K. HyeongHan, K. Finner, W. Lee+10 more
AstronomerDeep XMM-Newton and Chandra observations compare MACS J1752.0+4440 and ZwCl 1856.8+6616, two double-radio-relic, 1:1 mass-ratio mergers with similar relic separations but nearly an order-of-magnitude difference in total mass. At MACS J1752.0+4440’s northeastern relic, the surface-brightness discontinuity implies a Mach number of 1.4 ± 0.2; the temperature jump gives a weaker, 2σ constraint of ≲2.3, versus the radio-derived 3.1 ± 0.1. No discontinuity is detected at its southwestern relic or clearly detected at either ZwCl 1856.8+6616 relic. MACS J1752.0+4440 retains relatively low-entropy cores within Mpc-scale stripped-gas structures. Its nearly uniform tail brightness and southwestern plateau coincident with a third lensing mass peak favor an off-axis collision and complex assembly history. In ZwCl 1856.8+6616, the northern X-ray peak leads its BCG and lensing peak, while the hotter southern peak is laterally displaced from both. This asymmetry favors a phase near or after first apocenter and a possible slingshot-like gas morphology. Two TNG-Cluster simulation analogs show a minor merger followed by an off-axis major collision producing MACS-like tails and, later, ZwCl-like gas structures; these are analogs, not direct observations of either system’s history. The authors interpret the X-ray morphologies as independently confirming relic-based timing: MACS before and ZwCl after first apocenter, despite similar relic and lensing configurations.
PublicTwo pairs of colliding galaxy clusters can look similar in radio emission and maps of their mass yet be at different stages of their collisions. Deep X-ray observations reveal contrasting gas structures in MACS J1752.0+4440 and ZwCl 1856.8+6616. The first has surviving relatively low-entropy cores surrounded by long structures of stripped gas. A detected shock there appears weaker from the X-ray measurements than from radio measurements, although the temperature-based constraint is less precise. In the second system, gas peaks are displaced from the brightest galaxies and mass peaks, and no clear brightness discontinuity is detected at either radio relic. The researchers interpret these patterns as placing the first system before, and the second after, the clusters’ first maximum separation following their initial encounter. Simulated collisions produce resembling gas structures, supporting—but not directly establishing—a history involving an earlier smaller merger and an off-center major collision.
Young explorerTwo huge groups of galaxies have been crashing together. Scientists looked at their hot gas using X-rays. One has long trails of gas, and the other has gas shifted away from its galaxies. The scientists think these clues show different moments in the crashes, even though the groups look alike in other ways. Computer pretend-crashes made similar shapes, but they cannot tell us exactly what happened.
Rostom Mbarek
AstronomerThe authors propose an onset scenario for radiatively efficient AGN in which circumnuclear stellar and supernova-driven winds feed a compact disk reservoir with mass and partially ordered magnetic flux. If a coherent poloidal component survives inward advection, its amplification lowers plasma beta until mean Maxwell stresses dominate MRI turbulence, vertically squeezing the disk and creating a magnetically dominated wedge. In a quasi-force-free treatment, the wedge approaches a critical twist where net radial transport reverses, defining a saturation radius r_c ∼ 10 r_g. Disk–wedge pressure balance confines flux at this boundary, where incoming flux is preferentially shed, yielding B_r ∝ r^-2 inside. The field topology gives a normalized saturation flux φ ∼ 50, consistent with the MAD plateau in GRMHD simulations; this is a model derivation, not a new observational measurement. The compact, time-dependent saturation region is proposed as an X-ray corona candidate: collisionless and magnetized, plausibly pair-rich at high compactness, with hadronic pair injection only a conditional additional channel. The authors connect model scalings to observed coronal sizes, variability, and corona–jet power partition, rather than establishing the scenario observationally. They also suggest that Little Red and Blue Dots could be a disk-reservoir phase preceding luminous AGN activity.
PublicThis paper proposes a way for a supermassive black hole to begin powering a bright galactic nucleus. Winds from nearby stars and supernovae would supply gas and magnetic fields to a small disk around the black hole. If an organized part of the field survives the journey inward, it could strengthen enough to squeeze the disk and create a magnetically dominated region above it. The model predicts a compact boundary where magnetic flux accumulates and incoming flux is preferentially shed. Its calculated saturation level agrees with a plateau found in computer simulations. The authors suggest that this changing magnetic region could be the source of the nucleus’s X-rays. Under sufficiently intense conditions, it might also contain many particle–antiparticle pairs. They relate the model to observed X-ray-source sizes, variability, and the division of power between the X-ray region and a jet, but these connections do not establish the proposal as fact. They also speculate that Little Red and Blue Dots may represent an earlier stage before bright nuclear activity.
Young explorerThe scientists have an idea about how a giant black hole’s neighborhood starts to shine brightly. Winds from stars and exploding stars might bring gas and magnetic fields into a little spinning disk. The magnetic fields could squeeze the disk and make a small, changing region above it that gives off X-rays. Some of their calculations fit what computer models show, but this is still an idea, not something they have proved happens.
Noah Roux, Irene Tamborra, Maryna Mesiura
AstronomerThe authors solve neutrino flavor evolution in a two-dimensional half-annulus during the stalled-shock phase of a core-collapse supernova, using a polar-angle distribution, two effective azimuthal angles, and an energy distribution. Their setup represents LESA with an electron-neutrino excess in the North and an electron-antineutrino excess in the South. Electron-neutrino versus electron-antineutrino angular crossings occur in the electron-lepton-number-depleted South, while electron versus non-electron flavor energy crossings occur throughout the annulus for both neutrinos and antineutrinos. In these calculations, collisional instabilities drive conversion just before decoupling, fast instabilities are prominent in the South, and slow instabilities dominate elsewhere. Conversion is most efficient in the South and enhances the LESA dipole by 5–10%, independently of neutrino-mass ordering. These model findings suggest possible implications for global neutrino asymmetries and hydrodynamical instabilities, rather than demonstrating those effects in an observed supernova.
PublicThe researchers calculated how neutrinos—particles that can change between different types, called flavors—behave as they stop interacting with matter in a collapsing star. Their model includes LESA, an instability that makes the balance of electron neutrinos and their antiparticles different on opposite sides. Different mechanisms drive flavor changes in different regions, with the strongest conversion on the side richer in electron antineutrinos. In this model, flavor changes strengthen the LESA imbalance by 5–10%, regardless of the neutrino-mass ordering. The calculations suggest that direction-dependent flavor changes could influence large-scale particle imbalances and fluid instabilities in supernovae; they are not observations of an actual explosion.
Young explorerInside a collapsing star, tiny particles called neutrinos can change from one kind to another. Scientists used a model to study this when two sides of the star have different mixes of these particles. In their model, the particles changed most on one side, making the difference between the sides a little bigger. This might matter for how the star behaves, but the scientists did not watch it happen in a real star.
Antonio C. Rodriguez, Kareem El-Badry, R. Michael Rich+11 more
AstronomerThe authors report 1eRASS J042633.5−250226 (1eRASS J0426/Valeria), at 265 pc, as the third known magnetic white-dwarf propeller: a close binary in which rapid WD rotation ejects transferred material rather than allowing accretion. It was identified by combining SRG/eROSITA and Gaia data through the “X-ray Main Sequence.” TESS reveals AE Aqr-like flaring and orbital modulation at approximately 6.62 hr; phase-resolved Palomar/DBSP spectroscopy confirms the orbital period and gives K2 = 202 ± 7 km/s. ZTF shows month-long high/low-state changes. Palomar/CHIMERA detects optical pulsations on three nights, with the strongest detection at 26.8 s, but identifying this period as the WD spin requires confirmation. Low-state donor fitting gives a late K-type star with a temperature of 4100 ± 150 K. Optical Zeeman splitting suggests a candidate WD field of 26 ± 3 MG, from which the authors infer future evolution into a polar. The system is X-ray faint, with LX approximately 7 × 10^30 erg/s; neither radio emission nor an eROSITA X-ray spin period is detected. Its proximity, combined with evolutionary-model constraints on the propeller-phase duration, yields an estimated birth-rate density of approximately 8 × 10^−16 pc^−3 yr^−1. Agreement with the magnetic-cataclysmic-variable birth rate suggests, rather than establishes, that a substantial fraction undergo a propeller phase.
PublicAstronomers report a third example of a rare binary system in which a rapidly rotating magnetic white dwarf throws away material supplied by its companion instead of collecting it. Called 1eRASS J0426/Valeria, the system lies 265 parsecs away. Its brightness shows flares, an orbital cycle of about 6.62 hours, and high and low states lasting roughly a month. Spectroscopy confirms the orbital period and identifies a relatively cool companion star. Fast optical observations also reveal pulses, with the strongest signal repeating every 26.8 seconds, but more observations are needed to confirm that this is the white dwarf’s rotation period. A possible magnetic-field measurement leads the authors to predict that the system will eventually become a different type of magnetic binary called a polar. It is faint in X-rays and was not detected in radio observations. Combining its proximity with evolutionary models suggests that many magnetic white-dwarf binaries may pass through this material-ejecting stage; that broader conclusion remains an inference.
Young explorerAstronomers found two stars close together. They think one, a small star called a white dwarf, spins so fast that it tosses away stuff coming from its partner instead of keeping it. Their light flickers and flares. Some flashes repeat about every 27 seconds, but astronomers need to check whether that really tells us how fast the little star spins. This is only the third pair of this kind they have found.
M. C. Baglio, S. E. Motta, A. P. Nitindala+1 more
AstronomerThis review chapter synthesizes five decades of observations of neutron star low-mass X-ray binaries, following accretion from the outer disc to the stellar surface. It covers atoll and Z-sources, ultracompact binaries, accreting millisecond pulsars, and transitional millisecond pulsars, relating their spectral states, timing, and multiwavelength behaviour to inner-flow physics. Topics include Type-I bursts as probes of nuclear burning and stellar structure, boundary and spreading layers, and the role of relativistic jets and ionised winds in the accretion-ejection cycle. IXPE polarimetric observations provide new, model-dependent constraints on the geometry of the disc, corona, spreading layer, and jets beyond what spectroscopy alone can resolve, complemented by optical and infrared polarimetry.
PublicThis chapter reviews what astronomers have learned about neutron stars that pull gas from a low-mass companion star through a surrounding disc. As the gas falls inward, it releases gravitational energy; the neutron star's solid surface and magnetic field make these systems valuable for studying extreme physics. The review explains how changes in light, rapid variations, and thermonuclear X-ray bursts help researchers investigate the gas flow and the neutron star itself. It also discusses outgoing jets and winds. Observations from the Imaging X-ray Polarimetry Explorer measure the polarization of X-rays, adding clues about the arrangement of the emitting regions that their spectra alone cannot provide. Those geometric interpretations still depend on the models used.
Young explorerA neutron star is a tiny, very dense star that can pull gas from a nearby star. The gas swirls around it and gives off X-rays as it falls in. This chapter tells what scientists have learned by watching these stars, including bright bursts when fuel burns on their surfaces. Scientists also look at how the X-ray light is lined up to get clues about where it comes from. Those clues help, but they do not give a completely certain picture.
Ilias Cholis, Leo Qiyuan Hu, Yi-Ming Zhong
AstronomerThe study fits spatial templates to Fermi gamma-ray data at high Galactic latitudes over 0.3–900 GeV, searching for emission beyond known astrophysical components, including in the Galactic Stellar Halo region. The authors test multiple sky regions, alternative Galactic diffuse emission models, and fitting schemes to assess sensitivity to modeling complexity. They confirm the previously reported halo-like emission but interpret it as likely arising from the Fermi Bubbles rather than Galactic-halo dark matter annihilation. Updated templates for the Flat Bubbles and their Cocoons and Inner Bubbles jointly account for that emission. The authors also estimate these components’ fluxes and spectral properties. The revised model offers input for understanding the Bubbles’ origin, without establishing that origin.
PublicResearchers examined high-latitude gamma-ray observations from Fermi to look for radiation not explained by known sources. They tested several ways of modeling the sky and found that a previously reported halo-like glow is real. However, their analysis suggests it is probably emission from the Fermi Bubbles, rather than a signal of dark matter particles annihilating in our galaxy’s halo. Their updated model includes the Bubbles and smaller structures within them, which together explain the reported glow. They also estimated how much gamma-ray radiation these structures emit and how it varies with energy. The work may help researchers understand the Bubbles’ origin, but it does not settle that question.
Young explorerScientists studied a kind of light in space called gamma rays. They found a glow that other scientists had noticed before. It probably comes from big glowing shapes called the Fermi Bubbles, not from mysterious stuff called dark matter. When they included smaller shapes inside the Bubbles in their model, they could explain the glow. This may help them learn how the Bubbles began, but they do not know that yet.
José Carlos Olvera M., Daniela D. Doneva, Pablo Cerdá-Durán+2 more
AstronomerIn massive scalar-tensor gravity, a scalarized neutron star must shed its scalar field as it collapses into a black hole. Three-dimensional simulations of a realistic rotating progenitor show that dispersion stretches the emitted burst into a quasi-monochromatic kHz signal lasting more than 10,000 years, making continuous-wave search methods applicable. The study finds that directed searches targeting supernova remnants without a central pulsar would require sensitivity depths of 233–762 Hz^(-1/2) with the A+–ET–CE detector network. It estimates up to approximately three such signals in transit at any observational epoch. These are simulation-based findings and estimates within the specified gravity theory, not reported detections.
PublicThe researchers simulated a rotating neutron star collapsing into a black hole under a gravity theory that includes an extra field. In this theory, the star must shed that field during collapse. Their simulations suggest that the resulting brief burst spreads out as it travels, becoming a nearly single-frequency signal that lasts more than 10,000 years and oscillates thousands of times per second. Such a signal could be sought with methods designed for long-lasting waves, targeting supernova leftovers that lack a central pulsar. Detecting it would require the sensitivity levels calculated for the A+–ET–CE detector network. The researchers estimate that up to about three such signals could be traveling at any given time; none is reported as detected here.
Young explorerScientists used a computer to imagine a spinning star turning into a black hole. They tested a special idea about gravity in which the star has an extra field around it that it must let go. In their computer model, the short burst spreads out as it travels, turning into a steady wiggle that lasts more than ten thousand years. Scientists could look for these wiggles, but they would need very sensitive detectors. This study does not say they have found one.
Joel M. Velasco, Paolo A. Mazzali, Christopher Ashall+8 more
AstronomerThis exploratory study uses Gaussian Process fits to B- and g-band light curves of 362 CSP-I and CSP-II Type Ia supernovae to assess decline-rate metrics over multiple post-maximum timescales. The luminosity-width relation is calibrated on a clean subsample with host-independent distance moduli and Fitzpatrick (1999) reddening corrections. The authors find that Δm10(B) and Δm10(g) capture this relation effectively while mitigating the severe degeneracy of longer-timescale metrics for fast decliners with Δm15(B) ≥ 1.6 mag. They present continuous, piecewise linear models linking the normal and fast-declining regimes. The 10-day metrics closely approximate results from more complex colour-stretch parameters, need less post-maximum coverage than Δm15(B) or sBV, and offer greater sensitivity for slow decliners. The authors propose Δm10(B) as a practical tool for large photometric surveys and real-time classification; the abstract does not quantify its precision or demonstrate deployment.
PublicResearchers studied how 362 Type Ia supernovae fade after reaching their brightest point. They found that measuring the fading over 10 days in two optical bands effectively describes the relationship between a supernova’s luminosity and the duration of its light curve. This approach reduces an ambiguity that affects longer measurements for rapidly fading events. It also gives results close to those of more complicated methods while requiring a shorter span of observations after peak brightness. The authors suggest it could help large sky surveys and rapid classification of supernovae. This is an exploratory study, and the abstract does not report a numerical accuracy for the method.
Young explorerScientists watched 362 exploding stars to see how their light faded after it was brightest. They found that looking at how much the light faded in 10 days helped them understand the stars’ brightness without watching for as long as some other methods need. It also helped with stars that fade very quickly. They think this could help people studying lots of exploding stars, but it is still an early study.
Katherine Bruce, Anne M. Lohfink, Jaiverdhan Chauhan+3 more
AstronomerA systematic NICER spectral analysis of the 2019 and 2022 outbursts of SAX J1808.4-3658 finds the first clear evidence that its longstanding 0.9–1.0 keV feature varies systematically with brightness, strongly correlating with both continuum and blackbody flux. The authors interpret this as a direct coupling to accretion. The feature’s scaling and energy distribution differ between outbursts: it was stronger and broader in 2019, but weaker and more localized near 1 keV in 2022. In the high-density reflection interpretation, these differences correspond to an approximately two-order-of-magnitude change in reprocessor density, with log n_e ≈ 19.1 in 2019 versus ≈ 17.3 in 2022. The authors report their strongest constraints to date on the feature’s origin; the density explanation is model-dependent rather than a direct density measurement.
PublicResearchers used NICER to study X-rays from the accreting pulsar SAX J1808.4-3658 during its 2019 and 2022 outbursts. They found clear evidence that a previously known feature near 1 keV in its X-ray spectrum changes with the source’s brightness, closely tracking two components of its emission. This links the feature to the process of gathering material. The feature was stronger and spread across a wider range of X-ray energies in 2019 than in 2022. Models in which nearby material reprocesses the X-rays explain this difference through a roughly hundredfold change in that material’s density. This is a model-based explanation, but the observations provide the strongest constraints so far on where the feature comes from.
Young explorerScientists watched X-rays from a fast-spinning star while it gathered material. They studied two times when it became bright. A special little bump in its X-ray pattern changed as the star got brighter or dimmer, showing that the bump is linked to the material the star gathers. The bump was bigger and wider the first time. The scientists think nearby material packed more tightly together could explain why, but that explanation comes from a model.
Ramiz Aktar, Toru Okuda, Chandra B. Singh
AstronomerThe authors extend their shock-oscillation model of Sagittarius A* by including Compton scattering. Simulations predict radio–X-ray flare delays of 1–4 h, delays of 20–40 min between 334 GHz and 4.5 μm flares and 0.5–1 h between 334 GHz and 2–8 keV flares, and delays of 7–20 min and 0.5–1 h involving 22–43 GHz and 350 GHz radio flares. They report good agreement with recent observations. They interpret the synchrotron radio–bremsstrahlung X-ray delay as the sound-wave transit time from the near-horizon core to an oscillating shock, and inter-radio delays as transit times between frequency-dependent effective radii where the disc-surface optical depth is unity. In this picture, outward-propagating acoustic perturbations produce X-ray and lower-frequency radio peaks after higher-frequency radio peaks; inward-propagating waves generated by the upstream shock can reverse the ordering. Transit-time predictions qualitatively match the simulations, supporting this interpretation without establishing it as a uniquely demonstrated explanation.
PublicFlares from Sagittarius A*, the supermassive black hole, do not peak at the same time in every kind of light. The researchers updated a computer model of an oscillating shock in the surrounding material to include Compton scattering. Their simulations predict radio and X-ray flare delays of one to four hours, along with shorter delays between other wavelengths, which they report agree well with recent observations. They propose that sound waves traveling through the material around the black hole help explain these timing differences. In their interpretation, waves moving outward cause X-rays and lower-frequency radio light to peak after higher-frequency radio light, while waves moving inward can reverse that order. This explanation qualitatively matches the simulations, but the abstract does not establish it as the only possible cause.
Young explorerThe black hole called Sagittarius A* has material around it that makes flashes of light. Different kinds of light can flash at different times. Scientists used a computer model to explore why. They think waves traveling through the material, a little like sound waves, might help explain the wait between flashes. Waves going outward or inward could change which flash comes first. The model gives waiting times that fit recent observations well, but that does not prove the idea is the only explanation.
Yogeesh N, Monika Sinha, Vishal Parmar
AstronomerThis study incorporates neutrino emissivities from relevant Δ direct Urca processes into neutron-star cooling simulations, which the authors describe as a first systematic treatment of their cooling impact. In models containing Δ baryons, these additional weak-interaction channels efficiently remove heat through neutrino emission and can significantly accelerate cooling. The results suggest that Δ baryons could help explain neutron stars with unusually low surface temperatures, linking dense-matter composition to cooling observations. This is a simulation-based interpretation, not observational evidence that Δ baryons are present in neutron-star cores; a complete understanding of neutron-star cooling remains unresolved.
PublicNeutron stars cool partly by releasing neutrinos, particles that carry heat out of their dense interiors. Researchers simulated how this cooling would change if the interiors also contained particles called Δ baryons. In their simulations, additional neutrino-producing reactions involving these particles could make the stars cool much faster. This offers a possible explanation for neutron stars with unusually low surface temperatures, but the study does not establish that Δ baryons actually exist inside them. How neutron stars cool is still not fully understood.
Young explorerA neutron star is a very dense star that loses heat as tiny particles called neutrinos escape. Scientists used a computer to try out what would happen if special particles were inside the star. In their computer models, those particles could help more heat escape and make the star cool faster. This might help explain why some neutron stars have very cold surfaces, but scientists do not yet know whether those special particles are really inside them.
Rami Z. E. Alsaberi, Zachary J. Smeaton, Miroslav D. Filipovic+5 more
AstronomerATCA and MeerKAT radio-continuum observations of the Large Magellanic Cloud supernova remnant N 132D show spatial correspondence with X-ray emission in the central and left regions and the right shell, suggesting a close connection between thermal and non-thermal plasma. Polarisation measurements indicate predominantly radial magnetic fields, with mean fractional polarisations of 1.2%, 3.0%, and 4.0% at 2100, 5500, and 9000 MHz, respectively. A double-peaked Faraday-depth spectrum is interpreted as evidence for regions with differing magnetisation properties or magnetic-field geometry. ATCA rotation measures average approximately 2 rad m^-2 and reach approximately 338 rad m^-2. Under a constant-partition assumption between electron and magnetic-field energy densities, the authors estimate a magnetic field of approximately 90 microG and a minimum energy of 3 x 10^50 erg. The integrated radio spectrum follows a power law with spectral index -0.74 ± 0.01. These observations and assumption-dependent estimates constrain the remnant's magnetic structure and energetics and inform interpretations of particle acceleration and shock evolution.
PublicAstronomers used the ATCA and MeerKAT radio telescopes to study N 132D, the remains of an exploded star in the Large Magellanic Cloud. In several parts of the remnant, radio and X-ray emission trace similar structures, suggesting a connection between hot gas and the material producing non-thermal radio emission. The radio polarisation indicates that magnetic fields mostly point radially, rather than around the shell. A complex signal produced as polarised radio waves travel through magnetised material suggests differences in magnetisation or field geometry. Assuming a constant division of energy between electrons and magnetic fields, the researchers estimate a field strength of about 90 microgauss and a minimum energy of 3 x 10^50 ergs. The findings help constrain how magnetic fields, particle acceleration, and shocks behave in this remnant.
Young explorerScientists looked at radio signals from the leftovers of a star that exploded. Some radio-bright places match places that shine in X-rays. The signals give clues that magnetic fields mostly point outward, like spokes on a wheel, but their pattern is complicated. Scientists also estimated how strong the fields are and how much energy the leftovers hold, using an assumption about how that energy is shared.
Lingxiao Dang, Isabel Sander, Samar Safi-Harb+1 more
AstronomerAn X-ray study of MSH 15-52 and its young rotation-powered pulsar PSR B1509-58 uses Chandra, XMM-Newton, and eROSITA, complemented by MeerKAT radio data. The authors discover a southern counterpart to RCW 89 and identify a foreground X-ray source as a possible, not confirmed, additional SNR. Imaging and spectroscopy suggest that the northern and southern shell-like structures trace interstellar material heated by the forward shock. Low ionization timescales and possible hard power-law components leave room for particle injection or additional heating by PWN jets. Chandra spectral maps reveal hard non-thermal emission in the southern jet, with a photon index of approximately 1.6; interaction with the reverse shock and re-acceleration of the pulsar outflow are suggested interpretations rather than established mechanisms. Spatially resolved spectra of RCW 89 clumps reveal high-velocity, metal-rich ejecta with enhanced Ne and Mg. Comparison with one-dimensional core-collapse yield models favors an initial progenitor mass near 29 solar masses, but asymmetric explosion models can reproduce the abundance ratios with lower-mass progenitors. The study supports an interpretation of RCW 89 as part of a larger asymmetric remnant shell interacting with pulsar jets.
PublicAstronomers studied the debris of an exploded star, MSH 15-52, using three X-ray observatories and supporting radio observations. They found a southern counterpart to the bright northern region called RCW 89, helping reveal a larger, uneven shell. The shell’s X-rays suggest that the explosion’s outward-moving shock has heated surrounding gas, possibly with extra energy supplied by jets from the remnant’s rapidly spinning pulsar. A patch of energetic X-ray emission in the southern jet may indicate that the pulsar’s outflow encounters a shock moving back through the debris and gains energy again, but this explanation is not confirmed. Northern clumps contain fast-moving stellar debris enriched in neon and magnesium. Models suggest that the original star could have started with about 29 times the Sun’s mass, although models of uneven explosions also allow lower masses. A separate foreground X-ray source may be another supernova remnant, but remains a candidate.
Young explorerA star exploded and left a big cloud and a fast-spinning leftover star. Scientists used X-ray pictures to find a southern part of the cloud that they had not seen before. They think the explosion is heating nearby gas, and jets from the spinning star might add more energy. Bits of the broken star are moving fast. Scientists are still figuring out how big the star was before it exploded.
Ashwin Aravindaraj, Hui Zhu, Adrien Picquenot+1 more
AstronomerThe study estimates the magnetic energy spectrum of Tycho's supernova remnant by applying a two-point correlation method to a non-thermal X-ray flux image obtained with Poissonian-based Generalized Morphological Component Analysis (pGMCA). The derived turbulence length scale is shorter than that inferred in previous radio studies of Tycho. A second estimate, using X-ray rim thickness as an indicator of magnetic field strength, yields a turbulence scale consistent with the X-ray flux analysis. These observationally inferred turbulence scales are relevant to diffusive shock acceleration, in which magnetic turbulence scatters particles through repeated shock crossings; the abstract does not report a direct measurement of particle acceleration.
PublicMagnetic turbulence helps particles gain energy by repeatedly crossing the shock wave of an exploded star's remnant. Researchers studied this turbulence in Tycho's supernova remnant using an image of its non-thermal X-ray emission. Their analysis indicates a shorter characteristic size for the turbulence than previous radio studies inferred. A separate estimate based on the thickness of the remnant's X-ray rim, which provides clues about magnetic field strength, gives a consistent turbulence size. The findings probe conditions relevant to particle acceleration rather than directly measuring the acceleration itself.
Young explorerWhen a star explodes, it leaves a cloud behind. In a cloud called Tycho, messy magnetic fields can help tiny particles bounce back and forth and gain energy. Scientists used an X-ray picture to work out how big the magnetic wiggles might be. They seem smaller than earlier radio pictures suggested. Looking at how thick the cloud's X-ray edge is gave a matching clue about the wiggles' size.
Su-Yu Wan, Ruo-Yu Liu, Xing-Fu Zhang+1 more
AstronomerLHAASO observations reveal ultrahigh-energy gamma-ray emission from Cygnus X-3, with evidence for orbital modulation. The authors develop a unified binary–jet model for the contemporaneous GeV–PeV spectra and orbital light curves. In this model, anisotropic inverse-Compton scattering of stellar photons by relativistic electrons produces the GeV component, while escaping multi-PeV protons generate TeV–PeV emission through photohadronic and hadronuclear interactions. GeV modulation constrains the geometry, enabling the UHE data to probe proton escape and the circum-binary environment. The model attributes suppressed present-state hadronuclear emission to a fast accretion-disk wind displacing denser Wolf–Rayet wind material from proton trajectories. Changes in disk-wind strength, collimation, or orientation could increase exposure to the Wolf–Rayet wind and boost PeV luminosity by orders of magnitude. This offers a possible, not established, connection to brighter but unconfirmed PeV activity reported in the 1980s.
PublicLHAASO has detected extremely energetic gamma rays from Cygnus X-3, with evidence that their brightness varies over the binary’s orbit. The researchers propose a model that explains both the gamma-ray spectrum and the orbital brightness changes. In it, fast electrons boost starlight to gamma-ray energies, while even more energetic protons escape outward and interact with light and surrounding material. The model suggests that a wind from the accretion disk currently pushes much of the denser stellar wind out of the protons’ paths, limiting gamma-ray production. Changes in that disk wind could make the highest-energy emission much brighter. This might help explain reports of brighter activity in the 1980s, but those reports remain unconfirmed.
Young explorerScientists saw very powerful invisible light coming from a pair of stars called Cygnus X-3. There are clues that the light changes as the stars go around each other. The scientists think tiny, speedy particles help make this light. Their explanation says a wind can push material out of the particles’ way. If the wind changes, the light could get much brighter, but that is not a confirmed finding.
Matteo Ballelli, Federica Pompa, Christoph Ternes+2 more
AstronomerThe authors present an improved parametric model of core-collapse supernova neutrino emission that directly links neutrino luminosity and mean energy to stellar properties during emission. It incorporates proto-neutron-star convection and early evolution of the neutrinosphere radius. Simulated supernova neutrino event datasets for Super-Kamiokande are used to assess sensitivity to astrophysical properties in a future detection, rather than to analyze an observed supernova. The analysis finds that neutrino mass ordering is crucial in determining which model parameters such data could constrain.
PublicThe researchers developed an improved model of the neutrinos emitted when a star’s core collapses. It connects the strength of the neutrino emission and the particles’ average energy to properties of the collapsing star, accounting for internal churning and changes in the size of the region from which neutrinos escape. Using simulated signals for the Super-Kamiokande detector, they explored what a future detection could reveal about the star. Their analysis indicates that which properties could be measured depends strongly on the ordering of neutrino masses; it does not report an actual supernova detection.
Young explorerWhen a star’s middle falls inward, it sends out tiny particles called neutrinos. The scientists made a better model of how those particles come out, including how the star’s inside churns and how the place they escape from changes size. They used pretend signals to see what a detector might learn from a future star collapse. What it could learn depends a lot on which kinds of neutrinos are heavier than others. These were computer tests, not signals from a real star collapse.
Weiyu Wang, Rahul Sengar
AstronomerReanalysis of archival Parkes/Murriyang observations targeting supernova remnants and pulsar-wind nebulae in the Small Magellanic Cloud discovered PSR J0103-72, independently detected in two observations of its target field. With a spin period of 1.327 s and DM of 272 ± 13 pc cm^-3, it is the slowest known radio pulsar in the SMC and has the second-highest DM. No plausible associated supernova remnant or pulsar-wind nebula was identified. Subtracting the predicted Galactic foreground gives a residual DM of approximately 230–242 pc cm^-3, potentially indicating a long path through the SMC's ionized medium, enhanced ionized gas along the sightline, or both. Earlier searches had used FFT and fast folding algorithms, but the new FFT-based processing recovered the pulsar. The discovery demonstrates that candidates with weak Fourier-domain significance can reveal faint, narrow-duty-cycle pulsars missed by earlier extragalactic searches.
PublicAstronomers found a previously missed radio pulsar, PSR J0103-72, by searching old Parkes/Murriyang telescope observations of the Small Magellanic Cloud again. They detected it in two separate observations. It spins once every 1.327 seconds, making it the slowest-spinning known radio pulsar in that galaxy. Its radio signal shows substantial dispersion associated with ionized gas along its path. After accounting for the predicted contribution from our own galaxy, the remaining dispersion may reflect a long journey through the Small Magellanic Cloud's gas, unusually abundant ionized gas along the route, or both. No plausible associated supernova remnant or pulsar-wind nebula was found. The discovery shows that faint pulsars with brief pulses can be recovered from weak search candidates that earlier searches missed.
Young explorerScientists looked again at old telescope recordings and found a spinning object called a pulsar in the Small Magellanic Cloud. It sends radio pulses, and they spotted it in two recordings. It spins more slowly than any other radio pulsar known there. Its faint, short pulses had been missed before. Looking carefully at old recordings can help scientists find things they missed.
Fang-Stars Wei, Zelin Zhang, Zhenyu Zhang+1 more
AstronomerThis simulation study tests whether lensing-induced time-angle autocorrelations can distinguish departures from Kerr using an orbiting hot spot in the Johannsen-Psaltis metric with one deformation parameter. Ray-traced movies yield an approximately linear secondary ridge whose slope k and intercept b are proposed as future observables. Spin and deformation trace distinctive trajectories in the (k,b) plane, enabling joint constraints when orbital radius, observer inclination, and orbital angular velocity are specified. A Kerr reference region constructed by varying orbital angular velocity excludes the simulated slope-intercept pairs for some low-spin configurations with negative deformation parameters. Such exclusions occur for sub-Keplerian, Keplerian, and super-Keplerian motion, suggesting a potential non-Kerr diagnostic rather than an observational detection.
PublicThe researchers used simulated movies of a bright spot orbiting a black hole to explore a possible test of the geometry around it. Gravity bends the spot’s light into multiple images, producing patterns with different time delays and angular separations. Two quantities describing one of these patterns could help constrain both the black hole’s spin and departures from the Kerr model, provided key viewing and orbital properties are specified. In some simulations of slowly spinning black holes with a particular kind of departure from Kerr, these quantities fall outside the comparison range calculated for Kerr black holes. This happens for orbital motion slower than, matching, and faster than the Keplerian rate. The study proposes a promising future test using black hole flare movies; it does not report an observed departure from Kerr.
Young explorerThe scientists made pretend movies on a computer of a bright spot going around a black hole. The black hole bends the spot’s light, so copies of its picture can appear in different places and at different times. Some pretend movies made patterns outside the range found for their usual black hole model. Looking for those patterns in real movies might help test that model, but the scientists have not yet found this in a real black hole.
Baoxiang Wang, Tao Yang, Zhoujian Cao+3 more
AstronomerGW231123, the most massive binary black-hole merger observed to date, is a candidate hierarchical merger involving a black hole in the pair-instability mass gap. Its short in-band signal and previously inferred large component spins make inference particularly sensitive to near-merger waveform physics. An analysis over 11–448 Hz with the eccentric, spin-precessing TEOBResumS–Dalí effective-one-body model, including detector calibration uncertainty, favors eccentricity over the model’s quasi-circular counterpart with a Bayes factor of 10.2. The inferred eccentricity at 5.5 Hz is 0.34, with a 90% credible interval of 0.11–0.46. GW231123-like injection–recovery studies indicate that starting the analysis at 20 Hz, as previous studies did, can obscure eccentricity. Allowing eccentricity weakens the preference for a near-extremal secondary spin and lowers its posterior median to approximately 0.7, near the characteristic spin expected for a merger remnant. The authors interpret the combination of residual eccentricity, a mass-gap black hole, and remnant-like spin as consistent with hierarchical merging in a dense environment, rather than establishing that formation history uniquely.
PublicGW231123 is the most massive merger of two black holes observed so far. A new analysis of its gravitational-wave signal favors an elongated orbit over a nearly circular one. The signal is unusually brief, so details of the model used to describe the final stages of the merger matter greatly. Using a model that allows elongated orbits also reduces the inferred spin of one black hole: instead of strongly favoring an almost maximally spinning object, the analysis finds a typical inferred value near that expected for a black hole left behind by an earlier merger. Tests with simulated signals suggest that the frequency cutoff used in previous studies could hide the orbital elongation. Together, the findings support—but do not prove—a history in which an earlier merger produced one of these black holes, which then merged again in a dense environment.
Young explorerTwo black holes joined together and made tiny ripples in space that scientists detected. When scientists looked closely at those ripples, their new model fit better if the black holes had gone around each other on an oval path instead of a nearly round one. It also suggested that one black hole was not spinning quite as fast as earlier studies suggested. These clues could mean that one black hole had already been made when two other black holes joined together. Scientists think that story makes sense, but they do not know for sure.
Adithiya Dinesh, Alberto Domínguez, Alba Rico+3 more
AstronomerThe study develops a simulation-calibrated morphological framework for year-scale gamma-ray modulation in 120 Fermi-LAT blazar light curves spanning 18.1 years. Singular spectrum analysis selects oscillatory modes and periods; weighted wavelet Z-transform ridge tracking characterizes persistence, period drift, and cycle-to-cycle volatility. Among 97 quality-selected sources, PG 1553+113 and B2 1215+30 show persistent, coherent modulation consistent with stationary periods (Rank I), six show coherent modulation without established stationarity (Rank II), and 89 fall in Rank III. Neither Rank I nor Rank II significantly exceeds red-noise expectations. Calibration uses flux randomization, 10,000 red-noise simulations, and about 20,000 signal injections. Stationary 1–3-year injections attain Rank I in 63–97% of trials at SNR = 1, depending on period, and 100% at SNR = 2; 92% of drifting injections attain Rank II. The inferred 95% confidence upper limits on stable, approximately sinusoidal 1–3-year modulation are 7% of the sample at SNR ≥ 1 and 5% at SNR ≥ 2. PG 1553+113 has the lowest trials-corrected false-alarm probability, 4.7%, but no source is established as periodic. The framework characterizes modulation rather than identifying its physical mechanism. The two Rank I sources are proposed monitoring and continuous gravitational-wave search candidates; their apparent stability does not establish a binary origin.
PublicBlazars can brighten and fade in gamma rays, sometimes seeming to repeat on timescales of years. Such patterns have been proposed as clues to pairs of supermassive black holes or jets whose direction changes, but random variability can imitate a repeating signal. Researchers examined 120 blazar light curves covering 18.1 years and used simulations to test how reliably their method distinguishes stable repetition from changing patterns. Of 97 sources meeting their quality criteria, two—PG 1553+113 and B2 1215+30—showed persistent patterns consistent with a steady repeat interval. Six others showed coherent patterns whose intervals could not be established as stable. These counts were not significantly higher than expected from random variability, so none of the sources is proven to be periodic. The analysis places limits on how common stable, roughly wave-shaped variations lasting one to three years can be. The two strongest candidates merit further monitoring and searches for continuous gravitational waves, but their light patterns do not prove that they contain binary black holes.
Young explorerScientists watched bright things in space called blazars to see whether they got brighter and dimmer with a steady beat. Two looked like they might keep a beat, but messy changes can look like a beat by chance. Computer tests helped scientists check this. They still cannot say that any blazar truly repeats, or that two black holes make the pattern. They suggest watching the two promising ones more.
Shao-Ze Li, Yun-Wei Yu, He Gao+2 more
AstronomerThe study models a surviving post-merger neutron star injecting rotational energy into optically thick ejecta. Pair cascades redistribute this energy into a radiation-dominated photon–electron–positron nebula. A one-zone model includes pair creation and annihilation, photon injection, diffusion, and leakage through a jet-induced polar funnel. For typical model parameters, the early Compton y parameter greatly exceeds unity, producing saturated Comptonization for roughly 100 seconds to a few thousand seconds, depending on the remnant's magnetic field strength. Compton scattering exchanges energy while conserving photon number in scattering, yielding a Wien spectrum at the Compton equilibrium temperature: a Wien fireball. The modeled temperature falls from tens of keV to a few keV at early times. While the ejecta remain optically thick, funnel leakage rivals or exceeds adiabatic losses, with quasi-thermal emission whose isotropic-equivalent luminosity greatly exceeds the spin-down luminosity. The authors propose, rather than establish, this leakage as an origin of observed quasi-thermal components in short gamma-ray burst extended emission.
PublicIf a neutron star survives the merger of two neutron stars, its rotation can supply energy to the surrounding material while that material still traps light. The researchers model a hot cloud of light, electrons, and positrons inside this debris, including light escaping through a polar channel opened by a jet. In their model, repeated scattering brings the light into a characteristic thermal-like spectrum for about 100 seconds to a few thousand seconds, depending on the surviving star's magnetic field. The cloud cools, and escape through the channel can remove at least as much energy as expansion does while the debris remains opaque. The escaping light has a very high apparent luminosity when expressed as though it were emitted equally in all directions. The authors suggest this process could explain thermal-like components already observed in the lingering emission of short gamma-ray bursts; the model does not establish that connection.
Young explorerWhen two neutron stars crash together, one star might remain. The scientists used a model to explore how that spinning star could fill the stuff around it with hot light. A narrow opening could let some light escape while the cloud cools. They think this might explain part of the glow seen after some short space flashes, but they have not shown that it does.
Rahul Sengar, Laila Vleeschower, Matthew Bailes+3 more
AstronomerReprocessing the original Parkes Multibeam Magellanic Cloud surveys with high-harmonic folding of candidates near the noise floor yielded six pulsar discoveries. Five are in the LMC, bringing its known radio pulsar population to 49; one has a 3.8-second spin period, the longest known among Magellanic Cloud pulsars. The sixth lies toward the SMC but is associated with the Milky Way foreground. Four discoveries exhibit scintillation, one shows clear nulling, and others show possible nulling. An analysis of luminosities and duty cycles finds the current Magellanic Cloud sample consistent with Galactic canonical pulsars. These distant populations can help constrain the pulsar luminosity-function peak and may illuminate neutron-star populations formed at different metallicities. Population-synthesis simulations, rather than observations, suggest that deeper surveys could uncover many additional pulsars, including up to a handful of millisecond pulsars, conditional on the adopted upper limits for their parent populations. The discoveries demonstrate the value of archival reanalysis for survey completeness.
PublicAstronomers found six previously missed radio pulsars by searching old Parkes survey data again with techniques designed to recover very faint repeating signals. Five belong to the Large Magellanic Cloud, a satellite galaxy of the Milky Way, raising its known radio pulsar count to 49. One spins once every 3.8 seconds, making it the slowest known pulsar in the Magellanic Clouds. The sixth was found in the direction of the Small Magellanic Cloud but belongs to the Milky Way foreground. Four show signal fluctuations called scintillation; one clearly shows interruptions called nulling, while others may do so. The brightnesses and pulse durations of known Magellanic Cloud pulsars are consistent with those of ordinary Galactic pulsars. Computer simulations suggest that deeper searches could find many more, perhaps including a handful of very rapidly spinning millisecond pulsars, but that forecast depends on assumptions about their populations. The study shows that old observations can still yield new discoveries.
Young explorerScientists looked again at old recordings from a telescope and found six spinning stars that send out radio pulses, a bit like blinking lighthouses. Five are in a nearby galaxy called the Large Magellanic Cloud. The other is in our own galaxy. One turns more slowly than any other pulsar known in the Magellanic Clouds. A computer model suggests that looking harder could find many more, perhaps even a few very fast ones. Those are guesses to test, not stars already found.
Amy Secunda, Yan-Fei Jiang, Jenny E. Greene
AstronomerThree-dimensional, multi-frequency radiation magnetohydrodynamic simulations of the 1300–5940 Å-emitting region of an AGN disk develop a stochastic thickness asymmetry across the midplane. UV-optical light curves from the thinner upper side broadly follow traditional corona-driven X-ray reprocessing models. Those from the thicker lower side correlate weakly with X-rays and exhibit continuum reverberation lags 3–5 times the light-travel time. These simulated features agree with numerous recent observations, motivating an interpretation in which greater disk thickness increases X-ray absorption, reduces reprocessing at larger radii, and enhances the relative contribution of intrinsic disk fluctuations. In the simulations, long inter-radius light-curve lags measure the fluctuations’ inflow timescale. The authors propose that understanding these structural effects could enable disk-thickness predictions from UV-optical variability; the abstract does not establish this as a demonstrated observational measurement method.
PublicThe changing brightness of disks around active galactic nuclei can reveal how those disks work, but their internal physics remains poorly understood. In computer simulations, a turbulent disk happened to become thinner on one side and thicker on the other. The thinner side behaved broadly as expected if X-rays from a surrounding corona drive changes in ultraviolet and visible light. The thicker side tracked the X-rays less closely and showed delays 3–5 times longer than the time light would take to travel. These simulated patterns resemble many recent observations. The researchers interpret them as evidence that thicker disks absorb more X-rays, leave less X-ray light to be reprocessed farther out, and make brightness changes originating within the disk more prominent. They suggest that such brightness patterns could eventually help estimate disk thickness, rather than reporting a proven way to measure it.
Young explorerScientists used a computer to pretend to make a glowing disk in space. By chance, one side became thin and the other became thick. The thin side’s glow changed mostly along with X-rays, a kind of light we cannot see. The thick side’s glow did not follow the X-rays as closely, and some changes took longer. This looks like some things astronomers have seen in real disks. The scientists think changes inside a thick disk could help explain it. They hope watching a disk’s glow change could help them work out how thick it is.
Clément Ehrhardt, Maria Cristina Volpe, Miguel Ángel Aloy+1 more
AstronomerThis theoretical study explores how a non-zero transition magnetic moment could affect Majorana neutrino evolution in strong core-collapse supernova magnetic fields. The neutrino magnetic moment remains unknown. A schematic model illustrates the impact of resonant spin-flavor precession on the signal from a future Galactic supernova. Detailed simulations then examine a 17-solar-mass neutrino-driven supernova leaving a neutron star and a 26-solar-mass magnetorotational supernova leaving a black hole. The authors predict neutrino fluxes and event rates for the running JUNO and upcoming Hyper-Kamiokande experiments. In these simulations, transition magnetic moments of 10^-14 μB significantly affect the neutronization burst and accretion phase of the neutrino-driven case, while values as small as 10^-15 μB have significant early-time effects in the magnetorotational case. These are model-dependent predictions, not observed signals or measurements of the magnetic moment.
PublicScientists still do not know the magnetic moment of neutrinos, a property that could let strong magnetic fields affect these particles. This study asks how that interaction might change the neutrino signal from an exploding star, assuming neutrinos are of the Majorana type. The researchers use a simplified model and detailed simulations of two explosions: one leaving a neutron star and another leaving a black hole. They predict the signals that JUNO and the upcoming Hyper-Kamiokande experiment could receive. Their simulations suggest that very small magnetic moments could substantially change parts of the signal, with the black-hole-forming model affected at smaller values. No such effect has been observed here, and the neutrino magnetic moment remains unknown.
Young explorerWhen a big star explodes, it sends out tiny particles called neutrinos. Scientists wonder whether strong magnetic fields could change them. They used computer models of two kinds of exploding stars to imagine what particle detectors might see. The models say the changes could matter, even if the neutrinos respond only very weakly to magnets. But this is a prediction, not something they have seen happen.
Sobhan Kazempour, Sichun Sun, Zhiqing He+1 more
AstronomerThe study calculates thin-disk accretion and emission properties for static, spherically symmetric dyonic black holes in nonlinear electrodynamics (NLED). NLED coupling parameters modify the gravitational potential and strong-field geometry. Calculations of circular-orbit angular velocity, specific energy, and specific angular momentum indicate a smaller innermost stable circular orbit (ISCO), an inward shift of the disk’s thermal-emission maximum, and a higher local effective temperature relative to Schwarzschild and Reissner–Nordström solutions. Null-geodesic calculations also determine photon-sphere and shadow boundaries. Using a chi-squared goodness-of-fit test against Event Horizon Telescope horizon-scale angular-diameter constraints for Sagittarius A*, the authors report good statistical agreement for both dyonic NLED and purely magnetic models. This agreement concerns the tested size constraints; it does not establish that either model describes the actual black hole.
PublicThe researchers explored theoretical black holes with both electric and magnetic charges, using a nonlinear theory of electromagnetism. Their calculations suggest that this theory changes gravity close to the black hole, allowing stable circular orbits farther inward than in the standard comparison models. In their thin-disk calculations, the region of maximum thermal emission moves inward and the local temperature increases. They also calculated how light travels around these black holes to predict their shadow boundaries. A statistical comparison with Event Horizon Telescope measurements of Sagittarius A* found that both the electric-and-magnetic models and purely magnetic models agree well with the measured angular size. These are model predictions tested against observations, not a discovery that Sagittarius A* has these charges or follows this theory.
Young explorerScientists used math to imagine special kinds of black holes. Their calculations say that a thin disk of material could circle closer to the black hole, with its hottest glow moving inward and getting hotter. They also worked out the size of the dark shadow each kind could make. Those sizes fit telescope measurements of a real black hole called Sagittarius A* quite well. But fitting the size does not mean scientists know the real black hole is one of these special kinds.
P.S. Aswathi, Ling Sun
AstronomerThis review assesses electromagnetic and gravitational-wave constraints on hypothetical ultralight bosons from black-hole superradiance. Such particles could constitute some or all of the dark matter. The probes include electromagnetic black-hole spin measurements, spins inferred for merging binary black holes, searches for gravitational radiation from boson clouds, and possible cloud-induced effects on binary dynamics. The interpretation of these constraints depends on method-specific assumptions about black-hole formation, natal spins, ages, accretion histories, population priors, and boson self-interactions. The review emphasizes complementary signatures and systematic uncertainties rather than reporting a boson detection. Overlapping coverage at boson masses around 10^-13 to 10^-12 eV provides a particularly informative region for comparing constraints, provided their differing assumptions are taken into account.
PublicHypothetical particles called ultralight bosons might make up some or all of dark matter. This paper reviews how their gravitational interaction with spinning black holes, through a process called superradiance, can help test whether they exist. The evidence considered includes black-hole spin measurements and gravitational-wave observations, while other possible clues include radiation from particle clouds and changes to the motion of black-hole pairs. These approaches depend on assumptions about black holes and the particles themselves, so their limits need careful comparison. The review highlights an overlapping particle-mass range around 10^-13 to 10^-12 eV; it does not report a discovery of these particles.
Young explorerScientists wonder whether tiny particles we have not found could make up some of the universe’s hidden matter. This paper looks at ways to search for clues using spinning black holes and ripples in space. Different clues could help, but the answers depend on ideas scientists still need to check.
Hisham Anwer
AstronomerThe study analytically links the surviving isotope partition in the radium-225–actinium-225 decay sequence to the time available for parent decay in neutron-star merger ejecta. An Ac fraction of 0.1 generated solely by Ra decay requires at least 2.456 days, giving a consistency test for proposed source states. Subsequent activity also retains information beyond the mean production time: histories with the same mean birth time can yield different response crossings because their production-time distributions differ. A controlled radiation calculation shows how energy deposition and photon escape translate this nuclear contrast into a common light-curve pivot when ejecta properties are fixed. These analytical and calculated results, rather than reported observations, provide benchmarks for nucleosynthesis and radiation-transport models of late-time merger emission.
PublicRadioactive atoms in material thrown out by merging neutron stars may reveal not just which atoms were made, but when they were made. The researchers calculate that if actinium-225 comes only from the decay of radium-225, reaching an actinium fraction of one tenth takes at least 2.456 days. This can test whether a proposed mix of atoms is consistent with the time available. Their analysis also shows that two production histories with the same average creation time can still produce different patterns of radioactive activity. In a controlled calculation with fixed properties for the expelled material, energy deposited by decay and escaping light turn these differences into a shared pivot in the brightness curves. The work supplies theoretical tests for models; it does not report an observed merger light curve.
Young explorerWhen two neutron stars crash together, they throw out material with tiny atoms that change into other atoms over time. Scientists used math to show that these changes can give clues about when the atoms were made. Even groups of atoms made at the same average time can change differently if some were made earlier and others later. The scientists also calculated how this could affect the glow of the thrown-out material. These are clues from calculations, not something they watched happen in this study.
Wu-Long Xu, Jin Min Yang, Rui Zhu
AstronomerThis theoretical study examines p-wave Sommerfeld resonances for finite-size dark matter without specifying its internal structure. Sommerfeld enhancement may reconcile annihilation-cross-section requirements at different cosmic epochs, but point-like models can strongly constrain dark matter and mediator masses and their coupling. Finite size adds a parameter that may relax those constraints. The analysis finds that the p-wave contribution can exceed the s-wave contribution, although finite-size p-wave resonances are weaker than their point-like counterparts and retain similar velocity dependence. Extending the analysis to nugget dark matter with a small number of constituents yields p-wave enhancement behavior similar to the point-like case. These are theoretical findings, not observational detections.
PublicThe researchers explore whether giving dark matter particles a finite size, rather than treating them as points, changes how strongly they can annihilate with one another. A theoretical effect called Sommerfeld enhancement may help dark matter models meet different requirements at different stages of cosmic history, but point-like models can require tightly restricted masses and interaction strengths. In the calculations, finite size weakens resonant enhancement for a type of annihilation called p-wave, although its dependence on particle speed remains similar to the point-like case. The p-wave contribution can still be larger than another contribution called s-wave. Small dark matter nuggets made of a few constituents behave more like point-like particles. Finite size may loosen model restrictions, but the study does not establish that this happens in nature and does not specify the particles' internal structure.
Young explorerThe scientists used calculations to explore an idea about dark matter. What if its pieces have some size, instead of being treated as tiny points? They found that giving the pieces size can make certain boosts to how easily they destroy each other weaker, while the way those boosts change with speed stays much the same. Little bundles made of a few pieces acted more like tiny points. This is an idea studied with calculations, not something they saw happen in space.
Sebastian Bahamonde, Theodoros Nakas, Simon Iteanu
AstronomerThis theoretical study develops a systematic construction of exact, static, asymptotically flat black-hole solutions in shift-symmetric and Z2-symmetric beyond Horndeski theories, without imposing g_tt g_rr = -1, thereby allowing two independent metric functions. Two branches yield distinct forms of hair: khronometric hair, with a trivial shift-symmetry Noether current and associated propagating degree of freedom, and genuine scalar hair, for which both are nonvanishing. Both scalar profiles define a nontrivial preferred foliation. Focusing on the genuine scalar branch, the authors derive several exact solution families that are generally singular and carry primary hair associated with an independent scalar charge. They show that regularization can produce regular black-hole or solitonic configurations, with secondary rather than primary scalar hair. Linear perturbation analyses of the axial sector and the even-parity monopole provide evidence for stability of representative scalar-haired solutions under the modes examined, not a demonstration of stability against all perturbations.
PublicThe authors develop a mathematical method for describing black holes in a class of gravity theories that include an additional scalar field. Unlike earlier approaches, their method avoids a restrictive relationship between two parts of the geometry, allowing a wider range of solutions. They identify two distinct kinds of black-hole “hair,” meaning extra structure associated with the scalar field, and focus mainly on the kind that has a nontrivial propagating scalar degree of freedom. Their exact solutions generally contain singularities and an independent scalar charge, but they show how to obtain regular black-hole or soliton configurations in which the scalar hair is no longer independent. Tests of selected small disturbances provide evidence that representative solutions are stable against those disturbances; other kinds of disturbances remain outside the analysis. These are theoretical findings, not observations of actual black holes.
Young explorerScientists used math to explore possible black holes in a different theory of gravity. Their model includes an extra field, which is something that can have a value at each place. It can give a black hole extra features that scientists call “hair,” though it is not real hair. Many of their math examples have places where the description breaks down, but they showed how to make examples without those problems. They also checked some small wiggles, and the examples they tested showed signs of staying steady. They did not check every kind of wiggle or observe these black holes in space.
Hai-Tian Wang, Dicong Liang, Lijing Shao+1 more
AstronomerThe study tests a one-extra-spatial-dimension model in which projection produces apparent tensor, vector, and scalar polarizations, all fixed linear combinations of two underlying GR tensor waveforms and coupled to strain through standard detector antenna patterns. A frequency-domain Bayesian analysis of five compact-binary events constrains two rotation angles for two noncommuting rotation orderings that preserve propagation in the observed spatial subspace. Two events also receive three-angle fits for four orderings permitting propagation to tilt into the extra dimension. For GW250114, the maximum GR quantiles across tested orderings are approximately 0.6% for the two-angle fits and 4.6% for the three-angle fits after marginalizing over the third angle. Nevertheless, the GR reference point lies within the estimated 90% highest-posterior-density region in every case across the sample; these model-dependent constraints do not establish an extra dimension.
PublicCould gravitational waves reveal an extra direction in space? This study explores a model in which waves traveling in a space with one additional dimension could appear to have different patterns of distortion when projected into the three spatial dimensions we observe. Researchers compared this model with gravitational-wave data from five compact-binary events, testing different ways of orienting the extra dimension; two events received additional tests allowing wave propagation to tilt into it. Although the analysis gives different statistical positions to ordinary general relativity under different assumptions, its reference prediction remains within the estimated 90% high-probability region in every case. The study therefore constrains a possible extra-dimension model rather than providing direct evidence that an extra dimension exists.
Young explorerImagine a shape making a shadow: the shadow can look different from the shape itself. Scientists wondered whether ripples in space might look different to us if there were an extra direction we cannot see. They tried this idea using five ripple signals from pairs of objects in space. The usual explanation of the ripples still fits within the range their tests allow. They have not shown that the extra direction is real.
Zoha Laraib, Sherwood Richers, Alessandro Baroni+2 more
AstronomerQCNO maps an inhomogeneous forward-scattering neutrino Hamiltonian with advection and finite-range interactions onto TEBD2 product-formula quantum circuits, linking ideal many-body simulation, backend-aware execution, and fault-tolerant resource estimates. The authors reproduce exact many-body evolution of the suppressed mean-field-like transverse fast flavor instability through N=30. Their calculations show that even a single open-boundary interaction generates Rényi entanglement and non-stabilizer magic, while noisy backends still yield polarization RMSEs of approximately 0.1–0.3. The restricted active interaction graph permits circuit-depth and T-gate-cost estimates through N=50 for NISQ and fault-tolerant approaches. An approximately 10^-3 TEBD2 error in the fiducial ideal simulation motivates a proposed synthesis tolerance near 10^-7, corresponding to about 70 T gates per R_Z rotation. The generated circuit contains 1.4×10^4 T gates per qubit with open boundaries and twice that with closed boundaries, implying an application-level logical-T error target near 10^-7 for early fault-tolerant architectures. These are simulation findings and resource requirements, not a demonstration of fault-tolerant execution.
PublicThe researchers developed QCNO, a code for studying how interacting neutrinos change flavor using quantum circuits. Fully tracking their shared quantum behavior becomes increasingly costly as more particles and spatial detail are included. The code reproduces exact many-particle evolution for a particular flavor-instability problem with up to 30 neutrinos, and its calculations show that even one interaction can generate entanglement and another quantum resource called magic. However, execution on noisy backends still has substantial errors in the calculated polarization. The team also estimates circuit requirements for systems of up to 50 neutrinos. Those estimates indicate demanding accuracy and gate requirements for future error-corrected quantum computers; they do not establish that such a computation has already been performed.
Young explorerNeutrinos are tiny particles that can change between different types. Scientists made a computer tool to work out how they change when they interact. They checked its calculations for groups of up to 30 neutrinos. Noisy versions still made mistakes. They also estimated what future quantum computers would need to do these calculations more reliably, rather than showing that those future computers already work.
R. Prasad, Subhodeep Sarkar, Sudipta Sarkar
AstronomerThe recently identified Direct Wave (DW), a prompt non-quasinormal component of GW250114, enables a null test of horizon reflectivity, although whether the DW itself carries horizon information remains unclear. In the exotic compact object model considered, a partially reflecting surface returns inward plunge radiation through the gravitational potential barrier, producing a delayed DW echo with amplitude controlled by the absolute value of the surface reflectivity. The authors construct an echo template normalized to the observed DW and search quasinormal-mode-filtered data. They find no evidence for an echo, with ln B = -2.9, and obtain a 90% credible upper bound of 0.06 on the absolute value of the surface reflectivity, corresponding to a reflected energy fraction below 0.4%, for surfaces at distances from the would-be horizon ranging from 0.1 times the remnant mass scale, M_f, down to a Planck length. These constraints apply to the modeled reflecting surfaces; the echo is a conditional prediction, not a detection.
PublicResearchers used a recently identified, prompt gravitational-wave component called the Direct Wave in GW250114 to test whether the remnant might have a partially reflecting surface instead of a black-hole horizon. Such a surface is predicted to send some inward-moving radiation back out as a delayed echo. The team built a model of that echo, scaled it using the observed Direct Wave, and searched data filtered to remove quasinormal-mode signals. They found no evidence for an echo, reporting ln B = -2.9. Within the model, their 90% credible limit puts the absolute value of surface reflectivity below 0.06, equivalent to reflecting less than 0.4% of the incoming energy. This limit covers modeled surfaces located between 0.1 times the remnant mass scale, M_f, and a Planck length from where the horizon would be. It remains unclear whether the Direct Wave itself contains information about the horizon, and the non-detection does not establish that every alternative to a black hole is excluded.
Young explorerScientists studied a space ripple called the Direct Wave in GW250114. They asked whether the object left behind might have a surface that bounces some ripples back, like an echo. Their model says such an echo could happen, but they did not find evidence for one. Their test gave a number called ln B of -2.9. For the surfaces in their model, they found a 90% credible limit: the absolute value of reflectivity is less than 0.06, meaning less than 0.4% of the ripple energy would bounce back. They tested surfaces from a distance called 0.1 M_f down to a tiny distance called a Planck length from where the black-hole boundary would be. They still do not know whether the first ripple itself tells us about that boundary. Not finding an echo does not prove that every other kind of object is impossible.
Vishal Baibhav, Vicky Kalogera
AstronomerThis theoretical study challenges the common assumption that black holes formed through isolated massive-binary evolution inherit progenitor spins aligned with the orbital angular momentum. Alongside natal spins, it explores spin-up mechanisms acting before or during black-hole formation that can produce isotropic spin orientations or spins parallel or perpendicular to natal kicks. These mechanisms imply distinct signatures in spin magnitudes, spin-orbit misalignments, and effective inspiral spin. They allow isolated binaries to exhibit precession and negative effective inspiral spin, broadening the parameter space beyond configurations previously considered exclusive to dynamically assembled binaries. These are proposed physical possibilities and their implications, not reported observational detections; the origin of black-hole spins remains uncertain.
PublicBlack holes spin, but scientists still do not fully understand how they acquire that spin. A common assumption is that two black holes descended from a pair of massive stars should spin in line with the pair’s orbital motion. This study explores alternatives: processes before or during black-hole formation could give the spins other directions, including directions related to the kicks received at birth. The proposed mechanisms could produce different patterns in spin strength and orientation, including wobbling motion and an overall spin contribution opposing the orbit. Such behavior might therefore arise even in pairs that evolved in isolation, rather than only in pairs assembled through encounters. The abstract presents theoretical possibilities, not observations confirming them.
Young explorerBlack holes can spin like tops. Scientists often think that if two black holes grew from two stars that stayed together, their spins should point the same way as they circle each other. This study explores how that might not always happen: as black holes form, their spins might point sideways or even against the way the pair circles. That could make their motion wobble. These are ideas about what could happen, not things this study says it has seen.
Paul C. W. Lai, Chi-Yung Ng, Shumeng Zhang
AstronomerVLA polarimetry at 6 GHz resolves new structure in the Boomerang pulsar wind nebula G106.65+2.96: a 40-by-20-arcsecond elliptical core surrounding the pulsar and a 2-arcminute northern arc separated from the core by a gap. The arc comprises a bright northwestern lobe and a northeastern tongue-like feature, possibly produced by interaction between the pulsar wind and its environment. Polarization reveals a highly ordered, toroidal magnetic field, with strong linear polarization in all the small-scale features. The lobe’s approximately 60% polarization fraction is close to the synchrotron limit and substantially exceeds its lower-frequency value, implying significant depolarization. The authors show that Faraday rotation within the nebula can explain this behavior. A simple 3D model estimates a field strength of approximately 25–70 microgauss, assuming a median inclination of 60 degrees; the stated uncertainty reflects uncertainties in flux and distance.
PublicRadio observations reveal new details in the Boomerang nebula, a cloud powered by a pulsar. The images show an oval core around the pulsar and a separate northern arc containing a bright lobe and a tongue-like feature. These structures may arise where the pulsar’s wind interacts with its surroundings. The radio waves’ polarization indicates a highly organized, ring-like magnetic field. About 60% of the lobe’s emission is linearly polarized, much more than measured at a lower radio frequency. The researchers show that rotation of polarization within the nebula can explain this difference. Their simplified three-dimensional model estimates the magnetic field’s strength, but that estimate depends on an assumed viewing angle and uncertain brightness and distance.
Young explorerAstronomers used radio waves to look at a space cloud called the Boomerang. They found an oval around a tiny star called a pulsar and a curved shape nearby. The light gives clues that the cloud’s magnetism forms an orderly ring-like pattern. The star’s wind might help make the shapes, but the astronomers are not sure.
John M. Mehlhaff, Alexander Y. Chen, Martin Luepker+1 more
AstronomerThe authors report the first fully kinetic accretion simulations with initially finite angular momentum, restricted to axisymmetry. Motivated by tenuous, collisionless flows in low-luminosity active galactic nuclei such as M87* and Sgr A*, where ideal MHD may be inadequate, the simulations nevertheless reproduce magnetically arrested disk-like episodes of magnetic flux saturation and eruption. The authors attribute this resemblance largely to kinetic instabilities regulating disk pressure anisotropy, allowing fluid terms to dominate angular momentum transport. Effective treatment of vacuum regions also permits investigation of matter supply to the jet funnel: the simulations show no efficient penetration by accreting material. This suggests, but does not establish, that a pair discharge may be needed to sustain the Blandford-Znajek process. These initial axisymmetric findings require further testing, especially with three-dimensional kinetic simulations.
PublicAround black holes such as M87* and Sgr A*, the infalling gas is so sparse that its particles rarely collide, potentially limiting models that treat it as an ideal magnetized fluid. The researchers instead simulated the particles' behavior in a rotating flow, using a setup that assumes symmetry around an axis. Surprisingly, the simulated flow resembled fluid-model disks in which accumulated magnetic fields periodically erupt. The authors explain this similarity through instabilities that regulate how particle pressure differs between directions. In the simulations, infalling material did not efficiently enter the region feeding the jet. The authors therefore suggest that production of particle-antiparticle pairs may be needed to sustain a process that powers jets using black-hole rotation. These are preliminary simulation findings, not observations, and need testing in three dimensions.
Young explorerScientists used a computer to explore how very thin gas swirls toward a giant black hole. They followed tiny particles, but the gas still acted much like a flowing liquid, with magnetic fields building up and bursting out. Very little gas entered the place where a jet could start, so the scientists think new particles might need to be made there. This is an early computer test, not something they watched happen in space, and they need more tests.
Hu Liu, Fanping Li, J. Zhao+3 more
AstronomerThe cosmic-ray spectral knee may mark either the maximum acceleration energy of Galactic sources or a limit on Galactic confinement. To support species-resolved spectra, a goal of LHAASO over roughly 10 TeV to EeV energies, this work introduces a superposition-model method that reconstructs energy and logarithmic mass, lnA, using two composition- and energy-independent calibration lines. It uses electromagnetic and muon particle densities at a fixed distance from the shower axis rather than particle counts integrated over annular bands. For zenith angles below 40°, reported energy and lnA biases remain within ±5% and ±0.3, respectively, across compositions. The density-based method improves both resolutions, especially for heavy nuclei: reported energy resolution ranges from below 5% to approximately 15% above 1 PeV, while the best reported iron mass resolution is below 25% above 10 PeV. Dependence on the hadronic interaction model scales with lg(E/A) and is nearly composition-independent. These are reconstruction-performance findings; the abstract does not establish which explanation of the knee is correct.
PublicThe cosmic-ray spectrum has a bend called the “knee.” It could reflect a limit on how much energy sources in our Galaxy can give these particles, or on how well the Galaxy can hold them. Telling those possibilities apart requires reliable estimates of particle energy and type. This work introduces a method for LHAASO that estimates energy and a mass-related quantity from the densities of particles in air showers, measured at a fixed distance from the shower’s central axis. Compared with counting particles across ring-shaped regions, the density approach is reported to give more precise estimates, especially for heavy nuclei. Its reported performance applies under specified energy and arrival-angle conditions, and the estimates still depend on the model used to describe particle collisions. The work improves a measurement technique rather than determining the origin of the knee.
Young explorerTiny particles from space can make a shower of other particles when they hit the air. Scientists have a new way to use that shower to guess how much energy the space particle had and how heavy it was. They report better guesses, especially for heavy particles, but the guesses are not perfect. This could help explain a puzzle about space particles; it has not solved the puzzle yet.
Ziwei Ou
AstronomerThe authors analyze Fermi-LAT GeV data around the millisecond pulsar PSR J0437-4715, using its timing ephemeris to construct a gamma-ray pulse profile and define on- and off-pulse intervals. Binned likelihood analysis probes phase-dependent spectral properties. No spatial extension is detected in the off-pulse emission, with an upper-limit radius of 0.12 degree. The study also explores gamma-ray luminosity, X-ray luminosity, and bow-shock radius for a sample of pulsars with detected bow-shock pulsar wind nebulae. The outer-gap model’s efficiency for converting spin-down power into GeV emission is described as consistent with a termination shock close to the pulsar. This is a model-based interpretation, not a measured shock location; the nature of the off-pulse emission and its possible connection to bow-shock nebulae remain under discussion.
PublicResearchers studied high-energy gamma rays from the rapidly spinning pulsar PSR J0437-4715 using Fermi-LAT observations. They separated the repeating signal into pulse and between-pulse intervals and examined the gamma-ray spectra. Between pulses, they found no detectable spreading of the emission across the sky, setting an upper limit of 0.12 degree on its radius rather than proving it has no size. They also explored how gamma-ray brightness, X-ray brightness, and bow-shock size relate in a sample of pulsars with wind nebulae. A model of gamma-ray production is compatible with the pulsar’s wind encountering a nearby termination shock, but this does not establish where that shock is or what produces the between-pulse emission.
Young explorerScientists studied a very fast-spinning star that sends out flashes of light called gamma rays. They looked during the flashes and between them. Between flashes, they could not see the light spreading over a bigger patch of sky, but that does not mean the patch has no size. They also studied other spinning stars with clouds made by their winds. One idea fits with a place near the star where its wind slows down, but scientists are still working out where the between-flash light comes from.
Kazuki Kamiido, Yutaka Ohira
AstronomerA first-principles particle-in-cell simulation investigates the long-term evolution of a relativistic collisionless velocity shear in an initially unmagnetized electron–positron plasma. In the simulation, the Alves instability converts shear kinetic energy into thermal and magnetic-field energy; the resulting pressures drive plasma motion and form collisionless shocks. The shocks also generate magnetic turbulence required for shear acceleration. The authors propose that shock acceleration could supply high-energy particles for subsequent shear acceleration, potentially addressing its injection problem; this is a proposed consequence rather than a demonstrated acceleration result.
PublicThe researchers used a computer simulation to study neighboring streams of electrons and their antimatter counterparts moving at different speeds close to the speed of light, without an initial magnetic field. In the simulation, an instability turns energy from the difference in stream speeds into heat and magnetic fields. The resulting pressure pushes the plasma and creates shock waves that do not rely on particle collisions, along with turbulent magnetic fields. The authors suggest that these shocks could give particles the initial energy needed for further acceleration by the differing stream speeds, while the magnetic turbulence provides another necessary ingredient for that process.
Young explorerScientists used a computer to study tiny particles flowing very fast, with some streams moving faster than others. In the computer model, energy from those different speeds made heat and magnetic fields, and the pressure pushed the particles into shock waves. The scientists think those shocks might give some particles a boost, helping them get even more energy from the streams later.
Cheng-Rui Zhu, Yu-Lu Liu, Mei-Juan Wang+3 more
AstronomerUsing time-dependent AMS-02 flux measurements, the study finds that Li, Be, B, C, N, and O have solar modulation parameters consistent with those of protons and He within a modified force-field approximation incorporating rigidity-dependent modulation potentials. This consistency is a model-based finding, not a demonstration that all species undergo identical modulation. Assuming that Galactic cosmic rays with the same charge sign share modulation parameters, the authors predict daily Ne, Mg, and Si fluxes for 2011–2020; these fluxes are forecasts rather than reported measurements.
PublicThe Sun’s wind and turbulent magnetic fields change the number of cosmic-ray particles reaching the inner solar system. Using measurements from AMS-02, the researchers find that several kinds of atomic nuclei can be described by solar-influence parameters consistent with those for hydrogen nuclei and helium, within their chosen model. They then assume that particles with the same sign of electric charge share these parameters to predict daily amounts of neon, magnesium, and silicon cosmic rays for 2011–2020. Those predictions are not measurements of these three types of particles.
Young explorerTiny particles travel through space, and the Sun’s wind and magnetic fields change how many get close to us. Scientists looked at measurements of several kinds of particles. In their model, the Sun’s effects on these kinds looked similar. They used that idea to predict how many of three other kinds would arrive each day. Those predictions are guesses based on the model, not things they measured.
Divyansh Tripathi, Sudip Bhattacharyya, Pulkit Ojha
AstronomerThe study computes the long-term evolution of neutron-star low-mass X-ray binaries to investigate which system parameters and evolutionary phases favor persistent versus transient accretion. The calculations naturally produce more transients than persistents and typically yield a larger persistent-phase fraction at shorter orbital periods, with only partial agreement with observed source properties. The authors interpret the remaining discrepancies as motivation to improve focused models of transient accretion, such as thermal-viscous disk-instability models, and propose their evolutionary calculations as a way to discriminate among those models.
PublicA neutron star can draw matter from a low-mass companion star, producing an X-ray binary. Some of these systems accrete steadily, while others do so intermittently. This study uses calculations of their long-term evolution to explore why. The calculations produce more intermittent systems than steady ones and generally find that systems with shorter orbital periods spend a greater fraction of their evolution accreting steadily. These findings agree only partly with observations. The authors suggest that models explaining intermittent accretion need improvement and that their calculations offer a way to compare those models.
Young explorerA neutron star is a very dense star that can pull material from a nearby star. Sometimes the material flows steadily, and sometimes it comes in bursts. Scientists calculated how these star pairs might change over a long time. Their calculations made more pairs with bursts than pairs with steady flows. Pairs that circle each other faster usually spent more of their time with steady flows. The calculations match some things astronomers see, but not everything, so the explanations still need work.
Ana Laura García-Perciante, Merce Guerrero, Darío Núñez+1 more
AstronomerThis theoretical study examines a Vlasov gas in an external axisymmetric potential comprising a central term and a quadrupolar component that creates two potential wells along the symmetry axis. Independent N-particle simulations and statistical methods show that an initially homogeneous, isotropic configuration evolves toward an inhomogeneous state with overdensities at the wells. The quadrupolar term is selected to make the Hamiltonian dynamics integrable, enabling an analytic calculation of the final state and comparison with the simulations’ late-time behavior. Relaxation is interpreted through phase-space mixing. The model is a Newtonian analogue of particle motion in Kerr spacetime; possible applications to recently observed astrophysical phenomena are discussed, rather than established.
PublicThe researchers studied a mathematical model of particles moving in a gravitational potential with two preferred gathering places along its symmetry axis. Computer simulations and statistical calculations show that particles starting evenly spread, with no preferred direction of motion, develop denser concentrations at those two locations. The model was specially chosen so that its final distribution could also be calculated analytically and compared with the simulations. The researchers explain the settling process through mixing in the space of particle positions and motions. Their model provides a Newtonian counterpart to aspects of particle motion in Kerr spacetime. They discuss possible links to recently observed astronomical phenomena, but do not establish that the model explains those observations.
Young explorerImagine lots of tiny particles spread evenly, moving in all directions. Scientists made a pretend world with two places where the particles could gather. In their computer model, the particles became more crowded near those places. They also used math to work out how the particles would end up spread out. This was a model, not something they watched happen in the sky. It might help them think about things astronomers have seen, but they have not shown that it explains those things.
Samantha Creech, Francesca Civano, Daniel Wik+13 more
AstronomerThis study presents the first spectral modeling of 52 NuSTAR sources discovered in the latter half of the NEP-TDF campaign and a spectroscopic variability analysis of the full 112-source catalog, identifying seven variable candidates. Simultaneous NuSTAR and XMM-Newton observations, supplemented by 1.8 Ms of Chandra monitoring, provide broad-band coverage of approximately 0.5–24 keV to distinguish intrinsic coronal flux changes from changes in obscuring column density. The authors find that detecting variability requires roughly 1,000 or more total counts distributed across roughly 10 or more epochs. Comparisons with survey sensitivity are intended to inform population synthesis models of how variability affects faint-AGN detectability. Significant column-density variability is slightly more common on timescales longer than 100 days, suggesting only a slight dominance of the torus as its driver rather than establishing a unique obscurer location.
PublicAstronomers studied changing X-ray emission from faint active galaxies, where matter feeds supermassive black holes. These changes can happen because the hot X-ray-emitting region becomes brighter or dimmer, or because intervening material blocks different amounts of radiation. Combining observations from NuSTAR, XMM-Newton, and Chandra helps distinguish those possibilities. The study analyzed a catalog of 112 sources and identified seven candidates for variability. It found that detecting changes requires substantial data: about 1,000 or more recorded X-ray counts spread across about 10 or more observing occasions. The researchers also examined how brightness changes could affect which faint active galaxies surveys detect. Changes in obscuring material were slightly more often significant over periods longer than 100 days, weakly suggesting that the surrounding torus plays a somewhat larger role than other obscuring regions.
Young explorerScientists used telescopes to watch special light called X-rays from faraway galaxies with giant black holes. That light can change because the glowing stuff near a black hole changes, or because stuff in front of it blocks more or less light. Out of 112 sources, they found seven that might be changing. They needed lots of light signals and many visits to spot changes. Some changes in the blocking stuff were a little more common over longer waits. That gives a small clue about where the blocking stuff might be, but it does not tell us for sure.
A. Tortosa, L. Zappacosta, E. Piconcelli+51 more
AstronomerThe study tests whether steep X-ray spectra in luminous reionization-era quasars are associated specifically with efficient long-term SMBH growth. It analyzes 28 QSOs at z ≃ 5.85–7.56, with 26 included in correlation analyses, extending HYPERION mainly toward lower growth efficiencies and incorporating new XMM-Newton observations. Black hole masses and growth indicators were re-derived homogeneously using updated spectroscopy, including JWST measurements. No statistically significant correlation was found between coronal spectral parameters and black hole growth indicators. The luminous quasars systematically exhibit steep X-ray continua, with high photon indices and/or low high-energy cutoffs, consistent with cold coronae. A connection to rapid accretion remains a possible interpretation, not an established result. If steep spectra are common among early AGN, reduced count rates at fixed intrinsic luminosity could impair detection in future reionization-era surveys and affect population estimates.
PublicSome quasars in the early universe already contained black holes with a billion times the Sun’s mass. Their X-rays reveal conditions close to the growing black holes. Researchers studied 28 luminous quasars and used 26 to test whether their X-ray properties were linked to how efficiently their black holes had grown. They found no statistically significant relationship. Instead, steep X-ray spectra appeared across the sample, not just among the most efficiently grown black holes. These spectra are consistent with relatively cool coronae, the X-ray-emitting regions near the black holes; rapid accretion is a possible explanation. If such spectra are widespread among early active black holes, future X-ray surveys could have more difficulty detecting them, potentially affecting estimates of their abundance.
Young explorerScientists looked at X-rays from 28 very bright places around huge black holes in the young universe. Their X-rays suggest that the glowing material close to the black holes may be relatively cool. The scientists did not find a clear link between the X-rays and how efficiently the black holes had grown. If many early black holes shine this way, future searches might have trouble spotting them.
Yan Cao, Yong-Liang Ma, Yong Tang
AstronomerThe study assesses future space-based detection of gravitational-wave displacement memory, a general-relativistic prediction not yet detected. Its universal soft, low-frequency spectral form offers templates for matched filtering and parameter estimation; analogous soft signals may accompany velocity and integrated-displacement memory. For moderately relativistic, nonspinning compact-binary scattering and comparable-mass, quasi-circular, nonprecessing black hole mergers, the low-frequency spectra are described by soft displacement-memory waveforms with finite-frequency corrections. Under the adopted instrumental-noise models, simulated Bayesian analyses indicate that a single LISA-like detector can constrain memory amplitude and arrival time at matched-filter signal-to-noise ratios of order 10. BBO Stage 1 could measure null displacement memory from sufficiently loud stellar-mass compact-binary mergers. The paper also evaluates an idealized stochastic background of soft displacement-memory signals. These are modeled detection prospects, not detections.
PublicEinstein's theory predicts that gravitational waves can leave a lasting change called displacement memory, but this effect has not yet been detected. This study explores whether future space-based detectors could find its characteristic low-frequency signal from compact objects scattering past one another or black holes merging. Computer simulations using assumed detector-noise models suggest that a LISA-like detector could estimate the strength and arrival time of sufficiently strong memory signals. Another proposed detector, BBO Stage 1, could measure a type of displacement memory from sufficiently strong mergers involving stellar-mass compact objects. The researchers also assess an idealized background made up of many memory signals. These findings identify promising search targets rather than report an observation.
Young explorerWhen black holes come together, they can make ripples in space. Scientists think those ripples can leave a lasting change, like a little mark that stays after a wave passes, but nobody has found this space-memory effect yet. This study used computer tests to explore whether future detectors in space could notice it. The tests suggest they might, if the signal is strong enough.
Damiano F. G. Fiorillo, Alessandro Lella, Georg G. Raffelt+2 more
AstronomerThis theoretical study derives neutron-star emission rates for hypothetical scalar, vector, and pseudoscalar bosons coupling to electrons and muons, considering particle masses up to about 100 keV. For muonic vectors, direct incoherent lepton scattering competes with coherent excitation of the lepton population, electromagnetically driven by incoherent hadronic scattering through an effective in-medium coupling. For muonic scalars, the effective in-medium coupling to electrons always dominates in the calculation because of relativistically boosted emission. Pseudoscalars are emitted only through incoherent leptonic scattering. With superconducting protons, scalar and vector energy losses scale as T^4 and pseudoscalar losses as T^6, compared with T^8 for modified Urca neutrino losses. With normal-conducting protons, transverse-photon damping gives T^(11/3) for scalars and T^(17/3) for pseudoscalars; vectors emitted by nonrelativistic protons retain T^4 scaling. The authors propose using these results with observed neutron-star cooling ages to constrain leptophilic couplings; the abstract reports neither particle detections nor derived observational bounds.
PublicThe researchers calculate how neutron stars might produce hypothetical new particles and lose energy as those particles escape. Their calculations cover three particle types interacting with electrons and muons, with masses up to about 100 keV. The surrounding stellar material can create indirect emission routes: for one type coupled to muons, an indirect route involving electrons dominates the calculated emission. The predicted energy loss also depends on temperature and on whether the star’s protons are superconducting. These theoretical results could help researchers use observed neutron-star cooling ages to limit how strongly the proposed particles interact with matter. The study does not report discovering the particles or establishing those limits.
Young explorerScientists did calculations to ask whether very small, dense stars could make tiny particles we have not found yet. If those particles leave a star, they could carry away energy and help it cool. How this might happen depends on what is inside the star. Watching stars cool could help test the idea, but these calculations do not show that the particles exist.
Damiano F. G. Fiorillo, Alessandro Lella, Georg G. Raffelt+2 more
AstronomerThe authors derive neutron-star cooling constraints on hypothetical muon-coupled fifth forces. Their calculation finds that the abundant muon population responds coherently to electromagnetic fluctuations generated by proton–electron collisions, emitting fifth-force mediators and carrying away energy. They obtain g_Xμ ≲ 10^-13 for scalar masses m_φ ≲ 100 keV and vector masses 10^-5 eV ≲ m_V ≲ 100 keV, substantially stronger than SN 1987A cooling constraints. At smaller vector masses, muon depletion suppresses the coherent response; incoherent muon scattering nevertheless yields g_Vμ ≲ 2.5 × 10^-12 for 1.3 × 10^-7 eV ≲ m_V ≲ 10^-5 eV. The authors identify the combined bounds as the most sensitive probes of muonic interactions over a broad parameter range. These are derived constraints, not a detection of a fifth force.
PublicNeutron stars contain many muons, particles that are scarce in ordinary matter, making these stars useful for testing a hypothetical new force that acts on muons. The authors calculate that disturbances caused by collisions between protons and electrons can make many muons respond together, releasing particles that would carry the new force and remove heat from the star. This extra cooling lets them place strong limits on the force’s strength for a broad range of force-carrier masses—limits they report are much tighter than those from supernova SN 1987A. For very light carriers of one type, the force would reduce the muon population and weaken the collective effect, but individual muon scattering still provides limits. The work constrains a possible force; it does not establish that the force exists.
Young explorerA neutron star has lots of tiny particles called muons. Scientists worked out what might happen if muons felt a new kind of force that we have not found. Many muons could act together and send away tiny particles, taking some of the star’s heat with them. By studying this possible cooling, the scientists worked out limits on how strong the new force could be. They did not discover the force.
Yin-Da Guo, Richard Brito, Chen Yuan
AstronomerThe authors calculate the stochastic gravitational-wave background from ultralight scalar clouds formed around rotating black holes through superradiance, extending earlier calculations to include scalar self-interactions. These interactions can suppress the background, weakening constraints inferred from LIGO-Virgo-KAGRA null searches. In their model, LIGO at design sensitivity is insensitive to this background for decay constants f_s ≲ 3 × 10^17 GeV, independently of scalar mass. Under conservative assumptions and with f_s = 10^17 GeV, they forecast sensitivity to scalar masses of approximately 10^-13.0–10^-11.8 eV for the Einstein Telescope and 10^-13.2–10^-11.7 eV for Cosmic Explorer. The minimum decay constants predicted to yield detectable backgrounds are approximately 6 × 10^16 GeV and 3 × 10^16 GeV, respectively. These are theoretical background and detectability predictions, not detections of scalar clouds.
PublicA proposed ultralight field could form clouds around spinning black holes and produce long-lasting gravitational waves at nearly a single frequency. This study calculates the combined background of waves from such systems, including interactions within the field. The calculations show that these interactions can weaken the signal, making existing searches that found no signal less restrictive than previously inferred. The model predicts that LIGO, even at its design sensitivity, would not detect this background if the field's decay constant is at or below about 3 × 10^17 GeV. However, the planned Einstein Telescope and Cosmic Explorer could detect backgrounds from some moderately self-interacting clouds, depending on the field's mass and decay constant. These forecasts use conservative assumptions; the study does not report finding the clouds or their gravitational waves.
Young explorerScientists wonder whether tiny particles could make clouds around spinning black holes. Those clouds might send out ripples in space. The scientists used calculations to see how many clouds' ripples could add together. They found that particles interacting with each other could make the ripples harder to notice. Bigger future ripple detectors might notice some of them, but this study did not find any clouds.
