Astrophysics of Galaxies
Discrepancies between Chandrasekhar's theory of relaxation and $N$-body simulations
Kerwann Tep and Douglas C. Heggie
Globular clusters are systems which are known to be particularly well described by two-body relaxation. In recent decades many studies have shown that Chandrasekhar's orbit-averaged theory is able to reproduce many features of numerical simulations. However, it has been claimed that differences between the theory and simulation remain, such as an amplitude mismatch of the rate of change of the distribution function. In this paper we compare the theoretical predictions of Chandrasekhar's theory for anisotropic clusters to precise $N$-body data. We show that more careful $N$-body measurements are able to reduce the claimed mismatch. Nevertheless, we observe a dependency of the remaining mismatch on both position and anisotropy. While the dependence on anisotropy may be understood qualitatively on theoretical grounds, the radial dependence implies that spatial inhomogeneities, and therefore collective effects, may become unavoidable to resolve the residual mismatch between theory and simulations.
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Cosmology and Nongalactic Astrophysics
Analytical covariances for catalogue-based pseudo-$C_\ell$s
Kevin Wolz, Elyas Farah, Robert Reischke et al. (+2 more)
Multiple cosmological observables, such as the
galaxy overdensity or
cosmic shear, consist of fields sampled at the discrete positions of astrophysical sources. Recent work has presented methods to estimate the angular power spectra of such fields, avoiding the construction of pixelated sky maps and the finite-resolution effects associated with them. In this work, we present a method to estimate the disconnected (also known as "Gaussian") covariance of these angular power spectra, addressing subtle effects such as the effective area overlap between different catalogue-based fields and the additional Poisson-like variance arising from the discrete nature of the catalogues. The method relies on the so-called Narrow-Kernel Approximation to account for the contribution of distinct source pairs to the
estimator, while including the noise-like contributions from self-pairs exactly. We explicitly compare this approach with a brute-force method that can produce the exact covariance for sparse samples, and validate it against simulations. We show that the method is accurate in realistic scenarios, spanning both dense and noise-dominated
datasets (e.g.,
cosmic shear) and sparse, noise-dominated observables (e.g., fast
radio bursts). The method is implemented in the public code NaMaster.
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All authors Kevin Wolz, Elyas Farah, Robert Reischke, David Alonso, Andrina Nicola
Instrumentation and Methods for Astrophysics
Millimetre-scale spectrographs for next-generation photonic instrumentation
Emily Ronson, Robert J. Harris, Ariadna Calcines Rosario et al. (+1 more)
We present a set of ultra-compact spectrographs fabricated using two-
photon polymerisation, each under 1 mm in length and printed directly onto an optical fiber. This fully integrated,
alignment-free architecture enables extremely low-mass instrumentation with broad potential across astrophotonics, space systems, drone-based sensing, and
quantum optics. Two transmissive configurations are presented; they combine beam-expansion optics, dispersive elements, and stray-light suppression within monolithic printed structures optimised for J- and H-band operation. Coarse gratings provide resolving powers of approximately R = 30. Experimental characterisation confirms the feasibility of fiber-coupled, fully printed spectrographs and demonstrates their promise as deployable components for next-generation integrated photonic instrumentation.
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All authors Emily Ronson, Robert J. Harris, Ariadna Calcines Rosario, Viktoria Kutnohorsky
High Energy Astrophysical Phenomena
SPH methods in the modelling of compact objects
Stephan Rosswog
We review the current status of compact object simulations that are based on the Smoothed Particle Hydrodynamics (SPH) method. The first section of this review is dedicated to SPH as a numerical method for Newtonian, ideal gas dynamics and it should be fairly self-contained. It begins with the basics of the method, but also describes recent advances including various meshless derivatives or methods for treating shocks. A separate chapter summarizes general relativistic SPH, including its special relativistic limit, and it explains in some detail the recent development of full numerical relativity in SPH where matter is evolved together with a dynamical spacetime. The remainder of the review has an astrophysical focus, here we discuss the status of the simulations of white
dwarf–white
dwarf,
neutron star–
neutron star and
neutron star–black hole systems. For each type of system the emphasis is on gravitational-wave-driven mergers, but we also briefly summarize dynamical collisions that can occur in locations with large
stellar densities.
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Astrophysics of Galaxies
Fuelling the central region of galaxies with misaligned gas accretion
J. L. Tous, S. I. Raimundo, R. Riffel et al. (+3 more)
Recent studies have shown that the
accretion of kinematically misaligned gas fuels the central reservoir of
galaxies, triggering
nuclear activity and
star formation. In this work, we show that this specific
accretion channel can only sustain main-sequence levels of
star formation in
galaxies with $M_* \lesssim 10^{10} {\rm M_\odot}$. Using a sample of 201 kinematically misaligned
galaxies, and a comparison sample of 3689 aligned
galaxies, from the Mapping Nearby
Galaxies at Apache Point Observatory survey, we investigate the impact of kinematically misaligned gas on
star formation across
stellar mass. We characterise the global specific
star formation rate, central concentration and mass of ionized gas of our samples, and derive radial profiles of specific
star formation rate and ionized gas mass surface density. We find that misaligned
galaxies exhibit more centrally concentrated ionized gas than their aligned counterparts, with the strongest enhancement occurring at intermediate masses ($10^{10}$-$10^{10.6} {\rm M_\odot}$), where the central ionized gas density peaks. In
galaxies less massive than $10^{10} {\rm M_\odot}$, misaligned gas fuels
nuclear star formation at rates typical of
star-forming systems. At higher masses, however, the impact of this newly accreted gas is diluted by the larger pre-existing
stellar mass in the central regions, limiting its ability to rejuvenate the
star formation activity in these
galaxies. Our results also show that misaligned
galaxies with or without
nuclear activity exhibit similar central concentrations of ionized gas, suggesting that most have a reservoir capable of fuelling their supermassive black holes over timescales longer than typical
nuclear activity episodes.
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All authors J. L. Tous, S. I. Raimundo, R. Riffel, A. Puglisi, F. Shankar, M. Vestergaard
Instrumentation and Methods for Astrophysics
MIRA: a data management and education platform connecting students to robotic telescopes
Peter P. Pedersen, Lionel Garcia, Mahshid Alimi et al. (+3 more)
Hands-on
telescope experience is often used to drive student engagement in astronomy education, but scaling access to larger groups of students is operationally challenging. Consequently, students encounter only a fraction of the professional workflow, rarely engaging with the rigorous peer-review, time-allocation processes, or automated data reduction pipelines that govern modern research facilities. We present the design of MIRA (Mentored Investigations using Robotic Astronomy), a data management and educational platform that connects Swiss secondary school and undergraduate students with operational robotic observatories. MIRA structures the entire observation lifecycle: proposal, review, acceptance/rejection, scheduling, and observation. Following execution, the platform automatically reduces raw FITS frames (including astrometric calibration and photometry) and serves them via a web-accessible archive accompanied by Python-based analysis tutorials. By separating educational front-ends from low-level
telescope controls through Astra and ASCOM Alpaca, MIRA delivers an authentic scientific research workflow that bridges classroom learning with professional observatory operations.
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All authors Peter P. Pedersen, Lionel Garcia, Mahshid Alimi, David Degen, Florian Lienhard, Didier Queloz
Solar and Stellar Astrophysics
Search for double-line spectroscopic binaries in RAVE survey
Mikhail Kovalev
I present a study for double-line spectroscopic binaries content in RAVE DR6 spectra, using composite spectral model. Three complementing selections found 2813 composite spectra, belonging to 2605 unique targets. Also these results were compared with automatic classification based on t-SNE map, which shows good agreement. Additionally I identified several spectra affected by problems with wavelength calibration.
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Cosmology and Nongalactic Astrophysics
Probing Graviton Mass with MeerKAT PTA and SKA–PTA Forecasts
Zhi-Chao Zhao and Sai Wang
We present constraints on the graviton mass using the 4.5-year data release from the MeerKAT
Pulsar Timing Array (MPTA) and provide forecasts for the upcoming Square Kilometre Array PTA (SKA–PTA). By modeling the modified dispersion relation and the corresponding tensor correlation function for massive gravitons, we perform
Bayesian inference on the angular-correlation measurements under three noise configurations (DATA, ER, ALT). Our 90% credible upper limits on the graviton mass are $m_g < 2.10 \times 10^{-23}\,\mathrm{eV}/c^{2}$ (DATA), $m_g < 2.58 \times 10^{-23}\,\mathrm{eV}/c^{2}$ (ER), and $m_g < 2.25 \times 10^{-23}\,\mathrm{eV}/c^{2}$ (ALT). Including monopolar and dipolar contributions does not significantly alter these bounds, confirming that the constraints are driven by the quadrupolar tensor correlation. All results remain fully consistent with general relativity. For SKA–PTA, we forecast sensitivities down to $m_g \sim 10^{-24}\,\mathrm{eV}/c^{2}$ with a 10-year observing baseline and $m_g \sim 10^{-25}\,\mathrm{eV}/c^{2}$ with a 50-year observing baseline, representing order-of-magnitude improvements over current limits. This work demonstrates the power of current and future PTA observations to test fundamental aspects of
gravity in the nanohertz band.
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Earth and Planetary Astrophysics
Dust Growth in Binary Systems: Inhibition of dust settling and growth in circumbinary discs
Antoine Alaguero, Nicolás Cuello, Jean-François Gonzalez et al. (+4 more)
Stellar multiplicity alters the density structure of protoplanetary discs and thereby the initial conditions for
planet formation. Yet, the interplay between companion-disc interactions and
dust growth remains poorly understood. The goal of this work is to investigate to what extent the density structure of a disc undergoing
tidal interactions with a companion
star promotes or inhibits the growth of
dust grains. We perform a set of hydrodynamical simulations of protoplanetary discs orbiting one or both
stars of a binary, including
dust growth and fragmentation. We explore a range of companion orbits and compare the results with a single-
star reference case. We find that
dust growth is mainly driven by local accumulations of
dust. In circumbinary discs, the maximum grain size is up to five times smaller than in isolated discs. This result likely originates from the perturbations caused by the inner binary, which prevent
dust grains from properly settling and drifting. As a consequence, the conditions required to trigger strong clumping driven by the streaming instability are difficult to achieve. In contrast, circumstellar discs in binary systems exhibit grain sizes similar to those in isolated discs, leading to comparable conditions for strong clumping by the streaming instability.
Planet formation through core
accretion seems challenging in circumbinary discs harbouring binaries larger than a few au, suggesting that circumbinary
planets observed near the dynamical stability limit did not form in situ. Conversely, perturbations from external companions only marginally affect density-driven
dust growth compared to isolated systems.
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All authors Antoine Alaguero, Nicolás Cuello, Jean-François Gonzalez, Daniel J. Price, Maxime Lombart, Jeremy L. Smallwood, Philippe Thébault
Astrophysics of Galaxies
Enabling Cosmic Web Analysis at Gigaparsec Scales: A Multi Block Approach for DisPerSE
Ankit Singh, Frazer Pearce, Meghan Gray et al. (+1 more)
Cosmic filaments are the longest structures in the Universe and the dominant element of the
cosmic web, channelling matter onto clusters and shaping the environments in which
galaxies form and evolve. Accurate reconstructions of this network across gigaparsec volumes are increasingly important for cosmology and
galaxy evolution. However, the most commonly used topological filament finder, DisPerSE (Discrete Persistent Structures Extractor), faces a
memory bottleneck: it requires a Delaunay tessellation of the full input point set, preventing application to large simulations. Naively splitting the volume fails, as different sub-volumes yield inconsistent tessellations and filament networks. We present a frozen-core method that overcomes this bottleneck while preserving the global
topology. The volume is decomposed into overlapping blocks whose tessellations are filtered by a circumsphere criterion retaining only globally valid tetrahedra; a post-processing pipeline merges the tiled outputs through core filtering, deduplication, and boundary stitching. Validation against a monolithic reference on a $300\,h^{-1}\,\mathrm{Mpc}$ MDPL2 subvolume shows 99.6% total length recovery, 100% recovery of density maxima and minima, and 94.7% individual filament matching (the ${\sim}$5% of unmatched filaments are predominantly short, low-significance structures). We apply the method to the full $(1\,h^{-1}\,\mathrm{Gpc})^3$ MDPL2 box (92 million
haloes), producing a gigaparsec-scale filament catalogue. As a first application, we measure the connectivity ($\kappa$) for 22,900
haloes spanning $M_{200\mathrm{c}} = 10^{12}$-$10^{15.5}\,h^{-1}\,\mathrm{M}_\odot$, finding a power-law mass-connectivity relation that extends from group to cluster scales, providing the first confirmation in an $N$-body
halo catalogue that the theoretically predicted scaling holds across three decades in
halo mass.
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All authors Ankit Singh, Frazer Pearce, Meghan Gray, Gustavo Yepes
Instrumentation and Methods for Astrophysics
DUET: Design of a simultaneous InGaAs–CCD split-beam imager for ultra-cool dwarf exoplanet transit survey
Peter P. Pedersen, Clark Baker, Karolina Dziewiecka et al. (+4 more)
We present the design of DUET, a dual-channel imager being built for the SPECULOOS-Southern Observatory (SSO) to detect and characterise transiting terrestrial
exoplanets orbiting ultra-cool
dwarfs. A dichroic beamsplitter at 955\,nm directs visible light to a deeply-depleted silicon CCD and near-infrared light to a CMOS-based InGaAs detector, enabling fully simultaneous photometry with bandpasses from 0.4 to 1.7\,\textmu m. The near-infrared filters have been chosen to suppress sensitivity to atmospheric precipitable water vapour (PWV) variability, a dominant source of correlated noise in ground-based infrared photometry of cool
stars. We describe the optical and mechanical architecture, the dichroic and filter selection, the choice of detectors, and the control system.
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All authors Peter P. Pedersen, Clark Baker, Karolina Dziewiecka, Mathias Beck, Michaël Gillon, Amaury H.M.J. Triaud, Didier Queloz
Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics
Empirical verification of principal mode orthogonality and relative phase calibration in photonic lanterns
Adam K. Taras, Barnaby R. M. Norris, Christopher Betters et al. (+6 more)
Photonic lanterns efficiently map input spatial modes to single-mode outputs for applications like high angular resolution imaging and nulling interferometry. However, manufacturing limits prevent full control over the device's mode transfer
matrix at the design stage, making empirical characterisation essential. In this work we further analyse a
dataset of direct measurements of a photonic lantern's principal modes using digital off-axis holography over a 73 nm range near 1550 nm. By analysing the electric field directly, we find that the principal modes are significantly more orthogonal than random vectors in a space of the same size, as expected for near-adiabatic devices. We propose metrics for quantifying this effect, noting that mode converters with orthogonal principal modes provide better conditioned inverse solvers. We also simulate additional measurements that characterisation systems could take, where the orthogonality would be leveraged to determine the relative phase between principal modes.
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All authors Adam K. Taras, Barnaby R. M. Norris, Christopher Betters, Daniel S. Dahl, Nathan Long, Andrew Ross-Adams, Peter G. Tuthill, Jin Wei, Sergio Leon-Saval
Astrophysics of Galaxies
The Mysterious Case of Iron in XMPs: Anomalous High log(Fe/O) Observed in Extremely Metal-Poor Galaxies HSCJ1631+4426 and SDSSJ0811+4730
Aaron Myszka, Themiya Nanayakkara, Karl Glazebrook et al. (+8 more)
We present integral field spectroscopic observations of two local extremely metal-poor
galaxies (XMPs), HSCJ1631+4426 and SDSSJ0811+4730, obtained with the Keck
Cosmic Web Imager (KCWI) over the wavelength range $3545-5529$ Å at a spectral sampling of 0.5 Å, capturing bright nebular emission lines essential for determining gas-phase
metallicity and chemical enrichment measurements. Using integrated spectra, we derive oxygen abundances of $\rm12+\log(O/H)=7.079\pm0.010$ and $6.926\pm0.004$, and elevated Fe/O ratios of $\rm\log(Fe/O)=-1.57\pm0.17$ and $-1.28\pm0.07$, for HSCJ1631+4426 and SDSSJ0811+4730 respectively. Each
galaxy is fully contained within the $\sim$8” field of view, with 0.15” spaxels providing spatially resolved information. These measurements indicate unusually efficient iron enhancement at extremely low
metallicity; Fe/O ratios approach or exceed
solar despite oxygen abundances of only $\sim$2%
solar, inconsistent with enrichment from core-collapse
supernovae alone or delayed Type Ia
supernovae given the young ages of the systems. Comparison with chemical
evolution models suggests rare, highly energetic explosions such as bright hypernovae and/or pair-instability
supernovae are likely responsible. Our results reinforce the growing evidence that XMPs can reflect the nucleosynthetic processes of early energetic
stellar explosions, serving as local laboratories for chemical enrichment pathways prevalent in the early Universe.
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All authors Aaron Myszka, Themiya Nanayakkara, Karl Glazebrook, Sarah M. Sweet, Brent Groves, Nikole M. Nielsen, Jarle Brinchmann, Yuki Isobe, Chiaki Kobayashi, Haruka Kusakabe, Michael V. Maseda
High Energy Astrophysical Phenomena
Early Near-Infrared Excess and Rapid Disk-Corona Evolution in the Tidal Disruption Event 2024aepd
Yongxin Wu, Yanan Wang, Thomas M. Reynolds et al. (+38 more)
We present multi-wavelength observations of the
tidal disruption event (TDE) 2024aepd, spanning primarily the first $\sim$300 days after discovery. A prominent near-infrared (NIR) excess is detected as early as $\sim$40 days. Its nearly flat power-law spectrum strongly deviates from the Rayleigh-Jeans tail of the UV-optical blackbody. Although a conventional
dust-echo origin cannot be completely ruled out, free-free emission from a reprocessing photospheric envelope provides a more plausible explanation. The spectral break between the UV-optical and NIR components shifts to higher frequencies, while the inferred density-profile index remains nearly constant, suggesting evolving reprocessing conditions within a broadly unchanged density structure. In addition, the X-ray spectrum is initially dominated by a thermal disk component accompanied by a hard excess. From $\sim$178 days onward, the spectrum becomes power-law dominated and subsequently hardens, indicating the rapid emergence and strengthening of a hot corona. These results provide evidence for frequency-dependent reprocessing at early times and for the rapid development of a disk-corona system, placing new constraints on the structure and
evolution of the reprocessing layer around supermassive black holes.
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All authors Yongxin Wu, Yanan Wang, Thomas M. Reynolds, Shuyuan Wei, Shiyan Zhong, Zikun Lin, Megan Newsome, Sebastian Gomez, Iair Arcavi, Panos Charalampopoulos, Chun Chen, Rongfeng Shen, Ning-Chen Sun, David Aguado, Ismael Pérez-Fournon, Frédérick Poidevin, Zhongnan Dong, Niu Li, Weijian Guo, Hu Zou, Jingbo Sun, Nieves Castro-Rodríguez, Antonio Cabrera-Lavers, Ning Jiang, Hengxiao Guo, J. P. Anderson, Tomás E. Müller-Bravo, Seppo Mattila, Claudia P. Gutiérrez, Amit Kumar, G. Pignata, Xiangkun Liu, R. Dastidar, Brajesh Kumar, Xiaowei Liu, Bin Ma, M. Dennefeld, Francesca Onori, Lydia Makrygianni, Mariusz Gromadzki, Xuan Fang
High Energy Astrophysical Phenomena
Cosmogenic photon fluxes at ultra-high energies
Marcus Niechciol, Chiara Jane Papior and Markus Risse
During their propagation, ultra-high energy
cosmic rays produce cosmogenic
photons. The expected flux level of these
photons may vary by orders of magnitude depending on parameters such as the spectrum and composition of
cosmic rays at injection or the source distance. We investigate the
photon yields for various assumptions on injection parameters. The
photon yield is largest for
proton-emitting sources at about 15 Mpc distance for cosmogenic
photons above $10^{18}$ eV. While the
photon yield from
protons always exceeds the one from heavier
nuclei of the same total energy, the differences are reduced for larger source distances. Then, we quantify the cosmogenic
photon fluxes for different source scenarios. We regard mixed-composition scenarios that were found to provide a reasonable description of the data from the Pierre Auger Observatory. In addition,
benchmark scenarios leading to comparably high ("maximum") or low ("minimum")
photon fluxes are determined assuming pure
proton or pure iron primaries. For the mixed-composition scenarios that do not contain initial
protons, the predicted cosmogenic
photon fluxes are below present experimental limits by more than 1.5 orders of magnitude. In case of a substantial fraction of
protons at the highest energies, the related
photon flux might be in reach. Certain parameter combinations of pure
proton scenarios are constrained already by present
photon limits.
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Instrumentation and Methods for Astrophysics
Optical design of a direct fibre-fed MO-IFS for the NLOT
Nitish Singh, S. Sriram, Totan Chand et al. (+3 more)
The initial optical design and performance analysis of a dual-channel fibre-fed Multi-Object Integral Field spectrograph (Mo-IFS) being designed for a future National Large Optical/Infrared
Telescope (NLOT) in India. The front end will be a moveable lenslet+fiber based integral field unit. The spectrograph is designed to directly accept an f/4 beam from the approximately 200 optical fibers, each with a 100 um core diameter without additional fore-optics. The instrument consists of two optimized spectral channels covering wavelength ranges of 0.32-0.62 um (blue channel) and 0.60-1.00 um (red channel). The optical design aims to achieve moderate spectral resolutions of approximately R ~ 2700 in the blue channel and R ~ 2500 in the red channel while maintaining high throughput over a broad spectral range. The spectrograph architecture includes a fiber-fed entrance slit, collimator optics, dichroic beam splitting system, dispersive elements, and dedicated camera optics for each channel. Zemax simulations were carried out to evaluate image quality, spot size distribution, spectral resolution, and detector sampling across the full wavelength range. The current work presents the initial optical configuration, design methodology, and expected performance of the instrument.
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All authors Nitish Singh, S. Sriram, Totan Chand, Jurgen Schmoll, Bharat Kumar Yerra, Savitha M S
Solar and Stellar Astrophysics
Efficiency of Tidal Dissipation in Convective Flow Under Rapid Tidal Forcing
Hongzhe Zhou and Dong Lai
For close binaries and
star-
planet systems,
tidal interactions mediate the energy transfer between the orbital motion and the internal flows of the bodies involved, thus playing a central role in their
evolution. For
equilibrium tides, the associated energy transfer is commonly modeled through an effective viscosity acting on the
tidal flow. However, the scaling of viscous dissipation efficiency with
tidal frequency $\omega_\text{T}$ remains debated, particularly when $\omega_\text{T}$ greatly exceeds the convective eddy turnover frequency $\omega_\text{c}$. Previous numerical studies have addressed this issue by subjecting a turbulent convective flow to an oscillating background shear mimicking
equilibrium tides. In this work, we adopt a novel three-layered convective box – designed to represent a
stellar convection zone sandwiched between two stable layers – driven by an external periodic forcing. We quantify
tidal dissipation efficiency by the forcing power on the flow in steady state. Our results yield a shallower scaling of
tidal power per unit mass with $\omega_\text{T}$ than reported in earlier shear-flow simulations. This scaling is consistent with the prediction by \cite{Terquem2021}, suggesting that the effective turbulent viscosity depends only weakly on $\omega_\text{T}$, although our simulations are restricted to $\omega_\text{T}\lesssim 10\omega_\text{c}$. Moreover, we find no evidence of inverse energy transfer (or “negative viscosity”), a phenomenon observed in some prior shear-flow simulations. We further investigate the influence of rotation within the same local framework. Slow rotation ($\Omega\lesssim \omega_\text{T}$) tends to enhance the
tidal power, whereas fast rotation ($\Omega\gtrsim\omega_\text{T}$) significantly suppresses it. We discuss the limitations of our approach and the broader implications of our findings.
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Solar and Stellar Astrophysics
The coronal mass ejection productivity of solar active region 13664/8
Lijuan Liu, Yuming Wang, Quanhao Zhang et al. (+2 more)
In May 2024, NOAA active region (AR) complex 13664/8 was one of the most productive regions of the current
solar cycle, producing 12 X-class
flares and over 20 coronal mass ejections (CMEs) and triggering the strongest geomagnetic storm since 2003. We investigate why this AR complex was so CME-productive. Using primarily SDO/AIA and SDO/HMI observations, we analyzed its photospheric
magnetic evolution, eruption sources, eruption waiting times, and
magnetic parameters in comparison with five other ARs. The region initially contained only AR 13664 and exhibited limited
flare activity until AR 13668 emerged on May 4, after which clustered major
flares and CMEs occurred. Rapid, complex flux emergence substantially increased the region's area,
magnetic flux, complexity, and nonpotentiality. The increased complexity was manifested by at least 12 emerging bipoles and six collisional polarity inversion lines (cPILs) formed between nonconjugated polarities, all showing sustained collision and shearing and serving as eruption sources. Decay index distributions show systematically lower critical heights (<45 Mm) above CME source regions. The CME waiting time distribution exhibits two peaks, suggesting that multiple cPILs enhanced CME productivity by increasing both recurrent CMEs from the same source and disturbance-triggered CMEs from nearby sources. These results indicate that, in addition to sufficient nonpotentiality and rapid background-field decay, high
magnetic complexity accompanied by dynamical collisional shearing at multiple cPILs was crucial for the extreme CME productivity of AR 13664/8.
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All authors Lijuan Liu, Yuming Wang, Quanhao Zhang, Jingnan Guo, Yutian Chi
Solar and Stellar Astrophysics
Runaway OB stars within 1 kpc of the Sun
Juan Martinez Garcia, Nicholas Wright and Alexis Quintana
Runaway
stars are high-velocity
stars ejected from their birth environments that can provide insights into the kinematic history of the
stellar cluster they were ejected from. We derived runaway
star probabilities for 40 O-type
stars and $24,487$ B-type
stars taken from a recently published volume-complete sample of OB
stars within 1 kpc of the Sun. We fit a
Galactic rotation model to the observed proper motions of these
stars and identify runaway
stars using both a fixed 2D peculiar velocity threshold of $23\,km\,s^{-1}$ and by comparing individual peculiar velocities to the dispersion of the whole sample. We find runaway fractions of $17.5^{+0.1}_{-2.5}\%$ for O-type
stars and $6.9\pm0.1\%$ for B-type
stars; both using the fixed velocity threshold method. These values are consistent with previous studies, but with differences that are largely attributable to the underlying samples of OB
stars used in various studies to identify runaway
stars and to variations in the methods used to select them.
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Astrophysics of Galaxies
Relativistic Tidal Transitions of Saturated Kerr Boson Clouds
Yi-kun Li and Lang Cui
Rotating black holes can bind ultralight
bosons in macroscopic clouds whose level structure is swept by the
tidal field of a binary companion. Existing estimates of the resulting resonant transitions have largely used hydrogenic wave functions, even where the cloud grows most efficiently and the Kerr geometry appreciably deforms its quasibound states. I compute
tidal transition
matrix elements on the numerically determined saturation branches of the $|211\rangle$, $|322\rangle$, and $|433\rangle$ clouds. The calculation combines Kerr quasibound modes, their relativistic bilinear normalization, and an adiabatic uadrupolar perturbation of the Kerr metric. Across five $\Delta m=-2$ channels, the relativistic
matrix element differs from its hydrogenic value by as much as $21.67\%$. Corrections above $10\%$ persist when $99\%$ of the cloud lies within $7\%$ of the orbital separation. A component-resolved comparison attributes $78.7-82.5\%$ of the logarithmic change to the radial mode profile and $13.3-16.2\%$ to the bilinear normalization; the relativistic
tidal geometry supplies a smaller additional correction. Exact Newtonian multipoles and an independent complex-contour construction confirm the quadrupole
matrix elements. For resonances with intermediate Landau–Zener adiabaticity, the corrected
matrix elements change the predicted cloud depletion by up to $13.7\%$. Relativistic cloud structure is therefore quantitatively important for binary histories that cross saturated-cloud resonances.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Random walks around black holes and low-frequency X-ray variability
Arthur G. Suvorov
The
stochastic dynamics of a grain embedded within a turbulent fluid subject to strong gravitational fields can be formulated as a random walk on a Riemannian
manifold. Such
curvature-weighted walks provide a framework to model the intrinsic variability of
accretion onto compact objects. By solving the relevant Fokker-Planck equation on a black hole background, we find the counterintuitive result that the escape probability of a grain is actually higher compared to flat space. This is a consequence of the stretching of radial
cells near the event horizon: there is a greater spatial volume for the particle to wander through before being captured. By simulating a large number of grain trajectories, initially distributed on concentric shells with a density profile set by the thin-disc structure equations, we also study particle fluxes through the horizon. Shallower spectral indices emerge at low frequencies relative to flat space, primarily due to time dilation, and steeper ones at high frequencies. We find that Schwarzschild-weighted spectra broadly match observations of low-frequency X-ray variability from systems like Cygnus X-1 in their hard state, suggesting that
geometric drifts may be important in describing
stochastic accretion processes.
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Earth and Planetary Astrophysics
Observational planning for the 2026 August 5 Falcon 9 Upper Stage lunar impact
Benjamin Fernando, Jennifer Heldmann, Bill Grey et al. (+20 more)
On 2026 August 5, at approximately 06:35 UT, a spent Falcon 9 upper stage will impact the lunar surface near Einstein Crater. This event will occur on sunlit terrain near the eastern limb as seen from Earth. The impact flash and resultant ejecta plume from this event are potentially observable from ground- and space-based observational facilities. This event provides an opportunity to attempt the recording of an artificial impact in real-time; although many of the properties of the event (such as visual magnitude) are imprecisely predicted at present. Moreover, this event provides an opportunity to test a pipeline for localising impacts on the lunar surface for future seismic experiments, investigating the
dust and plume dynamics from impact events on the Moon, and considering hazards from artificial space debris impacts. Both professional and amateur astronomers are encouraged to attempt observations of this event.
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All authors Benjamin Fernando, Jennifer Heldmann, Bill Grey, John Ortiz, Bryan Euser, Darryl Z. Seligman, Eunhyeuk Kim, Anthony Colaprete, Elisa Maria Alessi, Detlef Koschny, Anthony Cook, Joel Green, Patrick King, Stacy Teng, Dawn Graninger, Arnold Goldberg, William Cooke, Mike F. Skrutskie, Kevin Schlaufman, Nicholas Schmerr, Carly M. Donahue, Carl A. Schmidt, Nancy J. Chanover
Astrophysics of Galaxies
A Catalog of Compact High-Velocity Clouds from the FAST All-Sky HI Survey (FASHI) DR2
Jin-Long Xu, Chuan-Peng Zhang, Xiao-Lan Liu et al. (+3 more)
High-velocity clouds (HVCs) – especially compact HVCs (CHVCs) – are thought to serve as gaseous tracers of dark-matter-dominated subhalos, providing a crucial empirical link between the predicted dark matter substructure and observed satellite
galaxies. In this paper, we present a new catalog of 192 CHVCs identified from the FAST All-Sky HI Survey (FASHI) Data Release 2 (DR2). Among these, 108 are ultra-compact HVCs (UCHVCs), the majority of which are new discoveries. We find that 185 of the 192 CHVCs are spatially and kinematically concentrated around the Andromeda
galaxy (M31), with a median LSR velocity of -296.1 km/s, suggesting physical association with M31. Adopting an M31 distance of 0.8 Mpc, we derive HI masses in the range 1.9*10^{5} to 4.0*10^{6} Msun and dynamical masses from 1.0*10^{7} to 6.3*10^{8} Msun. Approximately half of the CHVCs follow the baryonic Tully–Fisher relation. No optical counterparts are detected in Pan-STARRS1 imaging down to a limiting magnitude of m_g = 22.8. We conclude that these CHVCs likely represent a population of gas-rich, starless minihalos and provide an excellent sample for the search for dark
galaxies.
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All authors Jin-Long Xu, Chuan-Peng Zhang, Xiao-Lan Liu, Nai-Ping Yu, Mei Ai, Ming Zhu
Astrophysics of Galaxies
Features of the distribution of absorbing matter in the local system
V. I. Sorokina, V. V. Bobylev, G. A. Gontcharov et al. (+1 more)
V. I. Sorokina$^1$\footnote [99]{e-mail: vasilisushka05@gmail.com}, V. V. Bobylev$^2$, G. A. Gontcharov$^{2}$, A. T. Bajkova$^2$A detailed study of the
dust distribution in the Local System was conducted. Using the latest map by Gontcharov et al., smoothed distributions of
dust matter were obtained in projection onto the
galactic plane $XY$ using various smoothing parameters. Within the 2-kpc radius region around the Sun under study, key structural features associated with the Radcliffe Wave, Split, Sagittarius Spur Extension, Malpolon+Natrix, and Vela Ridge superclouds are clearly identified. It was shown that the Radcliffe Wave, Malpolon+Natrix, and Vela Ridge regions exhibit periodic perturbations of vertical coordinates with wavelengths ranging from 2.5 kpc (Radcliffe Wave) to 2 kpc (Malpolon+Natrix and Vela Ridge). No similar long-wavelength, high-amplitude oscillations of vertical coordinates were detected in the Sagittarius Spur Extension and Split regions.
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All authors V. I. Sorokina, V. V. Bobylev, G. A. Gontcharov, A. T. Bajkova
Instrumentation and Methods for Astrophysics
Design and Development of a Lab Prototype of a Fiber-Based Integral Field Spectrograph
Nitish Singh, S Sriram, Jurgen Schmoll et al. (+1 more)
Integral Field Spectroscopy provides simultaneous spatial and spectral information, making it a powerful technique for studying both point like and extended astronomical sources. As part of our effort to develop a compact Integral Field Spectrograph (IFS) for optical astronomy, we have designed and realized a fiber based prototype with a resolving power of ~800 at the H-$\alpha$ wavelength. The front end optics, including the fore optics and lenslet based integral field unit (IFU), have been designed and optimized. In the present work, we focus on the design and laboratory verification of a fiber only IFU module consisting of 37 fibers arranged in a precise hexagonal geometry to match the lenslet pitch. The back end of the system forms a linear fiber slit that feeds a laboratory built spectrograph. The optical design was optimized using ZEMAX, and the system was experimentally tested using a Neon emission lamp and
solar light. The measured spectra clearly show prominent features including the H-$\alpha$ lines, with dispersion and resolution consistent with theoretical predictions. Although lenslets are not yet integrated, this work establishes a validated methodology for accurate fiber
alignment for IFS. This results form a crucial step toward the full implementation of a lenslet fiber based IFS for the 2.34 meter Vainu Bappu
Telescope.
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All authors Nitish Singh, S Sriram, Jurgen Schmoll, Bharat Kumar Yerra
Cosmology and Nongalactic Astrophysics
Pushing the Primordial Frontier: Cosmological Collider Signatures at Strong Mixing
Javier Huenupi, Claudio Muñoz, Gonzalo A. Palma et al. (+1 more)
We develop an analytic treatment of
primordial non-Gaussianity in multifield inflation that is nonperturbative in the constant
curvature–isocurvature mixing strength $\lambda$. Using exact linear solutions for the coupled
curvature perturbation $\zeta$ and isocurvature perturbation $\sigma$, we construct dressed propagators and derive exact integral representations for the tree-level bispectra generated by the interactions $\dot\zeta^2\sigma$, $\dot\zeta\,\sigma^2$, and $\sigma^3$. This formalism resums
curvature–isocurvature transfer to all orders in $\lambda$ and applies for arbitrary values of the
entropy mass $\mu$. We obtain closed-form expressions for the leading squeezed limit of the bispectrum contributions and recover the well-known cosmological-
collider and quasi-single-field results in the weak-mixing limit. In the strong-mixing regime, where conventional transfer perturbation theory breaks down, we find that both the power spectrum and the bispectrum can be dramatically enhanced, giving rise to distinctive nonperturbative scaling laws for the reduced non-Gaussian amplitude. Together, these results open a new analytic window onto multifield inflation beyond the weak-coupling approximation and establish a framework for studying cosmological-
collider signals,
primordial-black-hole production, and loop corrections in strongly mixed inflationary dynamics.
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All authors Javier Huenupi, Claudio Muñoz, Gonzalo A. Palma, Spyros Sypsas
Cosmology and Nongalactic Astrophysics
Probabilistic redshift estimation of unresolved galaxies from multi-band background light maps
Shun-Sheng Li, Hendrik Hildebrandt and Ludovic Van Waerbeke
Accurate knowledge of the
redshift distributions of unresolved
galaxy populations is essential for extracting the cosmological information encoded in the
cosmic optical background. We present the first framework for estimating these distributions directly from multi-band maps of unresolved background light, using conditional normalising flows trained on realistic image simulations. For imaging qualities comparable to those expected from the synergy between the Euclid and Rubin LSST surveys, our model achieves sub-per cent accuracy in both the mean and standard deviation of the flux-weighted
redshift distributions when the training and target samples are statistically well matched. Furthermore, the network proves highly resilient to incomplete photometric coverage when combined with tailored data imputation strategies. To address the challenge of statistical mismatches between simulations and real observations, we propose incorporating observational quantities into the target variables, providing a built-in diagnostic to assess model reliability and uncertainty from the predictions themselves. We also demonstrate the feasibility of map-based tomographic analyses, showing that the model retains sufficient pixel-level detail to recover
redshift distributions for tomographically defined subsamples with near sub-per cent accuracy across all bins. These results establish conditional normalising flows as a viable tool for
redshift estimation of unresolved sources, opening new opportunities for component separation, signal interpretation, and cosmological inference using multi-band optical background fluctuations.
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Astrophysics of Galaxies
Revisiting Data Quality Control and Multiple-star Modeling in Wide Binary Gravity Tests: Confirmation of MOND-type Gravitational Anomaly at Low Acceleration
Kyu-Hyun Chae and Youngsub Yoon
Wide binary
stars provide natural laboratories for directly probing
gravity in the low-acceleration regime, as dark matter inferred from any viable
gravity has negligible effects on their internal dynamics. Various recent studies including
Bayesian 3D analyses have shown that wide binaries with separations greater than several thousand astronomical units experience MOND-type
gravity with a boost factor of $\gamma\approx 1.3-1.6$. However, results claiming preference for, or no deviation from, standard
gravity have also been published during the same period, particularly highlighting the roles of data quality control and realistic modeling of multiple-
star (i.e., triple and higher-order) systems that host hidden companion
stars. Here we carefully reexamine the issues of data quality control and modeling multiple-
star systems in statistical
gravity tests based on sky-projected 2D velocities of wide binary
stars. Through extensive tests including the acceleration-plane test, the $\tilde v$-distribution test, and the median-$\tilde v$-profile test (where $\tilde v$ is the sky-plane 2D relative velocity normalized by the Newtonian circular velocity between the two
stars), we show that proper data quality control or reasonable variation in multiple-
star modeling cannot remove the low-acceleration gravitational anomaly but confirms the MOND-type gravitational anomaly, particularly consistent with recent realistic MOND solutions of wide binary orbits. We find that studies claiming no evidence for the low-acceleration gravitational anomaly are consequences of bypassed calibration of the fraction of multiple-
star systems using the Newtonian-regime data, bias-introduction in data quality control that is not taken into account in
gravity tests, or insufficient statistics in the low-acceleration regime.
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