Conor Larison, Justin D. R. Pierel, Matthew Siebert+69 more
AstronomerSN Ares is a strongly lensed supernova at a spectroscopic redshift of 1.276 ± 0.002 in a massive, triply imaged host behind MACS J0308.9+2645. JWST/NIRSpec spectra show He features at 5876, 7065, and 10830 Å, together with Hα and Paβ. Comparisons with local core-collapse supernova spectra and light curves support a Type IIb classification, making Ares the highest-redshift spectroscopically identified member of this class. Local Type IIb light-curve comparisons place the spectrum at an estimated 34 days after radioactive peak in the rest frame, with uncertainties of −9 and +10 days, probing late-photospheric stripped-envelope evolution. A cluster lens model based on recent JWST data identifies Ares as the first-arriving image and predicts two further images in roughly 70 years or more, with magnifications of about 5 and 1.5. Planned NIRSpec multi-object spectroscopy is intended to refine the lens model, time delays, and magnifications and provide a template spectrum at the supernova position.
PublicAstronomers have discovered SN Ares, an exploding star whose light is magnified by the gravity of the galaxy cluster MACS J0308.9+2645. Its host galaxy appears in three images because the cluster bends its light along different paths. JWST spectra reveal both helium and hydrogen, and comparisons with nearby supernovae support classifying Ares as Type IIb, a kind of stellar explosion that has lost part of its outer envelope. It is the most distant member of this class yet identified through spectroscopy. Comparisons with nearby examples suggest that the spectrum caught Ares about 34 days after its radioactively powered brightness peak, measured in the supernova's own frame of time, with an uncertainty of roughly ten days. A model of the cluster's gravitational lens predicts that light from the same explosion will arrive along two other paths in about 70 years or more. These repeat appearances have not yet been observed. Planned JWST observations aim to improve the predicted arrival times and magnifications.
Young explorerAstronomers found an exploding star called Ares very far away. A big group of galaxies in front of it bends and brightens its light, a little like a magnifying glass. Using the James Webb Space Telescope, astronomers found signs of hydrogen and helium in the light, helping them work out what kind of explosion it was. Their model says light from the same explosion is taking two other routes to us and could show up again in about 70 years or more. Those extra views have not arrived yet, and astronomers plan more observations to make their predictions better.
Taili Yi, Jia-Wen Li
AstronomerThe study models magnetocentrifugal outflows from magnetically arrested discs (MADs) using steady, axisymmetric, trans-magnetosonic MHD equations along prescribed poloidal field lines, with disc scalings and base conditions motivated by GRMHD simulations. Inner-disc solutions accelerate strongly, reaching UFO-like velocities, while larger footpoint radii yield systematically slower outflows. The formal Newtonian solutions can enter the mildly relativistic regime, a limitation to bear in mind. Magnetic lever arms are typically several tens and can reach about 100. The model estimates that magnetic outflows remove about 55% of the angular momentum estimated between the disc boundaries; the fiducial mass-loss rate is about 14% of the disc accretion rate. These model results suggest, rather than observationally establish, that MAD outflows could explain ultra-fast absorbers in low-luminosity AGNs and X-ray binaries while efficiently removing disc angular momentum.
PublicFast-moving gas is often seen escaping from systems where black holes draw in matter, but what launches it remains uncertain. This study uses a mathematical model to explore whether strong magnetic fields in a magnetically arrested disc could drive that escape. The model produces faster gas from the inner disc and slower gas from farther out. It also suggests that the escaping gas can carry away a substantial amount of the disc's rotational momentum, helping matter move inward. In the reference model, the escaping mass amounts to about 14% of the disc's mass-accretion rate. These are model findings, not new observations, and the calculation uses Newtonian physics even where its predicted speeds become mildly relativistic. The authors propose this magnetic mechanism as a possible explanation for ultra-fast absorbing gas in certain active galaxies and X-ray binaries.
Young explorerGas can swirl around a black hole, and some of it rushes away. Scientists used a math model to see whether strong magnetic fields could help send that gas outward. In their model, gas starting closer to the black hole goes faster than gas starting farther away. The escaping gas also takes away some of the swirling motion, which can help other gas move inward. This is a possible explanation, not proof of how real black holes do it, and the model has limits when the gas gets very fast.
Fan Wu, Benzhong Dai
AstronomerThis study models diffuse neutrino emission from radiatively inefficient inner accretion flows in low-luminosity active galactic nuclei (LLAGNs) in the magnetically arrested disk (MAD) state, including all three flavors and both proton–proton and proton–photon production channels. If nonthermal protons receive approximately 5% of the accretion power, current IceCube data limit the fraction of LLAGNs hosting such neutrino-producing MAD flows to at most 2.3 × 10^-3; a smaller proton energy allocation permits a proportionally larger fraction. Independently, assuming that the comoving density of low-excitation radio galaxies approximately equals that of MAD-state LLAGNs gives an estimated MAD fraction of 1.6 × 10^-3. For this fraction, the predicted all-flavor intensity peaks at a neutrino energy of approximately 1.5 PeV, with Eν²Φν approximately 2.6 × 10^-9 GeV cm^-2 s^-1 sr^-1, compatible with current IceCube data and testable by IceCube-Gen2. Current data are beginning to challenge several earlier LLAGN RIAF predictions; the modeled MAD contribution can dominate beyond the cutoffs of most earlier spectra considered here. The inferred small fraction suggests, rather than establishes, that few LLAGNs receive sufficient coherent net poloidal magnetic flux.
PublicGas falling toward the central black holes of faint active galaxies could help produce the high-energy neutrinos arriving from across the universe. This study calculates the contribution from a strongly magnetized type of inflow called a magnetically arrested disk; it does not establish that these galaxies are the sources. If about 5% of the inflowing gas's power goes into high-energy protons, existing IceCube measurements allow no more than about 0.23% of these galaxies to host the modeled neutrino-producing flows. If less power goes into those protons, more galaxies could qualify. A separate estimate, based on an assumed link to a class of radio galaxies, puts the fraction near 0.16%. The resulting predicted neutrino signal is consistent with current measurements and could be tested by IceCube-Gen2.
Young explorerSome black holes have hot gas swirling around them, with strong magnetic fields. Scientists calculated whether this gas could make tiny particles called neutrinos that reach us from space. Their idea fits today's measurements only if these special swirls are rare, unless they give less energy to the particles that make neutrinos. A future detector could help test the idea, but we do not yet know whether these swirls make the neutrinos we see.
Ning-Ning Guo, Jian-Fu Zhang, Hua-Ping Xiao+1 more
AstronomerThis theoretical study incorporates synchrotron self-absorption (SSA) into polarized synchrotron radiative transfer and uses 3D MHD turbulence simulations to assess its effects on polarization statistics beyond the optically thin regime. In the simulations, SSA suppresses polarized intensity, steepens its low-frequency power-law slopes, and reduces scale-dependent anisotropy. Despite these changes, the magnetic-turbulence scaling slope remains recoverable. The results support extending polarization-statistical diagnostics to optically thick environments with SSA and provide a theoretical basis for interpreting multi-frequency radio polarization observations, rather than an observational validation.
PublicResearchers used three-dimensional computer simulations to study how turbulent, magnetized gas affects polarized radio emission when some of that emission is absorbed by the same material that produces it. In the simulations, this self-absorption weakens the polarized signal, steepens its low-frequency power-law behavior, and makes its patterns less direction-dependent across different scales. Even so, the researchers can still recover the scaling slope that describes the magnetic turbulence. The study provides theoretical support for using radio polarization to investigate turbulence in environments where self-absorption matters; it does not report a test using actual observations.
Young explorerScientists made a computer model of a place where magnetic fields swirl around and make radio light. Some of that light gets swallowed up before it escapes, making the light weaker and changing its patterns. But in the model, scientists could still read an important clue about the magnetic swirls. This suggests the light could help them study places like this in space, though this study used a computer model rather than observations of a real place.
Arthur G. Suvorov
AstronomerMagnetar outbursts may involve crustal failure, with excited magnetoelastic modes potentially explaining quasi-periodic oscillations observed in some X-ray tails. Unlike earlier torsional-mode calculations that assumed an intact crust, this study develops a code solving the axial sector of the linearised Einstein-Maxwell-Euler equations in a cavity containing inelastic 'plastic islands'. Tracking shear stresses allows cells to switch dynamically from elastic to inelastic states. In the simulations, these islands promote phase mixing; constructive mixing of reflected waves can trigger collective failure across large regions if the initial kick is sufficiently strong. Progressive loss of elastic support produces transient spectral features, offering a possible explanation for the variable occurrence of oscillations following giant flares and magnetar storms, rather than establishing their origin.
PublicSome high-energy outbursts from magnetars may be linked to failures in their crusts. Vibrations set off by such failures could explain the nearly repeating variations astronomers observe in X-rays after some outbursts. Earlier calculations treated the crust as intact; this study instead models regions that can lose their elastic strength as stresses build. In the simulations, these weakened patches cause vibrations to get out of step. If the initial jolt is strong enough, reflected waves reinforcing one another can make large areas fail together in an avalanche. As the crust loses elastic support, temporary features appear in the simulated vibration spectrum. The authors suggest this could help explain why oscillations appear inconsistently after magnetar outbursts, but the connection remains an interpretation.
Young explorerA magnetar is a kind of star that can give off powerful bursts. Scientists think its hard outer crust might sometimes break and make the star shake. They made a computer model where parts of the crust can stop springing back when pushed. In the model, a strong enough shake can make big patches give way together. The shaking also changes as more patches weaken. This might help explain why the X-ray light after some bursts has a repeating wiggle that does not always last, but scientists have not shown that this is what really happens.
Finia P. Jost, André da Silva Schneider, Almudena Arcones+4 more
AstronomerThe authors construct finite-temperature, composition-dependent EOS tables using an energy-density functional constrained by ab initio nuclear-matter calculations and neutron-star observations. Its distinguishing feature is a non-monotonic nucleon effective mass that increases above saturation density. They test nuclear-matter uncertainties in spherically symmetric core-collapse supernova simulations with an effective treatment of convective mixing. Within current constraints, incompressibility, symmetry energy, and high-density pressure cause only modest differences in early post-bounce evolution. Effective-mass density dependence has a much larger influence, especially in a high-core-compactness progenitor, where it changes the proto-neutron star contraction history qualitatively and can alter the explosion outcome relative to mean-field effective-mass behaviors. These simulation results depend on progenitor compactness and identify effective-mass parameterization as the dominant EOS uncertainty among the properties examined.
PublicThe researchers built new tables describing how hot, dense matter behaves and used them in computer simulations of collapsing stars. The tables are based on a nuclear model informed by calculations and neutron-star observations. Among the uncertain properties tested, the strongest influence came from how the effective mass of protons and neutrons—a quantity describing their behavior within dense matter—changes with density. In a model star with a highly compact core, this changed how the forming neutron star contracted and could change whether an explosion occurred. Other tested properties produced only modest differences soon after the collapsing core bounced. These are simulation findings, not observations of explosions, and their strength depends on the star's core compactness. The simulations assumed spherical symmetry and used an approximate treatment of convective mixing.
Young explorerScientists used computers to study what might happen when a star's middle squeezes down very tightly. They tried different rules for how the tiny pieces inside it behave. One rule made a much bigger difference than the others: how those pieces act as the material gets more crowded. In one model with a very tightly packed middle, changing that rule could change whether the star exploded. This happened in a simplified computer model, so it does not tell us what every real star will do.
J. M. Pollin, S. Curtis, C. Fröhlich+6 more
AstronomerThis modeling study compares explodability and nucleosynthesis for 66 non-rotating, solar-metallicity single-star and binary-stripped progenitors with ZAMS masses of 11–45 solar masses, using the spherically symmetric PUSH framework and nucleosynthesis post-processing. Both populations explode up to 22 solar masses; stripping changes explodability at higher initial masses. Successful models have similar explosion energies of about 0.4–1.3 B and remnant masses of about 1.4–2.0 solar masses. Yield differences are largest at low initial masses, particularly for explosive oxygen and silicon burning. Nickel-56 yields and iron-group abundances broadly match observations of core-collapse supernovae and HD 84937. Explodability is strongly treatment-dependent: comparison with time-dependent mixing-length calculations and a two-parameter criterion finds only five progenitors classified as successful explosions by all three approaches, although yield patterns can remain broadly similar among models that explode across treatments. Salpeter initial-mass-function-weighted yields differ by about 20% for most elements between populations, while potassium is enhanced by about a factor of 3.4 in stripped models, driven by the lowest-mass progenitors. Stripped models better match APOGEE-inferred empirical core-collapse S/Mg, K/Mg, and Ca/Mg ratios, but both populations overproduce sodium. The results support accounting for binarity while emphasizing uncertainty in predicted explosion outcomes.
PublicA companion star can strip material from a massive star and change how it later explodes and produces chemical elements. Researchers simulated 66 stars, comparing stars evolving alone with stars stripped by a companion. In their main calculations, both groups exploded at initial masses up to 22 times the Sun’s mass; stripping changed which heavier stars exploded. The strongest differences in element production appeared among the lower-mass stars studied. After weighting the models by a distribution of initial stellar masses, the stripped population produced about 3.4 times as much potassium, while most element yields differed by about 20%. Its sulfur, potassium, and calcium ratios relative to magnesium also agreed better with ratios inferred from observations, although both populations produced too much sodium. These are model results, not newly observed explosions. Different calculation methods disagreed substantially about which stars explode, even when their predicted element patterns were broadly similar. The study highlights both the importance of stellar companions and uncertainty in explosion modeling.
Young explorerA big star can have a companion that takes away some of its outer material. Scientists used computer models to ask whether this changes how the star explodes and which kinds of atoms it makes. The models suggest that it can: stars that lost material sometimes exploded differently and made more potassium. But different computer methods did not always agree about which stars would explode, so the answers are still uncertain.
Luming Sun, Xinwen Shu, Jiazheng Zhu+17 more
AstronomerLate-time HST/WFC3 and Gemini-N/GMOS observations of EP241021a at z=0.748 reveal a star-forming dwarf disk host after the transient faded below detection at approximately 300 days. The host has an effective radius of 1.7 kpc, a stellar mass of approximately 3 × 10^8 solar masses, and a star formation rate of approximately 5 solar masses per year. Combined with previous very long baseline interferometry, the observations place the transient in the disk at a projected nuclear offset of 0.95 ± 0.13 kpc. Host-subtracted optical light curves show the rebrightening ending near day 47, followed by a decline with a power-law index steeper than −3.3, coincident with a similar X-ray drop. The authors interpret this synchronous decline as consistent with jet shut-off and argue that month-long jet activity suggests sustained accretion fed by a tidal disruption event. The off-nuclear position and starburst host slightly favor a post-supernova micro-TDE, in which a natal kick sends a newborn compact object into a disruptive encounter with its binary companion. This interpretation is not definitive: the stellar-explosion versus TDE classification remains debated, and TDEs involving an off-nuclear intermediate-mass black hole or a stellar-mass black hole following dynamical scattering in a dense cluster remain viable.
PublicAstronomers studied the galaxy hosting EP241021a, an unusual X-ray flash whose prolonged X-ray glow and later optical brightening are difficult to explain with the traditional jet afterglow model. Once the flash had faded below detection about 300 days later, observations revealed a small disk galaxy forming stars rapidly. The event occurred in the galaxy’s disk, about 0.95 kiloparsecs from its center in projection. After accounting for the galaxy’s light, the researchers found that the optical brightening ended around day 47 with a sharp fall, matching a similar X-ray decline. They interpret this as possible evidence that a jet switched off after roughly a month of being powered by matter falling onto a compact object. A star being torn apart could supply that matter. The location and host galaxy slightly favor a scenario in which a supernova gives a newborn compact object a kick that leads it to tear apart its companion star. That explanation is not established: other star-disruption scenarios remain possible, and whether the event was a stellar explosion or a tidal disruption is still debated.
Young explorerAstronomers watched a strange flash in a small galaxy where many stars are being born. Later, its visible light and X-ray light both dropped quickly at about the same time. That might mean a powerful stream of material switched off. One idea is that a star exploded and left behind a tiny, very heavy object. A kick from the explosion may have sent that object toward a nearby partner star, tearing the partner apart and giving the flash more fuel. The flash happened away from the galaxy’s middle, which makes this idea a little more likely, but the astronomers still do not know for sure what caused it.
Manja L. Zimmerer, Thomas Siegert, Niklas C. Bauer+11 more
AstronomerUsing 20 years of INTEGRAL/SPI observations of the 1.8 MeV line, the authors test radial distributions of Galactic 26Al and compare the inferred mass distributions with Galactic chemical evolution models. In their baseline analysis, every tested source model favors a substantial classical-nova contribution, with best-fit fractions of 77–84%, contrasting with earlier estimates of negligible contributions or less than 10%. This interpretation alleviates the model overprediction of the 60Fe/26Al ratio and reduces the star formation rate inferred from 26Al to 1–2 solar masses per year, versus the greater than 5 required by previous population-synthesis fits. These source fractions remain model-dependent: directly separating nova and massive-star contributions is difficult. Future MeV telescopes could potentially identify individual massive stars such as Gamma-2-Velorum.
PublicRadioactive aluminum in the Milky Way provides clues to recent star formation, but interpreting it depends on which stars produce it. The researchers analyzed 20 years of gamma-ray observations and compared different models of how this material is distributed across the Galaxy. Their baseline fits favor classical novae supplying 77–84% of the signal, far more than earlier studies suggested. If that interpretation is correct, less aluminum would come from massive stars, lowering the inferred star formation rate to about 1–2 solar masses per year and easing a mismatch involving radioactive iron. The observations do not directly separate the sources, so the large nova contribution is a model-based inference rather than a firm measurement.
Young explorerScientists studied a special kind of light from radioactive aluminum in our galaxy. They used computer models to work out where the aluminum might come from. Their best-fitting models suggest that star events called novae could make much more of it than people thought. If so, the galaxy might be making new stars more slowly than earlier estimates suggested. But telling the different sources apart is still hard.
Victor Doroshenko
AstronomerThe author presents an all-sky eROSITA source catalogue extracted from the June 2020 eRASS1 press-release image, rather than the underlying survey data, which remain publicly available for only half the sky. The catalogue contains approximately 63,000 sources, with estimated completeness of about 50% above 3 × 10^-13 erg cm^-2 s^-1 in the 0.2–2.3 keV band and positional accuracy of roughly 1 arcmin. Validation uses the full eRASS1 catalogue over half the sky and several external catalogues. The resulting catalogue is described as comparable to 2RXS and provides initial coverage of the eastern Galactic hemisphere, where about 11,000 detections lack counterparts in ROSAT or other public X-ray catalogues; these are expected, but not established, to be genuine new X-ray sources. Calibrated HEALPix maps and the complete analysis pipeline are also released, supporting reproducibility and full-sky studies of extended emission and Galactic absorption.
PublicA researcher has turned a publicly released eROSITA X-ray picture of the whole sky into a catalogue of about 63,000 sources. Although the telescope surveyed the entire sky more than four times, the underlying data for only half the sky are publicly available, making this image-based catalogue a way to explore the other half. Checks against existing catalogues indicate positions accurate to about one arcminute, but the catalogue is estimated to include only about half the sources above a stated X-ray brightness threshold. In the eastern half of our Galaxy's sky, about 11,000 detections have no match in the public X-ray catalogues checked. They are expected to be genuine new X-ray sources, rather than confirmed discoveries. The researcher also releases calibrated sky maps and the analysis software for others to reproduce the work and study large-scale X-ray emission and absorption.
Young explorerA telescope called eROSITA made an X-ray picture of the whole sky. Scientists can get the detailed measurements for only half of that sky, so one researcher used the public picture to make a list of about 63,000 spots where X-rays come from. The list misses many spots, and their places are not exact. Thousands of spots do not match ones in older X-ray lists. They might be newly found X-ray sources, but that is not certain yet. The researcher also shared sky maps and the computer instructions used to make the list.
Paul A. Draghis, Erin Kara, Ehud Behar+7 more
AstronomerA high-resolution XRISM/Resolve observation provides the first detection of an intrinsic accretion-disk wind in the persistent black hole candidate 4U 1957+115. Absorption dominated by Fe XXV and Fe XXVI strengthens during the final approximately 40 ks despite only a 5–10% decrease in source flux. Ionization changes driven solely by this modest continuum variability cannot explain the absorption evolution, favoring an inhomogeneous outflow with changing line-of-sight properties. Shorter spectral integrations yield narrower features: the inferred turbulent velocity falls from approximately 350 km/s in the longer integration to at most approximately 70 km/s in the shortest selections. This suggests that temporal averaging contributes to the broader profiles, potentially biasing inferred wind properties and complicating identification of the launching mechanism. Although the wind's kinetic power is only a small fraction of the radiative luminosity, its mass-loss rate may still be dynamically relevant.
PublicXRISM has detected a wind from the disk around the black hole candidate 4U 1957+115 for the first time. Highly ionized iron in the wind absorbs some of the source's X-rays. This absorption changed strongly during the observation, even though the source dimmed only slightly. The researchers conclude that changes in ionization alone cannot explain the behavior, favoring an uneven wind whose properties along our view change over time. They also found that absorption features were narrower when they examined shorter stretches of data. Combining longer stretches may therefore make a changing wind appear more turbulent than it really is, making it harder to work out how the wind is launched. The wind carries relatively little energy compared with the source's light output, but the amount of matter it removes could still be important.
Young explorerScientists found gas blowing away from a disk around something they think is a black hole. They spotted it because the gas blocked some X-rays. The blocking changed a lot, even though the X-ray light got only a little dimmer. This suggests the blowing gas is uneven and changes as we look through it. Looking at short bits of the observation gave a different picture from putting many bits together: mixing them may make the gas seem more jumbled than it really is. Scientists still need to work out what makes this wind blow.
Sarah Recchia
AstronomerThis theoretical study develops a prescription for the projected electron–positron distribution around a moving pulsar, intended as a proxy for its inverse-Compton TeV-halo morphology when target photon fields are spatially uniform. For continuous injection, isotropic diffusion, and radiative losses, the line-of-sight integration is exact, leaving one numerical integral over injection history. Assuming constant injection luminosity and simplified energy losses yields a fully analytical expression that separates an energy-dependent spectral factor from a dimensionless, energy-dependent spatial factor. Comparison with the exact calculation gives good agreement across a broad range of energies and spatial scales, with appreciable deviations mainly near the injection-spectrum cutoff and far from the source, where emission is fainter. The prescription enables efficient, physically motivated templates that capture proper-motion-induced asymmetries; the abstract reports no observational test.
PublicThe researchers developed a faster mathematical way to predict the shapes of gamma-ray halos around moving pulsars. Their model follows electrons and positrons released continuously by a moving source as the particles spread and lose energy. If the surrounding light is evenly distributed, the projected particle pattern can stand in for the halo’s gamma-ray shape. The researchers first reduced the calculation to one numerical integral, then obtained a fully analytical formula by assuming a constant particle-injection power and simplifying energy losses. That formula agrees well with the more exact calculation over a broad range of particle energies and distances, but differs more near the highest injected particle energies and in faint, distant parts of the halo. This is a modeling result, not an observed detection, and could make it easier to analyze how halo shapes change with energy and pulsar motion.
Young explorerA pulsar is a star that sends out tiny particles as it moves. Those particles can help make a glow of gamma rays around it. The researchers made a math shortcut to work out what that glow might look like, including how the star’s movement could make it uneven. They checked the shortcut against a more exact calculation, not against pictures of a real glow. It worked well in many cases, but less well for particles near the model’s highest energies and in the faint glow far from the star.
Liji Zhong, Yong Shao
AstronomerThis POSYDON binary population synthesis study models electron-capture supernovae (ECSNe) from twice solar metallicity down to one ten-thousandth solar metallicity. ECSN formation occupies a narrow regime between oxygen-neon white dwarf formation and iron-core collapse, shaped by competition between core growth and envelope removal, including binary mass transfer and mergers. In these models, the lower initial primary-mass boundary is near 7 solar masses because of efficient convective overshooting in the adopted grids. The upper boundary increases with metallicity because stronger line-driven winds require greater initial masses to produce carbon-oxygen cores in the ECSN range. Stable mass transfer and mergers occupy distinct initial mass-ratio and orbital-period regions. Among ECSNe in bound binaries, residual envelopes imply approximately 30% Type II, 10% Type IIb, and 60% Type Ib outcomes. Across all channels, roughly one-third retain a bound companion at explosion; about 90% of those companions are main-sequence stars. Their modeled spin distribution is bimodal, with a rapidly rotating component associated with earlier mass transfer. Evolved-star and compact-object companions each contribute only a few percent. Combining modeled formation efficiencies with cosmic star-formation and metallicity histories predicts an intrinsic ECSN rate peaking at redshift 2–3 and declining at higher redshift. The predicted contribution integrated over cosmic history is approximately 1%–4% of all core-collapse supernovae. These are population-model predictions, not observational measurements.
PublicSome stars lie close to the boundary between leaving behind an oxygen-neon white dwarf and exploding through iron-core collapse. In this narrow middle ground, they can instead produce an electron-capture supernova. This study uses computer models to explore how exchanging material with another star, or merging with it, changes that outcome across different chemical compositions. The models predict that about one-third of these supernovae have a gravitationally bound companion when they explode. About 90% of those companions are stars still in their main hydrogen-burning stage, and some spin rapidly following earlier material transfer. Among explosions in bound pairs, the models predict that most have lost enough outer material to be classified as Type Ib, rather than the more hydrogen-rich Type II or IIb. Combining the simulations with models of the universe's star formation and chemical history suggests that electron-capture explosions account for about 1%–4% of all core-collapse supernovae over cosmic history. These estimates are predictions, not observed counts.
Young explorerSome stars can end their lives in a special kind of explosion. Whether this happens can depend on how much they grow inside and how much of their outside they lose. A nearby star can change things by taking material or joining together with them. Scientists used computer models to explore this. Their models suggest that about one in three of these exploding stars still has a star partner. These are computer predictions, not explosions the scientists counted in the sky.
Yue Wu, Ailing Wang, Senlin Pang+24 more
AstronomerEP251129a/GRB 251129A, detected by Einstein Probe at z=0.505, exhibits an early X-ray plateau lasting approximately 10^4 s, followed by rapid decay and spectral softening, and a second plateau extending to 60 days. Its early optical evolution is independent of the X-rays, indicating a distinct origin. The radio afterglow rises as Fν ∝ t^1.9–2.5 and peaks at approximately 36–40 days, strongly supporting an off-axis geometry. The authors interpret the ULGRB-like early X-rays as internal dissipation from a newborn millisecond magnetar undergoing gravitational-wave-dominated spin-down before collapsing into a black hole. An off-axis two-component jet with additional energy injection describes the early optical, radio, and late X-ray emission; fallback accretion onto the black hole is a possible power source. These model interpretations connect the event to both ULGRB-like engine activity and off-axis afterglows.
PublicEinstein Probe detected an unusual stellar explosion whose X-ray light showed two stretches of relatively steady brightness: one lasting about 10,000 seconds and another extending to 60 days. Visible light initially changed independently of the X-rays, suggesting a different source. Radio emission brightened rapidly and peaked around 36–40 days, providing strong evidence that the explosion’s jet was viewed away from its main direction. The researchers propose that the early X-rays came from a rapidly spinning, highly magnetic newborn star that later collapsed into a black hole. A model involving a two-part jet receiving extra energy explains the visible light, radio waves, and later X-rays. Material falling back onto the black hole might supply that energy, but this remains a possible explanation rather than an established finding.
Young explorerScientists saw an explosion far away in space. Its X-ray light stayed nearly steady twice, and its radio light grew brighter much later. They think we saw a jet from the side rather than looking straight into it. One possible story is that a tiny, fast-spinning star made the early X-rays and then became a black hole. Scientists are still working out what happened.
Victor Pop, Mohammed A. Chamma, Aishwarya Kumar+1 more
AstronomerFrequency-resolved fits to FRB 20210415C, a bright burst from the repeater FRB 20210219C detected across approximately 400–800 MHz, measure an empirical exponential-tail timescale scaling as τ_emp ∝ ν^α. Two complementary treatments of the underlying pulse width yield α = −3.95 ± 0.07 and −4.14 ± 0.08, both consistent with the commonly adopted ν^−4 scattering law. The inferred scattering time is approximately 8.0 ms at 583 MHz, at least 400 times Galactic foreground estimates, favouring a dominant contribution beyond the Milky Way without localising the scattering screen. Unlike profile asymmetry alone, which can arise from several effects, the measured frequency dependence provides direct evidence for the scattering law often imposed in catalogue analyses.
PublicA fast radio burst called FRB 20210415C has a fading tail whose duration changes with radio frequency in a way consistent with a commonly assumed scattering rule: the tail lasts longer at lower frequencies. Researchers measured this pattern across approximately 400–800 MHz, using two ways to account for the burst’s underlying width. A lopsided burst shape alone cannot establish scattering, because other effects can produce it too. Here, the measured frequency dependence supports the scattering interpretation. The inferred scattering delay is about 8 milliseconds at 583 MHz, at least 400 times estimates for the Milky Way’s foreground contribution. This favours scattering mainly beyond our galaxy, but the observations do not reveal exactly where it occurs.
Young explorerScientists studied a very quick flash of radio waves from space. The flash had a little fading tail that lasted longer in lower-frequency radio waves. They measured how the tail changed, and it matched a rule used to describe radio waves arriving along different paths. A tail by itself would not prove that this happened. The results suggest that most of this spreading happened outside our Milky Way galaxy, but scientists do not know exactly where.
Arthur G. Suvorov, Armen Sedrakian
AstronomerThis theoretical study examines differential rotation and its implications for continuous gravitational-wave searches in canonical twisted-torus neutron-star equilibria, where toroidal fields occupy regions of closed poloidal field lines. Surface spindown torques may couple inefficiently to these regions, allowing toroidal zones or magnetic voids to rotate faster than the electromagnetically braked component. An associated non-corotating quadrupole could emit at higher frequencies than poloidal components, depending on the microphysics of angular-momentum transport. The authors estimate dissipative timescales and their microphysical sensitivity, noting that dissipation can suppress persistent rotational lags. Simple models quantify how a quadrupole pattern speed differing from the observed spin shifts or smears its signal over a finite frequency band during finite observations. Consequently, single-template or narrowband upper limits constrain only the quadrupole contribution within the searched window, not necessarily the full frequency-integrated quadrupole. These are modeling results and search implications, not a reported detection.
PublicParts of a neutron star's interior might rotate faster than the portion being slowed by electromagnetic braking. This theoretical study explores how certain magnetic-field arrangements could allow that difference to persist, although dissipative processes might erase it. If a gravitational-wave-producing distortion rotates at a different rate from the star's observed spin, its signal could occur at a shifted frequency or spread across a band of frequencies. Using simple models, the researchers examine this effect over limited observing periods. Their conclusion concerns how searches are interpreted: a limit obtained by looking at just one frequency or a narrow band may constrain only part of a possible signal, rather than its full contribution. The study does not report a gravitational-wave detection.
Young explorerImagine a spinning star whose inside might turn faster than the part we can track. If a lopsided part inside spins at a different speed, it could make tiny ripples in space with a different beat, or with beats spread over a range. The researchers used simple models to explore this idea; they did not find these ripples. They also say the speed difference might not last. Looking for only one beat could miss part of a possible signal.
Matteo Lucchini, Benjamin Ricketts, Phil Uttley+4 more
AstronomerThis study examines how linear interpolation of precomputed grids of nonlinear X-ray spectral models can propagate computational errors into parameter inference. The authors test Bayesian sampling algorithms on mock inference problems and model real observations of an accreting black hole X-ray binary in soft and hard states. They find that linear interpolation can strongly bias parameter posteriors and distort the likelihood landscape, producing artificial posterior multimodality. This can reduce the efficiency of both sampling and fitting, making exploration to convergence extremely computationally expensive. The authors call for improved computational methods, suggesting better sampling algorithms and/or more sophisticated interpolation; the abstract does not report a validated remedy.
PublicComplex models used to interpret X-rays are often calculated in advance at a set of points. To estimate predictions between those points, researchers commonly connect them with straight lines, even when the model changes nonlinearly. This study tests how that shortcut affects the answers, using both simulated inference problems and real observations of a black hole drawing in matter from a companion star. The authors find that the shortcut can bias estimates of model parameters and create artificial competing answers, making reliable fitting much more computationally demanding. They suggest improving the methods used to explore possible answers or estimate values between calculated points, but do not report a proven fix.
Young explorerScientists use computer models to understand X-rays from a black hole pulling in material from a nearby star. To save work, they sometimes calculate only some model answers and draw straight lines to guess the answers in between. The researchers tried this with made-up test problems and real X-ray observations. They found that these guesses can push the answers the wrong way or make it look as if there are several answers when the extra ones come from the shortcut. Sorting them out can take lots of computer work. Better ways of guessing or searching might help, but this study does not show a finished fix.
S. Calderaro, G. Parisi, V. Sapienza+7 more
AstronomerThe authors apply two dendrogram-based techniques—a multivariate analysis and a deep-learning graph-based approach with different metrics—to Chandra narrow-band images and equivalent-width maps of Cassiopeia A, G292.0+1.8, Tycho's SNR, Kepler's SNR, and W49B. They identify clusters of maps tracing emission lines from elements expected to be synthesized in the same stellar layers and/or from plasma at similar temperatures. Comparisons reveal strong similarities between the Type Ia remnants Tycho and Kepler and between the core-collapse remnants Cassiopeia A and G292.0+1.8; W49B more closely resembles the latter group. Synthetic X-ray maps from a 3D hydrodynamic simulation of Cassiopeia A provide a separate reliability test. The methods quantify morphological similarities and differences and offer clues to chemical-species distributions and plasma temperature. Classification by explosion type is promising but has been tested on only a limited sample.
PublicResearchers compared X-ray maps of five supernova remnants, the remains of exploded stars, using two methods that group maps by their patterns. Some maps emphasize particular chemical elements, while others show the relative strength of their emission lines. Maps tended to group together when they traced elements expected to form in the same layers of a star, gas at similar temperatures, or both. The two remnants identified as Type Ia resembled each other, as did two remnants from collapsing stars; a fifth remnant, W49B, looked more like the collapsing-star group. The researchers also tested their results using artificial X-ray maps from a computer simulation of Cassiopeia A. The approach may help distinguish explosion types and investigate the distribution of elements and gas temperatures, but its classification performance has been tested on only a small sample.
Young explorerWhen a star explodes, it leaves behind hot material that can glow in X-rays. Scientists compared special pictures of five of these leftovers and found that some had similar patterns. Pictures showing certain kinds of material sometimes matched, perhaps because the materials formed in the same parts of a star or were at similar temperatures. The scientists also checked their method with pretend pictures made by a computer simulation. Matching these patterns might help tell how a star exploded, but they need to try it on more star leftovers.
Sikandar Akbar, Zahir Shah, Zahoor Malik+1 more
AstronomerThe study applies positive-unlabelled (PU) learning to 1623 blazars of uncertain type (BCUs) in Fermi-LAT 4FGL-DR4, using five classifiers trained on seven gamma-ray features with either 820 FSRQs or 1490 BL Lacs as the labelled class. Confidence is the fraction of 100 repeated five-fold splits in which at least three classifiers flag a source out of fold. At confidence ≥0.1, the reported categories contain 437 FSRQ-like candidates, 597 BL Lac-like candidates, 12 flagged in both modes and 577 in neither. On known sources, recall is 0.80 for FSRQs and 0.82 for BL Lacs at a false-positive rate of 0.08; labelled-only logistic regression performs at least as well, so PU learning provides no accuracy gain here. Excluding sky coordinates preserves known-source performance but adds 107 candidates and removes 30, consistent with coordinates acting as a selection shortcut. Checks against optical spectra and subsequent catalogue classifications give correctness rates of 84–100% for single-class BL Lac-like assignments and 58–83% for FSRQ-like assignments, depending on the sample. These spectroscopic follow-up samples are not representative of all BCUs. Candidates are fainter and closer to the Galactic plane than labelled sources, and the excess of unclassified BCUs near the plane remains unexplained. Confidences are released for all 1623 BCUs.
PublicResearchers used machine learning to suggest which of two blazar classes best fits 1623 objects whose types were uncertain in a gamma-ray catalogue. The suggestions are candidate classifications, not confirmed identities, and some objects were flagged as both types or neither. Checks using optical spectra and later catalogue classifications found that BL Lac-like suggestions were more reliable than flat-spectrum radio quasar-like suggestions. However, the checked objects came from spectroscopic follow-up and do not represent the full uncertain sample. The positive-unlabelled learning approach did not outperform a simpler model trained only on already classified sources. The researchers also excluded sky position from the inputs after finding evidence that it could act as a shortcut without improving performance on known objects. The candidates are fainter and closer to the plane of our Galaxy than the training sources; why extra unclassified objects occur near that plane remains unexplained.
Young explorerScientists asked computers to help sort 1623 space objects into two groups by looking for patterns in their light. The computers suggested groups for many objects, but some were still hard to sort. Checks showed that the suggestions were not always right, and the checked objects might not be like all the others. The new computer method did not do better than a simpler one. These are helpful clues, not sure answers.
Super-Kamiokande Collaboration, K. Abe, Y. Asaoka+97 more
AstronomerA spectral fit to 5003.0 days of Super-Kamiokande data yields an indication, rather than an established detection, of electron antineutrinos from the diffuse supernova neutrino background (DSNB). The analysis improves atmospheric-neutrino background rejection, updates systematic uncertainties, and refines the spectral fitting method. For a representative DSNB model, the best-fit flux above 13.3 MeV is 3.6 (+1.6, −1.5) cm⁻² s⁻¹, with 2.6σ tension with the null hypothesis (99.5% one-sided confidence level). Signal models with different spectral shapes give similar significances.
PublicResearchers analyzing 5003.0 days of Super-Kamiokande data report a tentative sign of electron antineutrinos from the diffuse background of supernova neutrinos. They improved methods for rejecting atmospheric-neutrino backgrounds, reassessed uncertainties, and refined how they fit the energy spectrum. With one representative model, the inferred flux above 13.3 MeV is 3.6 particles per square centimeter per second, with an uncertainty of +1.6 and −1.5. The statistical evidence is 2.6 sigma: suggestive, but not an established detection. Models with different energy distributions give similar levels of evidence.
Young explorerWhen stars explode, they send out tiny particles. Scientists looked through lots of data from a detector called Super-Kamiokande and found a hint of a background of these particles, called electron antineutrinos. They worked to separate this possible signal from other particles that could look like it. The hint is interesting, but they cannot yet be sure it is really there.
Andrew Mummery, Minghao Guo, Eliot Quataert+1 more
AstronomerGRMHD simulations follow the long-term evolution of a black hole accretion torus to t_max = 10^7 GM_•/c^3, enabling comparison with analytical spreading-disk models. General Relativistic Thin Disk Theory reproduces several aspects of the simulated evolution to within roughly a factor of two, despite the flow being geometrically thick, having dynamically dominant magnetically arrested disk (MAD) fields, and launching a powerful wind. It provides an inexpensive effective description of the bulk disk’s radial and temporal evolution and the time dependence of the horizon accretion rate. The authors attribute this agreement to global mass and angular-momentum conservation together with turbulent stress that they find to be local and density-independent, supporting the local-stress prescription used in analytical models. Simulated inner-disk accretion-rate fluctuations are log-normally distributed, consistent with a key assumption in models of observed variability; these findings are simulation results, not direct observations.
PublicResearchers used unusually long-running computer simulations to study how a ring of gas around a black hole evolves. A relatively simple theory designed for thin disks described several aspects of the simulated gas flow to within about a factor of two, even though the simulated disk was thick, strongly magnetic, and driving a powerful wind. The theory tracked how the main body of gas spread and how the rate of gas falling into the black hole changed over time. The authors suggest that the agreement comes from shared rules governing mass and angular momentum, together with the behavior of turbulent forces in the simulation. Fluctuations in the simulated inner flow also followed a statistical pattern assumed in some models of observed brightness changes. The study tests these ideas in simulations rather than through new telescope observations.
Young explorerScientists used a computer to watch a pretend ring of gas swirl around a black hole for a very long time. A simpler set of rules made for thin rings worked surprisingly well for parts of this thick, strongly magnetic ring, even while it blew gas away. The rules were not perfect, but they helped describe where much of the gas went and how quickly it fell into the black hole. This happened in a computer experiment, not in a real black hole watched through a telescope.
PUEO Collaboration, Q. Abarr, S. Agarwal+70 more
AstronomerThis paper presents the design and construction implementation of PUEO (Payload for Ultrahigh Energy Observations), a balloon-borne antenna array designed to detect Askaryan emission from ultrahigh-energy neutrino interactions in Antarctic ice. Sources of cosmic rays at energies ≳1 EeV are expected to produce neutrinos at comparable energies through interactions within source regions or during propagation over cosmological distances. Neutrino flux, flavor, and energy measurements could constrain the underlying acceleration and propagation processes, but the low predicted flux requires immense detection volumes. The paper covers design parameters through as-built validations; the abstract reports no neutrino detections.
PublicPUEO, short for Payload for Ultrahigh Energy Observations, is a balloon-borne array of antennas designed to detect signals from extremely energetic neutrinos interacting in Antarctic ice. These neutrinos are expected to accompany interactions involving the highest-energy cosmic rays, either near their sources or during their journey across the universe. Measuring the neutrinos could help scientists understand how cosmic rays gain energy and travel. Because so few neutrinos are predicted at these energies, detectors must monitor enormous volumes. This paper describes PUEO’s design, construction, and checks of the built instrument, rather than reporting a neutrino discovery.
Young explorerScientists have built a set of antennas called PUEO to ride on a balloon. It is designed to listen for signals made when tiny particles called neutrinos interact in Antarctic ice. Scientists expect these particles could help them learn about other super-energetic particles traveling through space. The signals are expected to be very rare, so PUEO needs to watch a huge amount of ice. This paper explains how PUEO was designed, built, and checked, not that it has found neutrinos.
H Lalrinfela, P.C. Lalremruati, Zodinmawia+1 more
AstronomerThis theoretical study calculates tidal contributions to neutron-star orbital precession around Sgr A*, using stellar configurations governed by the Tolman–Oppenheimer–Volkoff equations. The calculated tidal shift decreases steeply with pericentre distance and, for the configurations considered, with stellar compactness; larger quadrupolar tidal Love numbers k2 increase it. The behaviour reflects the strong dependence on (R/r_p)^5. Within the displayed parameter range, predicted tidal shifts reach only about 3.5 × 10^-18 microarcseconds, with tidal-to-general-relativistic precession ratios of approximately 10^-33 to 10^-28. General relativistic precession therefore overwhelmingly dominates, making direct detection of the tidal contribution exceptionally challenging under the adopted model assumptions.
PublicThe researchers calculated how tidal stretching of a neutron star could slightly change the orientation of its orbit around Sgr A*, the supermassive black hole. These are theoretical predictions, not observed orbital changes. In the models studied, closer approaches and stars that deform more readily produce larger tidal effects, while more compact stars produce smaller effects. Even the largest predicted tidal shift in the explored range is only about 3.5 × 10^-18 microarcseconds, vastly smaller than the orbital turning predicted by general relativity. The calculations suggest that detecting this tidal effect directly would be exceptionally difficult under the model's assumptions.
Young explorerScientists used math to imagine a tiny, very heavy star going around a giant black hole. The black hole's pull could stretch the star a little and make its path turn a tiny bit. Their math says this effect gets bigger when the star comes closer, but it is still much, much smaller than another turning effect described by Einstein's gravity theory. They have not seen this tiny stretching effect in an orbit, and their model says it would be very hard to spot.
Navin Sridhar
AstronomerAnalytical theory and kinetic simulations examine strong (a₀ > 1), superluminal X-mode electromagnetic waves in magnetized pair plasma, with regimes controlled by εB = a₀ωB/ω₀. For εB < 1, propagation ultimately breaks down through induced scattering. The background magnetic field supplies a restoring frequency ΩB; when this exceeds the scattering rate, the unattenuated propagation length increases from approximately εp^(−2/3) to εB^(1/2)/εp wavelengths, where εp = a₀ωp/ω₀. For a₀² > εB > 1, nonlinear plasma current damps the wave as it rides a motional electric field, making one half-cycle appear attenuated. These theoretical and simulation results have implications for fast radio burst durations and escape from surrounding plasma, rather than constituting observational measurements of bursts.
PublicUsing mathematical theory and computer simulations, researchers studied how intense electromagnetic waves travel through magnetized plasma made of electrons and their antimatter counterparts. They identify two behaviors. In one regime, scattering eventually disrupts the wave, but the magnetic field can delay that disruption and let the wave travel farther without weakening. In another regime, the plasma's nonlinear electrical response damps the wave, making one half of its oscillation appear weakened. The framework could help explain how long fast radio bursts last and whether their waves can escape the surrounding material; the abstract reports no direct observations of those bursts.
Young explorerScientists used math and computer models to study strong waves moving through a special kind of matter with a magnetic field. In one case, the field helps a wave travel farther before it gets jumbled. In another case, the wave gets weaker. This might help scientists understand brief flashes of radio waves from space, but it is not a report of watching those flashes happen.
Isaac Legred, Nicolás Yunes
AstronomerThe study describes how dynamical tides can alter the orbital evolution of a neutron star paired with a much lower-mass primordial black hole. Depending on the orbital configuration, tides can accelerate inspiral or drive outspiral, analogous to tidal evolution in giant planet–moon systems. The authors show how gravitational-wave emission mediates this evolution when neutron-star modes remain resonance-locked to the orbit. Possible pulsar-timing or gravitational-wave signatures are suggested, not reported as detections.
PublicA study explores how a neutron star and a much lighter primordial black hole could move around each other differently from typical pairs of compact objects. Tidal interactions, similar to those between giant planets and their moons, could make the pair spiral inward faster or move apart, depending on their orbit. The work describes how gravitational waves affect this process when vibrations in the neutron star stay synchronized with the orbital motion through resonance. These effects might be detectable through pulsar timing or gravitational waves, but the abstract reports no detection.
Young explorerImagine a neutron star and a much lighter black hole going around each other. The study says that tidal tugs, like those between a giant planet and its moon, could make them move closer faster or move farther apart. Ripples called gravitational waves help shape what happens when the star’s shaking keeps time with their orbit. Scientists think these effects might leave clues we could spot, but they have not reported seeing those clues here.
Ryo Yamazaki, S. Tomita, T. Takezaki+64 more
AstronomerLaboratory experiments investigate the early formation of quasi-perpendicular, supercritical magnetized collisionless shocks using a laser-produced Al piston expanding into magnetized N plasma in an initially uniform, 1 Torr nitrogen gas. The observed bright, asymmetric self-emission reverses its global morphology when the external magnetic-field polarity is reversed. Two-dimensional ideal-MHD simulations reproduce the main structural features and suggest that rippling is associated with vortices at the rounded piston leading edge rather than Kelvin–Helmholtz instability. The emission traces the Al–N interface, whose intrinsic width is consistent with an electron kinetic scale; its upstream side is predominantly N plasma. Identifying this interface enables discussion of shock formation in the magnetized N plasma with minimal Al contamination, rather than establishing a fully formed shock.
PublicResearchers used a laser to create an expanding aluminum plasma—a cloud of electrically charged matter—that pushed into nitrogen plasma in a magnetic field. They observed a bright, uneven, rippling boundary whose overall shape reversed when they reversed the magnetic field. Computer simulations reproduced the main features and suggested that swirls at the aluminum cloud’s rounded front, rather than a competing instability, were responsible for the ripples. The team identified the glowing boundary as the interface between aluminum and nitrogen, with mostly nitrogen just ahead of it. This helps researchers study the early formation of a collisionless shock in magnetized nitrogen while limiting confusion from aluminum mixed into that region; it is not a claim that a fully developed shock was demonstrated.
Young explorerScientists used a laser to make a hot cloud of aluminum push into a hot cloud of nitrogen. Magnets helped shape the clouds. The scientists saw a bright, wiggly edge, and its shape flipped when they reversed the magnetic field. A computer model suggested that little swirls helped make the wiggles. Finding where the two clouds meet helps scientists study how a special kind of shock wave might begin.
Ryo Yamazaki, T. Takezaki, T. Morita+64 more
AstronomerThe study uses high-power lasers, self-emission imaging, and collective Thomson scattering to investigate a forming quasi-perpendicular collisionless shock. An upstream emission tail is consistent with a shock foot, and ion heating and temperature anisotropy extend upstream of a ramp-like region. These observations support reflected-ion-related heating during early shock formation, but incident and reflected ion populations are not separately resolved. Future ion-distribution and plasma-wave measurements could clarify the heating’s role in dissipation and particle energization.
PublicResearchers used high-power lasers to study the formation of a magnetized plasma shock, where collective effects rather than particle collisions govern the abrupt change in flow. They observed a tail of light ahead of the main shock-like transition, along with heated ions whose temperatures differed by direction. These findings suggest that ions reflected back toward the incoming flow contribute to heating as the shock forms. However, the measurements could not distinguish incoming ions from reflected ones. Future measurements could help explain how this heating dissipates the flow’s energy and energizes particles.
Young explorerScientists used powerful lasers to watch a shock begin to form in a hot gas of charged particles. Ahead of the forming shock, they saw a glowing tail and signs that some particles were getting hotter. This suggests that particles bouncing back might help heat the gas. But they could not tell the incoming particles apart from the bouncing ones, so they need more measurements to find out.
Davood Rafiei Karkevandi, Mahboubeh Shahrbaf, Hamid Reza Moshfegh+2 more
AstronomerThis study constrains hypothetical in-medium neutron-to-dark-fermion conversion using neutron-star observations within a nonlinear σ–ω–ρ relativistic mean-field framework. The authors scan dark-fermion masses of 939–1500 MeV and repulsive self-interaction strengths Gχ of 1–100 fm² across 21 calibrated nucleonic EOSs, including 13 baseline models and soft and stiff limiting cases. Model stellar sequences must support at least 2 solar masses and satisfy GW170817 tidal-deformability bounds and NICER mass–radius constraints, with two NICER inference sets evaluated separately. Both analyses yield similar regions excluded by every EOS, with approximate minimum–maximum extents of 939–1300 MeV in mass and 1–11 fm² in Gχ; these extents do not specify a fully excluded rectangle. The baseline set has a common not-excluded region, but the full ensemble does not. Weak dark-sector repulsion is therefore robustly disfavored over a broad mass range within this EOS framework, while the remaining parameter space depends on EOS stiffness and the NICER analysis. This is a model-dependent constraint, not a detection of conversion or dark fermions.
PublicCould neutrons inside neutron stars turn into hypothetical dark particles? This study tests that possibility by comparing models with neutron-star observations, including gravitational-wave measurements and estimates of stellar masses and sizes. The researchers vary the dark particles’ mass and how strongly they repel one another, using 21 descriptions of dense ordinary matter. Within this modeling framework, observations consistently disfavor weak repulsion across a broad range of dark-particle masses. What remains not ruled out depends on the description of dense matter and on which of two NICER analyses is used. A core set of 13 models shares some not-ruled-out possibilities, but no such shared region remains across all 21 models. The study constrains a hypothetical process; it does not show that these dark particles exist or that neutrons actually convert into them.
Young explorerNeutron stars are very crowded stars. Scientists wondered whether tiny bits inside them could turn into a hidden kind of particle. They compared different pretend versions of these stars with real measurements. In their models, many possibilities did not fit when the hidden particles pushed each other apart only weakly. Some possibilities still fit some models, but the scientists have not found these hidden particles.
Francesca Bonaiti, Sonia Bacca, Ingo Tews
AstronomerThis review surveys recent ab initio calculations of finite nuclei aimed at constraining the nuclear-matter equation of state. It emphasizes links between finite-nucleus observables and bulk matter: neutron-skin thicknesses and electric dipole polarizabilities inform the density dependence of the symmetry energy, while monopole observables, including sum rules, constrain incompressibility. The abstract describes these diagnostic connections but reports no numerical constraints or new measurements.
PublicThis review examines calculations of atomic nuclei that can help scientists understand how nuclear matter behaves. It focuses on connections between properties of individual nuclei and those of nuclear matter in bulk. The thickness of a nucleus’s neutron-rich outer layer and its response to an electric field provide information about how the energy associated with neutron–proton imbalance changes with density. Other properties related to nuclear compression help constrain how difficult nuclear matter is to squeeze. The abstract presents an overview, not new measurements or numerical results.
Young explorerAn atom has a tiny middle called a nucleus. This review looks at calculations that help scientists learn how the stuff inside nuclei behaves. They study how neutrons spread near the outside, how a nucleus responds to an electric push, and how hard nuclear stuff is to squeeze. These clues can help them understand nuclear matter, but this summary gives no new measured answers.
Subha Mitra, Bharat Kumar
AstronomerThis theoretical calculation evaluates electron-neutrino and antineutrino diffusion mean free paths in hot, neutrino-trapped matter containing Δ(1232) isobars, relevant to proto-neutron stars and neutron-star merger remnants. It includes charged-current absorption using the NΔ weak vertex, neutral-current scattering on all baryons, and three-body antineutrino absorption with relativistic mean-field kinematics. The channel ν̄e + e− + n → Δ− dominates antineutrino opacity when the neutron and electron chemical potentials satisfy the stated in-medium Δ− energy threshold, even if the equilibrium Δ population is negligible. Where open at two to four times nuclear saturation density, it shortens the calculated antineutrino mean free path from a metre scale to a centimetre scale. Its effect on lepton-number diffusion is important only at low lepton fraction because antineutrinos are scarce at high lepton fraction. Electron-neutrino mean free paths also decrease through absorption on Δ− and, at low lepton fraction, the opening of nucleonic absorption. For fixed axial coupling, Δ spin reduces the Gamow–Teller strength per particle from 3 to 5/3. The supplied abstract contains unresolved placeholders for mean-free-path ranges and reduction factors, so their numerical values cannot be reported.
PublicCalculations suggest that a particular particle reaction could make dense matter much harder for electron antineutrinos to pass through inside newborn neutron stars and the remnants of neutron-star mergers. In the reaction, an antineutrino is absorbed together with an electron and a neutron, producing a particle called a delta-minus. If the matter meets the required energy condition, this can be the main way antineutrinos are blocked, even when almost no delta particles are present beforehand. At two to four times nuclear saturation density, the calculated distance antineutrinos travel between interactions falls from a metre scale to a centimetre scale. However, the effect on the diffusion of net lepton number matters only when the lepton fraction is low; at high lepton fraction, antineutrinos are too scarce to make much difference. The calculations also find shorter travel distances for electron neutrinos through other absorption reactions. These are theoretical findings, not observations, and the abstract leaves several numerical results as unresolved placeholders.
Young explorerScientists used calculations to study tiny particles moving through the very crowded stuff inside a newborn neutron star or what is left when two neutron stars join. They found that, if the conditions are right, one kind of tiny particle can get swallowed in a reaction instead of traveling farther. That could make its trips much shorter. But whether this changes how things spread through the star depends on what the star’s stuff is like. This is an answer from calculations, not something scientists watched happen.
Zun Wang, Yongchao Zhang
AstronomerThis theoretical reanalysis updates supernova bounds on the dark photon, U(1)_{B-L}, and U(1)_{L_mu-L_tau} gauge bosons using SN1987A cooling and energy-deposition constraints from low-energy supernovae. For the first two models, nucleon bremsstrahlung is recalculated in the one-pion-exchange approximation with full momentum and mass dependence; the analysis also accounts for the geometry of boson decay and absorption inside the core. Using the SFHo-18.8, 18.8-solar-mass profile, cooling bounds reach masses of about 230, 280, and 300 MeV, respectively, while low-energy-supernova bounds extend to about 450, 440, and 600 MeV. The reported constraints reach kinetic mixing epsilon of 5.8 × 10^-12, coupling g_BL of 2.9 × 10^-16, and coupling g_mu_tau of 6.4 × 10^-12. These are model-dependent constraints, not detections of the proposed particles.
PublicExploding stars can help test whether hypothetical particles exist: such particles could carry energy away from a star’s core or deposit energy elsewhere in the explosion. This study updates calculations for three proposed particles—the dark photon and two other light force-carrying particles—and uses cooling constraints from SN1987A and energy-deposition constraints from low-energy supernovae to limit their possible properties. The calculations refine how some of these particles could be produced and account for where they decay or are absorbed. With the stellar profile used, low-energy supernovae constrain higher particle masses than SN1987A cooling does. The work reports limits on these particles, not evidence that they have been found, and the numerical limits depend on the modeling assumptions.
Young explorerWhen a star explodes, it can give scientists clues about tiny particles we have not found. These particles might take energy away or leave it in another part of the star. Scientists used calculations and clues from exploding stars to work out which kinds of particles could fit. They did not find new particles; they narrowed down some possibilities, using a model of what happens inside a star.
Jyotijwal Debnath, Amodio Carleo, Delphine Perrodin+1 more
AstronomerThis theoretical study models polarization in hypothetical pulsar–black hole binaries by combining the Rotating Vector Model with numerical null-geodesic integration and polarization transport. It considers non-spinning and spinning black hole companions, including orbital-geometry evolution from relativistic spin–orbit coupling. For a non-spinning companion, the modeled polarization-direction change comes from the geometric shift caused by gravitational light bending. Black hole spin adds a frame-dragging geometric shift and a parallel-transport rotation defined relative to the authors’ chosen reference construction. The calculations predict substantial distortions of the characteristic S-shaped polarization position-angle profile, especially near superior conjunction, and a reversal of its overall sense of variation in the supermassive black hole system considered. Spin–orbit evolution also changes the orbital-phase dependence, particularly in that system. The effects depend on binary parameters and pulsar-spin orientation. These are model predictions, not observations of a pulsar–black hole binary; the authors propose polarization profiles as a possible probe of binary geometry when such systems are discovered.
PublicPulsars emit radio waves with a preferred polarization direction. This study calculates how that direction might appear to change if a pulsar orbited a black hole; it does not report observations of such a pair. In the models, the black hole’s gravity bends the radio waves’ paths, changing the predicted polarization pattern, especially when the pulsar passes behind the black hole. In the supermassive black hole example studied, the pattern can even change in the opposite overall direction. A spinning black hole introduces further effects, while gradual changes in the orbit also alter how the pattern varies around the orbit. One calculated rotation is defined relative to the researchers’ chosen reference. These predictions suggest that polarization could help reveal the geometry of pulsar–black hole pairs if they are discovered.
Young explorerA pulsar sends out radio waves that have a special direction, a bit like an arrow. Scientists used a computer to imagine a pulsar going around a black hole. Their calculations say the black hole could bend the waves’ paths and change how the arrow seems to turn. They have not seen this happen in such a pair. If they find one, the changing arrow might help them learn how the pair is arranged.
Guangzhou Guo, Zhen Pan
AstronomerHydrodynamic simulations of inspiralling neutron-star binaries are compared with a semi-analytic mode-coupling calculation of the quadrupolar fundamental-mode frequency shift through second order in tidal strength. The approaches agree in the perturbative regime but diverge in stronger tidal fields, where perturbation theory breaks down. In the modeled late inspiral, nonlinear tides lower the fundamental-mode frequency by about 10% for equal-mass binaries and produce an additional GW phase shift of order one radian relative to the linear tidal response. These theoretical results motivate nonlinear tides as a target for next-generation GW detectors; no observational detection is reported.
PublicAs two neutron stars spiral toward each other, their tidal pulls can couple the stars’ vibrations and change the gravitational waves they emit. This study explores those effects using fluid simulations and an approximate mathematical model. The two methods agree when the tides are relatively weak, but the approximation breaks down for stronger tides. The calculations indicate that, late in the inspiral, nonlinear tides lower a main vibration frequency by about 10% in equal-mass pairs and add a gravitational-wave phase shift of roughly one radian beyond the simpler linear prediction. These are theoretical findings, not observations, and suggest a possible target for next-generation gravitational-wave detectors.
Young explorerTwo neutron stars circling closer together pull on each other and make each other wobble. Scientists used computer simulations and math to study how those wobbles mix together. Their results suggest that near the end, the mixing makes one main wobble slower and changes the timing of the ripples the stars send through space. The math and simulations agree when the pulls are gentle, but the math stops working well when the pulls get strong. Future detectors might pick up these changes; the scientists have not seen them in real signals yet.
Milind Sarkar, Maria Giovanna Dainotti, Nikita S. Khatiya+8 more
AstronomerThe authors develop supervised high- versus low-redshift classifiers using 171 long-duration GRBs (>2 s) with measured redshifts and optical plateau emission, combining prompt-emission and plateau observables. They evaluate thresholds of z = 2.0, 2.5, and 3.0. The best classifier, at z = 2.0, has a training-set TPR of 0.741 and AUC of 0.841, with a train-to-test AUC difference within 4 percent. On complete-case data at this threshold, LASSO favors prompt-emission and absorption variables over plateau parameters, supporting classification without waiting for plateau signatures. X-ray absorption column density and prompt-emission peak flux are stably selected by both the optical and X-ray classifiers. The key novelty is the optical-plateau-selected training sample, not direct redshift measurement. Applicability must be viewed in light of the sample selection: heterogeneous optical follow-up, dust extinction, and chromatic afterglow behavior introduce greater incompleteness than in X-ray plateau samples. A publicly released web application is intended to help prioritize high-redshift candidates for follow-up.
PublicMany gamma-ray bursts are located by satellites, but measuring their redshifts remains difficult because rapid optical follow-up is often unavailable. This study trains machine-learning tools on 171 long-duration bursts with known redshifts and a plateau in their optical emission. The tools sort bursts into higher- and lower-redshift groups rather than measure exact redshifts. At the best-performing dividing point, redshift 2, the classifier identified 74.1 percent of high-redshift bursts in its training sample; its training and test scores for distinguishing the groups differed by no more than 4 percent. Early-emission and absorption clues were more useful than plateau properties in one analysis, suggesting classification need not wait for a plateau. However, uneven observations and other effects make the optical sample incomplete. A public web tool aims to help researchers choose bursts for follow-up.
Young explorerScientists studied 171 long flashes of light in space. They taught a computer to use clues from the flashes to sort them into two groups, so people can choose which ones to study next. The computer does not get every answer right. Some flashes are also harder to observe, so the flashes used to teach it do not give a complete picture.
Shamim Haque, Atharva Shinde, Asim Kumar Saha+2 more
AstronomerThis theoretical study maps conditions for twin stars in a large ensemble of hybrid equations of state constructed with a four-parameter Maxwell-CSS prescription. A sufficiently strong hadron-to-quark transition can produce a separate hybrid-star branch. Using TOV solutions, the authors identify twin-star existence boundaries in transition pressure and energy-density discontinuity: at fixed transition energy density and quark-matter sound speed, the allowed discontinuity range widens as transition pressure decreases below a maximum. Causality further truncates these boundaries. Applying CET, GW170817 and NICER constraints, the authors find conditional extrema among models surviving their adopted 2σ filters: a maximum twin-star mass of 2.05 solar masses, a maximum rest-mass-density discontinuity of 7.76ρ_sat, and an upper transition rest-mass density of 4.03ρ_sat. These are model- and filter-dependent bounds, not universal limits or evidence of a twin-star detection. The study also examines the effects of quark-matter stiffness and different confidence levels for observational constraints.
PublicCould matter inside a neutron star change into quark matter strongly enough to create a separate family of stars? This study explores that predicted possibility, called the twin-star scenario, using many theoretical descriptions of dense matter. The researchers map which combinations of transition pressure and abrupt density change allow such stars, then narrow the possibilities using theoretical limits and constraints from GW170817 and NICER. Among models passing their chosen uncertainty filters, the largest allowed twin-star mass is 2.05 times the Sun’s mass. That limit depends on the models and constraints used; it is not a measurement of a twin star. The researchers also examine how the resistance of quark matter to compression affects the possibilities.
Young explorerScientists wonder whether the stuff deep inside a neutron star could change into something called quark matter. If the change is strong enough, it might make a different kind of star. They used math to explore when that could happen and checked their ideas against clues about stars. This study does not show that these special stars have been found.
Jonathan I. Katz, Michael A. Nowak
AstronomerThe abstract outlines a proposed mechanism for recurrent X-ray transients in eccentric stellar–compact-object binaries. Mass transfer at periastron powers X-rays that evaporate material from the star; recoil from this loss is proposed to increase the orbital semi-major axis and eccentricity. The system would appear as an X-ray transient after successive periastron passages, with a gradually increasing recurrence period. It is interpreted as a recurrent, non-catastrophic Galactic analogue of a tidal disruption event. The abstract reports no observational measurements or simulation results establishing this scenario.
PublicThe abstract describes a possible explanation for repeating X-ray outbursts from a star orbiting a compact companion on an elongated path. Near their closest approach, material transferred from the star could produce X-rays, which would evaporate more material from the star. The resulting recoil is proposed to widen and stretch the orbit, making later outbursts occur farther apart in time. The authors compare this to a repeating, non-catastrophic version of a tidal disruption event within our Galaxy. This is a proposed explanation, not an observational finding demonstrated in the abstract.
Young explorerImagine a star and a very small, tightly packed space companion going around each other on a stretched-out path. Scientists suggest that when they come closest, some stuff from the star could move to its companion and make X-rays. Those rays could make more stuff leave the star, giving it a push that changes their path. The X-ray flashes might then repeat, with longer waits between them, instead of one big disaster. This is an idea about what could happen, not something this abstract shows has happened.
T. J. Hutchins, D. I. Jones
AstronomerThis theoretical study tests whether thermally induced crustal lattice-pressure perturbations can support neutron-star mass asymmetries large enough for gravitational-wave emission to set spin equilibrium in low-mass X-ray binaries. It self-consistently calculates temperature asymmetries from anisotropic heat transport in magnetised accreting stars, lattice-pressure perturbations, and the resulting elastic mountains. The framework uses the unified, thermodynamically consistent BSk19, BSk20, and BSk21 equations of state. Although earlier rough estimates suggested this mechanism might compete with temperature-induced capture-layer shifts, the detailed calculations find these mountains too small to dictate LMXB spin equilibrium. The authors also estimate their gravitational-wave emission; the abstract reports no observational detection or numerical emission levels.
PublicNeutron stars that draw matter from a low-mass companion may develop uneven temperatures and small, uneven concentrations of mass called mountains. As a star spins, such an imbalance could emit gravitational waves, potentially limiting its spin rate. This study calculates a proposed route to building those mountains: uneven heat flow in a magnetised star changes the pressure supplied by its solid crust and produces a mass imbalance. By treating these steps together using three models of neutron-star matter, the researchers find that mountains made this way are too small to determine the stars’ balance between spin-up and spin-down. They also estimate the gravitational waves these mountains would produce. These are theoretical findings, not a reported detection.
Young explorerA neutron star is a very small, very heavy star that can spin. Scientists used calculations to ask whether uneven heating could make tiny bumps on a star that is pulling in matter from a nearby star. A spinning bump could send out ripples in space called gravitational waves. In their calculations, these bumps were too small for those ripples to decide how fast the star spins. They did not report seeing the bumps or their ripples.
David Barba-González, Conrado Albertus, M. Ángeles Pérez-García
AstronomerThis computational study derives a warm-ion equation of state for neutron-star outer-crust conditions using microscopic molecular dynamics. It assumes a cold one-component-plasma composition with one representative heavy nucleus at each density, while refining the interactions through electron screening, finite-size Gaussian ion distributions, and efficient Ewald energy summation. The resulting P(n_B,T) covers baryon number densities of 7.48 × 10^-10 to 2.09 × 10^-4 fm^-3 and k_B T of 1–5 MeV. Within a thermal-effective description based on the thermal adiabatic index Γ_th, the simulations indicate that ion thermal effects are important at higher densities near the inner crust, even at moderate temperatures. These are model results, not observational measurements. The authors compare with other equations of state and provide tables and a neural-network parametrization through Zenodo.
PublicThe researchers used computer simulations to calculate how pressure depends on density and temperature in a model of a neutron star’s outer crust. Their model represents the ions with one kind of heavy atomic nucleus at each density and accounts for both their finite size and the way electrons modify their electrical interactions. The calculations indicate that heat-related ion effects matter in the denser region near the inner crust, even at temperatures the study describes as moderate. This conclusion comes from simulations and a particular description of thermal pressure, rather than observations of a neutron star. The team also supplies tables and a neural-network formula so others can use the calculated equation of state.
Young explorerScientists used a computer to pretend to have a tiny piece of a neutron star’s outer shell. They worked out how hard its hot little particles push as they become more crowded. In their model, heating the particles matters a lot in the more crowded part near the deeper shell. They did not measure this inside a real star; it is what their computer model showed.
Federico Leto di Priolo, Martyna Chruślińska, Davide Gerosa
AstronomerThe authors propose a target redshift, z_t, at which more than 90% of stars form with metallicity below 0.1 times solar, as a way to isolate binary black-hole mergers originating in metal-poor environments. Estimating this epoch requires reconstructing the cosmic star-formation-rate density as a function of iron abundance. Different combinations of empirical scaling relations yield substantially different estimates, from z_t approximately 4 to greater than 10. The paper presents a statistical framework for rapidly comparing astrophysical predictions with forecast observations from next-generation gravitational-wave detectors, including the Einstein Telescope and Cosmic Explorer. By quantifying merger-rate-density variations between the target epoch and the local Universe, the framework maps evolutionary trends and estimates the detection statistics needed to distinguish astrophysical variations from statistical fluctuations. These are model-dependent estimates and forecasts, not reported observational detections.
PublicFuture gravitational-wave detectors are expected to detect merging black holes far back in cosmic history. The authors propose identifying an early era when more than 90% of newly forming stars contained less than one-tenth the Sun’s proportion of elements heavier than helium. This could help researchers isolate black-hole mergers originating in such environments, because stellar composition influences the black-hole population. However, reconstructing when that era occurred depends strongly on the model used: estimates range from a redshift of about 4 to beyond 10. The study also introduces a statistical method to compare predicted merger rates at that early era and nearby, and to estimate how many detections would be needed to separate real changes from random fluctuations. It describes a proposed approach and forecasts, rather than new observations.
Young explorerWhen two black holes join together, they make tiny ripples in space. Future detectors should help scientists find these events from very long ago. The researchers suggest looking back to a time when almost all new stars had very little iron and other heavy ingredients. Those ingredients can affect the black holes that stars leave behind. But different models disagree about when that time was. The researchers also made a way to work out how many black-hole events scientists would need to spot a real change, rather than just a lucky pattern. This is a plan for studying future discoveries, not something they have already seen.
Aditya Sow Mondal, Mahasweta Bhattacharya, Swarnendu Jana+2 more
AstronomerSpectral analysis of 2022 NuSTAR and NICER observations of the accreting millisecond X-ray pulsar IGR J17062-6143 finds the source in a hard state at approximately 0.13–0.14% of the Eddington luminosity. The NuSTAR continuum is dominated by either a power law or disc-photon Comptonization by plasma with electron temperature ≳100 keV. Disc reflection signatures—a broad Fe K feature at 6–8 keV and a Compton hump peaking near 20 keV—are evident regardless of the continuum model. Fits with relxill suggest a disc extending close to the neutron star, at approximately 6–20 gravitational radii, with an inclination of about 41 degrees. NICER also detected type-II-like bursts for the first time in this source, with profiles mostly resembling mode-0 bursts and transitions from mode-0 to mode-1. Persistent pre-burst and burst spectra are described by absorbed Comptonization of disc- and blackbody-distributed seed photons, respectively, in a 1–3 keV corona. The burst origin remains unclear; interaction between the accretion disc and magnetosphere is suggested as a possible explanation, not established as the cause.
PublicObservations made in 2022 with the NuSTAR and NICER X-ray telescopes examined IGR J17062-6143, a rapidly spinning neutron star drawing in matter. It remained in a state dominated by high-energy X-rays, shining at about 0.13–0.14% of its Eddington luminosity, a reference luminosity used by astronomers. NuSTAR detected clear signs of X-rays reflected from the surrounding disc of matter. Models of that reflection suggest the disc reaches close to the star, though this distance is inferred rather than directly measured. NICER also recorded bursts resembling a category called type II, the first such detections reported for this source. Models describe both the steady emission and the bursts using photons scattered by hot electrons. What triggers these bursts is still uncertain: interaction between the incoming disc material and the star’s magnetic surroundings is one possible explanation.
Young explorerScientists used two X-ray telescopes to study a tiny, fast-spinning star that pulls in nearby stuff. They found signs that some X-rays bounced off a disc around the star. Their models suggest the disc comes very close to it. They also saw special bursts of X-rays for the first time from this star. They do not yet know why the bursts happen, but the star’s magnetism might help cause them.
M. Meenakshi, D. Mukherjee, G. Bodo+5 more
AstronomerThis simulation study follows the in situ evolution of cosmic-ray electrons (CREs) in compact AGN jets and winds to assess diagnostics of their synchrotron emission. In jets, CREs undergo multiple shock interactions along the spine toward the hotspot before entering the cocoon through backflows. In winds, acceleration occurs predominantly at the Mach disc, with occasional re-acceleration in turbulent cocoon backflows; the Mach disc is substantially more efficient than the forward shock, which weakens as the wind expands. Mixing of CRE populations makes the radio signatures dependent on their evolution, not just instantaneous conditions. All jet simulations show the flattest spectral indices near hotspots and progressive steepening away from them. Wind spectra steepen with distance from the Mach disc, especially at high radio frequencies because of radiative losses. The authors propose spatially resolved spectral indices, combined with emission and polarization signatures, as a diagnostic where compact-source morphology is ambiguous, particularly at low resolution.
PublicThe source of radio emission in compact outflows from active galactic nuclei remains uncertain. This study uses simulations to explore how energetic electrons evolve in narrow jets and winds, and how that history affects their radio signals. In the jet models, electrons encounter multiple shocks, and the radio spectrum becomes progressively steeper farther from the hotspot. In the wind models, electrons gain energy mainly at a shock called the Mach disc, which is more effective than the outer forward shock. Wind spectra also steepen farther from the Mach disc, especially at higher radio frequencies as electrons lose energy through radiation. Mixing of electron populations means a snapshot of local conditions cannot fully explain the emission. The authors suggest that mapping radio spectra, together with emission and polarization patterns, could help distinguish jets from winds when their shapes look alike; these are simulation-based findings rather than an observational demonstration.
Young explorerScientists made computer models of tiny, speedy particles in jets and winds from active galaxies. The particles get boosts at shocks, and their radio signals change as they travel and lose energy. Different groups of particles also mix together, so what happened to them earlier matters. In the models, the radio signals change with distance from the places where particles get strong boosts. The scientists think maps of these signals could help tell a jet from a wind, even when their shapes look alike. They still need to check how well this works in real galaxies.
Alejandro Cárdenas-Avendaño, Diego Rubiera-Garcia, Frederic H. Vincent
AstronomerThis work presents a unified semi-analytic prescription for emitting flows and time-dependent variability in black-hole movies, rather than observational results. An off-equatorial, nongeodesic Kerr rotation law is constructed by extending an equatorial specific-angular-momentum profile onto cylindrical surfaces, imposing zero polar four-velocity, and normalizing with the local full Kerr metric. A geodesic-like plunging prescription remains optional. The velocity field then advects variability modeled by a four-dimensional, inhomogeneous, anisotropic Matérn-like Gaussian random field. A single composite correlation tensor parametrizes a torus-like disk and central jet. The resulting effective model is intended as an implementation-ready prescription for time-dependent thick-disk and disk-jet emission in relativistic studies.
PublicThe authors present a mathematical recipe for making model movies of glowing material around a rotating black hole. Such movies need descriptions of both how the material moves and how its glow changes over time. Unlike approaches restricted to a flat central plane or an unchanging source, this recipe allows a thick, doughnut-like disk and a central jet, with changing patterns carried along by the modeled flow. It combines a prescribed motion in the black hole’s curved spacetime with a statistical description of variability. This is a modeling framework ready for implementation, not a report of observed black-hole behavior.
Young explorerThe researchers made a math recipe for pretend movies of glowing stuff around a spinning black hole. The recipe describes how the stuff moves and how its glow changes. It can include a thick doughnut-shaped disk and a jet in the middle. It is a way to build model movies, not a movie they watched in space.
Yuhe Zeng, Zhen Pan, Bin Liu+1 more
AstronomerThe study develops two complementary diagnostics for a distant supermassive black hole companion to a QPE source, within a model in which an extreme-mass-ratio inspiral produces eruptions through repeated accretion-disk crossings. The host black hole’s binary motion would introduce a light-travel-time modulation shared in phase by even and odd eruptions. Separately, if the orbiter is a surviving star, its survival constrains companions that would induce tidal disruption through von Zeipel–Lidov–Kozai eccentricity excitation. Applying these diagnostics to GSN 069, the authors find no in-phase timing modulation and hence no timing evidence for a binary, and constrain excluded companion parameter space. This null result does not rule out all companions; the stellar-survival diagnostic is conditional on a stellar orbiter.
PublicRecurring soft X-ray flares from galaxy centers might help reveal otherwise hidden companion black holes. In the model studied here, a small orbiting object produces flares whenever it crosses a disk around a supermassive black hole. A second supermassive black hole could shift the flare arrival times by moving the source closer to or farther from us. If the orbiting object is a star, its survival could also limit which companions are possible, because some would distort its orbit enough to cause tidal destruction. In GSN 069, the researchers find no predicted shared timing shift, so they find no timing evidence for a companion, while restricting some possible companion configurations.
Young explorerA galaxy’s middle makes X-ray flashes again and again. Scientists studied whether the flashes could help them find a hidden black hole nearby. In one galaxy, they did not find the timing change they looked for. That does not mean no hidden black hole is there. If a star makes the flashes, keeping it safe from being torn apart could give another clue.
Marcus DuPont
AstronomerThis theoretical study derives an exact similarity for point-mass accretion: at fixed temperature and composition, scaling mass, radius, and time together and density inversely preserves dimensionless flow, optical depths, and normalized spectra, while luminosity scales with mass. The result retains the full atomic cooling curve but applies only within specified two-body microphysics, radiation, and boundary laws; within that class, the fixed-velocity power-law rescaling is unique. Density-sensitive populations and thermal radiation break the symmetry, as illustrated using public Little Red Dot models. Even known luminosity and density normalization do not remove an exact central-mass–inward-drift degeneracy in a prescribed spherical inflow. A proposed feeding model adds dynamical consistency tests: for point-mass Bondi feeding at fixed ambient sound speed, luminosity and its conversion to retained growth determine the adjustment-to-growth timescale ratio independently of black-hole mass. For the critical isothermal Bondi profile with full retention, comparable timescales require gas mass comparable to the black-hole mass. More generally, steady spherical continuity constrains reservoir mass and minimum radial column from luminosity and transit time. Lower retention slows growth without changing this inventory at fixed supply and transit time.
PublicLight processed by dense gas can help researchers study a black hole, but this theoretical work shows why interpreting it is not straightforward. Under specified physical assumptions, a larger black hole with a correspondingly larger, less dense gas flow can produce the same relative pattern of light, although its total brightness changes. Some density-sensitive features break this similarity. Yet even knowing brightness and gas density does not uniquely determine the black hole’s mass in the spherical inflow model studied, because mass remains entangled with inward drift. The authors propose additional checks based on how the gas is supplied. These relate brightness, growth, and gas travel time to the required gas reservoir. In one particular feeding model, comparable adjustment and growth times require gas weighing about as much as the black hole. These are theoretical constraints, not reported observations.
Young explorerA black hole can grow by taking in gas. Scientists use light from the gas to learn about it, but this study’s calculations show that different black holes and gas flows can make similar-looking light. The scientists also suggest checking whether enough gas is available to feed the black hole. These are calculations, not a new black hole sighting.
Jakub Podgorný, Michal Dovčiak
AstronomerThis chapter reviews the publicly available, XSPEC-compatible KY family of relativistic spectro-polarimetric accretion models for X-ray binaries and active galactic nuclei. In Kerr space-time, the models calculate disc line profiles, reflection from coronal illumination, and thermal emission, including disc-corona interaction and self-irradiation; advanced timing variants also calculate X-ray, UV and optical reverberation. The Comptonized X-ray source is assumed to have an on-axis lamp-post or above-disc slab geometry. Local reprocessing treatments range from analytical approximations to detailed numerical tables, with precomputed STOKES spectro-polarimetric tables used for the most accurate treatment of partially ionized disc atmospheres. The chapter presents standalone, non-relativistic applications of these tables to a distant thin disc and a vertically extended equatorial obscurer, then describes KY ray tracing and individual models. Examples of fits to IXPE observations are shown, but the abstract reports no specific observational constraints or fit outcomes.
PublicThis chapter introduces freely available computer tools for interpreting radiation from matter falling toward black holes in X-ray binary systems and active galactic nuclei. The tools model the radiation's spectrum and polarization, and some also model delayed responses to changing illumination. They account for relativistic effects and assume particular shapes for the region producing the illuminating X-rays, such as a compact source above the disc or a layer over it. Different models use different levels of approximation, including detailed precomputed tables describing how matter transmits and reflects radiation. The chapter explains the tools and shows examples of fitting them to IXPE observations. It presents a modeling framework rather than reporting a new measurement or establishing which assumed geometry is correct.
Young explorerHot stuff around a black hole gives off light. Scientists use computer models to work out what that light might look like after it shines on nearby material and some of it bounces back. This chapter explains a set of those tools and shows examples of comparing their answers with light measured from space. The tools make guesses about how the glowing stuff is arranged; the chapter does not say those guesses have been proved right.
Ishfaq Ahmad Rather, Sarah Louisa Pitz, Jürgen Schaffner-Bielich
AstronomerThis theoretical study considers compact stars with a strong first-order transition to quark matter and an additional self-interacting bosonic dark-matter fluid. In the studied configurations, dark matter changes stability relative to the naive one-fluid criterion, removing the unstable segment between the hadronic and hybrid branches of twin-star sequences. Stable ultra-compact solutions with total compactness M_tot/R_grav ≥ 1/3 occur in two classes: dark-matter halos with f_DM ≳ 0.9 and dark-matter cores with f_DM ≲ 0.02. Their normal-matter surface redshifts differ: z = 2–3.468 for the halo class and z = 0.734–0.808 for the core class. Halo-class redshifts can exceed the Buchdahl limit of z = 2, providing a proposed dark-matter diagnostic. The models also admit hybrid-star 'ultimate twins' with similar masses and visible radii but different dark-matter contents, tidal deformabilities, and surface redshifts. Future X-ray and gravitational measurements of ultra-compact stars outside the allowed neutron-star mass–radius range could probe both dark matter and a quark-matter transition; these are model findings and proposed observational tests, not detections.
PublicCould dark matter change which extremely dense stars can remain stable? This theoretical study explores stars containing both ordinary matter, which can undergo an abrupt transition to quark matter, and a self-interacting form of dark matter. In the models, adding dark matter connects two otherwise separated families of stable stars. The researchers also find stable, exceptionally compact configurations with either a large dark-matter halo or a small dark-matter core. The two types predict different amounts of gravitational reddening of light leaving the ordinary matter, potentially offering a way to distinguish them. Some modeled stars have nearly the same mass and visible size yet different dark-matter contents, light reddening, and responses to tidal forces. Future X-ray and gravitational measurements could test these possibilities, but the study does not report observing such stars or detecting dark matter.
Young explorerScientists used models to imagine very tightly squeezed stars with some mysterious dark matter inside or around them. In these models, dark matter can help some stars stay stable, and two stars that look about the same size and weigh about the same can still be different inside. Light leaving the stars could become redder by different amounts, giving scientists a clue about those hidden differences. These are ideas from models, not stars the scientists have found.
Yutaka Fujita, Yuki Omiya
AstronomerXRISM/Resolve provides a kinematic viscosity constraint at the A3667 cold front, independent of existing imaging constraints. The velocity map shows a line-of-sight jump of 535 km/s, completed within the 100 kpc region immediately inside the front, where the only anomalously broad line is found. Interpreting the interface as a Rayleigh shear-diffusion problem gives ν ~ d²/(4T), with d ≲ 100 kpc. Adopting interaction times from the sizes of the interacting regions divided by the measured velocity yields dynamic-viscosity upper limits of 5.2 × 10³ and 3.3 × 10³ g/cm/s on the cool and hot sides, respectively: 6.4 and 0.72 times their Spitzer values. These are upper limits, not viscosity detections, because XRISM’s angular resolution limits the inferred shear-layer thickness and viscosity scales as its square. The constraints are consistent with imaging evidence for viscosity below the isotropic Spitzer value.
PublicAstronomers used XRISM to study how abruptly hot gas changes speed across a boundary in the galaxy cluster A3667. They measured a velocity difference of 535 kilometres per second along our line of sight. A model of how viscosity spreads a speed change across a boundary lets them use this observation to place upper limits on the gas’s viscosity, or resistance to shearing motion. The limits depend on estimated interaction times, and the transition layer could be thinner than XRISM can resolve, making the actual viscosity lower. This independent approach agrees with earlier evidence from images that the gas is less viscous than a standard theoretical estimate.
Young explorerGas in a giant group of galaxies is sliding past other gas. Astronomers saw a big change in how fast it moves across the place where the gases meet. They used this to work out a limit on how strongly the gas resists sliding. Their telescope cannot see every tiny detail, so they do not yet know the exact answer.
Mateus Zeferino Rennó, Cainã de Oliveira
AstronomerThe authors propose supplementing UHECR arrival-direction flux searches with two energy-weighted statistics: accumulated energy U and local mean energy per particle μ_E. U enhances the significance of sources with high-energy tails, while μ_E probes direction-dependent spectral shapes. They derive a generalization of the Li–Ma significance formula for continuous energy variables. Maximum-likelihood analysis in an exploratory Monte Carlo model indicates that these metrics can improve discovery potential by enhancing localized excesses and revealing hard-spectrum regions missed by particle-flux maps; this is not a reported source detection. The analysis also shows that integrating over right-ascension or declination bands smooths localized μ_E variations into minor perturbations. Thus, small- or intermediate-scale spectral structure remains compatible with the Pierre Auger Collaboration’s reported absence of declination-band spectral variations.
PublicFinding where ultrahigh-energy cosmic rays come from usually means looking for directions with unusually many arriving particles. This study proposes also examining the total energy and the average energy per particle in each region of the sky. In exploratory computer simulations, these measures helped highlight possible sources rich in high-energy particles and regions whose energy patterns were hidden in ordinary particle-count maps. The researchers also developed a statistical formula to assess such signals. These are proposed tools tested in simulations, not newly detected cosmic-ray sources. The study further shows that averaging across broad sky bands can largely wash out localized energy differences, so the Pierre Auger Collaboration’s reported lack of differences between declination bands does not rule out smaller regions with distinct energy patterns.
Young explorerScientists want to know where super-energetic space particles come from. Usually, they look for places in the sky where extra particles arrive. This study suggests checking how much energy the particles bring altogether and how much each one brings on average. In pretend skies made by a computer, these checks helped reveal clues that counting particles alone could miss. They have not found a new source this way yet. Mixing together particles from a big strip of sky can also hide differences in smaller patches, so a strip that looks much like the others could still contain a different little patch.
Poulami Dutta Roy, Tanmaya Mishra, Achal Kumar+1 more
AstronomerPopCWB is a Bayesian framework for forward inference of the binary black hole population using the unmodeled coherent WaveBurst (cWB) search. Instead of individual-event posterior samples, it uses simulated events reconstructed by cWB, with total masses estimated by machine-learning regression, to construct marginal probability distributions for the likelihood. Applied to cWB detections from the LIGO–Virgo–KAGRA third observing run, it constrains an astrophysically motivated population model incorporating pulsational pair-instability supernovae and dynamical mergers. Within this model, the analysis predicts a maximum black hole mass from stellar evolution of 45.5 solar masses, with reported uncertainty of +5.1/−6.1 solar masses, and infers a local binary black hole merger rate of 23.0 Gpc⁻³ yr⁻¹, with uncertainty of +16.6/−8.3 Gpc⁻³ yr⁻¹. These are population-model inferences, not direct measurements of a universal mass ceiling. The results are compared with existing population models.
PublicThe researchers present PopCWB, a method for learning about the population of merging black hole pairs by comparing models with detected events. It uses many simulated signals processed by the coherent WaveBurst search, together with machine-learning estimates of the pairs’ total masses, rather than detailed probability estimates for each individual event. Applied to detections from the third LIGO–Virgo–KAGRA observing run, the method tests a model that includes effects of certain stellar explosions and mergers driven by gravitational interactions. The model predicts a maximum mass for black holes produced by stellar evolution of 45.5 times the Sun’s mass, with uncertainty of +5.1/−6.1 solar masses. It also estimates a local merger rate of 23.0 events per cubic gigaparsec per year, with uncertainty of +16.6/−8.3. These estimates depend on the population model; they do not establish a maximum mass for every black hole.
Young explorerScientists want to learn about pairs of black holes that come together. They made lots of pretend black hole signals on computers and compared them with signals that detectors really found. Their new method helps them work out how heavy these black holes might be and how often pairs join together. Their model suggests a limit to how heavy black holes made by stars can be, but the answer is still uncertain. It is not a rule for every black hole.
Jiachang Zhang, Zhiyuan Li, Xiangdong Li+3 more
AstronomerTwo decades of multi-mission X-ray observations show that M81F4, a source toward M81, remains persistently luminous at approximately 10^38–10^39 erg/s in the 0.5–8.0 keV band and exhibits recurrent flares lasting a few hundred seconds, with peaks of a few 10^39 erg/s. The observed mean recurrence time is about 0.5 day, with a minimum of about 6 ks. The stacked flare profile rises rapidly and decays more slowly, without significant hardness evolution. Both flare and non-flare spectra are dominated by a hard power-law continuum; evidence for highly ionized Fe lines outside flares is marginal. These properties disfavor classical Type I and Type II bursts and lack a close analogue among known X-ray binaries. The authors favor, but do not establish, a magnetized neutron star accreting persistently at a high rate from an intermediate-mass donor, with disk–magnetosphere boundary instabilities producing the flares. If confirmed, this interpretation could identify a hidden X-ray binary population with sustained magnetically regulated accretion and brief super-Eddington episodes.
PublicObservations spanning two decades show that M81F4, an X-ray source seen toward the galaxy M81, stays bright while repeatedly producing short flares. Each flare lasts a few hundred seconds, with an observed average interval of about half a day; the shortest observed interval is about 6,000 seconds. Combining the flares reveals a quick brightening followed by a slower fade, without a significant change in the balance of higher- and lower-energy X-rays. The behavior does not closely resemble known X-ray binaries and argues against two classical types of X-ray bursts. The researchers favor an explanation involving a strongly magnetized neutron star drawing material from a companion star, with disruptions where the surrounding disk meets the magnetic field causing the flares. This explanation is not yet confirmed. If correct, the source could point to an overlooked population of binaries whose magnetically controlled feeding produces brief episodes above the Eddington luminosity limit.
Young explorerAstronomers watched an X-ray light in space called M81F4. It stays bright, but sometimes gets much brighter for a few minutes. Its flashes brighten quickly and fade more slowly. The scientists think a tiny, very dense star with a strong magnetic field might be pulling in material from another star. The flashes might happen when that material meets the magnetic field, but they do not know for sure yet.
Jitumani Kalita, Debaprasad Maity, Ayan Chatterjee
AstronomerThis theoretical study considers a non-extremal black hole immersed in a thermal bath, assuming its emitted Hawking radiation thermalises at the bath temperature. Beyond greybody factors and infrared and ultraviolet kinematic restrictions, the authors find that this assumption significantly reshapes the approximately Planckian spectrum and modifies the black hole decay rate. Applied to primordial black holes in the early universe, their treatment predicts faster evaporation for very light PBHs formed immediately after inflation, changing their lifetimes. Possible phenomenological implications are suggested rather than established observationally.
PublicBlack holes are expected to slowly lose mass by emitting Hawking radiation. This theoretical study asks how that process changes if a black hole sits in a hot environment and its emitted radiation reaches the same temperature as its surroundings. Under that assumption, the calculations change both the radiation’s spectrum and the rate at which the black hole loses mass. The authors predict that very light black holes formed just after the universe’s inflationary phase would disappear faster. This is a theoretical prediction, not an observed effect, and its possible consequences remain to be explored.
Young explorerScientists think black holes can slowly shrink by giving off tiny bits of energy. In this study, they used maths to ask what happens if a black hole is in a hot place and the energy it gives off becomes as hot as that place. Their calculations suggest that very light black holes from the universe’s earliest days could shrink away faster. They have not watched this happen.
Mark G. Alford, Liam Brodie, Michael Buballa+3 more
AstronomerThe authors calculate electron- and muon-neutrino absorption mean free paths in two-flavor color-superconducting (2SC) quark matter over densities and temperatures relevant to binary neutron star mergers. They use a Nambu–Jona-Lasinio model with self-consistent mean-field calculations, restricting absorption contributions to unpaired quarks because the 2SC gap is large. At low temperatures, absorption on down quarks is kinematically forbidden, so absorption on strange quarks dominates. Increasing temperature or neutrino energy opens the down-quark channel and shortens the mean free path. In equilibrated 2SC matter with electron lepton fraction Y_Le = 0.1, the calculations yield a degenerate neutrino gas with absorption mean free paths of meters or less, independent of temperature. These are model results, not observations of merger matter.
PublicThis theoretical study examines how far electron and muon neutrinos can travel before being absorbed in a proposed form of quark matter under conditions relevant to merging neutron stars. The calculations include only quarks that are not paired with other quarks. At low temperatures, absorption by down quarks is blocked by the reaction's energy and momentum requirements, leaving strange quarks as the main absorbers. Higher temperatures or neutrino energies allow down quarks to absorb neutrinos too, shortening the distance neutrinos travel. For one equilibrium composition, with an electron lepton fraction of 0.1, the model predicts a densely packed neutrino gas and absorption distances of meters or less regardless of temperature. The study does not establish that this form of matter is present in actual mergers.
Young explorerScientists used math to study tiny particles called neutrinos in a special kind of matter that might be found when two neutron stars crash together. In their model, some tiny pieces of matter can swallow neutrinos when it is cool. When it gets hotter, or the neutrinos have more energy, another kind can swallow them too, so they cannot travel as far. For one mix of this matter, the math says neutrinos travel only a few meters or less before being swallowed. This is a calculation, not something scientists watched happen in a star crash.
Jorge Terol Calvo, Marco Taoso, Andrea Caputo+2 more
AstronomerThe authors search the eROSITA-DE DR1 data for a monochromatic X-ray line from dark matter decay in the Large Magellanic Cloud halo over 1–9 keV. They find no evidence for such a line and derive lower limits on the dark matter lifetime. Interpreting these bounds for sterile-neutrino and axion-like-particle dark matter, they obtain upper limits on the active–sterile mixing parameter sin²(2θ) and the ALP–photon coupling g_aγ for dark matter masses of 2–18 keV. The results provide new strong constraints below 5 keV, rather than a detection of either candidate.
PublicResearchers searched X-ray data from eROSITA-DE DR1 for a signal that could arise if dark matter surrounding the Large Magellanic Cloud decays. Two possible dark matter particles—sterile neutrinos and axion-like particles—could produce an X-ray line at a particular energy. No evidence for this signal was found. The absence of a detected line lets the researchers place limits on how quickly such dark matter could decay and, under each particle interpretation, how strongly it could mix or interact with ordinary particles. The study tests dark matter masses from 2 to 18 keV and provides new strong constraints below 5 keV; it does not establish what dark matter is.
Young explorerScientists looked for a special kind of X-ray light around a galaxy called the Large Magellanic Cloud. Two possible kinds of invisible stuff called dark matter might make that light as they break down. The scientists did not find evidence of the special light. That helps them narrow down how those possible kinds of dark matter could behave, but it does not tell us what dark matter really is.
Caroline B. Owen, Alexandre Toubiana, Davide Gerosa
AstronomerThis paper develops an idealized Gaussian-based analytical model of how single-event parameter correlations and systematic biases affect inferred compact-binary population correlations. Within the model, correlations between two parameters at the single-event level increase uncertainty in their population-level correlation, potentially masking a genuine relationship. If waveform-model biases are correlated across a catalog, a population analysis targeting correlations can absorb those biases and misinterpret them as a population relationship. These are analytical findings rather than evidence of false correlations in an observed catalog; the model is intended to guide more detailed investigations.
PublicAs gravitational-wave detections accumulate, researchers are beginning to study how properties such as the masses and spins of compact binaries are related across the population. This paper uses a simplified mathematical model to explore how those studies could be misled. Linked uncertainties in the properties inferred for individual events can make a real population-wide relationship harder to detect. If errors in the waveform models produce related biases across many events, those biases can instead look like a population-wide relationship. The study identifies possible pitfalls; it does not show that a particular observed relationship is false.
Young explorerScientists study ripples in space to learn about pairs of objects moving together. They want to know whether some of the objects’ features tend to go together. Using a simple math model, this study shows how mistakes in working out those features could hide a real pattern or make a pretend pattern look real. It warns scientists what to watch out for, but does not show that they have found a pretend pattern in the sky.
Aditya Vaswani, Leor Barack, Oliver Long+1 more
AstronomerThe authors present a numerical scheme and implementation code for time-domain integration of the 1+1-dimensional Teukolsky equation with a point-particle source, using comoving, spatially compactified hyperboloidal coordinates. Comoving coordinates simplify imposing jump conditions along the particle’s worldline. Tests for a scalar field on a Schwarzschild background cover circular and scattering geodesic sources. A test implementation for the s = -2 Teukolsky equation demonstrates long-term stability and no nonphysical growing-mode behavior, with comparison to similar results using noncompactified characteristic coordinates. These are numerical demonstrations, not observations; full gravitational self-force calculations for extreme-mass-ratio scattering remain a future application.
PublicThe researchers introduce computer code for calculating how fields evolve around a black hole when a small particle moves nearby. Their coordinate system follows the particle and represents an infinitely extended region within a finite computational space. In numerical tests, the method avoids artificial growth that can spoil some other calculations. They test a scalar field for both an orbiting particle and a particle on a scattering path, then demonstrate long-term stability in a test calculation using an equation for gravitational disturbances. The work is a computational advance, not an astronomical observation. It could support future calculations of how a small object’s own gravitational field affects its motion during an encounter with a much more massive black hole.
Young explorerScientists made a new computer method to study a tiny object moving near a black hole. Some computer methods make pretend ripples grow when they should not. In their tests, the new method avoided that problem and kept working steadily for a long time. These were computer tests, not something seen in the sky. The method could help scientists do harder calculations about black-hole encounters later.
Bo-Xuan Ge
AstronomerUsing an existing numerical-relativity catalogue of equal-mass, head-on massive boson-star collisions, the authors construct branch-conditioned reduced-basis surrogates for the real (2,0) and (4,0) waveform modes and infer the dynamical merger branch without supplying intrinsic source parameters. On a frozen test set of 60 held-out samples, either mode correctly identifies the branch in every case, demonstrating that branch information is not confined to the dominant (2,0) mode. The inference recovers the absolute value of phi_c with a mean relative error of 4.30% and selects the correct lambda from 10, 50, 100, and 300 in 68.3% of test samples. These are results within the present noiseless simulation catalogue, not observational detections or demonstrated performance in noisy data.
PublicThe researchers tested whether gravitational-wave patterns from simulated boson-star collisions can reveal which dynamical merger branch a collision follows, without being given the objects' underlying parameters. They used an existing collection of equal-mass, head-on collision simulations to build simplified waveform models. In 60 held-out tests, either of two waveform components, labeled (2,0) and (4,0), identified the correct branch every time. The method also estimated the absolute value of a parameter called phi_c with a mean relative error of 4.30%. It chose the correct value of another parameter, lambda, from 10, 50, 100, and 300 in 68.3% of tests. These findings apply to the noise-free simulation collection studied; they do not establish how well the method would work on real, noisy observations.
Young explorerScientists used computer-made collisions of boson stars with equal masses, crashing straight into each other. They asked whether the waves from each pretend crash could tell them which kind of crash happened, without giving the computer the hidden details first. In 60 new tests, it picked the right kind every time using either of two parts of the waves. It also guessed a hidden number, the absolute value of phi_c, with an average relative error of 4.30%. For another number, lambda, it chose among 10, 50, 100, and 300 and was right in 68.3% of tests. These were computer tests with no noise, not measurements of real crashes, so we do not yet know whether it would work as well on noisy real signals.
Nikita M. Shirokov, Ilya Nachevsky
AstronomerFull 3+1 numerical-relativity simulations test Bondi’s prediction of runaway acceleration for a positive–negative active-mass pair. Constraint-satisfying initial data describe two complex scalar fields with identical self-interactions, one coupled to the Einstein equations with the opposite sign. Its stars have positive inertial and passive masses but negative active and ADM masses. Equal-and-opposite ADM-mass pairs accelerate together at constant separation, with total momentum remaining zero to within 0.5%. The acceleration follows Newtonian mass and separation dependence, reverses when the stars are exchanged, and is absent for same-sign pairs and isolated stars. No gravitational radiation is detected. These are simulated head-on pairs released from rest, not observed astrophysical systems. Runs generally reach a few percent of light speed; the longest reaches one tenth of light speed with both stars intact. The finite evolutions support the predicted behavior but do not demonstrate acceleration without limit. The authors identify these as, to their knowledge, the first numerical-relativity evolutions of asymptotically flat negative-ADM-mass bodies.
PublicCould two objects speed up together without moving farther apart? Computer simulations of Einstein’s gravity equations reproduce this behavior for a hypothetical pair of stars with equal and opposite gravitational masses. One star is made from a specially modeled field that contributes to gravity with the opposite sign; these are not observations of real stars. The simulated pair accelerates while keeping the same separation, and its total momentum stays consistent with zero to within 0.5%. The acceleration changes with mass and distance as Newton’s law predicts, and no gravitational waves are detected. In the longest simulation, both stars remain intact as the pair reaches one tenth of light speed. The results support an old theoretical prediction, but the simulations do not establish that the acceleration could continue forever.
Young explorerScientists made two pretend stars inside a computer. One had a strange kind of gravity. Together, the stars went faster and faster while staying the same distance apart, like two runners speeding up side by side. This happened in a computer, not in stars people have found in space. The test ended, so it cannot tell us whether they could keep speeding up forever.
Vaishak Prasad
AstronomerNRHJSur3dq8 is a family of numerical-relativity surrogate models for non-eccentric, aligned-spin binary black holes, inspired by an action-angle parameterization. It supplies Hamiltonian values, azimuthal action and an orbital clock as functions of phase, alongside waveforms, nearly analytic derivatives and modeling uncertainties. Slowly varying quantities are represented on shared adaptive Chebyshev elements and regressed with Gaussian processes; time-parameterized merger-ringdown elements replace the adiabatic description where it fails. Fixed-hyperparameter leave-one-out validation of the central AA variant gives unweighted mismatches of 1.6(+62/-1.5) × 10^-6 for the (2,2) mode and 2.8(+84/-2.7) × 10^-6 for all modes. Separately, sky-averaged, signal-to-noise-ratio-weighted in-sample mismatches against SXS training simulations range from 8.9 × 10^-7 to 2.8 × 10^-5 across total masses of 40–120 solar masses, using 32 orientations per simulation. The work also uses post-Newtonian hybridization and provides calibrated Gaussian-process predictive uncertainty. A full non-hybridized waveform evaluates in 12.5 ms on a single CPU call; a batch of 4096 achieves 0.43 ms per waveform at a 25 Hz starting frequency. These are simulation-based modeling and performance results, not observational measurements.
PublicThe researchers present a fast computer model of gravitational waves from two black holes spiraling together and merging, restricted to non-eccentric orbits and spins aligned with the orbit. It approximates detailed numerical-relativity simulations rather than reporting a newly observed merger. Tests that leave individual simulations out of training find small waveform differences, though with a substantial spread; comparisons with simulations used for training are reported separately. The model also tracks orbital dynamics, estimates its own modeling uncertainty and calculates how the waves change when the black holes’ physical properties change. A complete waveform takes 12.5 milliseconds in a single CPU call, with faster per-waveform processing in large batches. The work also joins waveforms to post-Newtonian calculations.
Young explorerWhen two black holes circle each other and join together, they make ripples in space. Scientists built a fast computer shortcut to work out what those ripples should look like for certain kinds of black-hole pairs. They checked it against more detailed computer calculations, not new sightings in space. The shortcut usually matched closely, but not perfectly, and it also estimates how uncertain its answers are.
Kentaro Sakai, ByungJun Kang, Akito Nakano+1 more
AstronomerThe study tests Bayesian reconstruction of non-Maxwellian electron distribution functions using synthetic collective Thomson scattering (CTS) spectra generated from known distributions. Sufficiently flexible candidate models recover the overall distribution shape. Bayesian evidence favors the ground-truth model when it is included; otherwise, it favors the candidate with the fewest parameters that adequately approximates the data. The selected model’s posterior describes characteristic distribution features and their uncertainties. The authors attribute additional spectral peaks to a combination of modified dispersion and reduced Landau damping. These synthetic-data tests support the method’s potential for objective inference from observed CTS spectra, but the abstract does not report an application to actual observations.
PublicThe researchers tested a way to infer how electrons are distributed by analyzing collective Thomson scattering spectra. They used computer-generated spectra whose underlying electron distributions were already known, rather than actual observations. Flexible mathematical models could reproduce the broad shape of those distributions. A Bayesian comparison favored the true model when it was available; otherwise, it favored the simplest candidate that adequately matched the data. The method also estimated uncertainty in the inferred features. The authors explain extra spectral peaks through changes in wave behavior and weaker damping. The tests suggest a route to interpreting real spectra, but do not demonstrate that step.
Young explorerThe researchers made pretend signals from electron patterns they already knew. Then they tested whether computer models could work backward to find those patterns. Models with enough flexibility found the main shapes. The comparison favored the true model when it was offered, or a simpler model that fit well when it was not. The tests used pretend signals, not real measurements.
Nikita M. Shirokov, Ilya Nachevsky
AstronomerThe authors report what they believe are the first three-dimensional numerical-relativity evolutions of massive Ellis–Bronnikov wormhole binaries, supported by a phantom scalar field with nowhere-positive energy density. They construct constraint-satisfying initial data and evolve isolated throats and pairs using adaptive mesh refinement. An isolated throat either collapses or inflates depending on the perturbation sign, with its instability rate agreeing with linear theory to within 1.9%. Initially stationary pairs repel for like-signed scalar charges and attract for opposite signs; the relative strengths approximately match the scalar force-law prediction, and only opposite-signed pairs merge. In a head-on merger, a common horizon encloses both still-open throats, subsequently loses 28% of its area while absorbing the scalar field, and approaches the Schwarzschild radius associated with the pair’s mass. Flybys produce no horizon, and both throats inflate. Each encounter emits a short gravitational-wave burst and a scalar dipole wave carrying comparable, negative energy. An isolated collapsing throat rings at the resulting black hole’s quasinormal frequency. No throat survives beyond a few orbital periods, even with tiny initial perturbations, so these simulated binaries do not inspiral. These are numerical findings, not observations, and their scope is limited to one phantom-scalar model, equal masses, one throat compactness, and zero spin.
PublicComputer simulations explore how pairs of hypothetical wormholes behave when held open by an unusual field whose energy density is never positive. In this model, the wormholes are unstable: a small disturbance makes an isolated wormhole either collapse into a black hole or expand. Pairs starting at rest repel if their field charges have the same sign and attract if the signs are opposite. A head-on merger produces a black-hole horizon around both wormholes while they are still open; that horizon then shrinks in area as it absorbs the unusual field. In simulated flybys, no horizon forms and both wormholes expand. Encounters release brief gravitational waves alongside waves in the supporting field that carry negative energy. None of the wormholes lasts more than a few orbital periods, so the pairs do not gradually spiral together. These are simulations, not detected wormholes, and the findings apply only to the particular field model and equal-mass, nonspinning configurations studied.
Young explorerScientists used computers to study imaginary space tunnels called wormholes. An unusual field helped hold them open, but they did not stay steady. Some grew bigger, and some collapsed into black holes. Two tunnels could push apart or pull together, depending on the field. They did not last long enough to slowly spiral together. This happened in one kind of computer model, not in wormholes scientists watched in space.
Luka Vujeva, João S. Santos, Brian C. Seymour
AstronomerThis theoretical work develops a formalism for low-frequency gravitational-wave lensing corrections when a binary source lies in the strong gravitational field of a massive black hole. Using the Hamilton–Jacobi equations for null geodesics, the authors construct a time-delay surface without the thin-lens approximation and directly evaluate its diffraction integral. For a stationary source at 10M, they report agreement with a relativistic wave-scattering model at the 6.5% level for peak amplification and the 0.3% level for the first diffractive fringe. At a source distance of 10^4 M, amplitudes agree with the weak-field point-mass lens to better than 1%, although noticeable dephasing appears between amplification peaks at higher frequencies. The authors describe the framework as valid from approximately 6M outward, connecting strong- and weak-field treatments of beyond-geometric-optics lensing. These are theoretical model comparisons, not observational results.
PublicA black hole can bend gravitational waves, changing how strongly they arrive and creating interference patterns. Standard wave-based calculations rely on assumptions that fail when the source is too close to the black hole. This study introduces a mathematical method that avoids treating the black hole’s bending effect as confined to a thin plane. In tests against other theoretical models, it closely reproduces selected features of the wave amplification both near the black hole and much farther away. The agreement is not exact: some amplification peaks become misaligned at higher frequencies. The method is intended to connect calculations across strong and weak gravity; the abstract reports no observations of actual gravitational-wave signals.
Young explorerA black hole can bend waves of gravity and make them stronger or weaker, a little like ripples adding together in water. When the waves start very close to the black hole, the usual math becomes less reliable. Scientists made a new way to do the math and checked it against other calculations. Many parts matched closely, but some did not line up perfectly. This was a math study, not a report of waves they had seen.
