V. E. Gianolli, P-O. Petrucci, S. Bianchi+42 more
AstronomerThis broadband study examines the soft X-ray excess, ultra-fast outflows (UFOs), and warm absorbers in 21 SUBWAYS AGN at 0.1 ≤ z ≤ 0.4, using simultaneous or quasi-simultaneous UV, optical, and X-ray observations. A two-coronae framework describes the emission with a warm, optically thick corona and a hot, optically thin corona. Optical/UV coverage constrains seed-photon temperatures to 0.1–5.5 eV; fitted warm-corona temperatures are approximately 0.1–0.9 keV, with photon indices above 2. However, 9 of 21 AGN require a hybrid model adding relativistic reflection, suggesting varying contributions to the soft excess. Among UFO-host observations, 4 of 7 favor the hybrid model. UFO hosts show lower warm-corona temperatures, harder hot-corona spectra, and positive hardness ratios, but these trends are limited by sample size and dependence on spectral parameters and instrumental response. No significant differences are found between AGN with and without warm absorbers. Reported correlations connect amplification factor with warm-corona temperature, optical depth with hardness ratio, and warm-corona slope and optical depth with UV luminosity. An anticorrelation between warm-corona optical depth and UFO velocity remains tentative.
PublicResearchers combined ultraviolet, visible-light, and X-ray observations of 21 active galaxy centers to investigate their excess low-energy X-rays and their relationship to fast-moving gas. They fitted the light with a model containing two hot emitting regions: a warmer, dense region and a hotter, more transparent one. For 9 of the 21 objects, the fits also required a contribution from relativistic reflection. This suggests that the excess X-rays may have more than one origin, with different contributions in different objects. Galaxy centers with ultra-fast outflows showed some differences in their fitted temperatures and X-ray spectra, but the small sample and sensitivity to modeling and instrument response make these trends uncertain. Objects with and without warm absorbing gas showed no significant differences. A possible link between the warm region’s opacity and outflow speed is also tentative.
Young explorerScientists studied light from 21 bright galaxy centers. They tried a model with two very hot regions to explain the light, but some centers also needed reflected light in the model. That suggests the extra X-rays might not all come from the same process. Centers with very fast gas blowing out showed some possible differences, but scientists need to be careful: they have only a small group to study.
Christopher Tiede, Zoltan Haiman
AstronomerThe authors model Balmer discontinuities in truncated circumbinary disks around supermassive black hole binaries during a non-accreting phase. Gas accumulation at the cavity edge can favor hydrogen n=2 bound-free absorption. Their simple model predicts the strongest breaks for orbital periods of months to years and total masses ≳10^6 solar masses, overlapping the periodically variable quasar populations anticipated in LSST and Roman HLTDS. For feeding rates of a few tenths of Eddington, they estimate that a few to 10% of periodic binaries at z≲1 should exhibit prominent breaks, with a larger fraction among more massive binaries discoverable at higher redshift. They propose periodic variability, intrinsic X-ray weakness, deficient ionizing emission, and, in favorable cases, a Balmer edge as a complementary test of binary candidates. These are model predictions and proposed diagnostics, not reported detections.
PublicA theoretical study suggests a way to help identify pairs of supermassive black holes. If a pair keeps the surrounding gas disk from extending inward, gas can pile up along the edge of the central gap. Hydrogen there may absorb light in a way that creates a sharp change in the spectrum, called a Balmer break. The model predicts the strongest breaks for pairs orbiting each other every few months to years and weighing at least about a million Suns combined. Under the assumed gas-supply conditions, a few to 10% of periodically varying binaries at redshifts below about 1 could show prominent breaks. The authors propose looking for this feature alongside periodic brightness changes, unusually weak X-rays, and a shortage of radiation capable of ionizing atoms. This combination could help test black hole pair candidates, but the study does not report observing such systems.
Young explorerImagine two enormous black holes circling each other inside a ring of gas. The scientists' model says gas could pile up at the ring's inner edge and soak up some kinds of light, making a sudden step in the light's rainbow. They suggest looking for that step together with repeating changes in brightness and unusually weak X-rays to help find black hole pairs. This is an idea about what we might see, not something they have seen yet.
Filippo Santoliquido, Jacopo Tissino, Marica Branchesi+1 more
AstronomerThis simulation-based forecast compares binary neutron star sky localization for two proposed Einstein Telescope configurations: a triangle at Euregio Meuse-Rhine and a 2L layout with interferometers in Sardinia and Lusatia. Full Bayesian parameter estimation, rather than Fisher-matrix forecasting, resolves multimodal sky posteriors for injections at 40–2000 Mpc with SNRs of 12–720. The analysis mainly considers high-frequency interferometers alone, representing an expected early-operation scenario before low-frequency instruments become available. It relaxes the long-wavelength approximation and includes Earth's rotation and higher-order modes, all reported to improve localization. For low- and moderate-SNR injections, the triangular configuration produces eight degenerate sky modes spanning both hemispheres and Earth's day and night sides, with 90% credible areas reaching approximately 20,000 square degrees. The 2L configuration instead produces one dominant mode containing at least 50% of the posterior probability, with a reported area advantage of one to two orders of magnitude. These forecasts favor 2L for multimessenger follow-up; they are not localization measurements from an operating ET.
PublicSimulations suggest that the layout chosen for the proposed Einstein Telescope could strongly affect how well astronomers can locate colliding neutron stars. The study compares a triangular observatory at one proposed site with a design placing interferometers in Italy and Germany. It mainly models the high-frequency instruments expected to operate first, before the low-frequency instruments arrive. For weaker and moderately strong simulated signals, the triangle leaves eight possible sky regions, with uncertainty covering a very large area. The two-location design instead gives one leading region containing at least half the inferred location probability, and the study reports areas 10–100 times smaller. This predicted advantage could help other telescopes search for light from the same mergers. It is a forecast, not a result from actual Einstein Telescope observations.
Young explorerScientists are planning a giant tool to listen for tiny shakes from two stars crashing together. They tried pretend signals to compare two ways of building it. Putting its parts in two far-apart places helped narrow down where to look better than a triangle in one place. That could help other telescopes find the crash, but it has not been tested with the real observatory yet.
B. Vaia, F. Gastaldello, S. Molendi+13 more
AstronomerUsing approximately 25 years of XMM-Newton EPIC-MOS2 out-of-field-of-view data through the end of 2025, this study tracks the unfocused particle-induced background across two complete solar cycles. The MOS2 outFOV count rate correlates tightly with the AMS proton flux, with about 1.1% intrinsic scatter, supporting Galactic cosmic-ray flux variations as the primary driver of background variability. The time series reveals solar-cycle modulation and signatures of the 22-year Hale cycle. Lomb–Scargle analysis identifies a dominant 11.28-year periodicity, while structure-function and wavelet analyses reveal persistent approximately 27-day modulation associated with solar rotation. A residual component does not scale with cosmic-ray flux; Compton-scattered high-energy X-ray photons are a possible explanation, not an established origin. The findings inform background monitoring and mitigation strategies for future X-ray missions such as NewAthena.
PublicAn analysis of roughly 25 years of data from XMM-Newton's EPIC-MOS2 detector shows that changes in its particle-related background closely track changes in protons arriving as Galactic cosmic rays. This unwanted detector signal can complicate X-ray observations. The researchers measured a very tight relationship with an independent proton measurement, supporting cosmic rays as the main cause of the background's variation. They also found patterns linked to the Sun: a dominant 11.28-year cycle, signatures of its 22-year magnetic cycle, and a persistent roughly 27-day pattern associated with solar rotation. Some background remains that does not follow the cosmic-ray flux. Scattered high-energy X-ray photons could explain this leftover component, but its origin is not established. The results can help guide efforts to monitor and reduce background in future X-ray missions such as NewAthena.
Young explorerAn X-ray telescope in space gets unwanted signals when tiny particles from space hit its detector. Scientists looked at about 25 years of records and found that these signals rise and fall very closely with the number of space particles. They also found repeating patterns linked to the Sun, including one about every 27 days as the Sun turns. A little of the unwanted signal does not follow the particles, and scientists are not yet sure what makes it. Knowing more about these signals can help people plan future X-ray telescopes.
Rafael C. R. de Lima, Pedro Martins Bailer
AstronomerThis simulation study quantifies artificial adiabaticity in MSW evolution when a numerically broadened supernova shock crosses the H resonance. For six three-dimensional blue-supergiant explosion models, individual rays were propagated through both stored profiles and profiles with a 2.2 km shock reconstruction preserving the densities on either side. The stored fronts span 1.6–1.7 grid zones. Across twelve configurations selected within each model’s shock-resonance energy band, reconstruction increases the ray-averaged crossing probability P_H by 0.44–0.76 in absolute terms, with median 0.56. A further thirty-fold narrowing changes these differences by at most 0.055. For all 12,878 rays in one configuration, the ray-specific sudden-limit formula closely matches propagation through the reconstructed front. The largest effect occurs where the density jump spans the resonance; the relevant energy band can be estimated from the presupernova density given the shock radius and compression, although effects extend beyond it. Separately, a parametrised-shock calculation with a published emission model predicts a −4.4% change in electron-neutrino charged-current counts in a 40 kt argon detector; the sign depends on source flavour composition. Combining reconstructed three-dimensional fronts with a consistent emission model remains future work.
PublicComputer simulations can blur the shock wave in an exploding star, making it look smoother than the physical transition should be. This study finds that the blurring can distort calculations of how neutrinos change type while passing through the shock. In six three-dimensional explosion models, the researchers compared the stored, blurred shocks with narrow replacements that kept the densities on either side unchanged. Across twelve selected cases, sharpening the shock substantially increased a probability used to describe neutrino evolution. Making the replacement much narrower changed the comparison only modestly, supporting its use as an approximation to a sudden crossing. These are simulation results, not observations of a supernova. In a separate, simplified calculation, changing neutrino conversion over time reduced the predicted electron-neutrino event count in a large argon detector by 4.4%; whether counts rise or fall depends on the neutrinos emitted by the source. A consistent detector prediction using the reconstructed three-dimensional shocks has not yet been made.
Young explorerWhen a star explodes, a strong wave rushes through it. Tiny particles called neutrinos pass through that wave and can change from one kind to another. In computer models, the wave’s edge can look too blurry. Scientists made that edge sharper in their models, and their predictions about the neutrinos changed. They have not seen this effect in a real exploding star. More work is needed to learn what these sharper models would mean for a machine that catches neutrinos.
David K. Khatami, David Vartanyan, Hai P. Le+2 more
AstronomerThis numerical study presents the first fully 3D, multi-group radiation-hydrodynamics simulations of shock breakout in a red supergiant explosion. In the simulations, large-scale asymmetries originating during core collapse can extend the breakout flash to days, with the duration set by the time required for the shock to wrap fully around the progenitor. Detailed 3D radiative-transfer post-processing produces synthetic multi-wavelength light curves and spectra. The predicted light-curve shape and peak brightness depend significantly on viewing angle, with the strongest asymmetry effects at shorter UV wavelengths. Optical light curves are less affected and more closely resemble a 1D spherical breakout. These simulation results, rather than reported observations, highlight the relevance of core-collapse asymmetries to interpreting future UV measurements, including those from ULTRASAT and UVEX.
PublicA supernova’s first flash of light appears when its shock breaks out of the star. In three-dimensional computer simulations of an exploding red supergiant, researchers found that unevenness created during the collapse of the star’s core can stretch this flash over days as the shock makes its way around the star. Their simulated light curves predict that the flash’s brightness and its changes over time can look substantially different from different viewing directions. These differences are strongest at shorter ultraviolet wavelengths; in visible light, the flash looks more like that of a spherical explosion. These are simulation predictions, not observations of an actual supernova, and they could help interpret data from upcoming ultraviolet space missions such as ULTRASAT and UVEX.
Young explorerWhen a big star explodes, a powerful wave reaches its outside and makes a bright first flash. Scientists used a computer to pretend to explode a huge red star. In their model, the wave did not reach every part of the outside at once, so the flash could last for days. It could also look different depending on which side you watched. The differences were biggest in ultraviolet light, a kind of light our eyes cannot see. This is what the computer model showed, not something the scientists watched happen to a real star.
Paul D. Lasky, Alexander Clevinger, Andre G. da Silva+2 more
AstronomerThe authors develop an inspiral-only gravitational-wave formalism to test the existence and order of phase transitions in neutron-star cores, probing the dense nuclear equation of state. They apply it to GW170817 and GW190425 and assess future sensitivity with synthetic injections for LIGO A+, A#, and Cosmic Explorer. The simulations predict that merger populations observed with A+ or A# could reveal a first-order phase transition within less than half the duration of a US PhD. This is a forecast, not a reported detection in the existing events. Inspiral-only observations cannot distinguish populations without phase transitions from those with second- or third-order transitions, or first-order transitions at relatively high densities.
PublicGravitational waves from neutron stars spiraling toward a merger may help reveal whether matter changes phase deep inside these extremely dense stars. The researchers developed a method using only the waves emitted before the stars merge and tested it on two previously observed mergers. They also simulated observations with future detectors. Those simulations suggest that collections of mergers observed with the planned LIGO A+ or A# upgrades could reveal a first-order phase transition, an abrupt kind of change in matter. The abstract does not report finding such a transition in the existing observations. The method also has limits: these pre-merger waves cannot distinguish no transition from second- or third-order transitions, or from first-order transitions that occur at relatively high densities.
Young explorerNeutron stars are very dense stars. When two circle closer together, they make tiny ripples in space. Scientists made a way to use those ripples to look for changes in the stuff deep inside the stars. They tried it on ripples already seen and on pretend signals for future detectors. The pretend tests suggest that watching many pairs could reveal one kind of sudden change inside the stars. That does not mean they have found it yet, and some kinds of changes would still look the same as no change at all.
Nishant Deo, Jyotirmoy Das, Jayanta Roy+12 more
AstronomerThe authors present the Phase II observing strategy for the Globular Clusters GMRT Pulsar Survey, using SPOTLIGHT to form 160 simultaneous synthesised beams rather than Phase I’s two phased-array beams. Adjustable beam overlap and antenna participation balance spatial coverage against sensitivity. Quantified losses from intra-channel dispersion smearing and finite sampling motivate dispersion-measure limits of 50 and 150 pc/cc for Bands 3 and 4, respectively. The new GPU-accelerated ORION pipeline combines PULSCAN Fourier-domain filtering with localised PRESTO parameter refinement. In single-beam simulated binary-pulsar tests, it runs approximately 15–30 times faster than the CPU-based Phase I pipeline, with comparable or higher folded detection significance. On-sky validation recovered four known globular-cluster pulsars with periods of approximately 5.4–406 ms; these are not new discoveries. With eight GPUs and 64 CPU cores, full 160-beam processing takes approximately 0.25–0.33 times the observation duration. Searches for highly accelerated and jerked binaries remain a target for future development.
PublicA survey of globular clusters—dense groups of stars—is expanding its search for pulsars, rapidly spinning stars whose signals appear as regular pulses. Its second phase uses 160 simultaneous observing beams, compared with two previously, to cover more sky at once. The setup can trade wider coverage for greater sensitivity. The team also introduces ORION, software that speeds up the search through the data. In single-beam tests using simulated pulsars in binary systems, it processed data about 15–30 times faster than the previous software, with comparable or stronger detection signals. Tests on real observations recovered four already-known pulsars, rather than discovering new ones. Using eight graphics processors and 64 CPU cores, the software processes the full 160-beam data about three to four times faster than the observations take to collect. The work establishes a framework for broader searches; improving searches for binaries with strong and rapidly changing acceleration is a future goal.
Young explorerSome stars send us signals that repeat like a ticking clock. Scientists want to find more of these stars in crowded groups of stars. Their new setup can look in 160 small directions at once instead of just two. They also made faster computer software to look for the signals. It worked much faster in tests with pretend star signals, and it found four stars that scientists already knew about in real observations. That does not mean they have found new stars yet, but these tools can help them keep looking.
S.K. Ocker, A.L. Piro
AstronomerThe authors show that source motion can generically explain all repeating FRBs with significant observed dispersion-measure variability, including apparently secular trends. Applying this interpretation to existing measurements, they infer lower limits on source space velocities ranging from roughly 20 to 2800 km/s and simultaneously constrain circumsource plasma properties to be comparable to those of compact HII regions. For sources with compact radio nebulae, they also infer upper age limits consistent with known Galactic magnetar ages. These are motion-based inferences rather than direct velocity measurements. The findings suggest, but do not establish, that strong DM variability marks young sources given natal kicks through prompt formation channels. Continued DM monitoring of a larger sample could further constrain compact-object formation physics.
PublicSome repeating fast radio bursts show changes over time in how much ionized material their signals pass through. The researchers show that movement of the burst sources could explain all repeaters with significant measured changes of this kind. Using existing observations and this motion-based explanation, they estimate minimum source speeds ranging from about 20 to 2800 kilometres per second, and infer surrounding gas conditions similar to those in compact regions of ionized hydrogen. For sources with compact radio-emitting nebulae, their estimated maximum ages are compatible with those of known magnetars in our Galaxy. The results suggest that the changing signals may identify young objects kicked into motion at birth, but they do not directly measure those kicks or establish this origin. Monitoring more repeating bursts could help test how compact stellar remnants form.
Young explorerSome things far out in space send us quick radio flashes again and again. Scientists have noticed that the amount of gas in the flashes’ path can change. They found that a flash-maker moving through the gas could explain these changes. If that explanation is right, some flash-makers must be moving very fast. They might be young stars left over after big explosions, given a strong push when they were born. Scientists need to keep watching more flashes to learn whether this idea is right.
Steve Schulze, Avinash Singh, Nikhil Sarin+69 more
AstronomerMultiwavelength and spectropolarimetric observations identify SN 2023iop (z = 0.1020) as the most extreme 87A-like event reported to date. It rose for at least about 88 rest-frame days to M_r ≈ −20.1 mag, placing it among hydrogen-rich superluminous SNe, and radiated at least about 4 × 10^50 erg. Its Type II-like spectra remain photospheric roughly 330 days after maximum, while 0.8–1.0% continuum polarization indicates asphericity. A hydrogen-rich pair-instability supernova model for a 190-solar-mass star reproduces the light curve through 150 days after peak but misses the late-time emission. A tentative [Ni II] λ7378 identification near 7300 Å implies about 0.02 solar masses of stable nickel-58, reached only by the most massive PISN models. The low-mass host is consistent with, but does not establish, the metal-poor progenitor required by this channel. Fallback accretion matches the light-curve morphology but not the colors. The authors favor a pair-instability explosion with circumstellar interaction supplying the late-time excess, although the spectra show no signatures of that interaction.
PublicSN 2023iop is an unusually bright, hydrogen-rich stellar explosion that took at least about 88 days to reach peak brightness. Observations show that it belongs to the slowly rising family exemplified by SN 1987A, but is the most extreme example reported so far. Polarization measurements indicate that the system is not spherical. The researchers favor a pair-instability explosion of an exceptionally massive star: a model involving a 190-solar-mass star matches the brightness evolution until 150 days after peak, but not the later emission. A possible nickel signature and the small host galaxy are consistent with this explanation, though neither confirms it. An alternative model involving material falling back and being accreted matches the brightness pattern but not the colors. The authors suggest that interaction with material surrounding the star supplies the extra late-time light, despite finding no spectral signatures of that interaction.
Young explorerAstronomers watched an exploding star called SN 2023iop grow brighter very slowly and become unusually bright. Their measurements suggest the explosion was not shaped like a perfect ball. They think a special kind of explosion of a very massive star may explain it, but their computer model does not explain all the light they saw later. They suggest the explosion might have hit material around the star and made extra light, but they have not found the expected clues for that idea in its light. They are still working out exactly what happened.
K. Boyne, O. Graur, M. Vincenzi+5 more
AstronomerFrom 31,636 light curves recorded by the DES supernova survey in 2013–2017, a custom two-stage random forest classifier selects 2,445 likely core-collapse supernovae within the rate-analysis footprint. The inferred volumetric rates span z = 0–1.3 in 11 bins, covering nine billion years of lookback time, and are well fit by R_CC(z) = R_0(1 + z)^alpha, with R_0 = (1.58 ± 0.17) × 10^-4 yr^-1 Mpc^-3 and alpha = 2.85 ± 0.25. The expected turnover at cosmic noon is not yet apparent. Rates are approximately 70% above predictions from recent cosmic star-formation histories assuming a Salpeter IMF. Adopting a Baldry and Glazebrook IMF and an 8–40 solar-mass progenitor range reconciles the discrepancy; an unidentified population of low-luminosity galaxies missed by star-formation histories is an alternative interpretation. The local stripped-envelope fraction is 31 ± 5%, with no detected evolution to z = 1.3. Together with an IMF analysis accounting for the missing-progenitor problem for hydrogen-rich supernovae, these findings favour both single massive stars and binaries as stripped-envelope progenitors, with the invariant fraction favouring binary channels.
PublicResearchers used a machine-learning classifier to identify 2,445 likely core-collapse supernovae—explosions of massive stars—from the Dark Energy Survey. They measured how frequently these explosions occurred across nine billion years of cosmic history, finding higher rates farther back in time over the range studied. An expected turnover in the rate is not yet apparent. The measured rates are about 70% higher than predictions based on recent histories of star formation and one commonly used assumption about the distribution of stellar birth masses. A different birth-mass distribution, together with an assumed exploding-star mass range of 8–40 times the Sun’s mass, can resolve that mismatch. Alternatively, star-formation histories may overlook a population of faint galaxies. Supernovae stripped of their outer envelopes account for 31 ± 5% of nearby core-collapse explosions, and this fraction shows no detected change across the studied period. The authors interpret their findings as favouring origins involving both single massive stars and stars in binary systems, with the unchanging fraction lending support to binary pathways.
Young explorerScientists searched a big collection of changing lights in the sky and picked out 2,445 likely explosions of massive stars. Looking far away lets them see farther into the past. They found that these explosions happened more often long ago, during the time they studied. There were also more explosions than some ideas about how stars are born had predicted. Changing those ideas could explain the difference, or there might be faint galaxies that were missed. Some exploding stars had lost their outer layers. The scientists think stars with a companion may help explain those explosions, but that is a clue, not proof.
Hirotaka Matsumiya, Kazumi Kashiyama, Tomonori Totani
AstronomerThe study models the connection between burst activity and persistent radio source (PRS) variability in FRB 20240114A using continuous electron injection from a central magnetar into a synchrotron-emitting magnetar wind nebula. Comparison with PRS spectra and flux variations implies an injected energy of approximately 10^48 erg during FAST observations from January to August 2024, compatible with a magnetar internal field of approximately 10^16 G. Within this model, the inferred magnetar age is approximately 10–20 years, while the emitting plasma’s bulk Lorentz factor is only weakly constrained to be at most roughly 10^3. The model predicts rapid PRS brightening with increased burst activity, followed by fading over decades through adiabatic cooling after activity ceases. Energetic arguments suggest that the observed hyper-active state, approximately 700 bursts per hour, has a duty cycle no greater than roughly 1%, broadly consistent with its detection rate in current FRB–PRS samples. These constraints and predictions depend on the proposed magnetar-nebula interpretation.
PublicFRB 20240114A produces repeated, brief radio flashes and has an associated persistent radio source whose brightness varies. Researchers compared those variations and the source’s radio spectrum with a model in which a highly magnetic neutron star supplies electrons to a surrounding nebula. In this interpretation, the star is only about 10–20 years old, and the energy supplied during observations from January to August 2024 fits what a magnetar with an extremely strong internal magnetic field could provide. These are model-based inferences, not direct measurements of the star’s age or magnetic field. The model predicts that stronger burst activity should quickly brighten the persistent source, but that the source would fade slowly over decades after the bursts stop. Energy considerations also suggest that the observed extreme activity—about 700 bursts per hour—is a rare phase, occurring no more than roughly 1% of the time.
Young explorerAstronomers studied something in space that sends out lots of quick radio flashes and also has a radio glow that changes in brightness. They tested an idea: a young, very magnetic star might feed tiny particles into a cloud around it, making the cloud glow. Their model says the glow should brighten quickly when the flashes get busier, then fade slowly for many years after the flashes stop. That is a prediction, not something they have watched happen all the way through. They also think its busiest flashing times cannot last very long compared with the quieter times.
Zhen Xie, Ruizhi Yang
AstronomerThis modeling study uses Vela as a representative nearby accelerator to examine how release history and local transport shape the multi-TeV all-electron spectrum. For equal total injected electron energy, a birth-time burst develops a cooling-limited boundary near 28 TeV at Vela’s age, while continuous release yields a broader high-energy tail from recently injected particles. The predicted Earth flux peaks over a finite range of diffusion coefficients because inefficient arrival competes with spatial dilution. Harder injection spectra and greater released energies enhance the multi-TeV contribution; the study maps parameter combinations capable of producing an observable spectral feature. With anisotropic diffusion, visibility also depends on the angle between the Vela–Earth direction and the local ordered magnetic field. These are model predictions, not a reported detection of a Vela feature. Future direct measurements beyond several TeV could distinguish release histories and constrain source energetics and local transport.
PublicVery energetic cosmic-ray electrons lose energy quickly, so nearby, young sources may leave recognizable patterns in the combined spectrum of electrons and positrons reaching Earth. Using Vela as an example, the researchers model two possibilities: particles released all at once when the source was born, or released continuously, with the same total electron energy in both cases. The burst model develops an energy-loss boundary near 28 trillion electronvolts, whereas ongoing release supplies fresh particles that extend the spectrum to higher energies. The predicted signal also depends on how particles spread, the energies they start with, the total energy released, and, when spreading is direction-dependent, the magnetic-field orientation. The study does not report an observed Vela signal; it suggests that future measurements at higher energies could help reveal how nearby sources release particles and how those particles travel.
Young explorerSome places in space send out tiny particles that lose energy as they travel. The scientists used a model of a place called Vela to ask: what if it sent the particles out all at once, or kept sending out new ones? In their model, sending new particles kept more high-energy particles around. How the particles spread out also changed how many could reach Earth. This is a prediction, not something they have spotted from Vela. Future measurements might help tell which story fits.
Sikandar Akbar, Zahir Shah
AstronomerAstroSat/SXT observations of the high-synchrotron-peaked blazar 1ES 1959+650 dated 2023 September 2 span 362 ks, with about 95 ks of good exposure. Six sub-band light curves across 0.6–7 keV show fractional variability of 3.7–6.5%, increasing with energy as E^(0.32±0.07). Accounting for the orbital-gap window function, the total-band power spectrum is consistent with red noise of slope −1.80, with a 95% range of −2.8 to −1.4. No significant periodicity is found (global p>0.57); the search had 90% detection probability for sinusoids with rms amplitudes above 1.9–3.7% at periods of 3–50 ks. The soft- and hard-band correlation is only marginal, with global p=0.04 or 0.07 depending on the assumed power-spectrum slope. Their lag is −1 ks, with uncertainties of +6/−10 ks, consistent with zero. No sub-band pair involving 0.6–0.8 keV has a significant correlation or lag, leaving energy-dependent delays of a few ks unresolved. A single hump has rise and decay times of roughly 0.4–0.6 d but is only marginally distinguishable from red noise (p≈0.05–0.07). The count-rate distribution is consistent with a lognormal distribution, and the hardness ratio has no significant flux dependence.
PublicAn AstroSat X-ray observation of the blazar 1ES 1959+650 found small brightness fluctuations that became stronger at higher X-ray energies. The measured variability ranged from about 4% to 7%. The changes were consistent with irregular variability dominated by slower fluctuations, rather than a clear repeating rhythm. The search found no statistically significant periodic signal, although sufficiently weak signals could have escaped detection. Lower- and higher-energy X-rays showed only tentative evidence of changing together, with no clear delay between them. Delays of a few thousand seconds could neither be confirmed nor ruled out. One broad rise and fall in brightness lasted roughly half a day on each side, but the evidence that it was distinct from the underlying random variability was marginal. The balance between higher- and lower-energy X-rays did not change significantly with brightness.
Young explorerAstronomers watched X-ray light from an object far away. Its brightness wiggled a little, and the higher-energy light wiggled more. They did not find a clear repeating beat. They also could not tell for sure whether one kind of X-ray light changed before another. One bump in brightness might just have been part of the usual random wiggles.
Pritam Banerjee, Kowsona Chakraborty, Niles Mondal+1 more
AstronomerThe authors develop a relativistically improved self-gravity prescription for GRSPH on a fixed black-hole spacetime, replacing the usual Newtonian momentum source term, which becomes invalid at relativistic fluid speeds. They derive each element’s weak gravitational field in its rest frame and transform it to the global frame, incorporating rest-frame distances and softening lengths, receiver time dilation, and relative motion. Applicability requires weak self-gravity, a fluid mass much smaller than the black hole’s, and a body small compared with its distance from the black hole. In tree-based GRSPH tests, the prescription reproduces boosted-polytrope self-gravity with median error below 1% through Lorentz factor 2 and maintains a two-polytrope binary over ten orbits. Simulations of solar-type stellar tidal disruptions by supermassive black holes show shifts in the disruption threshold, remnant core mass, and debris energy distribution. Some encounters retaining substantial cores with Newtonian self-gravity become nearly complete disruptions under the new prescription; these are simulation predictions, not observational findings.
PublicWhen a star passes close to a black hole, its own gravity helps hold it together against being torn apart. Many simulations calculate that internal pull using Newtonian gravity, an approximation that becomes invalid when the star’s material moves at a sizeable fraction of light speed. The authors develop a treatment that accounts for relativistic motion and test it in computer simulations. In simulated encounters between Sun-like stars and supermassive black holes, the new treatment changes how easily stars are disrupted, how much of their cores survives, and how energy is distributed among the debris. Some encounters that leave substantial cores under the older treatment instead produce nearly complete disruptions. These are computational results, not observations, and the method is limited to weakly self-gravitating bodies much less massive than the black hole and small compared with their distance from it.
Young explorerA star’s own gravity helps hold it together, but a nearby black hole can pull it apart. Scientists made a new way for computers to work out that holding-together pull when the star moves very fast. In their computer tests, some stars were almost completely torn apart when the older method left a big middle piece. These are pretend stars in a computer, not real stars they watched.
Snehasish Bhattacharjee, Yen-Chen Pan, Anirban Dutta+4 more
AstronomerAn expanded pre-maximum sample of Swift UltraViolet and Optical Telescope spectra reveals wavelength-dependent correlations between Type Ia supernova UV flux and decline rate. Slow decliners have higher near-UV (NUV) but lower mid-UV (MUV) flux than fast decliners; the NUV correlation near maximum is also recovered. Synthetic TARDIS spectra with enhanced 56Ni abundance suppress the MUV and increase the NUV, broadly reproducing the observed trend without establishing a unique cause. UV flux shows no significant correlation with ejecta velocity, while Si II 6355 pseudo-equivalent width exhibits trends similar to those with decline rate. No significant correlations with host-galaxy properties are found, though environment may contribute to residual diversity at similar decline rates. Early-excess events show enhancement mainly in the NUV rather than across the UV, suggesting that strong circumstellar interaction is not necessarily required. Brighter, hotter peculiar subclasses show higher UV flux, but the subclass sample is small and incomplete. The results favor multiple mechanisms with different wavelength-dependent contributions.
PublicType Ia supernovae differ substantially in their ultraviolet light, and the reasons remain uncertain. Using observations from Swift, researchers find that supernovae that fade more slowly emit more near-ultraviolet light but less mid-ultraviolet light than faster-fading ones before peak brightness. Computer-generated spectra broadly reproduce this pattern when the amount of nickel-56 is increased, offering a possible explanation rather than proof of the cause. The study finds no significant link between ultraviolet output and either the speed of the expelled material or host-galaxy properties, although a galaxy's environment could still account for some differences. Supernovae with extra early light show that enhancement mainly in the near-ultraviolet, suggesting that strong interaction with surrounding material is not necessarily needed. Unusual, brighter and hotter types also show more ultraviolet light, but that sample is small and does not include every subtype. Overall, several processes likely shape the ultraviolet differences.
Young explorerScientists looked at exploding stars using a telescope that sees ultraviolet light, which our eyes cannot see. Stars that faded more slowly had more of one kind of ultraviolet light but less of another kind than stars that faded quickly. In a computer model, adding more of a material called nickel-56 made a similar pattern, but that does not prove it caused the real stars' light patterns. The scientists think more than one thing helps make these explosions look different, and there is still more to learn.
L. Ducci, M. M. Serim, P. Romano+3 more
AstronomerA ~93 ks NuSTAR observation of the intermediate SFXT IGR J00370+6122 near the peak of its orbital modulation resolved a bright event into numerous 10–1000 s flares. The 3–70 keV luminosity varied by a factor of ~200, from ~10^34 to ~1.8 × 10^36 erg/s, with only ~40 s spent at the maximum. An absorbed double-Comptonisation model describes the spectrum, with parameters consistent with other low-luminosity accreting X-ray pulsars. This first detection of a double-hump continuum in this source extends that spectral state to intermediate SFXTs. Neither previously reported periodicity, ~346 s or ~674 s, was significantly detected, weakening but not ruling out their identification with the neutron-star spin. Approximately 21 years of Swift/BAT monitoring yield a refined orbital period of 15.6654 ± 0.0008 d. Quasi-spherical settling accretion, expected at these luminosities, is discussed as a framework for interpreting the flaring rather than established as its cause.
PublicA long NuSTAR observation caught the X-ray source IGR J00370+6122 producing a bright outburst made up of many shorter flares, each lasting 10 to 1,000 seconds. Its X-ray luminosity changed by roughly a factor of 200, reaching its maximum for only about 40 seconds in total. For the first time in this source, the researchers detected an X-ray spectrum with two broad humps, a pattern also seen in other faint, matter-accreting X-ray pulsars. They found no significant signal at either of two previously reported repeating intervals, making those intervals less convincing as measures of the neutron star's rotation. Separately, about 21 years of Swift/BAT monitoring refined the system's orbital period to 15.6654 ± 0.0008 days. The team discusses whether a model in which surrounding material settles toward the neutron star could explain the flares, but does not establish that explanation.
Young explorerAstronomers watched a star system give off bursts of X-rays, a kind of light our eyes cannot see. One big burst turned out to be lots of smaller flashes. The system became about 200 times as bright in X-rays, but stayed at its very brightest for only a short time. The scientists also found two broad bumps in the pattern of its X-ray light. They looked for two repeating beats that had been reported before, but did not find clear signs of either one. They are exploring whether material settling toward a neutron star could explain the flashes, but they do not yet know if that idea is right.
Timo Kravtsov, Hanindyo Kuncarayakti, Joseph P. Anderson
AstronomerThis study analyses MUSE observations of type Ibn supernova host galaxies, using H-alpha emission to trace association with star formation and strong-line diagnostics to estimate local metallicity. The sampled events are highly associated with star formation, typically lying within one of their host galaxies’ brightest H II regions. Their H-alpha normalized cumulative rank (NCR) distribution closely resembles that of Wolf-Rayet stars and indicates a stronger preference for star-forming environments than other core-collapse supernova types. Local metallicities are typically sub-solar. These environmental findings inform the debated progenitor channel but do not establish it: for a core-collapse origin, the strong stripping needed to produce helium-rich circumstellar material could involve Wolf-Rayet winds or binary interaction.
PublicAstronomers studied the galaxies hosting a sample of type Ibn supernovae to investigate what kinds of stars produce these explosions. Using MUSE observations, they traced nearby star formation with hydrogen emission and estimated the abundance of elements heavier than helium. The explosions typically occurred in some of their galaxies’ brightest star-forming regions, with a stronger association with star formation than other types of collapsing-star explosions. Their surroundings usually had lower heavy-element abundances than the Sun. The pattern of association with star formation closely resembled that of Wolf-Rayet stars, which lose material through powerful winds. However, the study does not settle the stars’ identities: stripping by a companion star remains another possible explanation for the helium-rich material surrounding these explosions.
Young explorerSome stars explode with helium-rich gas around them, and scientists want to know what those stars were like before they exploded. They studied the neighborhoods of a group of these explosions and found that they were usually in bright places where new stars are being born. Stars called Wolf-Rayet stars are found in similar places. That is a clue, not proof: the exploding stars might have blown off their outer layers, or a nearby partner star might have helped pull those layers away.
Clarissa Mora, Fabio Bacchini, Camille Granier+1 more
AstronomerParticle-in-Cell simulations investigate radiative variability during driven relativistic magnetic reconnection in strongly magnetized flux tubes forced to merge. In the simulations, the merger efficiently produces nonthermal particles and synchrotron emission whose variability follows the reconnection phases. The authors distinguish quasi-steady, weak driving at v_push ≤ 0.1c from strong driving above 0.1c. They interpret this transition as driving outpacing the typical flux-processing rate of steady collisionless relativistic reconnection, potentially introducing additional variability. Simulated light curves rise over 1–3 light-crossing times of the reconnecting region, and particle spectra develop power-law indices p ≃ 1.8–2.4. The rise times are compatible with observed very-high-energy flares of M87* and gamma-ray flares of the Crab Nebula, supporting driven reconnection as a viable framework rather than establishing it as the cause of those events.
PublicComputer simulations explore how merging magnetic structures could produce rapid, energetic flares near compact objects. As the structures reconnect, they accelerate particles that emit synchrotron radiation, and the simulated brightness changes with the stages of reconnection. Slow forcing produces a relatively steady response, while forcing faster than about one-tenth the speed of light leads to a strongly driven regime. The authors suggest that forcing magnetic structures together faster than reconnection can process them may add variability. The simulated flares brighten over one to three times the time light takes to cross the reconnecting region. These timescales are compatible with observed flares from M87* and the Crab Nebula, but the simulations do not establish that this mechanism caused those flares.
Young explorerThe scientists used a computer to push two bundles of magnetic field together. In their pretend space scene, the magnetic fields joined in new ways and gave tiny particles a big boost, making them shine. Pushing slowly made things fairly steady; pushing fast changed how the bright flashes grew. The flashes grew quickly enough that this might help explain some real flashes in space, but the computer test does not prove that real flashes happen this way.
M. Nava-Callejas, S. Goriely, N. Chamel
AstronomerMESA v.24.08.1 simulations investigate how photodisintegration of heavy rp-process ashes, potentially important above 4 GK, affects neutron-star superbursts in low-mass X-ray binaries. Models with 10% carbon-12 and 90% rp-process ashes ignite and reach luminosities comparable to the canonical 20% carbon-12/80% iron-56 fuel, whereas 10% carbon-12/90% iron-56 produces lower luminosity. Iron-56 remains the most abundant ash nuclide. Photodisintegration drives nucleosynthesis, while neutron, proton and alpha captures release energy at late times. Models also indicate that mass-number-64 nuclides or neon-20 reduce the carbon abundance required for ignition. These simulation results highlight the importance of the full accreted composition, rather than carbon content alone, for ignition, luminosity and nucleosynthesis.
PublicComputer simulations suggest that the ingredients in a neutron star’s crust can be as important as its carbon supply in triggering a powerful explosion called a superburst. A mixture containing 10% carbon-12 and 90% heavy nuclei left by earlier nuclear reactions could ignite and shine about as brightly as the standard modeled mixture of 20% carbon-12 and 80% iron-56. Replacing those heavy reaction leftovers with iron-56 at the same 10% carbon level produced a dimmer simulated burst. At sufficiently high temperatures, light can break heavy nuclei apart; later capture reactions release energy. The models also found that certain nuclei, including neon-20, help ignition occur with less carbon. These are simulation findings, not reported observations of actual bursts.
Young explorerScientists used a computer to study huge explosions on neutron stars. In their pretend stars, changing the mix of tiny bits of matter let an explosion start with less carbon, one of its fuels. Some mixes with less carbon could shine about as brightly as a mix with more carbon, but another mix made a dimmer explosion. It is a bit like cooking: all the ingredients matter, not just one. These results came from computer models, not from watching a real explosion.
Guan-Sen Wang, Xu Pan, Lei Feng
AstronomerThe authors use Chandra and Fermi-LAT observations of Omega Centauri to constrain dark matter annihilation through predicted inverse Compton emission from annihilation-injected electrons and positrons scattering starlight. Omega Centauri’s dense stellar radiation field enhances the predicted signal; its identification as a remnant dwarf-galaxy core remains an interpretation. The derived upper limits on the velocity-averaged annihilation cross section span MeV–TeV dark matter masses. The authors report limits around 10^-31 cm^3 s^-1 at tens of MeV, approximately two orders of magnitude tighter than existing constraints, and stronger constraints at masses from several GeV to TeV. These are limits within the proposed emission scenario, not a dark matter detection, and highlight starlight-induced inverse Compton emission as a probe in dense stellar systems.
PublicThis study uses observations of the dense star system Omega Centauri to test a possible signal of dark matter. If dark matter particles annihilate and produce electrons and positrons, those particles could boost starlight to higher energies. The researchers calculate this expected emission and use Chandra and Fermi-LAT observations to place upper limits on how readily dark matter could annihilate. They report limits about 100 times tighter than previous constraints for dark matter masses in the tens-of-MeV range, with improvements also reported from several GeV to TeV. The study constrains a possible dark matter process rather than reporting a detection.
Young explorerScientists looked at a crowded group of stars for clues about invisible stuff called dark matter. They worked out how dark matter might make particles that give starlight extra energy. Using telescope observations, they set stricter limits on how much of this could happen. They did not report finding dark matter.
R. Dokara, M. Kramer, A. Brunthaler+2 more
AstronomerRadio flux-density measurements from approximately 200 MHz to 6 GHz give the shell G42.1-0.2 a spectral index of −0.36 ± 0.08, establishing predominantly nonthermal synchrotron emission and supporting its identification as a supernova remnant. PSR J1909+0749 lies well outside the shell, with a cometary tail pointing toward its centre. The authors propose a common supernova origin; poorly constrained proper-motion measurements are consistent with, but do not establish, this association. Assuming the association and that the pulsar's characteristic age and dispersion-measure distance reflect the system's true age and distance, standard evolution equations place the remnant in the Sedov–Taylor phase in a medium of density about 1.5 cm⁻³. The inferred pulsar transverse velocity is approximately 1460 km s⁻¹, which would rank among the highest for Galactic pulsars.
PublicRadio measurements support identifying G42.1-0.2, a shell-shaped object, as debris from an exploded star. A pulsar—a spinning stellar remnant—lies far outside the shell, but its comet-like tail points back toward the shell's centre. The researchers propose that both came from the same explosion and that the pulsar has since travelled beyond the debris. Measurements of its motion are too uncertain to confirm this connection, although they are consistent with it. If the proposed connection and the adopted age and distance are correct, the pulsar's estimated sideways speed is about 1,460 kilometres per second, among the highest inferred for pulsars in our galaxy. Under the same assumptions, a standard model suggests the shell is still in the Sedov–Taylor stage of expansion.
Young explorerAstronomers studied a big shell in space. Its radio signals suggest it is leftover stuff from a star that exploded. Far outside the shell is a tiny spinning star with a tail pointing back toward the shell's middle. The scientists think the explosion may have made both, and the tiny star may have raced away very fast. But they are not sure yet: the measurements of how it moves are not clear enough to prove they belong together.
D. Kantzas, D.A. Langis, I. Liodakis+1 more
AstronomerMotivated by candidate TDE–neutrino associations, this study models the conditions under which tidal disruption events could be detectable in MeV–TeV gamma rays and high-energy neutrinos. A lepto-hadronic framework is applied to AT2019dsg, AT2019ehz, and ASASSN-14li, varying particle spectra, minimum proton Lorentz factor, energy partition, acceleration efficiency, magnetic compactness, and the presence of a compact corona. Predicted broadband spectral energy distributions and muon-neutrino spectra are compared with reference sensitivities for COSI, Fermi/LAT, CTAO, and KM3NeT/ARCA. Hard proton spectra and/or high minimum proton Lorentz factors favor TeV and neutrino detectability; GeV-bright models can instead be predominantly leptonic and neutrino quiet. In hadronically favorable configurations, AT2019dsg and AT2019ehz can reach CTAO and KM3NeT benchmarks. ASASSN-14li is more naturally MeV–GeV bright, with models constrained by its radio synchrotron emission. These are model-dependent detectability predictions, not reported detections or confirmed TDE–neutrino associations. Combined gamma-ray, radio, and neutrino observations could distinguish transparent, hidden, and lepton-dominated emission regimes.
PublicCould a star being torn apart produce detectable gamma rays and high-energy neutrinos? Motivated by possible, but unconfirmed, links between stellar disruptions and neutrinos, the researchers modeled three events: AT2019dsg, AT2019ehz, and ASASSN-14li. Their calculations suggest that proton populations weighted toward high energies offer the best prospects for detecting both TeV gamma rays and neutrinos. Bright GeV gamma-ray emission, however, can come mainly from electrons without a strong neutrino signal. Under favorable proton-driven conditions, the first two events could reach the reference sensitivity levels of CTAO and KM3NeT/ARCA. The third more naturally favors lower-energy gamma rays, and its radio emission limits the possible models. These are predictions rather than new detections. Observations spanning radio waves, gamma rays, and neutrinos could help identify which particles power these events and whether their radiation escapes or remains hidden.
Young explorerWhen a star is torn apart, it may make powerful light and tiny particles called neutrinos. Scientists used computer models of three such events to ask whether detectors could spot these signals. Some models with very energetic protons made both signals easier to spot. Other models made bright light but few neutrinos. These are predictions, not new sightings. Looking for several kinds of signals together could help scientists understand what happens.
Noam Soker
AstronomerThe author identifies a subtle point-symmetric morphology in HB9 (G160.9+2.6), a presumed core-collapse supernova remnant, through visual inspection. The identified features comprise paired ears, ears/nozzles, dents, and bright bars. Although the features are small and the symmetry subtle, the author considers the identification robust. The proposed interpretation is that at least two jet pairs shaped these features, forming part of a larger set of jet pairs that powered the explosion through the jittering-jets explosion mechanism (JJEM). The author argues for jet-driven rather than circumstellar-material shaping and regards the morphology as supporting earlier claims that JJEM is the primary core-collapse explosion mechanism. The jet origin and explosion mechanism are interpretations of the morphology, not directly observed results.
PublicA researcher examining HB9, the remains of a stellar explosion, identifies several small features arranged in opposite pairs: protrusions, openings, dents, and bright bars. The researcher considers this pattern reliable despite its subtle appearance. HB9 is thought to come from the collapse of a massive star. The author interprets the pattern as the imprint of multiple pairs of jets that helped explode the star, rather than shaping by surrounding material. This is presented as support for the idea that jets commonly power such explosions, but the visual pattern does not by itself establish how the star exploded.
Young explorerA star exploded and left a cloud called HB9. A scientist looking at the cloud sees little bumps, dents, and bright stripes in opposite pairs. The scientist thinks pairs of powerful sprays from the star helped make these shapes and blow the star apart. The shapes are faint, and this explanation is an idea, not something seen happening.
Jorge L. Rodríguez-Monteverde, Sebastiano Bernuzzi, William Cook+2 more
AstronomerThree-dimensional, fully general-relativistic magnetohydrodynamic simulations investigate strongly magnetized supramassive neutron stars near the mass-shedding limit, using a microphysical equation of state and initially poloidal fields with maximum strengths up to about 10^17 G. Magnetic instabilities produce mixed poloidal–toroidal configurations on Alfvén timescales shorter than a rotation period; subsequent evolution follows timescales set by the Lehnert number. Models sufficiently below the maximum mass develop differential rotation through magnetic angular-momentum redistribution and reach quasi-stationary states that remain dynamically stable for several rotation periods. Equatorial winds are baryon-matter dominated, with magnetization at most about 0.2, ejecting roughly 10^-3 solar masses over the simulated interval at rates reaching a few solar masses per second. Near or beyond the equilibrium sequence’s maximum-mass turning point, magnetic transport removes angular momentum from the core and triggers collapse. Black hole remnants have angular velocities up to about 49% higher and angular momenta at most about 8% lower than the initial stars. These are simulation results with possible implications for magnetars and long-lived neutron-star merger remnants, not evidence of indefinite stability or direct observational findings.
PublicComputer simulations explore what happens inside extremely magnetic neutron stars spinning close to the point of shedding matter. The initially unstable magnetic fields rapidly rearrange and shift rotational motion between different parts of each star. Stars sufficiently below the maximum mass settle into a new state, with different regions rotating at different rates, and remain stable for the several rotations simulated. They also launch matter-dominated winds from around their equators. Stars near or beyond the maximum-mass threshold instead collapse into black holes when magnetic forces move angular momentum away from their cores. The study suggests that extreme magnetic instabilities could affect magnetars and the stars left after neutron-star mergers, but it does not establish how long the surviving stars would remain stable.
Young explorerScientists used computers to model very heavy, fast-spinning stars with super-strong magnets. In the models, the magnets changed how different parts of each star spun. Some stars stayed together for the short time the scientists followed them and blew some matter away. Others collapsed into black holes. These were computer experiments, not stars watched in the sky.
S. Guns, C. Tandoi, D. Anbajagane+95 more
AstronomerThe authors searched four seasons (2019–22) of SPT-3G observations covering 1500 square degrees for bright, short-lived millimeter-wave transients from GRB reverse shocks, finding no candidate extragalactic events. Earlier simulations predicted that reverse shocks in long-duration GRBs would dominate detections on timescales shorter than a week, with some benchmark models yielding about 10 detections annually for SPT-3G. Updated simulations incorporating more realistic sensitivity, cadence, and detection procedures indicate nearly twice the detection sensitivity of prior estimates. The null search constrains the synthesized GRB populations rather than establishing an absence of reverse shocks. For a 10^51 erg GRB with Lorentz factor 100, the authors obtain f_RS < 0.57 and an Earth-directed all-sky reverse-shock rate below 1226 bursts per year at 90% confidence. For their most readily detectable model, a 10^52 erg “dirty” GRB with Lorentz factor 50, the corresponding limits are f_RS < 0.09 and fewer than 120 bursts per year.
PublicTelescopes that study the cosmic microwave background can also search for brief flashes of millimeter-wave light. Simulations suggested that SPT-3G on the South Pole Telescope might detect roughly 10 flashes a year in some models of reverse shocks associated with long-duration gamma-ray bursts. The researchers refined those simulations and searched four years of observations, but found no candidate events from beyond our galaxy. That result places limits on how common these flashes can be, with the limits depending on the assumed burst properties. For one standard burst model, fewer than 57% of gamma-ray bursts can have the modeled reverse-shock component at 90% confidence; the most detectable model considered is limited to fewer than 9%. The search does not show that such flashes never happen.
Young explorerScientists used a telescope at the South Pole to look for quick flashes of light from huge bursts far beyond our galaxy. Their computer models suggested they might find some, but they found no possible flashes of that kind in four years of observations. That does not mean the flashes never happen. It helps scientists work out how often certain kinds of flashes could happen without the telescope seeing any.
LIGO Scientific Collaboration, Virgo Collaboration, KAGRA Collaboration+97 more
AstronomerA search of LIGO and Virgo data from 10 April 2024 to 28 January 2025 targeted compact binaries with secondary masses of 0.2–1 solar masses, primary masses of 0.2–10 solar masses, and mass ratios of 0.1–1. Two of three pipelines produced outlier candidates, but none was significant enough to provide evidence for detection. Combining search sensitivity across both parts of the fourth observing run yields 90%-confidence upper limits on sub-solar-mass black hole merger rates of 50–5000 per cubic gigaparsec per year, depending on component masses. Interpreted within two illustrative dark matter scenarios, these limits constrain primordial black holes with a monochromatic mass distribution to dark matter fractions no greater than 0.018–0.032 at 1 solar mass and 0.10–0.18 at 0.35 solar masses for early-forming binaries. For late-forming binaries, the allowed fraction falls below unity above mass thresholds of 0.62–0.74 solar masses. In a dissipative dark matter model, fraction constraints reach 1.0–1.1 × 10^-5 for some minimum dark black hole masses below 1 solar mass; minimum masses above thresholds of 0.62–0.74 solar masses are excluded if these black holes constitute all dark matter. These interpretations depend on the assumed scenarios. For neutron star binaries containing sub-solar components, a simple fixed population model gives a merger-rate upper limit of 249 per cubic gigaparsec per year.
PublicResearchers searched LIGO and Virgo measurements for gravitational waves from merging compact objects, including objects lighter than the Sun. Some candidates stood out, but none was convincing enough to count as evidence of a detection. Combining the sensitivity of searches from both parts of the fourth observing run, the team set upper limits on how often such black hole mergers could occur: 50–5000 per cubic gigaparsec per year at 90% confidence, depending on the objects’ masses. They used those limits to restrict two proposed ways dark matter might form small black holes: black holes originating in the early universe and black holes forming in a dissipative dark matter model. These restrictions depend on the assumed models; they do not establish what dark matter is or show that these black holes exist. The study also limits merger rates for neutron star pairs containing at least one object lighter than the Sun, under a fixed population model.
Young explorerScientists looked for tiny stretches and squeezes in space that could come from two very small, heavy objects joining together. They found a few possible clues, but none was strong enough to say they had found one. That helps them set limits on how often these crashes happen and test some ideas about the universe’s mysterious dark matter. It does not tell us what dark matter is.
Amanda Malnati, Megan Kralj, Ken D. Olum
AstronomerThe authors propose a variant of model-switch thermodynamic integration for estimating Bayes factors, aiming to reduce estimator variance and essentially eliminate integration error. Sampling density in β is chosen proportional to the standard deviation of previously drawn samples. Instead of averaging many samples at each β, the method takes one sample at each point on a very dense β grid in both increasing and decreasing order to minimize thermic lag. In a toy model loosely based on signal recovery problems, adaptive sampling reduces the spread of Bayes factor estimates by a factor of 2.7. Tests use both direct posterior draws and Markov Chain Monte Carlo sampling; the reported improvement is demonstrated in this toy setting, not with astronomical observations.
PublicBayes factors help compare competing models, but calculating them accurately can be computationally demanding. The authors propose an adaptive method that concentrates sampling where earlier samples show more variability. It also sweeps through closely spaced values of a calculation parameter in both directions to reduce lag. In a simplified test problem loosely inspired by recovering signals, adaptive sampling reduced the spread of the estimates by a factor of 2.7. The method was tested with two sampling approaches. This is a computational demonstration in a toy model, rather than a result from observations; its broader performance is not established by the abstract.
Young explorerScientists use a number to help compare different explanations, but that number can be hard to work out. These researchers suggest checking more often in places where their calculation changes more, and going through the checks both forward and backward. In a simple pretend problem, this made their answers less spread out. That is a promising test, but it does not show that the idea works as well for every problem.
Yusen Wang, Zhonghai Zhao, Xinyu Zhu+3 more
AstronomerSelf-consistent three-dimensional radiative particle-in-cell simulations identify an ion-heating mechanism mediated by pair-enhanced radiative feedback in relativistic turbulence. The study derives a theoretical criterion for entry into a radiative-feedback-dominated regime and finds that pair loading promotes large, connected, optically thick structures. In the simulations, these persistent structures sustain intense localized ion heating, repeatedly produce hot-ion clumps, and substantially raise the mean ion temperature. The results provide a theoretical link between pair creation and sustained ion heating, motivating investigation of intermittent hot-ion production in black-hole coronae and gamma-ray burst outflows rather than demonstrating it observationally.
PublicComputer simulations suggest a way to keep ions hot in turbulent plasma moving at relativistic speeds. Adding particle–antiparticle pairs strengthens radiation feedback and helps large, connected regions that are difficult for radiation to pass through grow and persist. In the simulations, these regions repeatedly produce clumps of hot ions and raise the ions’ average temperature. The researchers also derive a theoretical condition for when radiation feedback becomes dominant. This offers a possible explanation to investigate for intermittent hot-ion production around black holes and in gamma-ray burst outflows, not an observational detection of the process.
Young explorerScientists used a computer to study swirling, super-hot matter. In their model, adding pairs of tiny particles helped make big patches that light could not easily pass through. Those patches lasted a long time and kept making clumps of very hot particles called ions. This might help scientists understand hot matter near black holes and in powerful space explosions, but they have not shown that it really happens there.
Hao-Fu Zhu, Guo-Zhu Liu
AstronomerThis theoretical study argues that non-Fermi-liquid behavior associated with superfluid and superconducting quantum criticality can relax the direct Urca proton-fraction threshold, conventionally Y_p ≈ 0.11–0.15. In the proposed regimes, smooth nucleon momentum occupations without a sharp Fermi surface and logarithmically temperature-dependent chemical potentials modify the standard beta-equilibrium relation. The authors conclude that direct Urca neutrino emission can become possible at low nuclear densities, potentially allowing it in low-mass neutron stars where the conventional threshold is rarely reached. The abstract presents a theoretical mechanism, not an observational detection.
PublicA process called direct Urca lets neutron-star matter emit neutrinos. Standard theories say it requires a minimum proportion of protons that low-mass neutron stars rarely reach. This theoretical study argues that unusual quantum behavior linked to superfluidity and superconductivity could change how particles behave and balance one another, relaxing that requirement. If this mechanism operates, direct Urca emission could occur even in lower-density matter inside low-mass neutron stars. The study does not report observing this emission in such stars.
Young explorerA neutron star is a very dense star. Scientists usually think it needs enough particles called protons to send out tiny particles called neutrinos in one special way. This study suggests that strange quantum behavior might let it do that with fewer protons than expected. That could make this possible in less-heavy neutron stars, too. It is an idea worked out with theory, not something the scientists report seeing.
Pablo Laguna, Octavio Guerrero, Kostas Kokkotas
AstronomerThis theoretical study tests radial stability of singular Tolman–Oppenheimer–Volkoff fireholes with a radiation equation of state: a naked negative point-mass singularity surrounded by positive-density fluid. Using the Prüfer phase method, the authors find that the fundamental radial mode becomes unstable when the outer boundary exceeds a critical radius Rc. Although Rc scales approximately like the equilibrium firehole radius R with central mass parameter, the thresholds depend strongly on confinement: Rc < R for vanishing Lagrangian pressure perturbation, while Rc ≈ R for vanishing radial displacement at a rigid wall. The regular zero mode is an equilibrium-family derivative with respect to inner lapse normalization at fixed central mass, giving the boxed threshold a turning-point interpretation; scaling symmetry implies Rc approaches R at large central mass. Variational bounds establish that the rigid wall is the most stabilizing separated, self-adjoint outer boundary condition and that the unbounded configuration is radially unstable. These are mathematical stability results, not observations of astrophysical objects.
PublicThe researchers mathematically studied hypothetical objects called fireholes, consisting of a negative-mass central point surrounded by fluid described by a radiation equation of state. They asked whether small inward-and-outward disturbances would remain stable or grow. Their calculations show that stability is lost if the surrounding fluid extends beyond a critical radius. A rigid confining wall allows a larger stable configuration than an outer boundary where the pressure disturbance vanishes. With a rigid wall, the stability limit is approximately the characteristic firehole radius; without any outer boundary, the configuration is unstable. The study concerns theoretical models, not observed objects, and tests radial disturbances rather than every possible kind of instability.
Young explorerScientists used math to study a strange, pretend object called a firehole. They asked what happens if its surrounding material gets a little squeeze. In their model, if the material spreads too far out, that little squeeze can grow instead of staying small. A hard wall can help keep it steady, but the wall must be close enough. This was a math study, not something scientists saw in the sky.
Milena Albino, Tuhin Malik, Márcio Ferreira+1 more
AstronomerThis equation-of-state study compares a new Bayesian-constrained SmallQ ensemble with the earlier NJL-GW ensemble. Both incorporate nuclear-matter constraints, NICER mass-radius data, GW170817, perturbative QCD, and causality. SmallQ relaxes the requirement that the maximum-mass neutron star have a large quark core, requiring only a core of any size. Both ensembles use a relativistic mean-field hadronic model with nonlinear meson interactions and a Nambu–Jona-Lasinio quark model with four- and eight-quark interactions. SmallQ places the phase transition at 3–4.5 ρ0, versus 2–2.5 ρ0 for NJL-GW, and yields smaller radii and tidal deformabilities, with better compatibility with the cited observations. Its quark matter has a larger strange-quark fraction, but its 2-solar-mass stars may contain little or no quark matter. A non-negligible fraction of SmallQ equations of state produces a positive mass-radius-curve slope at 1.8 solar masses; the reported fraction is negligible for nucleonic stars, while hyperonic stars always have negative slopes. These are model-dependent findings, not observational confirmation of quark cores.
PublicCould neutron stars contain cores of quark matter? This study explores that possibility with models constrained by existing neutron-star and gravitational-wave observations, along with theoretical requirements. Earlier models required the heaviest star supported by each model to have a large quark core. The new models allow that core to be any size, though they still require it to exist. Compared with the earlier set, they predict that quark matter appears at higher density and that stars have smaller radii and deform less under tidal forces. The authors report better agreement with the observations used. Even stars twice the Sun’s mass could contain little or no quark matter in these models. Some models also show a positive slope in the mass-radius relationship near 1.8 solar masses, unlike the reported behavior of models containing only nucleons or including hyperons. The study does not establish that real neutron stars have quark cores.
Young explorerScientists made models of very tightly packed stars to ask what might be inside them. They allowed the biggest star in each model to have a tiny center made of quark matter, instead of insisting on a big one. These models fit the star clues better than the older models did. But this does not prove that real stars have quark centers. Even some very heavy stars might have almost none.
Asim kumar Saha, Ritam Mallick
AstronomerThis theoretical study generalises causal bounds on neutron-star compactness and maximum mass to EOSs with a first-order transition between maximally stiff phases. With q equal to transition pressure divided by transition energy density and j equal to the fractional energy-density jump, the maximum compactness approaches 0.354 as either parameter tends to zero and is unchanged for q ≳ 0.67. Otherwise, it is typically reduced by ≲0.04 when the maximum-mass configuration is hybrid, and by up to 0.13 when it is the last hadronic configuration. With a Baym–Pethick–Sutherland crust and chiral-EFT polytrope matched at 1.1 times nuclear saturation density, supporting 2.01 solar masses excludes jumps above approximately 460–495 MeV fm⁻³; additionally requiring a radius of at least 11.6 km lowers this limit to approximately 235–395 MeV fm⁻³. These limits are independent of the matter above the transition but apply to onsets within approximately 0.2 saturation densities of the matching density. A separate EOS grid relaxes maximal stiffness and matches to perturbative QCD at 2.6 GeV. Compatibility with all listed observational constraints appears only at transition chemical potentials of 1200 and 1250 MeV; within the causal window, the largest jump agrees with the bound to grid resolution. Finally, inserting a transition at 2.01 solar masses into hadronic EOSs satisfying five pulsar constraints yields a narrow stable hybrid window, approximately 0.005 solar masses wide, for the lowest-break-density EOS, but none for three higher-break-density EOSs. These are conditional theoretical results, not detections of a phase transition.
PublicHow abruptly could matter change inside a neutron star without making the star unable to support its own mass? This theoretical study explores that question using models constrained by causality. A sudden change in matter can reduce the greatest compactness a neutron star can reach, although some model regimes leave the limit unchanged. Under specified assumptions about the lower-density layers and where the transition begins, the requirement that a star support 2.01 times the Sun’s mass limits the size of the energy-density jump. Adding a minimum-radius requirement tightens that limit. Further models constrained by high-density calculations and astronomical observations allow transitions only at some of the tested settings. One model also permits a very narrow mass range of stable stars with a transformed core, while three others do not. The findings constrain possible interiors; they do not show that such a transformation has been observed.
Young explorerA neutron star is a very tightly squeezed star. Scientists used maths to ask what would happen if the stuff deep inside suddenly changed into a different kind of stuff. Their models suggest that too big a change could stop the star from holding itself up. Some models allow a changed middle, but this does not mean scientists have seen one.
Ore Gottlieb, Matteo Cantiello, Cameron Norton+2 more
AstronomerThe authors combine analytic calculations, stellar evolution models, 3D general-relativistic magnetohydrodynamic simulations, and Monte Carlo population synthesis to model stars that capture asteroid-mass primordial black holes (PBHs; 10^17–10^23 g), which remain viable dark matter candidates. The framework predicts two outcomes: quiet consumption if growth is too slow or capture too late, and explosive disruption if an accretion disk forms before the host is consumed. Capture is dominated by three-body interactions with companions; for a solar-type star with a Jupiter analog, inspiral within the main-sequence lifetime requires a PBH mass of roughly 10^22 g or greater, while lighter PBHs generally need tighter companions. Central growth initially proceeds through inefficient, quasi-spherical Bondi accretion. The population calculations produce both outcomes, with final PBH masses of about 0.01–1 solar masses and disk-forming PBH spins near 0.8. In the models, disk winds and relativistic jets with powers of about 10^45–10^50 erg/s disrupt the star within minutes. Possible signatures include a roughly day-long UV/blue transient, a radio afterglow, and an X-ray flash or low-luminosity gamma-ray burst if the jet escapes. Rates could reach those of low-luminosity gamma-ray bursts only under optimistic capture assumptions and an order-unity PBH dark matter fraction. Low-mass, high-spin remnants are proposed as a complementary PBH probe and possible source of subsolar black hole mergers; these are theoretical predictions, not reported detections.
PublicCould a tiny black hole from the early universe destroy a star from within? This theoretical study models what might happen if a star captures a primordial black hole, a proposed dark matter candidate. The calculations suggest that interactions involving a planet or companion star are the main route to capture. Once at the star’s center, the black hole initially grows slowly. If material begins orbiting it in a disk before the star is swallowed, the models predict powerful winds and jets that tear the star apart within minutes. Otherwise, the black hole consumes the star quietly. An explosion might produce about a day of ultraviolet and blue light, followed by radio emission; an escaping jet could also produce an X-ray flash or a faint gamma-ray burst. Such events could be as frequent as low-luminosity gamma-ray bursts only if primordial black holes make up a large fraction of dark matter and capture is sufficiently efficient. The study does not report observing these events; it predicts possible signals and black hole remnants that could help test the idea.
Young explorerScientists used calculations and computer models to imagine what could happen if a star caught a tiny black hole left over from the early universe. Their models suggest that the black hole might slowly swallow the star without an explosion. But if the star’s material starts swirling in a disk around the black hole soon enough, strong winds and jets could tear the star apart and make a bright flash. Scientists have not reported seeing this happen in this study. These are ideas about what to look for in space.
Jian-Hao Shi, Bao-Jun Cai, Bao-An Li+1 more
AstronomerA perturbative analysis of dimensionless stellar-structure and tidal-response equations yields a largely EOS-insensitive scaling between tidal deformability Λ and the central pressure-to-energy-density ratio X = Pc/εc. Derived without choosing a specific EOS model and validated against a broad ensemble of physically viable EOSs, the relation links inspiral tidal measurements to a central EOS parameter, rather than primarily to pressure near twice nuclear saturation density. Applying the relation to deformabilities inferred from events such as GW170817 enables inference of X; the abstract does not report event-specific values. Conditional on the previously established effective upper bound X ≲ 0.381, the authors infer Λ_TOV ≳ 9.1, with a quoted uncertainty of ±0.5 on the bound, for maximum-mass neutron stars on stable mass-radius sequences. This theoretical bound separates their tidal response from the black-hole value Λ_BH = 0; it is not a direct measurement of maximum-mass stars.
PublicGravitational waves can reveal how easily a neutron star is distorted by tidal forces. This study develops a theoretical relationship connecting that distortion to the ratio of pressure to energy density at the star’s center, potentially revealing core properties that these signals have largely left inaccessible. The researchers checked the relationship against a broad range of physically viable descriptions of dense matter and found it largely insensitive to which description was used. Applied to tidal distortions inferred from gravitational-wave events such as GW170817, it allows that central ratio to be estimated. Assuming a previously established upper limit on the ratio, the study also derives a nonzero minimum tidal response for maximum-mass stable neutron stars, unlike the zero response of black holes. That minimum is a theoretical inference, not a newly observed measurement.
Young explorerA neutron star is a very tightly packed star. Pulling on it can change its shape a little. Scientists worked out a rule that could use clues from gravitational waves to tell them about the pressure and energy deep inside. They checked the rule with many possible descriptions of star matter. If an earlier limit is right, their calculations say even the heaviest stable neutron stars must change shape a little under a tidal pull, unlike black holes.
D. Chernyak, T. Eda, M. Eizuka+63 more
AstronomerA KamLAND search for the diffuse supernova neutrino background (DSNB) targets electron antineutrinos through inverse beta decay at 8.3–30.8 MeV, using exposures of 9.02 kton-year at 8.3–9.3 MeV and 9.42 kton-year at 9.3–30.8 MeV. A new deep-neural-network selection yields seven candidate events, consistent with a background-only expectation of 16.2 ± 9.4 events, including selection-related systematic uncertainties. An analysis of energy and radial distributions finds no significant DSNB excess. The resulting 90% confidence-level DSNB flux upper limits are 38–43 per square centimeter per second, depending on the assumed model. Model-independent electron-antineutrino flux limits are also reported, providing some of the most stringent constraints below 13.3 MeV. The work demonstrates neural-network classification as a promising method for suppressing neutron-associated backgrounds in liquid-scintillator detectors.
PublicResearchers used the KamLAND detector to search for electron antineutrinos from the diffuse background produced by supernovae. A new neural-network method for sorting detector events selected seven possible signals, but this count was consistent with the uncertain number expected from background processes alone. An analysis of the events’ energies and positions found no significant evidence for the supernova neutrino background. Instead, the team set upper limits on its flux: 38–43 electron antineutrinos per square centimeter per second at 90% confidence, depending on the assumed model. They also set limits that do not depend on a particular background model, including some of the tightest constraints below 13.3 MeV. The event-sorting method shows promise for reducing neutron-related interference in liquid-scintillator neutrino detectors.
Young explorerScientists used a detector called KamLAND to look for tiny particles from exploding stars. A new computer sorting method picked out seven possible clues. But other things in the detector could explain those clues, so the scientists did not find clear evidence of the particles they wanted. Instead, they worked out limits on how many could be passing through. Their new sorting method looks promising for helping separate wanted clues from unwanted ones.
Domenico Impiombato, Giacomo Bonnoli, Elisa Prandini+2 more
AstronomerA two-year homogeneous optical campaign with the Asiago Schmidt 67/92 cm telescope monitored the TeV-emitting HBLs 1ES 1959+650, H 1426+428, and PG 1553+113. More than 17,000 R- and I-band measurements span 957 source-filter sessions and about 420 h between 2024 February and 2026 January. Uniform differential photometry and classical F-tests using two independent comparison-star pairs yield robust intraday variability only in H 1426+428: 15/43 analysed R-band sessions and 5/40 I-band sessions. No significant intraday variability is detected in the other two sources under the adopted statistical framework. For H 1426+428, duration-weighted duty cycles are 28.0% in R and 7.0% in I, calculated using only variable sessions with a measured local characteristic timescale. Inferred local extrapolated doubling/halving timescales are approximately 5–15 min in the observer frame. The authors interpret the findings as evidence that rapid optical synchrotron variability is intermittent and state-dependent, and highlight the supporting role of dense, uniform monitoring with robotic small- and medium-aperture facilities.
PublicAstronomers spent two years tracking the visible-light brightness of three blazars, objects whose powerful jets also emit very-high-energy gamma rays. Using the Asiago Schmidt telescope, they collected more than 17,000 measurements in two optical bands. Only H 1426+428 showed statistically robust brightness changes within individual observing sessions; the other two showed no significant changes of this kind under the team's tests, which does not establish that they never vary. For H 1426+428, locally inferred and extrapolated times for the brightness to double or halve were roughly 5–15 minutes as seen by the observer, rather than necessarily complete doubling or halving events directly recorded over those intervals. The authors interpret the results as showing that rapid optical changes occur intermittently and depend on the source's state. The campaign also demonstrates how sustained optical monitoring can support observations at higher energies.
Young explorerAstronomers used a telescope to watch light from three very faraway objects with powerful jets. They watched many times over two years. One object, called H 1426+428, sometimes changed brightness quickly enough for their tests to clearly notice. The tests did not find such quick changes in the other two, but that does not mean those objects never change. Watching again and again helps astronomers learn when these faraway lights become more active.
Marco Figliolia, Gaetano Lambiase, Ali Övgün+1 more
AstronomerThis theoretical study examines an axisymmetric rotating black-hole solution in general relativity coupled to nonlinear electrodynamics, with deformation parameter g. Weak-field Gauss–Bonnet lensing and shadow calculations on the spherical seed give a spin-insensitive bound g/M ≲ 1.26 when a conservative approximately 10% tolerance on the Sgr A* ring size is imposed. Analytic eikonal quasinormal-mode shifts are even in g and yield a consistent independent ceiling. For the rotating geometry, the authors derive zero-angular-momentum-observer scalars and analyze horizons, the ergoregion, photon orbits, and the ISCO. They formulate Comisso–Asenjo reconnection-driven energy extraction, identify negative-energy states, and integrate power over allowed radii. A tolerated fractional deviation from Kerr extraction power defines an additional spin-dependent bound, conditional on the model parameters. The combined constraints narrow the admissible deformation range within a deliberately simplified, single-layer equatorial setup; testing with horizon-scale and ringdown data remains a prospect rather than a reported detection.
PublicThe researchers calculate how black holes might behave in a theory where electromagnetic fields follow nonlinear rules. A parameter called g measures the model’s departure from the standard Kerr description. Requiring a calculated shadow size to stay within roughly 10% of the Sgr A* ring size limits that departure. Calculations of black-hole vibrations give a compatible limit. The team also models energy extraction through magnetic reconnection and defines another limit by allowing only a chosen departure from Kerr’s predicted power. Together these theoretical tests restrict the model more strongly. They do not establish that real black holes have this modification: the extraction calculation uses a deliberately simplified setup, and further tests with observations are proposed.
Young explorerScientists used math to imagine black holes that work a little differently from the usual kind. They checked how big a dark shadow would look, how the black hole could vibrate, and how energy might escape from its spin. Their calculations help limit how different these imagined black holes could be. They have not shown that real black holes work this way, and their model leaves out some details.
Fabian Gittins, Harsh Narola, Thibeau Wouters+3 more
AstronomerThis study presents the first fully Bayesian assessment of the Einstein Telescope’s ability to detect tidal resonances in binary neutron-star inspirals. Using a simulated year of observations and analysing the 200 loudest signals, the authors find that resonant modes could be identified, with sensitivity to gravitational-wave phase shifts as small as ΔΦ ≈ 0.03 in favourable events. They also find that neglecting resonances can bias inferred tidal deformabilities. These simulation-based results support tidal-resonance asteroseismology with future detectors; they are not an observational detection.
PublicAs two neutron stars spiral together, their changing tidal forces can excite vibrations that carry clues about the stars’ interiors. Researchers tested whether the future Einstein Telescope could detect the effect of these vibrations on gravitational waves. They simulated a year of observations and analysed the 200 strongest signals. The study indicates that the telescope could identify these vibrations in some signals, including very small changes in wave phase under favourable conditions. Ignoring the vibrations could also skew estimates of how easily the stars deform under tidal forces. These are forecasts from simulations, not measurements of actual neutron-star vibrations.
Young explorerWhen two neutron stars circle closer together, they can make each other wobble. Those wobbles could help us learn what is inside them. Scientists made pretend signals on a computer to see whether a future detector called the Einstein Telescope could spot the wobbles. Their test suggests it could, especially when the signals are strong. They have not spotted these wobbles in real signals in this study.
D. Tsiklauri
AstronomerThis theoretical and computational study extends a 1D nonlinear relativistic plasma-wakefield model to intense proton-bunch trains under the comoving-coordinate approximation. For a two-bunch driver, adaptive integration agrees with exact cold-fluid invariants to machine precision, identifying interface corners as step discontinuities in the potential’s second derivative within the model. For 100 micro-bunches, a closed-form, parameter-free piecewise envelope describes initial coherent quadratic growth, nonlinear phase accumulation and detuning, and an asymptotic saturation level set by nonlinear energy conservation. The framework also analytically tracks transient overshoot and its decay toward saturation using an exact phase-slip integration length scale. These are model results, not experimental measurements. The authors propose the inexpensive envelope bounds as a baseline for parameter searches before multidimensional PIC simulations, and as groundwork for optimizing asymmetric drivers intended to exceed the symmetric transformer-ratio limit of 2; that optimization is not demonstrated here.
PublicThe researchers developed a simplified mathematical model of plasma waves driven by a train of intense proton bunches. Their numerical calculation closely matches exact mathematical checks for a two-bunch case. For a train of 100 bunches, their formulas describe how the wave first grows, then loses synchronization with the driving train and approaches a limiting strength, sometimes temporarily overshooting it. These findings come from a one-dimensional model, not an experiment or a full multidimensional simulation. The authors propose using the fast calculations to narrow down designs before running more demanding simulations. They also see the method as groundwork for designing differently shaped proton drivers that could improve accelerator efficiency, rather than demonstrating that improvement.
Young explorerImagine a line of tiny pushes making a wave bigger. Scientists used math and a computer to study something like that with proton bunches making waves in plasma. In their simplified model, the wave grows, but the pushes stop keeping time with it, so it cannot keep growing forever. They hope this math will help plan better particle accelerators. They have not shown that improvement in a real machine.
Fabio Buffoli
AstronomerThis theoretical study analyzes single-particle Penrose extraction in an ingoing Kerr-Vaidya spacetime with decreasing mass, enforcing exact four-momentum conservation at particle decay. A covariant bound limits the local extraction efficiency to the instantaneous Kerr value and reduces to the Bardeen-Press-Teukolsky limit at the horizon. For fixed spin parameter, the exact transport law dE/dtau = -(dm/dt)(r/Sigma)p_r^2 implies energy gain along every timelike geodesic as the mass decreases. The net gain separates into a local Penrose contribution and two transport contributions, evaluated numerically for two mass-loss laws. At fixed spin parameter a, extraction requires a mass-loss rate below alpha_crit(a) = (M-a)/Delta v, a boundary associated with approaching extremality; no such boundary occurs at fixed a/m. The transport law also extends to Kerr-Newman-Vaidya spacetimes. Crucially, the mass-loss rates needed for dynamically important effects lie far outside astrophysical rates; these are theoretical results, not observational findings.
PublicCan a particle take extra energy from a spinning black hole if the hole is also losing mass? This theoretical study separates two effects: energy gained when a particle breaks apart near the hole, and energy gained as particles travel through the changing gravitational environment. The researchers prove that the breakup itself cannot be more efficient than the corresponding process around a black hole with the same mass and spin but no ongoing mass change. Their equations nevertheless show an additional energy gain during travel as the hole loses mass. Numerical calculations explore this contribution under two assumed patterns of mass loss. Whether extraction has a limiting mass-loss rate depends on how the spin is assumed to change. The important caveat is that these changing-gravity effects become significant only at mass-loss rates far beyond those relevant to astrophysical black holes.
Young explorerImagine a spinning black hole that is getting lighter. Scientists used math to ask how a tiny particle could get energy near it. They found that when the particle splits, there is still a limit to how much energy that step can give. But the particle can also gain energy while moving near the shrinking hole. This is a math study, not something they watched happen in space. The hole would have to lose weight much faster than real black holes are expected to for the extra effect to matter.
