inside that area, the observations disfavor some models of bright merger flashes, including models with larger amounts of expelled material under specified viewing and model assumptions. These are limits on possible counterparts, not a confirmed optical detection or proof that the source contained an object lighter than the Sun.
Young explorerScientists got an alert about a possible crash in space and used a telescope to look for a flash. They found four lights that changed, but each changed too slowly to look like the quick flash they were checking for. Two telescopes together searched a big part of where the crash might have been, but not all of it. If a flash was in the searched area, the pictures help show how bright some kinds of quick flashes could have been. The scientists did not confirm a flash from this possible crash.
M. C. Baglio, S. E. Motta, A. P. Nitindala+1 more
AstronomerThis review chapter synthesizes five decades of observations of neutron star low-mass X-ray binaries, following Roche-lobe overflow through the accretion disc to the stellar surface. It covers atoll and Z-sources, ultracompact binaries, accreting millisecond pulsars, and transitional millisecond pulsars, linking spectral states, timing, and multiwavelength behaviour to inner-flow physics. Topics include Type-I bursts as probes of nuclear burning and stellar structure, boundary and spreading layers, and the role of relativistic jets and ionised winds in the accretion-ejection cycle. IXPE polarimetric results, alongside optical and infrared polarimetry, offer new but model-dependent constraints on emission-region geometry that spectroscopy alone cannot resolve.
PublicThis chapter reviews what five decades of observations have taught astronomers about neutron stars drawing gas from low-mass companion stars. The gas forms a disc and releases gravitational energy as it falls toward the neutron star, whose solid surface and magnetic field help shape the system's behaviour. The review explores different kinds of these binaries, bursts caused by nuclear burning, regions where incoming gas slows onto the surface, and jets and winds that carry material away. It also presents results from IXPE, which measures X-ray polarization—the orientation of the light's oscillations. These measurements provide new clues about the arrangement of the emitting regions, beyond what X-ray spectra alone can reveal, but the inferred geometry depends on the models used to interpret the data.
Young explorerA neutron star is a very dense star that can pull gas from a nearby star. The gas swirls around it in a disc and gives off X-rays as it falls in. This chapter brings together what scientists have learned by watching these pairs of stars, including bright bursts and gas shooting or blowing away. It also describes measurements of how the X-ray light wiggles. Those clues help scientists work out where the light comes from, but they do not give one certain picture.
M. H. Reno, T. Venters, M. Abrate+97 more
AstronomerPOEMMA-Balloon with Radio (PBR), planned for a super-pressure balloon flight in Spring 2028, combines fluorescence and optical Cherenkov telescopes with a radio instrument as a pathfinder for POEMMA. One objective is astrophysical-alert follow-up through atmospheric tau decays from Earth-skimming tau neutrinos. Motivated by KM3NeT's reported muon event with E_mu = 120 (+110, -60) PeV, the authors assess PBR's sensitivity to a specific boosted-dark-matter scenario, using that scenario and the observation to set a fluence scale. For spectra above roughly 10^8 GeV, their analysis indicates discovery potential at dark-matter energies above 10^9 GeV, extending down to 1.5 × 10^8 GeV for some beyond-Standard-Model parameters. These are model-dependent capability estimates, not a dark-matter detection or an established explanation of the KM3NeT event. The methodology can also apply to other beyond-Standard-Model physics affecting tau production in Earth.
PublicA balloon mission planned for Spring 2028 could help test an explanation involving very energetic dark matter for an unusual particle event reported by KM3NeT. The mission, called POEMMA-Balloon with Radio, is designed in part to look for signals from particles called taus decaying in the atmosphere after Earth-skimming neutrino interactions. The researchers assess its capabilities using one specific boosted-dark-matter model and the reported event to estimate how much dark matter might arrive. Their analysis suggests that the mission could discover such a source at sufficiently high energies, with the accessible energy range depending on the model's unknown parameters. This is a forecast of what the instrument might detect, not evidence that dark matter caused the reported event. The approach could also test other proposed physics that changes how taus are produced inside Earth.
Young explorerScientists plan to send a special telescope up on a balloon in Spring 2028. It will look for tiny flashes made when certain particles break apart in the air. They worked out whether it might also help find signs of very fast dark matter. In one possible dark-matter story, they think it could, if the particles have enough energy. But this is a prediction about what the telescope might see, not a discovery of dark matter.
Anson Kost, Huaiyu Duan
AstronomerThis theoretical study applies Landau damping to collective flavor excitations in dense neutrino media and explicitly demonstrates weak damping of stable and metastable modes. For a continuous neutrino energy distribution, infinitely many dispersion-relation branches can exist and extend to large wave numbers. If the distribution of the difference of neutrino lepton numbers (DLNs) has one or more zero crossings, the least-damped resonant branches and metastable branches can undergo inverse Landau damping at certain wave numbers and become unstable. The authors also introduce convolved DLN distributions as a framework for understanding the physical origins of slow and fast flavor instabilities in core-collapse supernovae and neutron star mergers. These are theoretical findings and interpretations, not reported astronomical observations.
PublicNeutrinos can change between types called flavors. This theoretical study examines how collective patterns of flavor change behave in a dense neutrino gas. It finds that stable and temporarily stable patterns fade only weakly. When neutrino energies span a continuous range, infinitely many distinct branches of these patterns can exist. Under particular conditions in the neutrino distribution, some patterns can grow instead of fading, becoming unstable. The authors also introduce a mathematical tool to help explain flavor instabilities in exploding stellar cores and merging neutron stars. The abstract reports theory, not observations of these events.
Young explorerNeutrinos are tiny particles that can change kinds. Scientists used math to study how lots of them change together. Some patterns fade slowly, but under special conditions, others can grow. This work may help explain what neutrinos do when stars explode or neutron stars come together; it is not a report of watching this happen.
Mohamed Ould El Hadj, Sam R. Dolan
AstronomerThis theoretical study introduces a Debye-inspired series decomposition for the time-domain response of compact, horizonless bodies to scalar-field perturbations. It separates exterior propagation, surface reflection, and successive interior transmissions, with a geodesic interpretation. Applied to two illustrative Schwarzschild-star spacetimes—a neutron-star-like model with R>3M and an ultracompact model with R<3M—the closed-form reconstruction agrees well with the exact waveform and converges even at early times, capturing the prompt response. In the neutron-star-like case, low-order terms mainly describe ringdown and a non-modal contribution associated with the sub-threshold branch cut. In the ultracompact case, the series separates a prompt/ringdown contribution from successive echo-like wavepackets arising through repeated interior propagation. The proposed Debye-QNM description identifies modes within individual propagation channels, complementing the standard QNM description of collective resonances obtained by resumming those contributions. These are results for idealized scalar-field models, not observational detections.
PublicThe researchers present a new mathematical way to understand how a wave responds to a very compact body without an event horizon. Their method separates the signal into parts that travel outside the body, reflect from its surface, or pass through its interior repeatedly. They test it on two idealized models, one resembling a neutron star and another that is more compact. The reconstructed signals agree well with the exact model waveforms, including their earliest features. For the more compact model, the method reveals an initial response followed by echo-like wave packets produced by repeated travel through the interior. It also complements an existing way of describing the signal's ringing by distinguishing resonances of individual travel routes from collective resonances. The study concerns theoretical scalar-field waves, not echoes detected from real astronomical objects.
Young explorerImagine a wave meeting a very tightly packed ball in space. Some of the wave goes around it, some bounces off, and some travels inside. The scientists made a new math recipe that keeps track of those different trips. They tried it on two pretend space objects, and it matched the waves in their models well, even at the start. In the more tightly packed model, waves traveling inside again and again made little signals like echoes. These are things found in the math models, not echoes heard from a real star.
Sara Rinaldi, Olindo Zanotti, Michael Dumbser
AstronomerThis theoretical and numerical study models relativistic detonations by incorporating reaction energy into the total energy density and evolving the reactant mass fraction, preserving the formal structure of mass and energy-momentum conservation and the inert Rankine-Hugoniot relations. A shock-following finite-volume ALE scheme with second-order TVD reconstruction is operator-split from a locally implicit reaction solver. The authors also propose an efficient conserved-to-primitive variable conversion algorithm. They numerically resolve Zel'dovich-von Neumann-Doering detonation profiles up to shock-front Lorentz factors of approximately 7. Their analysis identifies a special-relativistic departure from Newtonian behavior: the Zel'dovich pressure jump reaches a minimum and then increases with mass flux, rather than decreasing monotonically. Possible implications for extractable energy are suggested, not established; these are theoretical and numerical findings, not observations.
PublicThe researchers used theory and computer calculations to study detonation waves moving at speeds where special relativity matters. Their model tracks both the energy released by a reaction and how much unreacted material remains. Their numerical method follows the moving shock and calculates the wave's internal structure, reaching shock-front Lorentz factors of about 7, a measure of relativistic motion. The analysis reveals an unexpected pressure trend: as more material passes through the shock per unit area and time, a characteristic pressure jump first falls and then rises. In the Newtonian case, it only falls. This difference might affect how much energy can be extracted from such a wave, but the paper does not establish that consequence or report an astronomical observation.
Young explorerThe scientists used math and computers to study an explosion wave moving so fast that the special rules for things near the speed of light matter. They found that, in their calculations, a pressure jump at the wave first gets smaller and then bigger as more stuff flows through it. Without those special rules, the pressure jump just gets smaller. This might change how much energy could be taken from the wave, but they do not yet know that. They studied a model, not an explosion they watched in space.
Jaroslaw A. Nowak
AstronomerStrangeMC simulations of charged-current (anti)neutrino interactions in argon predict that reconstructed Lambda yields and momenta, together with a kaon-vetoed Sigma+ tag, respond to in-medium hyperon potentials at SBND and DUNE energies. A detector-level forecast treats production cross sections, fluxes and efficiencies as nuisance parameters and uses muon kinematics to calibrate production. It projects a determination of U_Lambda at rho* = 0.82 rho_0, independent of the potential's low-density exponent, with 1.5 MeV statistical and ±31 MeV total uncertainty. The largest uncertainty contribution, 18 MeV, comes from the convention for applying the potential in the cascade. For momentum-independent potentials, this would provide a check with different systematics on the tighter hypernuclear constraint of ±3.3 MeV at rho*. U_Sigma remains undetermined. In the GM1 and FSU2H relativistic mean-field equations of state anchored to hypernuclear and Sigma-atom depths, the maximum neutron-star mass depends on Lambda NN repulsion, which these data do not constrain.
PublicParticles called hyperons can be created when neutrinos or antineutrinos interact inside atomic nuclei. As the hyperons pass through nuclear matter, their motion carries information about the forces they experience—forces that also affect whether hyperons appear inside neutron stars. Using simulations of argon, the researchers forecast how experiments at SBND and DUNE energies could test the potential experienced by Lambda hyperons. This is a forecast, not a reported measurement: the projected total uncertainty is ±31 MeV, much larger than the statistical uncertainty of 1.5 MeV, with the largest contribution coming from how the simulation applies the potential. The proposed measurement would offer an independent check of an existing, more precise constraint, but would not determine the Sigma potential. It also would not constrain the Lambda-related repulsion that controls the maximum neutron-star mass in the two stellar models considered.
Young explorerScientists used a computer to imagine tiny particles called hyperons moving through the middle of an atom. How they move could help us learn about the pushes and pulls they feel. Those pushes and pulls also matter inside very dense stars called neutron stars. The computer study suggests a way future measurements could check one of these pushes and pulls, but there is still a lot of uncertainty. It does not tell us how heavy a neutron star can be.
Jaroslaw A. Nowak
AstronomerThis StrangeMC-based study forecasts constraints on hyperon single-particle potentials from charged-current neutrino and antineutrino interactions on argon-40 at SBND and DUNE energies. Reconstructed Lambda yields and momenta, together with a kaon-vetoed final-state-interaction Sigma+ tag, probe the potentials. A detector-level Fisher analysis, profiling production uncertainties and using muon kinematics to calibrate production, finds the best sensitivity to U_Lambda at rho* = 0.82 rho_0, independently of the low-density power-law exponent gamma. The forecast statistical precision is 1.5 MeV, but the total uncertainty is ±31 MeV; the largest contribution, 18 MeV, comes from the cascade convention for applying the potential. This would provide a different-systematics check of the ±3.3 MeV hypernuclear constraint at rho*, rather than a competitive precision determination. U_Sigma remains unconstrained. Separately, relativistic mean-field calculations for n p Lambda Sigma- matter, anchored to hypernuclear and Sigma-atom depths and including the phi meson, give maximum masses of 1.94 solar masses for GM1 and 2.03 solar masses for FSU2H. These masses depend on a high-density Lambda NN term that the neutrino observables do not constrain, leaving the high-density aspect of the hyperon puzzle unresolved.
PublicHyperons are particles that could appear inside neutron stars, making their matter less resistant to compression and reducing the largest mass a star can support. This study uses computer calculations to forecast whether neutrino interactions in argon could help test how hyperons behave in nuclear matter. At energies relevant to SBND and DUNE, the proposed analysis could check an existing constraint on Lambda hyperons using different sources of experimental uncertainty. However, its forecast total uncertainty is ±31 MeV, much larger than the existing ±3.3 MeV constraint, and it would not constrain the Sigma hyperon potential. Separate neutron-star calculations give maximum masses of 1.94 and 2.03 times the Sun's mass for two models. Those predictions still depend on an interaction at high density that this neutrino approach cannot determine, so the study does not settle how hyperons affect the heaviest neutron stars.
Young explorerNeutron stars are incredibly tightly packed stars. Tiny particles called hyperons might be inside them and could change how much weight they can hold. Scientists used a computer to explore a test: send tiny particles called neutrinos into the centers of argon atoms and study the hyperons they make. The test might help check how one kind of hyperon behaves, but it would still leave big uncertainties. It would not yet tell us what those particles do deep inside a neutron star.
Mario Misas Arcos, Alberto T. Pérez, Carlos F. Sopuerta
AstronomerNumerical calculations identify intrinsic exceptional points and eigenstate hysteresis in the quasinormal-mode spectrum of Kerr-Newman black holes, unlike the previously reported Kerr case requiring an auxiliary scalar field. A hyperboloidal formulation of the coupled gravito-electromagnetic Teukolsky equations, solved with a Chebyshev pseudospectral method, yields four exceptional points in the ℓ=m=2 spectrum at up to 99.974% of extremality, including one associated with a new repulsion. The mode gaps close with square-root branch-point behavior. Quasistatic parameter loops enclosing one or more exceptional points exchange the coalescing modes, confirming eigenstate hysteresis in these calculations rather than through astronomical observations.
PublicCalculations of rotating, electrically charged black holes reveal special points where two of their characteristic ringing patterns merge. The researchers locate four such points, including ones extremely close to the black holes’ theoretical extremal limit. When they slowly trace closed paths around these points in the calculation’s parameter space, the merging patterns exchange identities rather than simply returning to their starting states. This is called eigenstate hysteresis. The effect arises without the extra scalar field needed in earlier work on rotating, uncharged black holes. These are numerical findings, not observations of real black holes.
Young explorerA black hole can have different ringing patterns, a little like a bell. Scientists used computer calculations to study black holes that spin and have electric charge. They found special places in their calculations where two ringing patterns become the same. Slowly changing the settings in a loop around those places can make the patterns swap. They found this in the calculations, not by watching a real black hole.
Samuel S. H. Tse, Qishan Liu, Kenny C. Y. Ng+2 more
AstronomerThe study evaluates a proposed direct-detection channel for light dark matter boosted through interactions with cosmic rays: quasi-elastic scattering on carbon that ejects a neutron in a large liquid scintillator detector. The signature pairs a prompt signal from neutron propagation with a delayed neutron-capture gamma ray after approximately 210 microseconds. The authors project that a 100 kt·yr exposure could probe parameter space beyond that accessible to free-proton signals studied previously. They also assess directional reconstruction using the displaced neutron-capture vertex, but find no material sensitivity improvement because of the large nucleon scattering angle. These are sensitivity projections, not a reported dark-matter detection.
PublicThe researchers explore a possible way to search for light dark matter after cosmic rays give it extra energy. In their proposed search, dark matter would strike carbon in a large liquid detector and knock out a neutron. A prompt signal followed about 210 millionths of a second later by a gamma ray from the neutron's capture would provide a distinctive paired signature. They predict that an exposure of 100 kiloton-years could test dark-matter possibilities beyond those covered by earlier studies of signals from free protons. Trying to infer the incoming direction from where the neutron is captured adds little sensitivity, because the scattering can send the neutron off at a large angle. The study does not report finding dark matter.
Young explorerScientists are thinking about a new way to look for invisible stuff called dark matter. If tiny bits of it get a boost from fast particles in space, they might bump into carbon in a big tank of liquid and knock out a particle called a neutron. The neutron could make one signal and then, a little later, another when it gets caught. The scientists think looking for these pairs could help search in new ways, but they have not found dark matter this way. Following where the neutron goes would not help much, because the bump can send it far off course.
