Cosmology and Nongalactic Astrophysics
Filament-Arm Node Systems (FANS): A new probe of the winding and chirality of the cosmic web
Pedro da Silveira Ferreira and Renyue Cen
We define Filament-Arm Node Systems (FANS), a new class of
cosmic-web objects consisting of multiple filament arms connected to a common node, and use their geometry to construct an object-based test of
cosmic chirality. With the
cosmic-web node providing a natural reference point, FANS span characteristic scales of ~60Mpc/h, allowing the coherent winding of their arms around the node to be measured directly. We define
cosmic spirality as the amplitude of this winding and handedness as its signed clockwise (CW) or counter-clockwise (CCW) sense. We further introduce an axis-conditioned extrinsic
estimator that searches for the projected signature of a coherent three-dimensional axial pattern of the handedness field, corresponding to a preferred axis of winding. Applying these measurements to two distinct SDSS filament reconstructions, and assessing their significance with sign-flip nulls and 27 controlled variations of the FANS construction parameters, we find no significant preference for CW or CCW winding, either globally or around a preferred axis. The data are therefore consistent with parity
symmetry, as expected in standard LCDM cosmology. We additionally find that
cosmic spirality decreases with
cosmic time, a trend that may reflect the gravitational straightening of filament arms. These first constraints establish FANS as a new probe of
cosmic-web
symmetry and large-scale morphology and provide a baseline for future parity tests with the much larger filament samples expected from upcoming surveys.
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Instrumentation and Methods for Astrophysics
Search for Long-Transient Gravitational Waves from Supernova SN2023ixf using GFH-v2 Pipeline
Sandhya Sajith Menon, Lorenzo Pierini, Pia Astone et al. (+24 more)
We present a directed search for long-transient gravitational waves from the possible newborn magnetar remnant of SN2023ixf, a nearby Type II core-collapse
supernova in the M101
galaxy. The analysis uses LIGO Hanford and Livingston data from Engineering Run 15, using coincident data lying within the on-source window associated with the
supernova. We target signals from a rapidly rotating, non-axisymmetric
neutron star whose
spin-down is dominated by gravitational-wave emission, producing a power-law decrease in frequency and a corresponding decrease in strain amplitude. The search is performed with the GFH-v2 pipeline, based on the Generalized Frequency Hough transform. No candidate survives the coincidence and follow-up analysis. We therefore set upper limits on the maximum detectable distance as a function of initial frequency and ellipticity. For the highest ellipticity interval, the 90% upper limits reach distances of about 1-2.5~Mpc across most of the analysed band. Although these limits are below the distance to M101, the search provides the first application of GFH-v2 to a nearby core-collapse
supernova and characterizes its performance on real detector data.
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All authors Sandhya Sajith Menon, Lorenzo Pierini, Pia Astone, Cristiano Palomba, Francesco Safai Tehrani, Lorenzo Silvestri, Ornella Juliana Piccinni, Simone Dall'Osso, Stefano Dal Pra, Sabrina D'Antonio, Sergio Frasca, Dafne Guetta, Paola Leaci, Michal Bejger, Alicia Calafat, Evan Goetz, Rafel Jaume Amengual, Ian Jones, David Keitel, Andrzej Krolak, Iuri La Rosa, Andrew Melatos, Joan-Rene Merou, Lorenzo Mirasola, Claudio Salvadore, Alicia M. Sintes, Karl Wette
High Energy Astrophysical Phenomena
Bridging the Population Synthesis of Supermassive Binary Black Holes and the Gravitational Wave Background
Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito et al. (+1 more)
Pulsar Timing Arrays (PTAs) constrain population properties of supermassive binary black holes (SMBHBs) through the observation of the gravitational wave background (GWB). Unlike other approaches that interpolate population-synthesis libraries or only consider the mean of the strain spectrum, here we capture its full strain probability density directly from semi-analytic population models. We apply our new method to the semi-analytic SMBHB population model, independently reproducing the parameter estimation for this model performed by the NANOGrav Collaboration with their 15-yr data. We also show the extent to which discrete SMBHB contributions to the GWB resolve degeneracies in the population parameter space. Finally, using the source-count intensity as the intermediate product in our calculation, we map PTA observations, as a proof of principle, to the SMBHB model based on the
galaxy merger prescriptions from numerical hydrodynamical simulations "Illustris". We find the effect of delay times $\tau$ between kiloparsec and subparsec SMBHB separations following
galaxy mergers, finding $h_{\rm c}$ spanning $(1$-$6)\times10^{-16}$ and $N_{\rm c}$ spanning $(0.3$-$7.1)\times10^{-3}$ for $\tau$ up to 8 Gyr.
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All authors Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito, Xiaoming Bi
Astrophysics of Galaxies
Improving constraints on the Yukawa correction at the Galactic Center with multiple stellar orbits
GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar et al. (+76 more)
We investigate the presence of a Yukawa-like correction ($\propto \, \alpha e^{- r/\lambda}$) to Newtonian
gravity at the Galactic Center, using a multi-
star fitting code, including the newly discovered
star S$301$, to improve the constraints obtained using S$2$ orbit alone. We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of
stars S$2$, S$55$, S$29$, S$38$ and S$301$ collected by
GRAVITY,
GRAVITY$^+$, NACO and SINFONI instruments, covering the period from $1992$ to $2025$. Compared to
GRAVITY Collaboration 2025 (Paper I), in which only S$2$ was fitted, the tightest bound on the Yukawa coupling is again reached at $\lambda = 3\cdot10^{13}\,\rm m\ (\sim 200\,AU)$, where we find $|\alpha| < 6 \cdot10^{-4}$, an improvement of roughly a factor five. The addition of S$301$ extends the constraint to short ranges that were inaccessible to S$2$, yielding $|\alpha| < 0.004$ at $\lambda =10^{12}\,\rm m$ and $|\alpha| < 0.006$ at $\lambda =5\cdot 10^{11}\,\rm m$, while S$29$, with its larger apoapsis, gives $|\alpha| < 0.1$ at $\lambda \sim 2\cdot10^{15}\,\rm m$. The latter two represent the tightest limits at these scale lengths on a Yukawa correction obtained to date around a supermassive black hole.
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All authors GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar, A. Berdeu, J.-P. Berger, G. Bourdarot, W. Brandner, Y. Cao, C. Correia, S. Cueves Cardona, R. Davies, D. Defrère, F. Delplancke-Ströbele, A. Drescher, F. Eisenhauer, L. Esteras Otal, M. Fabricius, H. Feuchtgruber, S. Flesch, N.M. Förster Schreiber, Q. Fournier, P. Garcia, R. Garcia Lopez, R. Genzel, S. Gillessen, F. Gonté, X. Haubois, S.F. Hönig, M. Houllé, S. Joharle, J. Kammerer, A. Kaufer, P. Kervella, L. Kreidberg, L. Labadie, S. Lacour, O. Lai, R. Laugier, J.-B. Le Bouquin, J. Leftley, R. Li, B. Lopez, D. Lutz, F. Mang, A. Mérand, F. Millour, M. Montargès, N. Morujão, H. Nowacki, M. Nowak, J. Osorno, T. Ott, S. Pappert, C. Paladini, T. Paumard, K. Perraut, G. Perrin, R. Petrov, N. Pourré, S. Rabien, D.C. Ribeiro, S. Robbe-Dubois, M. Sadun Bordoni, J. Sanchez-Bermudez, J. Sauter, J. Scigliuto, J. Shangguan, T.T. Shimizu, F. Soulez, C. Straubmeier, E. Sturm, M. Subroweit, C. Sykes, L.J. Tacconi, P. Thévenet, I. Urso, F.H. Vincent, J. Woillez, G. Zins
Instrumentation and Methods for Astrophysics
Approximating the statistics of a gravitational wave background
Mikel Falxa
The astrophysical origin of the gravitational wave background (GWB) reported by
pulsar timing array (PTA) collaborations has yet to be confirmed. A GWB signal made of the sum of individual gravitational wave (GW) from the population of supermassive black hole binaries (SMBHB) would show the imprint of a discrete Poissonian statistics in its spectral properties. In this work, we propose a tool based on the saddlepoint approximation method to estimate the distribution of characteristic strain for any given population model. This tool can be used for
Bayesian inference or for a quick visualization of the statistics of the GWB from the output of more realistic semi-analytical models. We introduce the general family of variance mixture Gaussian distributions that models heavy-tailed behavior distributions that is expected for a non-Gaussian GWB signal. We show that setting the correct hierarchical priors to a Gaussian free spectrum PTA likelihood is effectively equivalent to a non-Gaussian likelihood. Using ideal simulations, we compare the performance of the saddlepoint approximation with a log-Normal distribution to infer the parameters of the astrophysical model from the statistics of the GWB and show that correctly modeling higher order moments is essential. Future PTA analyses should include the statistics of the GWB in their pipelines.
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Solar and Stellar Astrophysics
R-matrix calculations for opacities: V. Temperature-density dependence of photoabsorption cross sections and opacity spectra of oxygen ions O VI and O VII
Divya Chari, Sultana N Nahar and Anil K Pradhan
We present R-
matrix photoabsorption cross sections for Li-like oxygen O VI and He-like oxygen O VII and examine how
plasma broadening modifies them as a function of temperature and density in astrophysical and laboratory high-energy-density (HED)
plasma sources. All atomic systems are subject to
plasma environment effects, and the propagation of radiation depends on photoabsorption via bound-bound transitions as spectral lines and autoionizing resonances in bound-free photoionization cross sections. We identify and illustrate low and high temperature-density limits for the onset of
plasma broadening in O VI and O VII, demonstrating general features and methodology applicable across a broad range of
plasma conditions. Calculations are presented along two representative isotherms corresponding to the solar base of convection zone (BCZ) at $T = 1 \times 10^6$ and $2 \times 10^6$ K, and electron densities $N_e = 10^{18}$-$10^{23}$ cm$^{-3}$. Autoionizing resonances progressively dissolve into the continuum with increasing electron density at each isotherm, flattening and merging into the background cross sections at BCZ conditions, at much lower densities than bound-bound line features require. Illustrative examples are given for energy regions containing Rydberg resonance series, including large photoexcitation-of-core (PEC) resonances. Comparisons with previous Opacity Project results reveal that (i) the R-
matrix photoionization cross sections cover a much higher energy range where a significantly richer spectrum of autoionizing resonances are present that are not included in OP, and (ii) the corresponding monochromatic opacities show significant quantitative differences. This work is generally applicable to modeling HED
plasmas in astrophysics, and to the analysis of transmission spectra in laboratory experiments on inertial confinement fusion (ICF) devices.
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High Energy Astrophysical Phenomena
Raj Kishor Joshi, Brynmor Haskell, William Cook et al. (+1 more)
Magnetic fields are fundamental for
neutron star physics and play a central role in powering the extreme phenomenology of magnetars, including Soft Gamma Repeaters and Anomalous X-ray
Pulsars. However, the structure and stability of their internal
magnetic fields remain largely unconstrained, as they cannot be directly probed by electromagnetic observations. Using 3D general-relativistic magnetohydrodynamics simulations across a range of rotation rates and
magnetic field strengths, we identify two distinct evolutionary regimes leading towards dynamically stable
magnetic configurations. In rapidly rotating
stars, the Alfvén crossing timescale exceeds the rotation period, allowing differential winding to amplify a strong toroidal
magnetic component before the onset of instabilities, leading to long-lived, stable configurations. In contrast, in magnetically dominated
stars, instabilities in the poloidal field drive rapid field decay, leaving only a comparatively weak toroidal component. These results imply that the internal
magnetic structure of
neutron stars depends sensitively on their rotational state: rotation-dominated
stars like
radio pulsars develop strong toroidal fields, while magnetars are characterized by predominantly poloidal configurations. Our findings therefore show that a
neutron star's rotational history shapes its internal
magnetic structure, providing a unifying physical picture that connects the observed diversity of
neutron star classes to their hidden field configurations.
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All authors Raj Kishor Joshi, Brynmor Haskell, William Cook, Sebastiano Bernuzzi
Solar and Stellar Astrophysics
Amplification of active region equatorial dipole
Ismo Tähtinen
The effect of active region parameters on the
evolution of solar axial dipole is well understood. However, their effect on the solar equatorial dipole has not been studied in detail. Understanding the development of the equatorial dipole is important as it drives the interplanetary
magnetic field on intracyclic timescales (~ 1yr). We study how the latitude, tilt angle, and the polarity separation affect the
evolution of solar equatorial dipole. We use dipole flux transport (DFT), a
matrix implementation of surface flux transport (SFT) model, to simulate the dipole
evolution of synthetic bipolar
magnetic regions (BMRs) with a wide range of tilt angles and latitudes. We also study the
evolution of active regions in HMI SHARP database and their associated BMRs. We quantify the dipole
evolution by means of the maximum and mean amplification and the growth and decay times of the equatorial dipole. Tilt angle controls the amplification of the equatorial dipole, with larger tilt angles leading to stronger equatorial dipole. Latitude controls the timescale at which the equatorial dipole grows and decays. Low-latitude regions produce the longest living equatorial dipole. We find that only 31% of anti-Joy regions experience amplification of equatorial dipole, compared with 96 of regularly tilted active regions. Latitudes and tilt angles of active regions can have considerable effect on the solar equatorial dipole. Systematic changes in their properties could increase/decrease the strength of the equatorial dipole relative to the solar activity, which could lead to similar relative change in geomagnetic activity. We suggest that large low-latitude coronal holes and relatively high geomagnetic activity in the declining phase of solar cycle 20, could be related to emergence of unusually low-latitude active regions that produced strong and persistent equatorial dipole.
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Astrophysics of Galaxies
A new clump-based star formation model for galaxy simulations: implications for high-redshift compact star clusters
Shu Horie and Hidenobu Yajima
We develop a new
star formation model for
galaxy simulations in which
star-forming gas clumps are identified on-the-fly and converted into
stars with an efficiency $\epsilon_{\rm SF}$ set by the clump surface density $\Sigma_{\rm c}$, calibrated against radiation hydrodynamics simulations of
star cluster formation. Applying this model to isolated disc
galaxies embedded in
haloes of $M_{\rm h}=10^{9}$, $10^{10}$ and $10^{11}\,\mathrm{M_\odot}$, with disc compactness corresponding to
redshift $z=0$–$10$, we find that more compact discs form more massive and denser clumps. The maximum clump mass increases from $\sim 10^{5}$ to $\sim 10^{7}\,\mathrm{M_\odot}$, and the fraction of clumps exceeding the surface density of $300\,\mathrm{M_\odot\,pc^{-2}}$ rises from $0.25$ to $0.38$ between $z=0$ and $10$ in $10^{10}\,\mathrm{M_\odot}$
haloes.
Star formation becomes correspondingly bursty, and the global
star formation efficiency after three disc rotations increases from $5 \times 10^{-3}$ to $2 \times 10^{-1}$ in $10^{10}\,\mathrm{M_\odot}$
haloes and from $2 \times 10^{-2}$ to $4 \times 10^{-1}$ in $10^{11}\,\mathrm{M_\odot}$
haloes as the
redshift increases from $z=0$ to $10$. The accompanying feedback disrupts the gas discs of the most compact systems, while prominent stellar spiral arms emerge. Self-gravitationally bound
star clusters form only in compact discs. We find no bound
star clusters at $z \leq 2$ in $10^{10}\,\mathrm{M_\odot}$
haloes, whereas the bound cluster mass fraction reaches $\approx 40$ per cent at $z \geq 8$ and $\approx 70$ per cent in the most compact $10^{11}\,\mathrm{M_\odot}$
halo. These fractions are broadly consistent with those inferred for high-$z$ clumpy
galaxies observed by the James Webb Space
Telescope.
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High Energy Astrophysical Phenomena
A cosmic-ray database update: CRDB v4.2
Davud Maurin
The
cosmic-ray database, CRDB, has provided data and meta-data to the community since 2013. We present a new release, CRDB v4.2, which includes data and time series published in the last three years (from AMS-02, CALET, DAMPE, LHAASO, etc.),
datasets missed in previous releases, and all peer-reviewed ultra-high energy
cosmic-ray data (both historical and recent
datasets). These data and meta-data are available from the web interface or from the CRDB pip-installable Python library. This release includes results from more than 60 experiments and publications, corresponding to 4534 new data points and 131624 time-series data points.
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Instrumentation and Methods for Astrophysics
Optical Flashes from Beam-Driven Light Sails with the Roman, Rubin and Euclid Observatories
James Guillochon and Abraham Loeb
The primary challenge of rocket propulsion is the burden of accelerating the spacecraft's own fuel. Light sails leave the propellant at home, with the achievable speed set by the sail area, the thermal tolerance of its material, and the power of the driving array. In GL15 we showed that leakage from a microwave array driving such a sail between habitable worlds produces Jansky-level
radio transients lasting tens of seconds at $100$~pc. We take that leak to optical and near-infrared, where Fresnel matching would shrink the aperture to $\sim\!20$–$100$~m at $1\,\mu{\rm m}$, but the intensity on that aperture is $2\times10^{8}\,{\rm W\,m^{-2}}$, five orders above published directed-energy loadings. Spreading $1.5$~TW at $\sim20\,{\rm kW\,m^{-2}}$ is a $\sim10$~km phased array, pushing the emitters; Lubin's $10^{3}\,{\rm W\,m^{-2}}$ loading is a $40$~km array, comfortable but more expensive. A tenth-wave delay on $40$~m tiles sized so one tile still covers the sail leaks $0.054$ of the power ($80$~GW) into a
halo. The typical Galactic detection is a single $\sim30$~s peak at $m_{\rm AB}\simeq19.4$ in F146 at $8$~kpc; a pair $87$~s apart, about one in five, is the confirmation test. Roman's Galactic Bulge Time Domain Survey reaches $109$~kpc at $8\sigma$ on a faint host, so a pointed flash of that
halo is visible from anywhere in the
Galaxy if the beam points at us. For $10$–$40$~km optical beamers held to $\sim\lambda/10$ at $v_{\rm max}\gtrsim250\,{\rm km\,s^{-1}}$, $N_{\rm det}=1$ wants $\Gamma_{6{\rm h}}\simeq16$ and a null search limits $\Gamma_{6{\rm h}}\lesssim49$, a factor-of-three window in launch rate. The real threshold is set by PSF-coincident stellar and instrumental transients. If intensity-limited optical beamers are commonly employed in our
galaxy, this activity could be revealed by Roman, Rubin and Euclid at no additional observing cost.
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High Energy Astrophysical Phenomena
Mining the time axis with TRON - III. Discovery of a nulling pulsar towards the SMC with MeerKAT
T. Blecher, M. Geyer, O. M. Smirnov et al. (+21 more)
We report on the discovery of a nulling
pulsar, PSR J0052$-$7551, in archival MeerKAT L-band observations of the Small Magellanic Cloud (SMC). The discovery was made using the image-plane transient detection pipeline, TRON, which creates a residual image for each time sample and uses a heuristic
pruning strategy to identify promising candidates in the resulting temporal image cube. The TRON pipeline triggered on the approximately minute timescale variability associated with the nulling behaviour of a canonical
pulsar. Follow-up MeerKAT UHF-band beamformer observations revealed a
pulsar with a
spin period of 0.55 s and a measured period derivative of 6.1(6)$\times$10$^{-17}$s$\cdot$s$^{-1}$. The source is seen in projection toward the periphery of the SMC, and has a dispersion measure value of 29.24(2) pc$\cdot$cm$^{-3}$, which is on the order of the expected Milky Way contribution along the line of sight. We use a Gaussian Mixture Model to fit the nulling behaviour which yielded a nulling fraction of $\sim 32$%. We find that the null lengths are consistent with an exponential distribution indicating a
stochastic process. Additionally, power spectra of the UHF visibility data reveal an unexplained quasi-periodic feature at ~5$-$7 s that cannot be attributed to the source itself, RFI, or standard instrumental effects. Following on from previous image-plane detections of
pulsars by the TRON approach, which relied on either scintillation or eclipsing behaviour, this is the first detection triggered by nulling. This discovery confirms TRON's sensitivity to a wide range of astrophysical phenomena of medium timescale duration.
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All authors T. Blecher, M. Geyer, O. M. Smirnov, A. Coelen, I. Heywood, I. Pelisoli, A. K. Hughes, J. S. Bright, V. Prayag, T. Myburgh, C. Tasse, B. Hugo, J. S. Kenyon, H. L. Bester, S. J. Perkins, J. Dawson, V. G. Samboco, A. J. T. Ramaila, B. Ngcebetsha, I. Sihlangu, C. Choza, V. S. Dhillon, N. Castro Segura, J. McCormac
Astrophysics of Galaxies
ALMA Reveals an Explosive Outflow Candidate in IRAS 16119–5048
Yongquan Luo, Jianjun Zhou, Tie Liu et al. (+24 more)
We present a multiwavelength study of the massive
star formation region IRAS 16119-5048 (I16119) using ALMA ATOMS Band 3 and
QUARKS Band 6 observations, complemented by archival ATCA
radio continuum and Spitzer mid-infrared data. The CO (2-1) emission reveals a system of high-velocity streamer-like structures around the central region. Using dendrogram analysis of velocity-channel maps followed by linking in position-position-velocity space, we identify 16 approximately radially distributed streamers whose projected trajectories converge toward a common central region. The kinetic energy of the outflows is at least an order of magnitude lower than those of most known explosive outflows, while their mass entrainment and momentum rates are high compared with typical protostellar outflows, suggesting that I16119 may represent a low-energy explosive outflow candidate. Dense-gas and photodissociation-region tracers reveal shell-like structures associated with the 8 $\mu$m emission, indicating that feedback from the H II region may influence the streamer morphology. The 1.3 mm continuum resolves 27 dense cores along a fragmented filamentary structure. Their separations are consistent with thermal Jeans or cylindrical fragmentation, while the collect-and-collapse scenario is unsupported. The dense cores also show evidence of mass segregation, with the most massive cores concentrated near the inferred explosive centre. We suggest that I16119 is a plausible low-energy explosive outflow candidate, possibly triggered by dynamical interactions among centrally concentrated massive cores. However, the complex velocity structure and possible contamination from individual core-driven outflows prevent a definitive classification. More sensitive, higher angular-resolution observations are required to confirm the nature of the outflow.
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All authors Yongquan Luo, Jianjun Zhou, Tie Liu, Jarken Esimbek, Siju Zhang, Xindi Tang, Sami Dib, Prasanta Gorai, Mika Juvela, Leonardo Bronfman, Patricio Sanhueza, Jihye Hwang, Fengwei Xu, Kee-Tae Kim, Guido Garay, Chang Won Lee, Tapas Baug, L. Viktor Tóth, Gang Wu, Dalei Li, Yuxin He, Yingxiu Ma, Dongdong Zhou, Toktarkhan Komesh, Weiguang Ji, Dezhao Meng, Jiasheng Li
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
LZ nuclear recoil event from inelastic singlet-doublet scalar dark matter
Disha Bandyopadhyay, Debasish Borah and Pankaj Borah
We study the possibility of explaining the recently reported high-energy nuclear recoil event by the LUX-ZEPLIN (LZ) collaboration within the framework of singlet-doublet scalar dark matter (DM). Considering DM to be the CP even mass eigenstate formed out of a scalar doublet and a real scalar singlet, both being odd under an unbroken $Z_2$
symmetry, we find the parameter space of the model consistent with correct relic abundance and direct-detection limits on elastic scattering rates. A large part of the parameter space can also lead to inelastic up-scattering of DM with a rate and recoil energy consistent with the recent LZ event. Depending upon the singlet-doublet mixing, the model allows a much wider range of currently allowed parameter space compared to the pure scalar doublet DM limit, which is disfavored due to non-observations of high-energy
neutrinos from solar-captured DM annihilation by the IceCube experiment. Presence of $Z_2$-odd right-handed
neutrinos also leads to other interesting phenomenology related to the origin of light
neutrino masses and leptogenesis.
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Astrophysics of Galaxies
Irreducible-Mass Balance for Magnetized Null Horizons with an Internal Current Sheet
Remo Ruffini and Giorgio Sonnino
We begin with a general question: how does the irreducible mass of a magnetized black hole change when the horizon is not stationary? The null Raychaudhuri equation gives an exact area balance for any smooth null horizon, without assuming stationarity or axisymmetry. When the horizon is axisymmetric and admits an integrable quasilocal
Hamiltonian, this geometrical identity becomes an energy balance. The equation keeps area growth, rotational and electromagnetic work, nonstationary focusing, canonical-flux corrections, and internal-boundary terms separate. We then turn to Wang's self-gravitating split-monopole Blandford-Znajek engine. In the weak-field and slow-rotation regime, P/M_H\ll1 and a/M_H\ll1, our general balance reproduces Wang's mass- and angular-momentum loss rates. The irreducible mass, M_{irr}=\sqrt{A_H/(16\pi)}, reveals what those rates do not show by themselves. It measures the part of the rotational work absorbed irreversibly by the horizon. At fixed
magnetic flux and under impedance matching, half of the instantaneous rotational work leaves as electromagnetic power. The other half increases the horizon area and M_{irr}. The assumptions behind this reduction are derived explicitly. A minimal nondissipative world-volume action makes the current-sheet contribution vanish through O(p^2\epsilon^2). Direct power counting of Wang's perturbative fields, together with a compatible canonical-flux prescription, gives a relative focusing and canonical correction of O(p^2)+O(\epsilon^2). These estimates mark the range in which the reduced Blandford-Znajek trajectory remains controlled. Extending that trajectory to high
spin requires an additional extrapolation. Relating the quasilocal horizon loss to energy measured at infinity requires a separate asymptotic flux calculation.
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High Energy Astrophysical Phenomena
Oblique Collision of a Relativistic Cold Shell with an Ideal Reflecting Wall
Jonathan Granot, Prasanta Bera, Michael Rabinovich et al. (+1 more)
Relativistic flows are common in astrophysics and often form shocks when different parts of the flow collide at relativistic relative velocities. Such collisions are often oblique, forming two shocks whose shocked fluids are separated by a contact discontinuity, which is treated here as an ideal reflecting “wall” where the flow on either side is modeled separately. The latter is modeled in the lab frame $S$ as a uniform cold planar shell propagating into
vacuum at velocity $v_1=\beta_1c$ normal to its
vacuum interface, colliding with the wall at an incidence angle $\alpha_1$. The collision point $P$ moves along the wall at a velocity $v_p=v_{1}/\sin\alpha_1$, and a boost along the wall at $v_p$ leads to a steady-state frame $S'$ where this problem is highly simplified. However, a “super-luminal” regime exists where $v_p>c\Leftrightarrow\tan\alpha_1<\Gamma_{1}\beta_{1}=(1-\beta_{1}^2)^{-1/2}\beta_1$ and no steady-state frame $S'$ exists. It corresponds to only very small $\alpha_1$ in the Newtonian regime, but nearly all $\alpha_1$ in the relativistic regime. We solve this problem \textit{fully analytically} using integral conservation laws, in the attachmrnt region where point $P$ is attached to the wall. This region of parameter space is bound at high $\alpha_1$ by the detachment line, which coincides with the sonic line for a cold initial shell. A weak-shock solution exist in all this region, while a strong-shock solution exists only in the sub-luminal attachment region – between the luminal line and the detachment/sonic line where the two solutions coincide and beyond which point $P$ detaches from the wall and shocked fluid spills into the
vacuum.
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All authors Jonathan Granot, Prasanta Bera, Michael Rabinovich, Paz Beniamini
High Energy Astrophysical Phenomena
Timing Gravity with Pulsars in the Strong Field
Riccardo Della Monica and Ivan de Martino
We propose a novel approach for the timing of
pulsars orbiting a supermassive black hole, which implements the fully relativistic calculations of the
photon travel time into a robust timing model. We generate realistic mock catalogues of
pulsar times-of-arrival for several putative
pulsars on tight orbits around the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*). Then, we perform a proof-of-concept sensitivity analysis to forecast the accuracy that future observational facilities, like the Squared Kilometer Array, will achieve in the characterization of the parameters of our timing model. Our analysis shows how the observation of
pulsars at the Galactic Center will open an incredibly promising avenue for the characterization of the physical properties of Sgr A*, which can improve by at least three orders of magnitude the current constraints on the black hole's mass achieved with the S-
stars and event-horizon scale observations.
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Earth and Planetary Astrophysics
Long-baseline ATLAS photometry of the seven main-belt asteroid targets of the Emirates Mission to the Asteroid Belt
Nicolas Erasmus, Josef Ďurech, David E. Trilling et al. (+6 more)
The Emirates Mission to the Asteroid Belt (EMA) will use the MBR Explorer spacecraft to fly past six main-belt asteroids – (10253) Westerwald, (623) Chimaera, (13294) Rockox, (88055) Ghaf, (23871) Ousha and (59980) Moza – before rendezvousing with, and deploying a lander onto, the extremely red (269) Justitia. We present a homogeneous analysis of a decade of sparse photometry of all seven targets from the Asteroid Terrestrial-impact Last Alert System (ATLAS). For each object we derive absolute magnitudes and phase slopes in the ATLAS c and o bands, the c-o colour on a common phase slope, a rotation period from a Lomb-Scargle periodogram of the phase-corrected light curve, and a light-curve amplitude setting a lower limit on elongation. Five periods are secure – 3.243 h for Rockox, 33.1 h for Justitia, 3.64 h for Westerwald, 14.6 h for Chimaera and 4.36 h for Moza – and agree with independent work; for Ousha aliasing leads us to adopt the published 8.35 h, while Ghaf remains unresolved. Lightcurve inversion gives a unique convex shape and
spin state for Rockox and two pole solutions for Chimaera, Moza and Justitia; no model was obtained for Ghaf, Ousha or Westerwald, though Westerwald's
spin axis must be retrograde. Combining the c-o colour with an albedo class from the phase slope, we classify the sample as one dark C-type (Chimaera), three probable S-types (Westerwald, Ghaf, Moza), two X-complex objects (Rockox, plausibly M-type, and Ousha, possibly E-type), and the exceptionally red L/D-type Justitia, whose (c-o) = 0.48 is redder than typical Jupiter Trojans. This only partly matches the mission's family-based expectation of a predominantly primitive target set, so we present these as testable predictions. Those of Ghaf and Ousha are least secure – both disagree with published work and have unresolved or aliased periods – and warrant follow-up.
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All authors Nicolas Erasmus, Josef Ďurech, David E. Trilling, Larry Denneau, John L. Tonry, Henry Weiland, Ken W. Smith, Javier Licandro, Miguel R. Alarcon
Cosmology and Nongalactic Astrophysics
Ultra-slow-roll Inflation with Non-perturbative Non-Gaussianity and Scalar Induced Gravitational Waves
Manuel Drees and Chenhuan Wang
An ultra-slow-roll phase during inflation could potentially produce the right abundance of primordial black holes (PBHs) for them to form all of dark matter (DM). We consider such a scenario, carefully treating the transitions from slow to ultra slow roll inflation and back, using a parametrisation of the inflaton potential that can describe inflation from the time when CMB scales crossed out of the horizon until its end. A $\delta N$ analysis shows that this model can possess $O(1)$ non-Gaussianity. When computing the primordial black hole abundance, we keep the full non-linear relation between
curvature perturbations and the density contrast and consider the non-Gaussianity to all orders. We find that $O(1)$ non-Gaussianity is sufficient to enhance the PBH abundance by orders of magnitude, leading to reduced gravitational wave (GW) signals for fixed PBH abundance. The signal to noise ratio is computed for future gravitational wave observatories. We find that, in spite of the reduced strength, the GW signal is well above the sensitivity of LISA if PBHs form a significant component of DM.
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Solar and Stellar Astrophysics
An Eccentric Massive Protobinary Assembled via a Core-merger Parabolic Encounter
Yao Wang, Yichen Zhang, Rubén Fedriani et al. (+14 more)
Most massive
stars form in binary systems, which profoundly influence their subsequent
evolution. However, how such systems form remains poorly understood, with several competing scenarios proposed, including disk fragmentation, core fragmentation and capture. Determining the orbital architectures of massive binaries, particularly during their earliest embedded phases, is therefore crucial for distinguishing among these formation pathways, but direct measurements of their three-dimensional motions have remained exceptionally challenging. Here we present high-resolution, multi-epoch sub-millimeter-to-centimeter ALMA and JVLA observations of the massive protobinary IRAS 07299$-$1651, complemented by JWST and VLT infrared imaging. We detect orbital proper motion of the binary components, enabling a full three-dimensional orbital reconstruction. Combining orbital fitting, multi-wavelength continuum modelling, hydrogen recombination line kinematics and jet observations, we find that the preferred orbital solutions are highly eccentric and close to parabolic, while both circumstellar disks are strongly misaligned with the orbital plane. These properties are naturally explained by a “core-merger” scenario in which the two protostars originated independently from initially unbound cores that recently underwent a near-parabolic encounter, producing an eccentric binary with a current separation of about 200 au. These findings suggest that the core-merger process may represent an important pathway for forming eccentric massive binaries.
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All authors Yao Wang, Yichen Zhang, Rubén Fedriani, Kei E. I. Tanaka, Viviana Rosero, Kai Yang, Morten Andersen, Maria T. Beltrán, Mélisse Bonfand, Yu Cheng, James M. De Buizer, Yihuan Di, Guido Garay, Prasanta Gorai, Zhi-Yun Li, Yao-Lun Yang, Jonathan C. Tan
High Energy Astrophysical Phenomena
Correlation between X-ray and gamma data of Swift measurements
Istvan I. Racz, Lajos G. Balazs, Istvan Horvath et al. (+1 more)
Several studies over the last two decades have used canonical correlation analysis (CCA) to study the relationships between main {\gamma}-ray (e.g. fluence, peak flux, and duration) and main X-ray (flux, decay and spectral index, and hydrogen column density) data from gamma-ray bursts (GRBs). In this paper, we revisit this approach using a much larger
dataset to identify potential new insights into these relationships. We used CCA to investigate the interrelationship of the aforementioned gamma-ray and X-ray parameters. Using the derived canonical variables, we calculated their correlations (canonical loadings) with the original data. Consistently with previous research, the analysis revealed that gamma-ray fluence and X-ray flux have the strongest correlation, while the X-ray decay index and spectral index have a lower contribution. Interestingly, our analysis of a much larger
dataset reveals that the HI column density makes a significant contribution to the overall correlation. This finding, in the context of the collapsar model for long GRBs, could be interpreted as an indication that the progenitor
star ejected an HI envelope during the GRB.
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All authors Istvan I. Racz, Lajos G. Balazs, Istvan Horvath, Sandor Pinter
Cosmology and Nongalactic Astrophysics
Recovering Large-Scale Clustering of Missing Galaxies for Galaxy–Gravitational-Wave Cross-correlations
Tathagata Ghosh and Surhud More
We present a framework for completing
galaxy catalogs from flux-limited surveys which reconstructs the missing
galaxy population while preserving its clustering properties. This is particularly important for cosmological analyses using gravitational-wave (GW) dark sirens without electromagnetic counterparts, such as binary black hole mergers, which constitute the majority of GW detections. As GW detectors probe increasingly larger distances,
galaxy catalogs become progressively incomplete owing to survey flux limits. Current state-of-the-art statistical host identification methods typically account for this incompleteness by assuming that the missing
galaxies are uniformly distributed in comoving volume. While this approximation can mitigate biases due to incompleteness, it neglects the clustering of
galaxies within the
cosmic web. Since
galaxies and GW sources are both expected to trace the underlying large-scale structure, their spatial distributions are correlated, making a homogeneous reconstruction physically unrealistic, a shortcoming which our framework addresses. As a proof of concept, we apply the method to simulated
galaxy catalogs with different flux limits and observational selection functions. Our approach provides a significantly more realistic completion of incomplete
galaxy catalogs than the commonly adopted homogeneous-in-comoving-volume approximation, enabling more robust cosmological inference from gravitational-wave dark sirens.
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Cosmology and Nongalactic Astrophysics
Conformally Interacting Dark Energy with Early and Late-Time Measurements
Shambel Sahlu, Abunie Gezahegn, Amare Abebe et al. (+2 more)
The conformal interacting dark energy (CIDE) model is investigated by introducing a scalar field representing dark energy (DE) coupled to dark matter (DM) via a conformal transformation, thereby yielding a class of scalar-tensor theories. The interaction term ${Q}$, that indicts the flow of energy between the dark sectors is proportional to the trace of the energy momentum tensor of the DM fluid, $T^{\mathrm{DM}}_{\mu\nu}$, as ${Q}=\frac{C'(\phi)}{2C(\phi)}g^{\mu\nu}T^{\mathrm{DM}}_{\mu\nu}$, where $C(\phi)$ is the conformal function of a scalar potential (coupling) field. We assume the power-law parametrization $C(\phi)\propto (1+\phi)^m$, with $m$ a coupling parameter, and determine the direction and magnitude of the energy flow between the DM and DE components. The dynamical nature of DE is modeled by the two conformal interacting scenarios, CIDE and $w$CIDE, with $w$ the DE equation of state parameter. To test the viability of each model, we constrain them using a combination of early- and late-time cosmological data, namely: CMB measurements from the South Pole
Telescope, Planck 2018, and the Atacama Cosmology
Telescope (DR6) (CMB SPA); BAO data from the Dark Energy Survey (DESI DR2 BAO); and
Supernova Type Ia distance compilations (PantheonPlus, PantheonPlus + SH0ES, Union3, and DES Dovekie). Parameter inference is performed with Monte Carlo Markov Chain (MCMC) simulations using COBAYA and a modified CLASS. Further statistical analysis using the Akaike information criterion (AIC) and the
Bayesian information criterion (BIC) is summarized to assess the viability of the model in comparison with the standard cosmological model, investigating the model's potential to alleviate the $H_0$ and $S_8$ tensions.
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All authors Shambel Sahlu, Abunie Gezahegn, Amare Abebe, Gonzalo J. Olmo, Diego Rubiera-Garcia
Earth and Planetary Astrophysics
A semi-analytical Ring-Arc model for Plutino perturbations
Yue Chen and Jian Li
Neptune's 2:3 mean motion resonance induces an asymmetric spatial distribution of Plutinos. We previously proposed a 9000-point-mass arc model that successfully captures the resulting influence on planetary ephemerides. However, integrating thousands of point masses involves significant computational cost. In this paper, to more efficiently simulate the total perturbation of Plutinos, we develop a semi-analytical Ring-Arc model described by gravitational potentials. This model consists of an outer ring and two inner arcs, representing the resonant spatial distribution of Plutinos. The model parameters are derived from observed Plutinos and theoretical sampling, yielding consistent structures. Numerical simulations show that the perturbations on the Sun-Neptune and Sun-Saturn distances from the semi-analytical Ring-Arc model agree with those from the 9000-point-mass arc model within 4% over 50 years, while outperforming a simple ring model in comparison with the bias-corrected Plutino population. Our semi-analytical approach preserves the dynamical characteristics while significantly enhancing computational efficiency, offering a state-of-the-art tool for ephemeris modelling.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Exact Cancellation of Horizon Modes in Kerr Ringdown
Kei-ichiro Kubota, Yusuke Manita, Hayato Motohashi et al. (+1 more)
Ringdown gravitational waves probe black hole spacetimes via quasinormal modes (QNMs). Recent studies have reported oscillatory features in QNM-filtered waveforms, and have led to conflicting interpretations as to whether they represent a near-horizon "direct wave". Reexamining a particle plunging into a Kerr black hole, we show that the saddle-point approximation underlying the proposed interpretation fails near the horizon. Our exact analysis reveals that every source-induced horizon-mode pole is canceled by an infinite tower of Matsubara zeros, independently of orbital and black-hole parameters. The first four stages of this sequential screening are also confirmed by time-domain numerical integration. Thus, within the near-horizon perturbative framework, source-induced horizon-mode signals do not survive at late times.
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All authors Kei-ichiro Kubota, Yusuke Manita, Hayato Motohashi, Daiki Watarai
Earth and Planetary Astrophysics
That's no moon: Exomoon survival and detection limitations
Alicia Pérez-Rodrigo and Isabel Rebollido
While moons are ubiquitous in the Solar System, exomoons have not yet been unambiguously confirmed despite the discov- ery of over 5,600
exoplanets. We investigated the reasons for this lack of detections by reviewing high-impact literature searches, assessing dynamical stability and detectability constraints, and comparing these with the moon population in the Solar System. We compiled a homogeneous catalogue of 24 proposed exomoon candidates, including stellar, planetary, and inferred lunar parameters. For each case we applied Hill, Roche, and Laplace stability criteria and estimated detectability limits for current and forth- coming instruments. In addition, we tested 6038 confirmed
exoplanets against the same stability and mission-specific observational filters for a given range of moon parameters. A large fraction of the potential exomoon candidates investigated in the literature are either inconsistent with long-term stability or produce signals below Kepler sensitivity. Only 8 of the 13 candidates meet at least one of the stability criteria. Our extended analysis highlights 27 promising targets for exomoon searches with PLATO, while moons with Solar-System-like properties remain below current thresholds. The lack of exomoon detections is likely due to a combination of the inefficient formation of stable massive moons and limited instrumental sensitivity. Other processes, such as early moon loss during planetary migration or giant impacts, may also influence moon survival. Future searches should prioritise systems that combine long-term dynamical stability with favourable observational conditions for next-generation photometric and astrometric facilities.
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Solar and Stellar Astrophysics
Statistical structure and physical interpretation of the fillout factor distribution in contact binary stars
A. Poro, K. Li, E. Paki et al. (+2 more)
Contact binary systems exhibit complex evolutionary behavior governed by mass transfer, angular momentum loss (AML), and Roche geometry. The fillout factor ($f$) is widely used as a descriptor of the degree of overcontact, yet its physical and statistical role remains nonuniformly defined across the literature. We used a compiled observational sample of W UMa-type contact binaries to construct a data-driven classification framework based on $f$ and its relation to fundamental system parameters. Unsupervised clustering applied to the one-dimensional $f$ distribution reveals a robust three-class structure corresponding to shallow-, medium-, and deep-contact configurations. The statistically determined boundaries are located at $f \simeq 0.257$ and $f \simeq 0.561$, with a stable silhouette score of $S \simeq 0.613$. The stability of this classification is confirmed through perturbation tests in $f$ and parameter-conditioned samples. A random forest regression model shows that 60.7% of the variance in $f$ can be explained by the considered physical and
geometric system parameters, with
geometric parameters providing the largest predictive contribution. Among the considered parameters, the mass ratio emerges as the dominant predictor. The identified subclasses therefore appear to reflect a continuous
geometric sequence rather than discrete physical states, governed by the progressive
evolution of the Roche equipotential configuration under mass transfer and AML. Notably, the second boundary separating medium- and deep-contact systems shows lower stability than the first boundary, suggesting that the transition toward deep contact may be more sensitive to the physical composition of the analyzed sample.
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All authors A. Poro, K. Li, E. Paki, F. Alicavus, N. Alan
Earth and Planetary Astrophysics
The effect of the atmospheric C/O ratio on interiors of hot Jupiters
Esther van Dijk, Yamila Miguel and Paul Mollière
The atmosphere is the outer boundary of a gas giant
exoplanet's interior. Therefore, compositional changes in the atmosphere can affect interior inferences. Typically, only
metallicity is considered in atmospheric boundary conditions, while other elemental ratios, in particular the C/O ratio, are assumed to be solar. In light of the observational constraints now achievable with JWST, this assumption might no longer be justified. In this work, we investigate the effect of the C/O ratio on atmospheric boundary conditions, interiors and radii of hot Jupiters. We construct an atmospheric boundary grid, consisting of one-dimensional atmospheric models in radiative-convective and thermochemical
equilibrium. This grid is coupled to a static interior structure model at the radiative-convective boundary (RCB). Because in the temperature regime of hot Jupiters, the C/O ratio determines the dominant species in the atmosphere, it can significantly alter the opacity and, consequently, the pressure and temperature at the RCB. This temperature change propagates into the convective interior, thus affecting the calculated radius. The radius difference relative to a solar C/O-atmosphere significantly exceeds observed radius uncertainties of 3 per cent for
planets with
equilibrium temperatures $\gtrsim$ 1500 K and super-solar atmospheric
metallicities. As an example, we demonstrate that, for WASP-19~b, higher C/O ratios result in higher inferred intrinsic temperatures. These results highlight the importance of treating atmospheric composition and interior structure as a coupled system. As atmospheric constraints improve, incorporating measured C/O ratios into atmospheric boundary conditions is necessary to obtain robust inferences of hot Jupiter interiors.
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Instrumentation and Methods for Astrophysics
One Merger, Three Bands: Multiband Detection Rates and Parameter Estimation of Stellar-mass Binary Black Hole Coalescences from Millihertz to Kilohertz
Anson Chen and Jun Zhang
Stellar-mass binary black holes sweep through the millihertz, decihertz, and kilohertz gravitational-wave bands before merger, making them
prime targets for multiband observations. We forecast their detection rates and parameter-estimation precision for networks combining the millihertz observatories LISA, Taiji, and TianQin; the decihertz concepts LGWA, AMIGO, and AMIGO-5; and the ground-based LVK and
Cosmic Explorer. Using the binary-black-hole mass and
redshift distributions inferred from GWTC-4, we first estimate the single-band yields and then account explicitly for detector lifetimes and relative mission start times when calculating multiband rates. For a signal-to-noise-ratio threshold of 8, the LISA–Taiji–TianQin network is expected to detect $53.6^{+19.7}_{-14.1}$ systems in the millihertz band, while the largest three-band yield is $23.5^{+8.7}_{-6.2}$ events for LISA–Taiji–TianQin combined with LGWA. The yield is maximized when the decihertz observation begins approximately $0$–$3\,{\rm yr}$ after the millihertz mission. Ground-informed subthreshold searches with a threshold of 5 increase the multiband yields by a factor of approximately $4$–$5$, reaching $125.1^{+46.1}_{-32.9}$ events for the same network. Fisher-
matrix forecasts for a GW150914-like source show that decihertz observations provide the dominant improvement in most multiband parameter constraints, whereas millihertz data primarily sharpen the detector-frame chirp mass and sky localization. Combining the three bands improves the chirp-mass precision by orders of magnitude relative to ground-based observations alone and can reduce the localization area and coalescence-time uncertainty substantially. These results demonstrate that coordinated mission scheduling and targeted subthreshold searches are essential for realizing the scientific potential of stellar-mass multiband gravitational-wave astronomy.
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High Energy Astrophysical Phenomena
LOFAR follow-up of sources in the First LHAASO Catalogue
Maria Arias, Timothy Shimwell, Martin Hardcastle et al. (+1 more)
The First LHAASO Catalogue lists 90 sources of very-high-energy gamma-ray emission, many without an established counterpart at other frequencies, reopening the question of which Galactic accelerators produce the highest-energy
cosmic rays. We search for low-frequency
radio counterparts to the 55 1LHAASO sources that fall within the Galactic fields of the LOFAR Two-metre Sky Survey Data Release Three (LoTSS-DR3), using 144~MHz continuum maps at $6''$ and $20''$ resolution, complemented with archival data from other
radio surveys where available. We present an overview of the
radio emission towards all 55 sources, and identify the structures potentially associated with the gamma-ray emission. We report 24 new
supernova remnant (SNR) candidates, nine flat-spectrum
radio shells with faint or no infrared counterpart, and six sources with no clear Galactic
radio emission present in the LOFAR maps. A bootstrap analysis shows that 23 of the 50 sources in the Galactic plane footprint (46%, for $|b| \leq 5$) overlap a catalogued SNR, whereas random placement yields only $10.0\pm2.8$ matches even if the underlying Galactic SNR population is ten times larger than currently catalogued; in the outer
Galaxy, where chance
alignment is rarest, 4 of 12 sources coincide with an SNR against a null expectation of $\lesssim2$. We estimate that at least a quarter, and up to half, of the 1LHAASO Galactic-plane sources genuinely reside in SNR environments, consistent with a population dominated by
pulsar wind nebulae, SNR–PWN composites, and
cosmic-ray-illuminated clouds. Individual results include a new SNR candidate inside the TeV shell HESS~J1912+101, a
radio candidate for the SNR hypothesised to explain the GeV emission of 1LHAASO~J1945+2424, and the first proposed counterparts of 1LHAASO~JJ0056+6343u and 1LHAASO~J2200+5643u.
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All authors Maria Arias, Timothy Shimwell, Martin Hardcastle, Roland Timmerman