Earth and Planetary Astrophysics
Simultaneous Double Transits of Phobos and Deimos as Seen from the Martian Surface: A Millennium Catalogue
Samuel Cody
I present the first systematic catalogue of simultaneous
solar transits of both Phobos and Deimos as observed from the surface of Mars. Using the JPL mar099 ephemeris (Brozovic et al. 2025) and SPICE toolkit, I searched the millennium 1600-2600 CE for epochs at which both Martian moons project onto the
solar disc at the same instant for at least one surface location. I identify 8565 grazing double transits, 49 partial-overlap double transits (both moons simultaneously on the
solar disc, with at least one partially cut off by the limb), and 17 full double transits in which both moons lie wholly within the
solar disc at the same moment. All events cluster tightly around the Martian equinoxes (Ls ~ 0 deg or 180 deg) and within +/- 9 deg of the equator, reflecting the near-equatorial orbital inclinations of both moons. I derive a hard theoretical latitude limit of +/- 13.1 deg beyond which simultaneous double transits are geometrically impossible. The next observable partial double transit, excluding less prominent grazing events, is predicted for 2034 April 17. The next full double transit, with both moons wholly inside the
solar disc, with a gap between each silhouette and the
solar limb, occurs on 2118 November 20. The geometries for both these events were confirmed with JPL Horizons. I provide uncertainty estimates based on the Brozovic et al. covariance model, with predicted position errors growing from ~1 km for near-term events to ~600 km at the catalogue boundaries, and note that the JAXA MMX mission (~2031) will dramatically reduce uncertainties for all post-2030 predictions.
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Earth and Planetary Astrophysics
Periodic Wobble of the Post-Perihelion Jet Structure Around 3I/ATLAS
Toni Scarmato and Abraham Loeb
We analyse data on the post-perihelion morphology, including jet position angles (PAs) and coma dominated photometry of the interstellar object 3I/ATLAS. From Hubble Space
Telescope (HST) images processed with a Larson Sekanina rotational gradient filter, we measure the PAs of three main persistent jet like features between November 30 and December 27, 2025 and fit a weighted
Fourier model in a period scan. The dominant jet PA wobble yields Pjet = 7.20 +/- 0.05 h. An independent Gr (R band) time-series photometry data set, using two different apertures from MPC station L92, analyzed with nightly offsets and 30 minute binning, gives Pphot = 7.136 +/- 0.001 h (formal 1sigma), with a semiamplitude A about 0.311 mag and scatter sigmajit about 0.089 mag. The close agreement beetwen the periods supports a characteristic post-perihelion period of about 7.1 h. We interpret this period as an attitude precession/nutation (non principal axis rotation) traced by jet orientation and coma flux redistribution. The jet structure precesses about the rotation axis with a characteristic angular excursion of order about 20 degs, and the rotation axis is aligned with the sunward direction to within about 20 degs.
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Earth and Planetary Astrophysics
Experimental and numerical modeling of liposome congregation in meteorite craters of Early Earth
Vladimir M. Subbotin, Benjamin A. Turner, Brian A. Davies et al. (+2 more)
This paper provides experimental and numerical evidence supporting the occurrence of liposome congregation at the floors of meteor craters on Early Earth. This work builds on our earlier research, which demonstrated that liposomes submerged in a shallow Archean pond are protected from harmful UV radiation. This protection allows them to survive long enough for autocatalytic replication of amphiphiles and for mutation and selection of assemblies that maximize membrane stability. For liposomes to fuse, grow, exchange contents and membranes, and divide, they need to establish a population, which means forming a dense conglomerate that enables close physical contact. The study demonstrates that such a congregation is feasible in bowl-shaped meteor craters on Early Earth, especially under periodic seismic disturbances.
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All authors Vladimir M. Subbotin, Benjamin A. Turner, Brian A. Davies, Alric G. Lopez, Gennady Fiksel
Earth and Planetary Astrophysics · Cross-listed from gr-qc
Improved constraints on modified Newtonian gravity from Cassini radio tracking data
R. S. Park, A. Hees, B. Famaey et al. (+2 more)
We report an updated constraint on the
Solar System quadrupole parameter $Q_2$, which encodes the external field effect predicted by modified
gravity versions of the modified Newtonian dynamics (MOND) paradigm. Using the
dataset employed to compute the DE440 planetary ephemerides and estimating it simultaneously with other parameters included in the planetary ephemerides, we find $Q_2 = (1.6 \pm 1.8) \times 10^{-27}\,\mathrm{s}^{-2}$ (1-$\sigma$), representing an improvement of 40% over previous estimates. We also show explicitly that the contribution to the MOND prediction of $Q_2$ from the
Solar System's largest
planet, Jupiter, is at the 0.05% level, validating the approximation of retaining only the Sun in theoretical calculations. With this new constraint on $Q_2$, we update previously acknowledged tensions with external
galaxy rotation curves, now leading to discrepancies at the $3$-$15\sigma$ level depending on the detailed mass modeling or the subset of
galaxies considered. Within the Milky Way itself, the $Q_2$ constraint imposes an upper bound of only 2% (at 95% confidence) on the MOND boost to the
galactic radial acceleration (i.e., the ratio of the observed over baryonic Newtonian acceleration) at the position of the Sun, in strong tension with current observational limits. The updated $Q_2$ posterior finally confirms that
Solar System measurements provide stronger constraints than current wide-binary data on classical modified
gravity versions of MOND.
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All authors R. S. Park, A. Hees, B. Famaey, H. Desmond, A. Durakovic
Solar and Stellar Astrophysics
The SB9 catalogue: status, comparison with non-single stars from Gaia DR3 and evolution to SBX
T. Merle, A. Jorissen, S. Alexandre et al. (+9 more)
The Ninth Catalogue of Spectroscopic Binary Orbits (SB9) is a comprehensive compilation of spectroscopic binaries (SBs) with orbital parameters sourced from literature, comprising approximately 4000 systems (2800 single-lined and 1200 double-lined). This work presents the latest status of SB9 after two decades of development, detailing the statistical properties of SBs through orbital period distributions and eccentricity-period diagrams categorized by spectral type and evolutionary stage. We performed a rigorous cross-match with
Gaia Data Release 3 (DR3) to update astrometric parameters and compare SB9 with the
Gaia DR3 Non-Single
Star (NSS) catalogue. Our methodology utilized positional separations, magnitudes, and proper-motion back-propagation for identification. The final SB9 version updated by D. Pourbaix includes 4003 systems, including higher-order multiples: 152 triples, 71 quadruples, and 14 higher-order systems. Of these, 3976 have
Gaia DR3 identifiers; 21 are too bright and six too faint for detection. Ten SB9 systems with periods exceeding 1180 days were spatially resolved by
Gaia DR3. We identified a common sample of 827 binaries cross-matched with
Gaia NSS, with 655 considered highly reliable based on period and eccentricity differences under 10%. The limited overlap (20-30% of SB9) results from NSS selection cuts, brightness limits, and temporal baselines. This study highlights the complementary strengths of both catalogues and establishes a
benchmark sample for binary
star research. Finally, this work marks the transition of SB9 into SBX (The eXtended Catalogue of Spectroscopic Binary Orbits), featuring a modern relational database, improved web interface, and Virtual Observatory access standards to enhance data quality and accessibility for the
stellar community.
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All authors T. Merle, A. Jorissen, S. Alexandre, J. Desuter, C. Loup, A. Tokovinin, G. Traven, M. Van der Swaelmen, S. Van Eck, G. Van de Steene, J. Southworth, G. Sadowski
Cosmology and Nongalactic Astrophysics
Ly{\alpha} forest bounds on sterile neutrino production via neutrino self-interactions
Priyank Parashari, Vera Gluscevic, Yue Zhang et al. (+3 more)
Sterile
neutrinos in the keV mass range have long been considered a well-motivated dark matter (DM) candidate. In this work, we explore a sterile
neutrino production mechanism through active
neutrino self-interactions in the early universe, assuming that they constitute the full DM abundance. We implement a self-consistent treatment of the sterile-
neutrino free streaming and the active-
neutrino self-interactions on structure formation, which yield a unique scale-dependent modification to the linear matter power spectrum. We then set bounds on this scenario using a combination of the
cosmic microwave background and Ly$\alpha$ forest constraints. Specifically, we utilize the two recent likelihoods derived from eBOSS data: (i) an effective field theory (EFT) based full-shape likelihood and (ii) a compressed likelihood obtained from the PRIYA-simulation emulator. We produce some of the most stringent observational constraints to date on sterile
neutrino DM, comparable to the bounds from the most stringent laboratory constraints.
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All authors Priyank Parashari, Vera Gluscevic, Yue Zhang, Simeon Bird, Mikhail M. Ivanov, Adam He
Instrumentation and Methods for Astrophysics
Improved Identification of Satellite Trails in ACS/WFC Imaging Using a Modified Radon Transform
David V. Stark, Norman Grogin, Jenna Ryon et al. (+1 more)
We present a new approach to identify satellite trails (or other linear artifacts) in ACS/WFC imaging data using a modified Radon Transform. We demonstrate that this approach is sensitive to features with mean brightness significantly below the background noise level, and it is resistant to the influence of bright astronomical sources (e.g.,
stars,
galaxies) in most cases. Comparing with a set of satellite trails identified by eye, we find a trail recovery rate of 85% and a false detection rate (after removing diffraction spikes that are easily filtered) of 2.5%. By performing an analysis using a much larger ACS/WFC data set where false trails are identified by their persistence across multiple images of the same field, we identify the Radon Transform parameter space and image properties where our
algorithm is unreliable, and estimate a false detection rate of $\sim10\%$ elsewhere. We apply our method to ACS/WFC data taken between 2002 and 2022 to determine both the frequency of satellite trail contamination in science data and also the typical trail brightness as a function of time. We find the rate of satellite trail contamination has increased by approximately a factor of two in the last two decades, but there is no clear systematic
evolution in the typical trail brightness. Our satellite trail identification program is available as part of the acstools package.
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All authors David V. Stark, Norman Grogin, Jenna Ryon, Ray Lucas
Solar and Stellar Astrophysics
Long-term eclipse time variations in white dwarf binaries
Amalie Yates, S. G. Parsons, A. J. Brown et al. (+15 more)
The overwhelming majority of eclipsing white
dwarf (WD) binary systems show quasi-periodic variations in eclipse timings on many year timescales. Currently, the mechanism behind these eclipse time variations (ETVs) is not known, with the main competing theories being the planetary hypothesis and the Applegate/Lanza mechanisms. Here, we present a comprehensive study of 43 WD binary systems, the vast majority of which have more than a decade of eclipse timing measurements, analysing their global properties to determine which driving force is the likely origin of the observed ETVs. Long-term, high-speed photometry data obtained with ULTRACAM, ULTRASPEC and HiPERCAM have allowed us to track the
evolution of the ETVs in these systems, and analyse any previously unseen trends. From this analysis, we find a clear difference in the level of observed ETVs past the fully convective boundary, where systems with partially radiative companion
stars consistently showing high levels of variation. While some systems may be affected by the presence of an unknown
planet, the results from this study strongly indicates that an Applegate- or Lanza-like mechanism is the most likely driving force for the timing variations seen in the majority of systems in this sample. However, as found in previous studies, the Applegate/Lanza mechanisms are still not able to reproduce the large and rapid timing variations seen in the vast majority of systems, with the companion
star to the WD unable to provide sufficient energy on these short timescales.
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All authors Amalie Yates, S. G. Parsons, A. J. Brown, N. Castro Segura, V. S. Dhillon, M. J. Dyer, J. A. Garbutt, M. J. Green, D. Jarvis, M. R. Kennedy, P. Kerry, D. Kilkenny, S. P. Littlefair, J. McCormac, J. Munday, I. Pelisoli, E. Pike, D. I. Sahman
Solar and Stellar Astrophysics
On the Origin of Coronal Picoflare Jets
Annu Bura, Daniel Nóbrega-Siverio, Tanmoy Samanta et al. (+1 more)
Small-scale jet-like eruptions, such as picoflare jets and jetlets, are recognized as potential contributors to coronal heating and
solar wind acceleration, yet their physical origin is still not fully established. Using ultra-high-resolution extreme ultraviolet imaging
datasets from the Extreme Ultraviolet Imager on board the
Solar Orbiter mission, we investigate tiny coronal jets observed off-limb in the Sun's polar regions. Visual inspection reveals that the majority of these jets exhibit distinct morphological features, including a bright spire accompanied by a dark eruptive jet component. We analyzed eleven of these jets in detail and found that their spatial and temporal scales are comparable to previously reported jetlets, while their kinetic energies are two to three orders of magnitude lower, placing them in the picoflare regime. The bright and dark components show distinct dynamics, with the dark structures generally displaying lower speeds. A comparison with coordinated Interface Region Imaging Spectrograph and the Atmospheric Imaging Assembly on board the
Solar Dynamics Observatory data, together with 2.5D radiative-MHD simulations performed with the Bifrost code, reveals a one-to-one morphological correspondence between the dark counterparts and cool chromospheric surges accompanying the bright jet spire. This association suggests that flux emergence and
magnetic reconnection at low atmospheric heights may produce coupled bright-dark structures, providing a plausible mechanism for the generation of picoflare jets. Our results demonstrate
Solar Orbiter's ability to resolve the dynamics of small-scale jets and place new constraints on their origin.
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All authors Annu Bura, Daniel Nóbrega-Siverio, Tanmoy Samanta, Jayant Joshi
Earth and Planetary Astrophysics
Possible stratospheric emission in the warm Neptune GJ 436 b from high-resolution spectroscopy
Luke Finnerty, Michael P Fitzgerald, Jerry W Xuan et al. (+26 more)
We present high spectral resolution $L$ band (2.91–3.85 $\mu$m) observations of the warm Neptune GJ 436 b from Keck II/KPIC. KPIC's single-mode fiber feed reduces the $L$ band sky background by a factor of 100, significantly improving sensitivity compared to a seeing-limited spectrometer and enabling a tentative ($\rm SNR = 3-4$) cross-correlation detection of GJ 436 b with a thermally inverted atmospheric model. In contrast with recent results from $JWST$ and high-resolution transmission spectroscopy, our
retrieval analysis prefers the presence of H$_2$O, and possibly CH$_4$, molecular features in emission. The broad-band continuum flux associated with the maximum-likelihood model is substantially higher than expected based on both the $\sim670\rm\ K$
equilibrium temperature of GJ 436 b and previous results from low-resolution spectroscopy. We demonstrate that the loss of continuum information during the processing of high-resolution spectra makes our analysis effectively insensitive to the absolute continuum level of the
planet, and that scaling the maximum-likelihood model to match the broad-band flux measured from low-resolution observations of GJ 436 b results in a detection of similar strength in cross-correlation. These results could be explained by a thermal inversion arising above a haze layer in the upper atmosphere of \gjb. Further observations, ideally post-eclipse in order to break the $K_p - \Delta v_{sys}$ degeneracy, are needed to clarify this possible detection. This work demonstrates the potential of $L$ band high-resolution spectroscopy for characterizing significantly smaller and cooler
exoplanets compared with hot Jupiters.
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All authors Luke Finnerty, Michael P Fitzgerald, Jerry W Xuan, Daniel Echeverri, Nemanja Jovanovic, Dimitri Mawet, Geoffrey A Blake, Ashley Baker, Randall Bartos, Benjamin Calvin, Sylvain Cetre, Jacques-Robert Delorme, Greg Doppmann, Katelyn Horstman, Chih-Chun Hsu, Julie Inglis, Joshua Liberman, Ronald A López, Evan Morris, Jacklyn Pezzato-Rovner, Jean-Baptiste Ruffio, Ben Sappey, Tobias Schofield, Andrew Skemer, J. Kent Wallace, Nicole L Wallack, Jason J Wang, Ji Wang, Yinzi Xin
Astrophysics of Galaxies
There and back again? Neutral outflows in z~3.5 quiescent galaxies
Pengpei Zhu, Kei Ito, Francesco Valentino et al. (+16 more)
Neutral gas
outflows play a crucial role in the
baryon cycle of
galaxies, their properties provide key insights into the transition from
star formation to quiescence. In this work, we investigate the neutral gas
outflow of 23 massive ($M_\star = 10^{10.1-11.6}\,\rm M_\odot$) quiescent
galaxies (QGs) at z=2.82–4.61, selected from the JWST NIRSpec (R~1000) and NIRCam program DeepDive. We trace the neutral gas
outflows using the NaI Doublet absorption lines and detect excess NaI D in 13/23 (57%) targets, of which 7/23 (30%) show blueshifted absorption with velocity offsets $|{\Delta}v|$ >~ 150 km/s. The z ~ 3.5 targets have ${\Delta}v$ similar to those of their local counterparts; they are also equivalent when compared in SFR–${\Delta}v$ space. We derive mass
outflow rates and identify the most extreme neutral gas
outflow rate $\log(\dot M_{\rm out} / \mathrm{M_\odot \, yr}^{-1})=2.68\pm0.27$ beyond the local Universe, coincident with an X-ray AGN. For all NaI D detected systems, the inferred mass
outflow rate can, in principle, suppress ongoing
star formation; however, the
outflows are unlikely to escape their hosts, suggesting recycling on relatively short timescales (~3–180 Myr), depending on the assumed potential and launching radius. All NaI D detected targets occupy the LI(N)ER region of the BPT diagram and/or are X-ray detected, but we find no strong correlation between ongoing AGN and the neutral
outflow: 2/4 broad-line/X-ray AGNs are NaI D undetected – yet, the
outflows can be powered by fossil/episodic AGNs, and one broad-line target shows a possible P-Cygni profile that indicates strong
outflows. As neutral
outflows alone are not able to permanently quench
star formation by removing gas in our sample at z ~ 3.5, the presence of gas cycling in and out of massive passive systems may instead be the signature of feedback-regulated quenching-maintenance processes.
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All authors Pengpei Zhu, Kei Ito, Francesco Valentino, Massissilia Hamadouche, Gianluca Scarpe, Katherine E. Whitaker, Takumi Kakimoto, William M. Baker, Anna R. Gallazzi, Steven Gillman, Rashmi Gottumukkala, Christian Kragh Jespersen, Minju Lee, Allison W. S. Man, Georgios Magdis, Masato Onodera, Rhythm Shimakawa, Aswin Vijayan, Po-Feng Wu
Astrophysics of Galaxies
Molecular Gas Excitation in z ~ 0.7 Gas-Rich Post-starburst Galaxies from SQuIGGLE
Vincenzo R. D'Onofrio, Justin S. Spilker, Rachel Bezanson et al. (+10 more)
Many post-starburst
galaxies at $z\sim0.7$ have been shown to retain substantial molecular gas reservoirs yet host low ongoing
star formation, suggesting that the remaining gas may be inefficient at forming
stars during the early post-burst phase. We present new Atacama Large Millimeter/submillimeter Array CO(5-4) observations of nine gas-rich post-starburst
galaxies at $z\sim0.7$ from the Studying Quenching in Intermediate-z
Galaxies: Gas, angu$\vec{L}$ar momentum, and
Evolution (SQuIGG$\vec{L}$E) survey, providing a view of the molecular gas excitation in these systems. Combined with existing CO(2-1) data, we detect CO(5-4) in 8/9 targets and find that most have moderate CO excitation with $r_{52}\equiv L'_{\rm CO(5-4)}/L'_{\rm CO(2-1)}\approx0.1-0.3$. These systems show no clear trend between $r_{52}$ and either total or surface-density of
star formation. Specifically, all objects have $\Sigma_{\mathrm{SFR}} \sim 0.01-1\ \text{M}_\odot\ \text{yr}^{-1}\ \text{kpc}^{-2}$, consistent with compact, modest
star formation, even when allowing for buried activity, as these
galaxies decline from their peak. One object J1448+1010, which has clear optical, mid-infrared, and
radio indicators of an active
galactic nucleus, is an outlier with $r_{52}\approx0.6$; its elevated excitation likely requires significant non-
stellar heating, with a contribution from potentially obscured
star formation. Together, most gas-rich SQuIGG$\vec{L}$E post-starbursts have moderately excited molecular gas alongside little to modest
star-forming activity, indicating that the remaining gas hosts relatively suppressed
star formation efficiencies instead of strong buried starburst activity.
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All authors Vincenzo R. D'Onofrio, Justin S. Spilker, Rachel Bezanson, Robert Feldmann, Andy D. Goulding, Jenny E. Greene, Mariska Kriek, Anika Kumar, Yuanze Luo, Desika Narayanan, David J. Setton, Katherine A. Suess, Margaret E. Verrico
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Minimal Dark Matter: Generalized Framework and Direct-Detection Sensitivity
Spencer Griffith, Juri Smirnov, Laura Lopez-Honorez et al. (+1 more)
Minimal electroweak dark matter models are compelling due to their simplicity, though calculations of their freezeout abundance are complicated by nonperturbative effects due to Sommerfeld enhancement and bound-state formation. It has been shown that all individual multiplet scenarios beyond the doublet lead to direct-detection signals above the
neutrino floor and thus within the reach of next-generation experiments. If no signals are found, would minimal dark matter be excluded? Yes for the simplest models, but it has been unknown for the important extension of two multiplets coupled by
Higgs interactions (
Higgs-coupled minimal dark matter). We present a generalized framework for calculating nonperturbative effects for such models that also covers the case of individual multiplets. In this framework, we calculate nonperturbative effects on freezeout as well as the prospects for direct detection, correcting shortcomings and omissions in the literature. Importantly, for the mixed Majorana (odd) and Dirac (even) multiplet combination 3M2D (and marginally the 5M4D), we find that the predicted direct-detection signals can extend below the
neutrino floor. Fully testing minimal dark matter will thus require more than direct-detection experiments.
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All authors Spencer Griffith, Juri Smirnov, Laura Lopez-Honorez, John F. Beacom
Astrophysics of Galaxies
Bonnor-Ebert sphere collapse in filamentary structures
Stefan Heigl and Andreas Burkert
Star formation within filaments may arise due to the growth of cores according to linear perturbation theory. This implies a minimum core separation, as shorter modes would not be able to grow. While many observations agree with core separations by theoretical predictions, some observations also show
star forming cores which lie closer together than the minimum wavelength given by perturbation theory. We explore whether non-linear effects during the late stages of core growth can explain the discrepancy between theory and observations. We perform three-dimensional hydrodynamical simulations with the Ramses code to follow the
evolution of initial perturbations within filaments and compare the measured growth rates to expectations from theoretical models. Non-linear
evolution sets in as soon as the core mass reaches a value where the gravitational potential is not any longer dominated by the cylindrical potential of the filament but by the spherical potential of the Bonnor-Ebert sphere. Consequently, core collapse is not triggered by the loss of hydrostatic stability of the filament but by the loss of hydrostatic stability of the Bonnor-Ebert sphere. As the core is embedded in the filament, the maximum core mass is given by the pressure within the filament which results in a constant line-mass threshold for core collapse. As core collapse is triggered as soon as overdensities reach a certain line-mass, cores which form as large line-mass perturbations during filament formation can go into direct collapse even if their separation is closer than predicted by linear perturbation theory. Therefore, our result can explain the discrepancy between theory and observations.
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Astrophysics of Galaxies
Teen TITANS simulations – I. Inefficient intermediate-mass black hole seeding via stellar collisions in young massive clusters
Benedetta Mestichelli, Sara Rastello, Michela Mapelli et al. (+2 more)
Young massive clusters (YMCs) provide favorable environments for frequent
stellar collisions, potentially leading to the formation of very massive
stars (VMSs) and seeds of intermediate-mass black holes (IMBHs). We investigate the role of repeated
stellar collisions in YMCs using TITANS, a new suite of 18 direct $N$-body simulations. Our models span cluster masses $10^5 - 10^6\,\rm M_\odot$, half-mass densities $\rho_{\rm h}=100 - 10^5\,\rm M_\odot\,pc^{-3}$, and include high
primordial binary fractions, consistent with observations of massive
stars in young clusters. Overall, our simulations assume cluster properties that are typical of YMCs in the low-
redshift Universe. We find that repeated
stellar collisions are efficient only in the densest clusters with short relaxation times and are absent in systems with $\rho_{\rm h}<500\,\rm M_\odot\,pc^{-3}$ and $t_{\rm rh}>1.3\,\rm Gyr$. Rapid mass segregation allows massive
stars to sink to the cluster center, merge, and undergo subsequent collisions, even in clusters with long core-collapse times. However, collision chains are typically triggered by
primordial binary mergers and usually involve only two collisions. In our simulations, only three VMSs form through repeated collisions and reach $m_*>330\,\rm M_\odot$, while most VMSs have $m_*<300\,\rm M_\odot$ and form through
primordial binary mergers. None constitute viable IMBH seeds, as their helium cores fall in the (pulsational) pair-instability regime. We form five IMBHs from
stellar collisions involving
stars at different evolutionary stages, while the dominant channel is the merger of
stellar-mass black holes, producing twelve IMBHs. For properties typical of local YMCs,
stellar collision chains are therefore inefficient in producing IMBHs more massive than $140\,\rm M_\odot$, as most collisionally formed VMSs attain masses that fall in the pair-instability regime.
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All authors Benedetta Mestichelli, Sara Rastello, Michela Mapelli, Manuel Arca Sedda, Marica Branchesi
Earth and Planetary Astrophysics
Identifying Exoplanets with Deep Learning VI. Enhancing neural network mitigation of stellar activity RV signals with additional metrics
Naomi McWilliam, Zoë L. de Beurs, Andrew Vanderburg et al. (+12 more)
The measurement of
exoplanet masses using the radial velocity (RV) technique is currently limited by
stellar activity, which introduces quasiperiodic variability signals that must be modeled and removed to enhance the sensitivity of the RV measurements to
exoplanet signals. Neural networks have previously been demonstrated effective in modeling
stellar activity signals in HARPS-N
solar data using white light cross correlation functions (CCFs). Building on this work, we train a neural network on six years of HARPS-N
solar data with additional parameters commonly associated to
stellar activity, including chromatic CCFs, line shape metrics, spectral activity indicators, total
solar irradiance (TSI) light curves from SORCE and TSIS-1, and TSI time derivatives. Our results show that parameters such as the bisector inverse slope and Na D equivalent widths do not significantly improve the neural network's ability to predict activity-induced RV variations compared to using the white light CCFs alone. However, parameters such as unsigned
magnetic flux, the TSI and its time derivative, S-index, H-alpha equivalent width, chromatic CCFs, contrast, and full width at half maximum do improve the neural network's ability to predict RV scatter. Our new model reduces the RV scatter in a held-out test set from 147.1 cm/s to 93.3 cm/s, consistent with supergranulation noise levels reported in previous studies. These results suggest that finding effective tracers for (super)granulation will be critical to train models capable of further mitigating RV jitter, and necessary for characterizing Earth analogues.
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All authors Naomi McWilliam, Zoë L. de Beurs, Andrew Vanderburg, Javier Viaña, Annelies Mortier, Lars A. Buchhave, Andrew Collier Cameron, Rosario Cosentino, Xavier Dumusque, Adriano Ghedina, Ben Lakeland, Marcello Lodi, Mercedes López-Morales, Dimitar Sasselov, Alessandro Sozzetti
High Energy Astrophysical Phenomena
Addressing the Impact of Solar Modulation Systematic Uncertainties on Cosmic-Ray Propagation Models
Isabelle John, Alessandro Cuoco and Mattia Di Mauro
We perform a comprehensive analysis of
cosmic-ray propagation using the time-dependent AMS-02 flux measurements covering a full
solar cycle, with particular emphasis on the role of
solar modulation. We fit two representative
Galactic propagation scenarios, convection- and re-acceleration-dominated models, in combination with three
solar modulation prescriptions: the standard force-field approximation, an extended force-field model with a
rigidity break, and the heliospheric propagation code $\texttt{HelMod}$. The inclusion of time-resolved antiproton data provides a unique probe of charge-sign-dependent modulation effects and low-energy systematics. We find that the force-field approximation can describe positively charged
nuclei reasonably well outside the
solar maximum in convection-dominated models, but fails during periods of high
solar activity and for antiprotons at all times. In re-acceleration scenarios, strong degeneracies between
solar modulation and low-energy propagation lead to unphysical results when simple modulation models are employed. Across all models, we identify systematic uncertainties of order 10-15% in the reconstructed local interstellar spectra and propagation parameters, driven by limitations in current
solar modulation modelling. Compared to the percent level error of current measurements, these uncertainties significantly limit the precision of
cosmic-ray studies. Future time-dependent measurements spanning a full 22-year
solar cycle will be crucial to reduce these uncertainties.
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Cosmology and Nongalactic Astrophysics
Pushing spectral siren cosmology into the third-generation era: a blinded mock data challenge
Matteo Tagliazucchi, Michele Moresco, Alessandro Agapito et al. (+6 more)
Gravitational wave (GW) spectral sirens offer a promising method for measuring cosmological parameters using GW data only - without relying on external
redshift information such as electromagnetic counterparts or
galaxy catalogs - by exploiting distributional features in the population of GW sources. The advent of third-generation detectors like the Einstein
Telescope (ET) will provide catalogs three orders of magnitudes larger than current ones, raising questions about the scalability and robustness of existing inference pipelines. We present a blinded mock data challenge that tests three public pipelines with distinct numerical implementations, namely, $\texttt{ICAROGW}$, $\texttt{CHIMERA}$, and $\texttt{pymcpop-gw}$, on simulated ET observations containing the best $\mathcal{O}(10^4)$ binary black hole mergers that can be observed in 1 year. We assess their computational performance, validate their agreement in a blinded setting, and forecast cosmological constraints. We find that, thanks to GPU acceleration, these pipelines can process the events expected from ET within a manageable timeframe. All pipelines recover consistent cosmological and population parameters. Assuming a flat $\Lambda$CDM model, we measure $H(z)$ at $z\sim1.5$ with 2.4% precision, and achieve a mean precision on $H(z)$ of 2.8% across $0.7<z<1.8$ with a catalog of $\sim 12,000$ high-S/N events. This corresponds to joint constraints of $\sim 10%$ on $H_0$ and $\sim 26%$ on $\Omega_{\rm m,0}$. We also identify the events that contribute mostly to constraining cosmological parameters, showing that low-distance sources near population features drive the constraining power on all cosmological parameters, while higher-distance events primarily constrain $\Omega_{\rm m,0}$. Our results establish a validated, performance-tested framework for spectral siren cosmology in the era of third-generation GW observatories.
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All authors Matteo Tagliazucchi, Michele Moresco, Alessandro Agapito, Michele Mancarella, Sarah Ferraiuolo, Simone Mastrogiovanni, Nicola Borghi, Francesco Pannarale, Daniele Bonacorsi
High Energy Astrophysical Phenomena
Relativistic Magnetohydrodynamic Simulations of Giant Magnetar Bursts
Koushik Chatterjee, Alexander Philippov, Andrei M. Beloborodov et al. (+3 more)
Gradual crustal deformation can generate strongly twisted
magnetic fields around magnetars, potentially triggering
giant flares with total energies exceeding $10^{44}\,\mathrm{erg}$. In this Letter, we present the first relativistic magnetohydrodynamic simulation of a surface shear-driven magnetar eruption, capturing reconnection-driven
plasma heating, the ejection of relativistically hot
plasma, and the formation of a hot fireball confined within the inner magnetosphere. We find that
magnetic reconnection in the equatorial current sheet launches a hot trailing
outflow capable of powering the initial spike observed in
giant flares, while simultaneously leaving behind a thermally stratified fireball with sufficient thermal energy to produce the pulsating, decaying tail. Together, these features provide a self-consistent physical framework for understanding the observed energetics of magnetar
giant flares. The eruption also expels a magnetically dominated
giant plasmoid carrying up to $\sim 9\%$ of the magnetosphere's total
magnetic energy. Furthermore, our simulation demonstrates how the plasmoid drives the formation of a blast wave—an important ingredient in models linking magnetar eruptions to fast
radio bursts.
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All authors Koushik Chatterjee, Alexander Philippov, Andrei M. Beloborodov, Kyle Parfrey, Bart Ripperda, Elias R. Most
Astrophysics of Galaxies
A Chemodynamical Census of the Milky Way's Ultra-Faint Compact Satellites. I. A First Population-Level Look at the Internal Kinematics and Metallicities of 19 Extremely-Low-Mass Halo Stellar Systems
William Cerny, Ting S. Li, Andrew B. Pace et al. (+13 more)
Deep, wide-area photometric surveys have uncovered a population of compact ($r_{1/2} \approx$ 1-15 pc), extremely-low-mass ($M_* \approx$ 20-4000 $M_{\odot}$)
stellar systems in the Milky Way
halo that are smaller in size than known ultra-faint
dwarf galaxies (UFDs) and substantially fainter than most classical globular clusters (GCs). Very little is known about the nature and origins of this population of "Ultra-Faint Compact Satellites" (UFCSs) owing to a dearth of spectroscopic measurements. Here, we present the first spectroscopic census of these compact systems based on Magellan/IMACS and Keck/DEIMOS observations of 19 individual UFCSs, representing $\sim$2/3 of the known population. We securely measure mean radial velocities for all 19 systems, velocity dispersions for 15 (predominantly upper limits),
metallicities for 17,
metallicity dispersions for 8, and $\textit{Gaia}$-based mean proper motions for 18. This large new spectroscopic sample provides the first insights into population-level trends for these extreme satellites. We demonstrate that: (1) the UFCSs are kinematically colder, on average, than the UFDs, disfavoring very dense dark matter
halos in most cases, (2) the UFCS population is chemically diverse, spanning a factor of $\sim$300 in mean iron abundance ($\rm -3.3 \lesssim [Fe/H] \lesssim -0.8$), with multiple systems falling beneath the "
metallicity floor" proposed for GCs, and (3) while some higher-
metallicity and/or younger UFCSs are clearly
star clusters, the dynamical and/or chemical evidence allows the possibility that up to $\sim$50% of the UFCSs in our sample (9 of 19) may represent the smallest and least-massive
galaxies yet discovered.
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All authors William Cerny, Ting S. Li, Andrew B. Pace, Joshua D. Simon, Marla Geha, Alexander P. Ji, Alex Drlica-Wagner, Jordan Bruce, Oleg Y. Gnedin, Eric F. Bell, Sidney Mau, Ivanna Escala, Daisy Bissonette, Alessandro Savino, Anirudh Chiti, Evan N. Kirby
Cosmology and Nongalactic Astrophysics
Tommaso Moretti, Noemi Frusciante, Giovanni Verza et al. (+1 more)
We present a hydrodynamical description of isolated spherical voids in modified
gravity (MG), extending the standard General Relativity (GR) and dynamical dark energy treatment by encoding
gravity modifications into effective couplings that enter the Euler and Poisson equations. This yields a compact non-linear
evolution equation for the Eulerian density contrast, controlled by a time- and density-dependent effective gravitational strength, and provides a direct map between model functions and void observables. We apply the framework to the luminal Galileon class of models, where derivative self-interactions generate Vainshtein screening and might lead to a breakdown of the physical branch in sufficiently underdense regions. Exploiting this feature, we apply the void-informed viability requirement that translates into bounds on the theory parameter space and, equivalently, on the minimum attainable void depth as a function of
redshift. For viable parameters of a concrete model, we quantify the impact of MG on isolated void
evolution, the Lagrangian to Eulerian mapping, and the shell-crossing threshold. Relative to GR, we find a clear hierarchy of MG effects, with ${\cal O}(10\%)$ modifications in the gravitational couplings, percent-level shifts in the void density
evolution, and sub-percent deviations in both the mapping and the shell-crossing thresholds. Moreover, within the adopted parametrization, we show analytically that voids always lie in an unscreened regime on the physical branch. Overall, the formalism provides a self-consistent route to predict void dynamics and consistency constraints in a broad class of MG models.
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All authors Tommaso Moretti, Noemi Frusciante, Giovanni Verza, Francesco Pace
Earth and Planetary Astrophysics
New Kreutz Sungrazer C/2026 A1 (MAPS): Third Time's the Charm?
Zdenek Sekanina
This paper describes progress achieved in early investigations of the orbital motion and light curve of comet C/2026 A1 (MAPS), the third ground-based discovery of a Kreutz sungrazer in the 21st century. The highly unusual trait of the comet that has so far been ascertained is its extraordinarily long orbital period. The most recent orbital computations make it increasingly likely that the object is a fragment of one of the comets observed by Ammianus Marcellinus in AD 363, thereby strengthening evidence in support of the contact-binary hypothesis of the Kreutz system. In this context, the comet is the only second-generation fragment of Aristotle's comet that we are aware of to appear after the 12th century. It does not look like a major fragment, but rather like an outlying fragment of a much larger sungrazer. In 363 it apparently separated from a parent different from the lineage of comet Pereyra. The light curve of comet MAPS has so far been fairly smooth, without outbursts. To reach the brightness of comet Ikeya-Seki, the comet would have to follow an r^(-17) law in the coming weeks, which is unlikely.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Light dark sector via thermal decays of Dark Matter: the case of a 17 MeV particle coupled to electrons
Marco Graziani
Recent experimental observations, most notably those reported by the ATOMKI and Positron Annihilation into Dark Matter Experiment (PADME) collaborations, have hinted anomalies that may indicate the presence of a new resonance with a mass around $17\,\text{MeV}$, potentially interacting with both nucleons and electrons. Since 2020, ATOMKI has observed this resonance in
nuclear transitions from excited to ground states in ${}^{8}\mathrm{Be}$, ${}^{4}\mathrm{He}$, and ${}^{12}\mathrm{C}$. More recently, in 2025, PADME, operating at the Laboratori Nazionali di Frascati, has also hinted a similar excess, in this case in the $e^{+}e^{-}$ final-state events originating from positron annihilation on fixed-target atomic electrons of Carbonium. This concordance strengthens the case for a common underlying origin, potentially involving a new
boson, conventionally referred to as $X_{17}$. Despite these intriguing developments, the global experimental landscape remains highly dynamic, particularly in light of recent MEG~II constraints, and a definitive confirmation or exclusion of the $X_{17}$ hypothesis is still lacking. Within this evolving and exciting context, this thesis investigates whether a hypothetical $17\,\text{MeV}$ particle, coupled to electrons as suggested by the PADME observations, could function as a mediator between the Standard Model and previously unexplored hidden sectors. Such a mediator could, in principle, offer a novel pathway toward addressing one of the principal outstanding inconsistencies of the Standard Model: the nature and origin of dark matter.
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Solar and Stellar Astrophysics · Cross-listed from nucl-th
Yuan-Zhuo Ma, Georgios Palkanoglou, Joseph Carlson et al. (+7 more)
We present theoretical and experimental evidence for a new phase of matter in
neutron-rich systems that we call
multimodal superfluidity. Using ab initio
lattice calculations, we show that the condensate consists of coexisting s-wave pairs, p-wave pairs in entangled double pair combinations, and quartets composed of bound states of two s-wave pairs. We identify
multimodal superfluidity as a general feature of single-
flavor spin-1/2 fermionic systems with attractive s-wave and p-wave interactions, provided the system is stable against collapse into a dense droplet. Beyond
neutrons at sub-saturation densities, we demonstrate that this phase appears in generalized attractive extended Hubbard models in one, two, and three dimensions. We elucidate the mechanism for this coexistence using self-consistent few-body Cooper models and compare with Bardeen-Cooper-Schrieffer theory. We also derive the form of the effective action and show that
spin, rotational, and parity
symmetries remain unbroken. Finally, we analyze experimental data to show that p-wave pair gaps and quartet gaps are present in atomic
nuclei, and we discuss the consequences of this new phase for the structure and dynamics of
neutron star crusts.
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All authors Yuan-Zhuo Ma, Georgios Palkanoglou, Joseph Carlson, Stefano Gandolfi, Alexandros Gezerlis, Gabriel Given, Ashe Hicks, Dean Lee, Kevin E. Schmidt, Jiabin Yu
Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
Characterization of compressible fluctuations in solar wind streams dominated by balanced and imbalanced turbulence: Parker Solar Probe, Solar Orbiter and Wind observations
C.A. Gonzalez, C. Gonzalez and A. Tenerani
Characterizing compressible fluctuations in the
solar wind is essential for understanding their role in
solar wind acceleration and heating, yet their origin and
evolution across different
turbulence regimes remain poorly understood. In this study, we carry out a statistical analysis of the properties of compressible fluctuations in
solar wind dominated by balanced and imbalanced
turbulence. Using in-situ measurements from Wind,
Solar Orbiter, and Parker
Solar Probe, we investigate the scale dependence of density and
magnetic field fluctuations and their correlations with
plasma beta and radial distance. Our results indicate that
solar wind compressibility is likely affected by both expansion effects and compressible dynamics governed by local
plasma conditions. The non-Alfvenic wind is dominated by anti-correlated fluctuations, whereas the Alfvenic wind contains a mixture of correlated and anti-correlated fluctuations, though the latter remain prevalent. While the anti-correlated component is consistent with MHD slow magnetosonic modes, the correlated (fast mode-like) component is not reproduced by predictions from either linear MHD theory or nonlinear models of forced compressible fluctuations. Nevertheless, the dominant slow mode component explains the observed dependence on beta and the enhanced density fluctuations measured by Parker
Solar Probe. This further suggests that slow mode waves contribute significantly to the compressible energy budget near the Sun and may play an important role in
solar wind heating and acceleration close to the Sun.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
David Alonso-González, David Cerdeño, Marina Cermeño et al. (+1 more)
New exotic particles with MeV masses, such as
axion-like particles or light dark matter, can be emitted from core-collapse
supernovae (SNe) with semi-relativistic velocities. Due to their speed dispersion, they would arrive at Earth as an extended packet with a time spread that can be as large as tens of millennia for typical detectors. It has been argued in the literature that the superposition of packets from all
galactic SNe would give rise to a smooth and stationary diffuse flux that could be observable on terrestrial experiments. In this article, we critically examine this hypothesis by carrying out a numerical simulation of the
galactic history of SN explosions. We show that, although the particle packets do overlap, due to the short observational time window, each of them only contributes with a very narrow range of energies and with an intensity that depends on the SN distance. As a consequence, the energy dependence of the resulting flux is extremely sensitive to the
stochastic nature of the SN population and far from smooth. This has profound implications for the expected signature in terrestrial experiments, which displays a spectral shape that is not properly described by the smooth approximation. We develop a numerical tool to compute this
stochastic galactic flux for generic semi-relativistic particles, which also allows us to explore sub-MeV particles, where the smooth diffuse flux approach does not hold. To test this framework, we revisit existing bounds on
axion-like particles and fermionic dark matter, finding weaker constraints than previously reported.
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All authors David Alonso-González, David Cerdeño, Marina Cermeño, Andres D. Perez
Astrophysics of Galaxies
MUSEQuBES: Probing Anisotropies in Gas and Metal Distributions in the Circumgalactic Medium
Sayak Dutta, Sowgat Muzahid, Joop Schaye et al. (+9 more)
We investigate the azimuthal dependence of HI and OVI-bearing gas in the circumgalactic medium (CGM) of 113 isolated
galaxies in the
redshift range $0.12<z<0.75$, including 91 new measurements from the MUSE
Quasar-fields Blind Emitters Survey (MUSEQuBES). Of these, measurements for 46
galaxies lie within the virial radius ($R_{\rm vir}$), including 36 non-face-on systems for which azimuthal angle ($\phi$) measurements are robust. The HI covering fraction (k_HI) within $R_{\rm vir}$ of low-mass ($7<\log(M/M_{\odot})\leq 9$)
galaxies, for a threshold column density of ${\rm log}_{10}(N(HI)/{\rm cm}^{-2})=14.5$, exhibits an enhancement along both the disk plane ($\phi\lesssim20^{\circ}$) and in the polar direction ($\phi\gtrsim70^{\circ}$). In contrast, such a bimodal distribution is not observed for higher mass
galaxies ($9<\log(M/M_{\odot})\leq 11.3$). Similarly, the OVI covering fraction (k_OVI), for a threshold of ${\rm log}_{10}(N(OVI)/{\rm cm}^{-2})=14.0$, shows a tentative enhancement along both the projected major and minor axes for low-mass
galaxies. In contrast, \OVI-bearing gas around higher-mass
galaxies appears more uniformly distributed, with no significant azimuthal dependence. Finally, using the
halo circular-velocity-normalized pixel-velocity two-point correlation function (TPCF), we find that OVI absorbers are kinematically narrower along the disk plane compared to the polar directions of the host
galaxies with similar
stellar mass distributions. The observed isotropic distribution of OVI in high-mass
halos suggests that its spatial distribution is governed by global
halo properties; however, the OVI kinematics retain
memory of the site of origin.
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All authors Sayak Dutta, Sowgat Muzahid, Joop Schaye, Sean Johnson, Edmund Christian Herenz, Ismael Pessa, Ramona Augustin, Nicolas F. Bouché, Joey Braspenning, Sebastiano Cantalupo, Sourav Das, Martin Wendt
High Energy Astrophysical Phenomena
A break in the X-ray loudness of Markarian 590: evidence for an AGN spectral state transition?
B. Palit, A. Rozanska, A. G. Markowitz et al. (+8 more)
Using decade-long multi-band Swift observations of the changing-look AGN Markarian 590, we identify a clear break in the dependence of the X-ray loudness parameter $\alpha_{\rm ox}$ on the source
accretion rate. This break could be potential evidence for an
accretion state transition, analogous to that observed for X-ray binaries. The $\alpha_{\rm ox}$ follows a pronounced 'V'-shaped dependence on Eddington ratio $\lambda_{\rm Edd}$, with a statistically significant break at $\lambda_{\rm Edd} =0.021\pm0.008$, consistent with the Eddington-ratio threshold associated with changing-look events in
quasars. This behavior is indicative of a change in the inner
accretion flow, from a truncated disk with a dominant hot corona at low
accretion rates to an inward extending disk with enhanced UV emission and a prominent warm Comptonizing layer at higher rates. The UV and X-ray Eddington ratio tracers also show consistent breaks at $\lambda_{\rm Edd}\sim0.004$. Mkn~590 evolves through distinct phenomenological
accretion phases, from a faint, hard X-ray dominated state, through a flaring phase, to a bright, UV/soft X-ray dominated phase and exhibiting variability on month-, year-, and decade-long timescales. This overall
evolution is shorter than classical viscous timescales but broadly consistent with propagating thermal fronts in the
accretion disk. We also found a declining
radio-to-X-ray luminosity ratio with increasing $\lambda_{\rm Edd}$, indicating a relative suppression of
radio emission as the disk becomes more dominant with respect to the X-ray corona. Taken together, these results provide evidence that Mkn~590 is undergoing a state transition, supporting a broad analogy between changing-look AGNs and X-ray binaries.
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All authors B. Palit, A. Rozanska, A. G. Markowitz, D. Lawther, M. Vestergaard, J. J. Ruan, T. Saha, G. Walsh, A. Borkar, M. Sniegowska, K. X. Lu
Astrophysics of Galaxies
Interstellar Formation of Thioethanal (CH$_{3}$CHS). Gas-Phase and Ice-Surface Mechanisms involving Secondary Sulfur Products
N. Rani, S. Vogt-Geisse and S. Bovino
The formation pathways of sulfur-bearing species in the interstellar medium are crucial to understand astrochemical processes in cold molecular clouds and to gain new insights about the sulfur budget in these regions. We aim to explore the recently detected, thioethanal (CH$_{3}$CHS) formation mechanisms from thioethanol (CH$_{3}$CH$_{2}$SH) as a precursor in addition to secondary sulfur products. The electronic structure methods and density functional theory for both gas-phase and ice-grain surface environments is employed. To mimic interstellar ice-mantles, we use medium (W6) and large amorphized (W22) water clusters as implemented in Binding Energy Evaluation protocol. A barrierless formation mechanism for CH$_{3}$CHS under low-temperature interstellar conditions is identified, in the gas phase. Surface environments modulate activation barriers in a site-specific manner, elucidated through both Langmuir-Hinshelwood and Eley-Rideal initiated surface reaction pathways. Compared to oxygen analogs, sulfur chemistry enables alternate pathways due to weaker S-H bonding, with a competing route forming ethane-1,1-di-thiol (CH$_{3}$CH(SH)SH), on the ice-grain surface, potentially reducing CH$_{3}$CHS yields. The first accurate binding energy for thioethanol on water ice is also reported, confirming its greater
volatility than ethanol. The proposed mechanism offers a tentative hypothesis for the apparent mutual exclusive detections of the CH$_{3}$CH$_{2}$SH and CH$_{3}$CHS in TMC-1, Orion, and Sgr B2(N), that further requires validation through quantitative astrochemical modeling and also to distinguish this chemical differentiation from observational sensitivity limitations. These qualitative findings highlight the multifaceted chemical behavior of sulfur-bearing organics in the interstellar medium and support CH$_{3}$CH(SH)SH as promising astro-chemical targets.
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