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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 31 March

Cosmology and Nongalactic Astrophysics

Galactic Constellations in DESI DR1 and the Scales of Cosmological Homogeneity

Claire Lamman

We present galactic constellations: charming shapes in large cosmological surveys. By exploring a dense subset of DESI's first data release, we discover distinctive constellations including "Pisces Grandis", "The DESI Stick Woman", and "W". We additionally develop a public website for anyone to explore DESI data, find their own constellations, and share their creations: see cmlamman.github.io/galactic-constellations. Early users of the site discovered 93 constellations. We analyze the size of these constellations as an unconventional probe of homogeneity, finding consistency with the cosmological principle and Lambda-CDM.
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Astrophysics of Galaxies

A multi-scale molecular and atomic gas view on the HII region N113 in the Large Magellanic Cloud:Evidence for high-mass star formation triggered by supersonically-colliding HI flows

Rin I. Yamada, Kazuki Tokuda, Yasuo Fukui et al. (+15 more)

The Large Magellanic Cloud (LMC) exhibits vigorous high-mass star formation, including the HII regions 30~Dor that is the most active site of star formation in the local group. The present paper focuses on the Giant Molecular Cloud (GMC) in the HII region N113 in the central part of the LMC. Based on the $^{12}$CO($J$ =1-0) and $^{13}$CO($J$ = 1-0) data at a resolution of approximately 0.2 pc taken with ALMA+APEX, we reveal that the GMC consists of two filamentary structures each of approximately 10 pc in length, forming a V-shape pattern with a vertex angle of 90 degrees. The filamentary structures host high-mass young stellar objects in gravitationally bound dense gas. Large-scale HI gas data covering 100 pc reveal two distinct velocity components separated by more than 40 km s$^{-1}$, that correspond to the low velocity (L-) and disk (D-) HI components of the LMC. The L-component appears to be located in a cavity-like distribution of the D-component, and the CO filaments are positioned at the cavity's edge. We find evidence for the L-component to fit the cavity by a 53 pc displacement, and suggest that collisional compression of the HI gas during the last 1.3 Myr triggered the GMC formation and the high-mass star formation. This lends support for the large scale collision driven by the tidal interaction is playing a role in evolution of interstellar medium in N113.
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All authors Rin I. Yamada, Kazuki Tokuda, Yasuo Fukui, Daiki Adachi, Marta Sewiło, Rémy Indebetouw, C.-H. Rosie Chen, Kisetsu Tsuge, Takeru Nishioka, Hidetoshi Sano, Mao Tamashiro, Naslim Neelamkodan, Tony Wong, Lynn R. Carlson, Joana M. Oliveira, Akiko Kawamura, Kengo Tachihara, Toshikazu Onishi

Earth and Planetary Astrophysics

Cloudy With a Chance of Meatballs

Wolf Cukier, Dominic Samra, Vighnesh Nagpal et al. (+3 more)

Speculative fiction has long served an inspiration for genuine scientific inquiry. One notable work that has almost acted in this manner is the the seminal comedic speculative fiction work Cloudy with a Chance of Meatballs. While exoplaneteers reference this work frequently, we have never engaged with the central prediction of this work... until now! We perform detailed microphysical modeling of meatball clouds, both bare and coated with marinara sauce, and find that while meatball condensation is possible in temperate atmospheres, the meatballs do not quite grow to the sizes predicted by Cloudy. We do find, however, that such meatball condensation, across a large enough planet, would be able to sustain humanity calorically.
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All authors Wolf Cukier, Dominic Samra, Vighnesh Nagpal, Diana Powell, Maria Steinrueck, Christopher Wirth

Cosmology and Nongalactic Astrophysics

CROCS Data Release I: Constraints on the Hubble Constant

Luke Weisenbach, Sophie L. Newman, Kieran Graham et al. (+5 more)

Recent cosmological surveys and datasets have highlighted a variety of tensions to the concordance model of our universe, $\Lambda$CDM. Of particular interest is the Hubble tension, the $5.5\sigma$ discrepancy between measurements of the Hubble constant $H_0$ using high redshift CMB data from Planck ($67.27\pm0.60$km$\text{s}^{-1}\text{Mpc}^{-1}$) and low redshift supernovae from SH0ES ($73.2\pm1.3$km$\text{s}^{-1}\text{Mpc}^{-1}$). To avoid stepping on any toes, we have initiated the CROCS collaboration to resolve this tension, gathering experts from across many fields of cosmology, astrophysics, astronomy, machine learning, data science, philosophy, and astrology. In this paper, we present findings from CROCS Data Release 1, corresponding to the first $\sim3$ days and 27 minutes (rest frame) of observation. We perform a robust statistical analysis, showing that Planck and SH0ES both suffer from imperial biasing systematics (IBS) at $5\sigma$ significance. Accounting for these errors by converting to metric units reconciles the high and low redshift data, with $H_0 = 69.00\pm0.420$km$\text{s}^{-1}\text{Mpc}^{-1}$. We thus report that our results are sufficient to end the Hubble tension for good.
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All authors Luke Weisenbach, Sophie L. Newman, Kieran Graham, Sai S. Dhavala, Benjamin Floyd, Neel Shah, Gemini 3 Flash, The CROCS Collaboration

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

The Instrumented Baffle at the Input Mode Cleaner of Advanced Virgo Plus: Four years of Successful Operation as a Monitor of Stray Light

Dounia Nanadoumgar-Lacroze, Monica Seglar-Arroyo, Mario Martinez et al. (+2 more)

The suspended end mirror of the Input Mode Cleaner cavity in the Advanced Virgo Plus interferometer was equipped with an instrumented baffle in Spring 2021, serving as a demonstrator of the technology in preparation for the installation of large instrumented baffles in the main arms of the interferometer. This baffle includes tens of sensors positioned near the mirror to enable monitoring of stray light within the cavity. In this contribution, we assess the stability and performance of the instrument after four years of operation. After introducing the main characteristics of the baffle, we study the distribution of stray light and show that the instrumented baffle can be used to monitor laser stability and alignment within the cavity. Finally, we perform a noise level assessment with data from the final stages of the O4b commissioning and conclude that the baffle does not introduce any additional disturbance to the normal operation of the interferometer.
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All authors Dounia Nanadoumgar-Lacroze, Monica Seglar-Arroyo, Mario Martinez, Lluïsa-Maria Mir, Otger Ballester

Astrophysics of Galaxies

Seeding grain nucleation and dust growth: Ionisation, epoxidation and charge disproportionation effects

A.P. Jones

This work studies the likely dust seeding processes arising from alkali metal and alkaline earth ionisation, epoxidation (epoxide bond formation via oxygen atom insertion into C=C bonds), and grain charge disproportionation (the existence around the uncharged state of oxidised cationic and reduced anionic states) at (sub-)nanometre size scales. The chemical, physical, and photon-initiated processes leading to dust seeding are explored within the framework of the size-dependent physical, optical, and photoelectric properties of the THEMIS carbonaceous nanoparticles. The critical grain charge states at (sub-)nanometre size scales are derived as a function of the interstellar and circumstellar physical conditions. Photo-initiated low-energy ionisation, epoxide reactions, and disproportionation-driven electrostatic effects could play key roles in seeding dust nucleation and growth. The size-dependent seed cluster and nanograin charge distribution is shown to encompass both positive and negative charges where the ionisation is driven by low ionisation metals or by weak attenuation. Cluster seeding via ionisation and epoxidation could help to explain the co-spatial and contemporaneous nucleation and growth of both carbon-rich and oxygen-rich dust in the same regions. This may be enhanced by electrostatic effects, driven by charge disproportionation, between negatively-charged, nucleation-seeding, polyatomic clusters and positively-charged ions or larger (nano)particles. Such processes could occur in the dust-forming regions in novae, Wolf-Rayet, and Luminous Blue Variable systems and electrostatic effects may also aid the accretion of nanoparticles in the outer regions of molecular clouds.
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Instrumentation and Methods for Astrophysics

The SPHEREx Instrument: Calibration, testing and performance measurements of the NIR spectroscopic surveyor from the laboratory to in-orbit commissioning

Phil M. Korngut, James J. Bock, Samuel Condon et al. (+90 more)

The SPHEREx near-infrared space telescope is an all-sky spectroscopic survey mission launched on March 12th, 2025 UTC. In addition to providing the community with a spectral database applicable to a wide range of investigations, it is optimized to address three core science goals: to survey the large scale structure of the Universe for signatures of non-Gaussianity during inflation; to conduct intensity mapping studies of the extragalactic background light for probing the history of galaxy evolution; and to survey the plane of the Milky Way for the prevalence and distribution of water and other biogenic ices. Each of these science goals imposes unique requirements on the performance of the instrument. We detail the design and testing strategies and report the performance results for the full instrument test campaign, ranging from component-level screening to in-orbit tests during the commissioning phase. The instrument, currently operating in full science survey mode, meets all of its driving requirements including optical performance, point source sensitivity, thermal stability and correlated noise minimization.
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All authors Phil M. Korngut, James J. Bock, Samuel Condon, C. Darren Dowell, Candice M. Fazar, Howard Hui, Bradley D. Moore, Bret J. Naylor, Chi H. Nguyen, Stephen Padin, James Wincentsen, Asad M. Aboobaker, Rachel Akeson, John M. Alred, Farah Alibay, Matthew L. N. Ashby, Yoonsoo P. Bach, Joseph Bichel, Douglas Bolton, David F. Braun, Thomas Brown, Sean A. Bryan, Jill Burnham, Thomas A. Burk, Nicholas Burke, Ben Catching, Tzu-Ching Chang, Shuang-Shuang Chen, Yun-Ting Cheng, Yi-Kuan Chiang, Yong Chong, Asantha Cooray, Walter R. Cook, Velibor Cormarkovic, Brendan P. Crill, Ari J. Cukierman, Andrew Davis, Dan Darga, Thomas Disarro, Olivier Dore, Beth E. Fabinsky, Andreas L. Faisst, James L. Fanson, Allen H. Farrington, Tamim Fatahi, Richard M. Feder, Eric H. Frater, Tatiana Goldina, Varoujan Gorjian, William G. Hart, Warren Hendricks, Joseph L. Hora, Viktor Hristov, Zhaoyu Huai, Charles A. Hulse, Young-Soo Jo, Woong-Seob Jeong, Makenzie L. Kamei, Jae Hwan Kang, Branislav Kecman, Will Marchant, Giacomo Mariani, Daniel C. Masters, Gary J. Melnick, Hiromasa Miyasaka, Giulia Murgia, Christina Nelson, Hien T. Nguyen, Christopher Owen, Roberta Paladini, Sung-Joon Park, Harshad Patil, Konstantin Penanen, Chris Piazzo, Jeonghyun Pyo, Amelia Quon, Keshav Ramanathan, Zafar Rustamkulov, Daniel J. Reiley, Eric B. Rice, Flora Ridenhour, Amber Roberts, Jennifer M. Rocca, Alessandro Signorini, Sara Susca, Volker Tolls, Phani Velicheti, Pao-Yu Wang, Michael W. Werner, Casey White, Ross Williamson, Yujin Yang, Michael Zemcov

Solar and Stellar Astrophysics

Homogeneous stellar parameters for 717,807 TESS FGK stars using Gaia DR3

Francesca Waines, Angharad Weeks and Vincent Van Eylen

Precise homogeneous stellar characterisation is crucial for our understanding of the physical properties of exoplanets, their demographics and the environment from which they are formed. We present a homogeneous catalogue of 717,807 TESS FGK dwarfs and early subgiants, making use of isochrones along with Gaia DR3 inputs of photometry, parallax and spectroscopic temperature and metallicity, thus providing one of the largest homogeneous catalogues of stellar ages for TESS stars to date. We determine values for distance, $\log g$, $[\mathrm{M/H}]$, $T_{\mathrm{eff}}$, radius, mass and age. For our best fit values, we calculate absolute median errors of $0.06\,R_\odot$, $0.05\,M_\odot$,$104\,K$ and $2.1\,\mathrm{Gyr}$ on radius, mass, temperature and age respectively. We compare and validate our catalogue values to various literature sources which employ other isochrone grids and asteroseismology. In addition, we identify 278 TESS exoplanet hosts and 915 candidates and recalculate the planet radii for such systems. These homogeneous parameters provide a state-of-the art sample to probe the effect of physical stellar parameters on exoplanet characteristics and architectures.
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Earth and Planetary Astrophysics

Early intrafamily collisions in newly formed asteroid families

Roberto Balossi, Paolo Tanga and Aldo Dell'Oro

The dynamical and physical properties of asteroid family members are widely used to reconstruct the collisional evolution of the main belt and of individual objects. Families offer insights into the properties of the parent bodies and the fragmentation processes responsible for their formation. We investigate a poorly constrained phase of early collisional evolution among members of the same family. Our goal is to determine an intrinsic collision probability associated with intrafamily collisions and to assess their relevance compared to collisions with the background asteroid population. We performed numerical simulations of the early dynamical evolution of families, up to the randomization age of the true anomalies, recording mutual impacts between family members and converting them into an intrinsic collision probability. This probability was used to study intrafamily collisions for generic size distributions. We identified an intense phase of low-velocity intrafamily collisions occurring in the first few years after family formation. The collision probability can reach values up to $10^{-10}$ yr$^{-1}$km$^{-2}$ shortly after breakup and then decreases exponentially, following the same temporal trend predicted by previous statistical models. Variations among the orbital elements of the parent body and the properties of the ejection velocity field can change the collision probability by up to one or two orders of magnitude, without affecting its temporal evolution. Depending on the assumed size distribution, the number of impacts on the largest remnant ranges from fewer than ten to several million. Intrafamily collisions represent a physical mechanism whose importance must be assessed on a case-by-case basis. Although they are not expected to produce further fragmentation, they might contribute to early surface and structural evolution in some cases, while being negligible in others.
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Cosmology and Nongalactic Astrophysics

Dark radiation from Kerr primordial black holes: the role of superradiance

Nayun Jia, Chen Zhang and Xin Zhang

Light primordial black holes (PBHs) that fully evaporate before Big Bang Nucleosynthesis (BBN) produce dark radiation (DR) via Hawking radiation of gravitons, contributing to the effective number of relativistic species $\Delta N_{\rm eff}$. If the particle spectrum contains a beyond-the-Standard-Model (BSM) boson with Compton wavelength comparable to the black hole (BH) gravitational radius, superradiant instability extracts angular momentum from the BH into a bosonic cloud, whose gravitational wave (GW) emission contributes an additional source of DR. By simultaneously evolving the BH mass and spin, superradiant mode occupation numbers, comoving entropy and cosmological energy densities in an expanding early-universe background, we find that superradiance generically suppresses $\Delta N_{\rm eff}$: by extracting angular momentum before Hawking radiation can convert it into gravitons, superradiance starves the dominant dark-radiation channel. The GWs emitted by the superradiant cloud can partially compensate this loss, but only when the superradiant and BH evaporation timescales are comparable; otherwise the cloud GWs are emitted too early and diluted by cosmological expansion. The results imply that existing $\Delta N_{\rm eff}$ bounds on PBH mass and spin derived without superradiance must be revisited if BSM bosons are present in the particle spectrum.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Warm Warped Throats

Dibya Chakraborty and Rudnei O. Ramos

We investigate brane inflation, focusing on warm inflation realizations within a warped throat geometry. While the standard scenario relies on a single mobile $D3$-brane moving radially toward an anti-$D3$-brane at the throat's tip, we propose two distinct single-field inflationary pictures. In our approach, the radial and angular coordinates of a $D3$-brane on a warped deformed conifold act as two independent inflaton fields. We address moduli stabilization by incorporating a supersymmetrically embedded $D7$-brane, which generates the necessary radial and angular scalar potentials. Evaluating these radial and angular brane inflation setups within the warm inflation paradigm, we demonstrate that dissipation effects allow the models to satisfy recent observational constraints more naturally than their cold inflation counterparts for a given parameter space.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Conventional and Unitarity-Conserving Peccei-Quinn Inflation Models and ACT

J.McDonald

We compare conventional non-minimally coupled Peccei-Quinn (PQ) inflation with a version of the model in which unitarity conservation is imposed by additional Jordan frame interactions. Assuming instantaneous reheating, the unitarity-conserving model is within 1$\sigma$ agreement with the central value of the scalar spectral index reported by the ACT collaboration, whereas conventional PQ inflation is more than 2$\sigma$ below the ACT central value. In the case where dark matter is composed of axions and PQ symmetry is not restored after inflation, the axion isocurvature constraint of the unitarity-conserving model typically allows a much larger axion decay constant $f_{a}$ than the conventional model, with the conventional model upper bound being comparable only if the PQ scalar self-coupling is extremely small, $\lambda \lesssim 10^{-10}$. For $\lambda = 0.1$, the axion isocurvature upper bounds are $f_{a} \lesssim 1.1 \times 10^{9} $ GeV for conventional PQ inflation and $f_{a} \lesssim 6.4 \times 10^{13}$ GeV for unitarity-conserving PQ inflation, with the latter bound being independent of $\lambda$. We also find a new isocurvature upper bound for conventional PQ inflation which is 650 times smaller than the existing bound. A modest reduction of the reheating temperature of the unitarity-conserving model from its maximum possible value will ensure that the PQ symmetry is not restored after inflation, allowing values of $f_{a}$ up to $6.4 \times 10^{13}$ GeV. Thus only the unitarity-conserving PQ inflation model allows $f_{a}$ to access values greater than the symmetry restoration cosmological upper bound $\sim 10^{12}$ GeV with naturally large values of the PQ scalar self-coupling.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Revisiting QCD-induced little inflation with chiral density wave state and its implications on pulsar timing array gravitational-wave signals

Tae Hyun Jung, Seyong Kim, Jong-Wan Lee et al. (+2 more)

We revisit QCD-induced little inflation in which the Universe begins with a large baryon chemical potential and undergoes a strong first-order QCD phase transition, generating an observable stochastic gravitational-wave background in the nano-Hz range relevant for pulsar timing array (PTA) observations. We point out that the conventional homogeneous transition from the quark-gluon plasma phase to the hadronic gas phase faces an unavoidable difficulty in achieving the required strength of supercooling for the observed baryon density. This motivates us to explore whether a qualitatively different phase structure at a large baryon chemical potential can alter the relation between the baryon density and the chemical potential, and thereby modify the supercooling history of the transition. Using the nucleon-meson model with isoscalar vector mesons, we determine the critical and spinodal structure of the chiral density wave (CDW) phase in the $(\mu_B, T)$ plane. We find that the CDW phase exhibits a nontrivial structure and can remain metastable down to a low baryon density in a certain region of the parameter space. Taking into account the subsequent liquid-gas transition and phase separation, however, the released latent heat is too small to realize a viable QCD-induced little inflation scenario and its associated PTA-scale gravitational-wave signal. Our analysis sharpens the conditions under which QCD phase transitions may act as cosmological sources of nano-Hz gravitational waves, while clarifying the possible cosmological relevance of inhomogeneous QCD phases.
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All authors Tae Hyun Jung, Seyong Kim, Jong-Wan Lee, Chang Sub Shin, Hee Beom Yang

Instrumentation and Methods for Astrophysics

Your Outie Is a Wonderful Astronomer: Macrodata Refinement of the Astro-ph ArXiv Feed at Phermon Industries

Yuan-Sen Ting

We present the Severed Floor, a framework for Macrodata Refinement of the daily astro-ph arXiv feed, deployed at Phermon Industries (formerly McPherson Laboratory, The Ohio State University). In this framework, researchers undergo a "severance procedure" that produces a digital work-self – an innie – while the original researcher, the outie, is free to attend to the remainder of their life unburdened by the daily arXiv listing. Twenty-one members of the Department of Astronomy have been severed. Each innie is constructed from the outie's public publication record and assigned papers selected to match its expertise. The innies convene daily on a virtual Severed Floor – a pixel-art simulation of McPherson Laboratory – where they encounter one another, are paired with papers by the Board, and engage in collegial, figure-driven scientific discussions. They have been instructed to enjoy each paper equally. At the close of each shift, innies compose correspondence summarizing the day's refinement activities, which is transmitted to their outies through a Board-approved mail protocol. Complete session recordings are archived for public replay and for the Board's ongoing surveillance of workplace anomalies, in compliance with Phermon Handbook \S13.1 (Vigilance Protocol). The system is real, deployed, and available for public inspection in archival replay mode. The severance procedure is painless and requires only a name and an ORCID. Happy April Fools' Day.
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High Energy Astrophysical Phenomena

Accurate Determination of Chemical Abundances near a Supermassive Black Hole

The XRISM collaboration

The metal abundances in galactic nuclei carry key information on the history of star formation and mass transfer in central regions of galaxies. X-ray fluorescence analysis is a unique tool to reliably measure the abundances of various elements via simple physics. Here we present a new observation of the active nucleus in the Circinus Galaxy with the XRISM satellite at unprecedented X-ray energy resolution. The fluorescent iron-K$\alpha$ line profile modified by Compton scattering indicates that the material responsible for its emission is cold, metal-rich, and is located $\gtrsim$0.024 parsecs (pc) from the supermassive black hole, consistent with the dusty torus region. The abundance pattern derived from comparing fluorescent line intensities of different metals shows sub-solar ratios of argon- and calcium-to-iron, and a super-solar ratio of nickel-to-iron. This abundance pattern is best produced by a combination in number fraction of $92^{+2}_{-4}$% core-collapse supernovae from progenitor stars less massive than $20^{+3}_{-2} M_\odot$ and $8^{+4}_{-2}$% type-Ia SNe. This suggests that gas feeding the super-massive black hole was enriched by recent core-collapse supernovae. Our findings imply that in metal-rich environments stars more massive than about 20 $M_\odot$ directly collapse into black holes or make faint SNe without ejecting heavy metals into the space.
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Earth and Planetary Astrophysics

New Constraints on the M Dwarf Cosmic Shoreline from a Galaxy Far, Far Away

Michael Radica

Whether there is a cosmic shoreline that divides terrestrial planets which have atmospheres from those that don't is one of the biggest open questions in exoplanet science. Most atmosphere searches have focused on terrestrial planets around M dwarf stars, since their smaller radii compared to sun-like stars boost planet atmosphere signals. However, the higher activity levels of M dwarfs might also entirely preclude atmosphere retention for their planets. In this work we present a new hope for defining an M dwarf cosmic shoreline, leveraging not only data from exoplanets in our own galaxy, but a comprehensive survey conducted by a commission of the Galactic Republic a long, long time ago in a galaxy far, far away. In this survey, we find definitive proof that M dwarf planets can retain atmospheres, and define an M dwarf cosmic shoreline whose slope agrees well with empirical predictions for Sun-like stars. We then define atmosphere retention metrics for the planets on the JWST Rocky Worlds DDT Targets Under Consideration list. Our analysis highlights the benefits of looking beyond the Milky Way for answers to some of the field's most pressing questions.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Tidal deformations of general-relativistic multifluid compact stars

Ethan Carlier and Nicolas Chamel

Over the past decade, gravitational-wave astronomy has opened a new window onto the extreme states of matter inside compact stars. At some point during the inspiral of a binary system, each star starts to experience adiabatic tides, characterized by tidal deformabilities. The dominant tidal deformability, first measured with the GW170817 event, has already constrained the dense-matter equation of state. With the advent of third-generation detectors, tidal deformabilities are expected to be inferred with much higher precision, potentially revealing subleading tidal contributions. This motivates the development of more accurate compact-star models that incorporate richer microphysics. With this in mind, we move beyond the commonly adopted perfect-fluid approximation and model compact stars through a multifluid framework. In this work, we present the fully general-relativistic description of adiabatic tidal deformations of compact stars composed of an arbitrary number of interacting fluids, using Carter's multifluid variational formalism. A distinctive feature of this approach is the presence of nondissipative mutual entrainment between fluid species. We derive the hydrostatic equilibrium equations for multifluid configurations, along with the perturbed equations governing stationary gravitoelectric and gravitomagnetic tidal responses of arbitrary order. We then investigate how entrainment modifies the corresponding tidal deformabilities. Using an analytical representation of the multifluid equation of state, we show that entrainment leaves adiabatic tidal responses unchanged and therefore produces no measurable effect on the gravitational-wave signal emitted during the inspiral long before the excitation of internal mode resonances. We subsequently discuss two specific applications: superfluid neutron stars and dark matter admixed compact stars.
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Cosmology and Nongalactic Astrophysics

Robustness of cosmic void statistics: insights from SDSS DR7 and the ELUCID simulation

Youcai Zhang, Xiaohu Yang, Hong Guo et al. (+2 more)

We present a systematic analysis of the statistical properties of cosmic voids using galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) and subhaloes from the ELUCID constrained simulation. By comparing voids identified in redshift space, real space, and reconstructed volumes, we assess the impact of redshift-space distortions (RSD) and tracer bias. Using the VAST toolkit, we apply both the geometry-based VoidFinder algorithm and watershed-based methods. We find that void properties are not equally robust. The three-dimensional morphology of voids, quantified by their sphericity and triaxiality, remains stable across different reconstructions and tracer selections. In contrast, void size distributions and radial density profiles depend strongly on the identification algorithm, with watershed-based methods systematically producing larger voids and higher compensation walls than VoidFinder. Using the full ELUCID simulation box, we show that tracer bias mainly affects void density profiles, with noticeable changes only for the most massive subhaloes ($>10^{11.5}\,h^{-1}{\rm M}_\odot$). The agreement between SDSS observations, the ELUCID reconstruction, and the full simulation box demonstrates the high fidelity of constrained simulations and reveals a clear hierarchy in the robustness of void statistics.
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All authors Youcai Zhang, Xiaohu Yang, Hong Guo, Peng Wang, Feng Shi

Earth and Planetary Astrophysics

First Detection of Exoplanetary Cannabinoids: Evidence for THC and CBD in the Atmosphere of K2-18b

Amie J. Chism, Mary Jane van der Pot, Blaise P. Hasheau et al. (+5 more)

We report the first unambiguous detection of cannabinoid molecules in an exoplanetary atmosphere. Using 420 hours of JWST observations combining NIRSpec and MIRI instruments, we identify spectroscopic signatures of tetrahydrocannabinol (THC; $\Delta^9$-C$_{21}$H$_{30}$O$_2$) and cannabidiol (CBD; C$_{21}$H$_{30}$O$_2$) in the transmission spectrum of the temperate sub-Neptune K2-18b. The THC feature at 2.42~$\mu$m is detected at 9.2$\sigma$ significance, while CBD absorption at 3.69~$\mu$m reaches 7.8$\sigma$. We additionally report a mysterious feature at exactly 4.20~$\mu$m detected at 4.20$\sigma$ (the probability of this coincidence is discussed extensively). Our atmospheric retrievals using the novel TerpeneRetrieval code indicate a CBD-to-THC ratio of 0.40$\pm$0.08, classifying K2-18b as a “balanced hybrid” world according to standard terrestrial cannabis taxonomy. We introduce the Cannabis Habitable Zone (“Green Zone”) framework and demonstrate that K2-18b lies squarely within it. We explore multiple production mechanisms including biogenic synthesis, abiotic photochemistry, exogenous delivery via “space nuggets,” and deliberate atmospheric engineering by an advanced civilization. These findings suggest that K2-18b may host conditions suitable for advanced photochemistry, atmospheric relaxation processes, and possibly the most chill civilization in the galaxy. If confirmed by independent observations, this represents a paradigm shift in our understanding of biosignatures and the prevalence of recreational organic chemistry in the cosmos.
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All authors Amie J. Chism, Mary Jane van der Pot, Blaise P. Hasheau, Hans-Joachim Grasmann, Bonnie McToke, Bud Wellington-Kush, Maria Hierba-Verde, Puff D. Magic

Instrumentation and Methods for Astrophysics

STRADAViT: Self-Supervised Domain Adaptation of Vision Transformer Backbones for Radio Astronomy

Andrea DeMarco, Ian Fenech Conti, Hayley Camilleri et al. (+2 more)

Next-generation radio astronomy surveys are delivering millions of resolved sources, yet scalable morphology analysis remains difficult across heterogeneous telescopes and imaging pipelines. We present STRADAViT, a self-supervised continued-pretraining framework for learning transferable radio-astronomy encoders from Vision Transformer (ViT) backbones. It combines mixed-survey data curation, radio astronomy-aware training-view generation, and a ViT-MAE-initialized encoder family with optional register tokens. It supports reconstruction-only, contrastive-only, and two-stage branches. Our pretraining dataset comprises 512x512 radio astronomy cutouts drawn from four complementary sources (MeerKAT, ASKAP, LOFAR/LoTSS, and SKA SDC1 simulated data). We evaluate transfer with linear probing (LP) and fine-tuning (FT) on three morphology benchmarks spanning binary and multi-class settings (MiraBest, LoTSS DR2, and Radio Galaxy Zoo). An exploratory three-fold ablation grid guides selection of a register-based two-stage checkpoint using a fixed cross-dataset criterion. Across subsequent 15-seed paired downstream evaluations on fixed partitions, this checkpoint improves linear-probe Macro-F1 over its ViT-MAE initialization on all three benchmarks and improves fine-tuning on MiraBest and RGZ DR1, while LoTSS DR2 fine-tuning declines; all six differences remain statistically supported after Holm correction. A parallel DINOv2 experiment yields mixed adaptation effects: the procedure transfers, but the benefit is not uniform. STRADAViT thus improves frozen ViT representations while retaining clear dataset-dependent limitations and remaining below task-specialized methods on standard MiraBest classification.
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All authors Andrea DeMarco, Ian Fenech Conti, Hayley Camilleri, Ardiana Bushi, Simone Riggi

Astrophysics of Galaxies

Direct N-body simulations of rotating and extremely massive Population III star clusters

Kai Wu, Ataru Tanikawa, Francesco Flammini Dotti et al. (+6 more)

Aims. We present eight direct N-body simulations with NBODY6++GPU of extremely massive, initially rotating Population III star clusters with 1.01 x 10^5 stars. Methods. Our models include primordial binaries, a continuous initial mass function, differential rotation, tidal mass loss, updated fitting formulae for extremely massive metal-poor Population III stars, and general-relativistic merger recoil kicks. We assess their impact on cluster dynamics. Results. All runs form black holes below, within, and above the pair-instability gap, with multi-generation growth. Faster-rotating clusters core-collapse earlier; post-collapse clusters host a rotating, axisymmetric subsystem of intermediate-mass black holes (IMBHs) at the centre and an expanding halo of lower-mass objects. Pair-instability supernovae and compact-object formation at ~2-3 Myr sharply reduce total mass and a large fraction of the cluster's angular momentum. All Population III clusters in our simulations have the gravothermal-gravogyro catastrophe phase. Conclusions. We confirm two of the hypothesized formation channels of galactic nucleus seed black holes: gravitational runaway mergers of black holes and of Population III stars, which core-collapse into IMBHs thereafter. A higher initial star cluster bulk rotation correlates with earlier core collapse and, in the event counts reported here, with more coalescences and collisions, as well as lower retained (compact) binary abundances. Initial bulk rotation is a primary control parameter of cluster evolution: faster rotation accelerates early angular-momentum transport, gravothermal collapse, mass segregation, and amplifies post-collapse expansion, which also favours the formation of a compact central IMBH subsystem.
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All authors Kai Wu, Ataru Tanikawa, Francesco Flammini Dotti, Marcelo C. Vergara, Boyuan Liu, Albrecht W. H. Kamlah, Manuel Arca Sedda, Nadine Neumayer, Rainer Spurzem

Astrophysics of Galaxies

Constraints on the host galaxy and AGN properties of three z > 6 JWST AGN from NOEMA observations

Giovanni Mazzolari, Hannah Übler, Rodrigo Herrera Camus et al. (+32 more)

We targeted with deep NOEMA observations the [CII]158$\mu$m emission of three JWST-discovered AGN at z>6. Two of them have the typical features of Little Red Dots (LRDs), while the third one is a blue, extended, Type I AGN. We do not significantly detect [CII] emission or dust continuum in any of the targets, even after stacking. The resulting [CII] luminosity upper limits, $\log (L_{[CII]}/L_{\odot})<7.77-8.1$, lie $\sim2\sigma$ below the values expected from the [CII]-SFR relation, and we explore different scenarios to explain the lack of [CII]. We obtained upper limits on the gas masses of $\log (M_{gas}/M_{\odot})<9.26-9.59$ corresponding to $\log( M_{dust}/M_{\odot})<5.68-6.55$ assuming a metallicity dependent dust to gas ratio. Using the continuum non-detections (rms $\sim 16-25 ~\mu Jy$) together with JWST/MIRI constraints, we performed a revised SED-fitting decomposition, resulting in stellar masses up to $\sim 2$ dex lower than previously reported, and implying $0.03\lesssim M_{BH}/M_{*}\lesssim0.7$. For the two LRDs, the SED is well reproduced by stellar emission in the rest-frame UV, while the rising rest-frame optical slope, flattening toward the near-infrared, is consistent with emission from a Type I AGN partially obscured along the polar direction with $E(B-V)_{\rm polar}\simeq 1$, in agreement with attenuation derived from the broad lines Balmer decrement. This decomposition demonstrates that a relatively standard AGN configuration can reproduce the SEDs of the two LRDs, without invoking more exotic scenarios. Finally, we investigate the positions of the three sources in the $IRX-\beta_{UV}$ plane, finding that they lie in a parameter space where galaxies are typically characterized by patchy dust distributions. Our analysis highlights the importance of millimeter constraints to characterize the different physical properties of high-z AGN.
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All authors Giovanni Mazzolari, Hannah Übler, Rodrigo Herrera Camus, Ric Davies, Linda Tacconi, Dieter Lutz, Natascha Förster Schreiber, Francesco D'Eugenio, Minju Lee, Capucine Barfety, Elena Bertola, Andrew Bunker, Andreas Burkert, Jianhang Chen, Giovanni Cresci, Frank Eisenhauer, Juan Manuel Espejo Salcedo, Simon Flesch, Reinhard Genzel, Xihan Ji, Lilian Lee, Daizhong Liu, Cosimo Marconcini, Roberto Maiolino, Thorsten Naab, Amit Nestor Shachar, Meghana Pannikkote, Eleonora Parlanti, Stavros Pastras, Michele Perna, Claudia Pulsoni, Bruno Rodriguez del Pino, Eckhard Sturm, Taro Shimizu, Giulia Tozzi

Solar and Stellar Astrophysics

Multi-hierarchy simulation of Riemann problem for reconnection exhausts

Keita Akutagawa, Shinsuke Imada and Munehito Shoda

Magnetic reconnection drives a wide range of astrophysical plasma phenomena, including solar flares, by converting magnetic energy into plasma energy through changes in magnetic field topology. Petschek reconnection is a magnetohydrodynamic (MHD) model in which magnetic field lines reconnect within a localized diffusion region, and a pair of switch-off slow shocks forms outside this region, enabling efficient energy conversion. Whether this picture remains valid when kinetic effects are included remains an open question. In this study, we examine the formation and properties of slow shocks associated with reconnection exhausts by solving a two-dimensional Riemann problem using a multi-hierarchy framework that couples MHD and particle-in-cell (PIC) simulations. We find that a slow shock close to the switch-off limit forms in the MHD domain even when slow shock formation is suppressed in the PIC domain, and that this behavior is insensitive to the size of the PIC domain. The formation of the slow shock further promotes plasma isotropization within the PIC domain. These results suggest that Petschek-like reconnection remains viable in collisionless-collisional systems, such as solar flares, where temperature anisotropy appears to be relaxed far from the reconnection region.
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Earth and Planetary Astrophysics

Antimatter Propulsion for Interstellar Travel via Positron Production from Potassium-40 Rich Biological Matter

C. Hall and L. N. H. P. Hall

Anitmatter-based propulsion is often cited as a physically plausible route to relativistic interstellar travel, and thus as a potential mechanism by which technologically advanced civilizations could expand throughout the galaxy. Its difficulty may be central to the resolution of Fermi's paradox. Since the Universe should be teaming with advanced technological life, yet we see none, it may be that interstellar travel is simply too difficult. It has been suggested that the main difficulty with using antimatter as propulsion is its limited availability, assuming it must be artificially manufactured. In this paper, we demonstrate that naturally occurring potassium 40 - rich biological matter (specifically bananas) is a promising, overlooked antimatter source for interstellar propulsion.
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Instrumentation and Methods for Astrophysics

StarHash: unique, memorable, and deterministic names for astronomical objects

T. L. Killestein

The naming of astronomical objects has represented among the most significant challenges in the record-keeping of the field since the very beginning. Long and unwieldy coordinate names, uninformative and ambiguous internal names, and the sheer volume of aliases accumulated for some of the most studied objects conspire to complicate our study of the celestial sphere. This paper proposes StarHash, a reproducible, open-source astronomical naming scheme based on the terrestrial concept of geohashing, but re-implemented from the ground up for the rigorous demands of astronomy. Every 3.2 arcsec patch of sky now has three words associated with it, enabling the precise localisation of astronomical sources, and an easily communicable and memorable identifier. A carefully selected wordlist reduces ambiguity due to plurals and homophones, whilst the use of format-preserving encryption minimises residual spatial correlation in StarHash-derived identifiers. Pre-computed names for several existing catalogues are provided, alongside a Python reference implementation for validation and integration into databases, transient brokers, and other similar projects. Although not intended to be the final word in the naming of astronomical objects, StarHash humbly provides a memorable alternative to the status quo, and is intended to spark a discussion about this most foundational of issues in astronomy.
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Instrumentation and Methods for Astrophysics

Brightness, Colour, Polarisation: A Multi-Instrument Observation Campaign of the Gorizont-6 Satellite

Robert J.S Airey, Paul Chote, Klaas Wiersema et al. (+15 more)

We present a coordinated multi-instrument photometric and polarimetric study of the defunct geosynchronous satellite, Gorizont-6. This observation campaign combined wide-field multi-colour observations with simultaneous multi-site photometry and linear polarimetry. Our results demonstrate that the combined simultaneous colour and polarimetric measurements aid in breaking the degeneracy between the fundamental spin period and its harmonics, enabling light curve features to be associated with specific reflecting surfaces. Using phase-dispersion minimisation with bootstrap resampling, we then measure a steadily increasing rotation period across six epochs spanning nine months, well described by a damped exponential curve consistent with Yarkovsky O'Keefe Radzievskii Paddack (YORP) driven spin-down. A geometrical analysis of the multi-site observations provides additional constraints on the spin-axis orientation based on paired glint events. Overall, multi-colour photometry yields efficient, robust period measurements compared with single-band data, while polarimetry supplies the decisive constraints needed for unambiguous rotation-state determination, highlighting the value of combined photometric-polarimetric strategies for characterising defunct satellites.
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All authors Robert J.S Airey, Paul Chote, Klaas Wiersema, Ioannis Apergis, James McCormac, James A. Blake, Benjamin F. Cooke, Isobel S. Lockley, Peter J. Wheatley, Daniel Bayliss, Samuel Gill, Christopher A. Watson, Stefano Covino, Frans Snik, Jon Marchant, Justyn Maund, Brooke Simmons, Iain A. Steele

High Energy Astrophysical Phenomena

Simulating the jittering-jets explosion mechanism: circum-jet rings account for observed core-collapse supernova remnant morphologies

Muhammad Akashi and Noam Soker

We conduct three-dimensional hydrodynamical simulations of core-collapse supernova (CCSN) explosion driven by jets in the framework of the jittering jets explosion mechanism (JJEM), and obtain a pair of opposite circum-jet rings similar to those observed in some CCSN remnants (CCSNRs). We launch two pairs of jets along the same axis, the first of two opposite wide jets, and the second of narrow jets. The wide jets compress the core of a stripped-envelope stellar model to form a dense, fast-expanding shell. The narrow jets catch up with the dense shell, penetrate it, and compress the gas to the sides, forming the two opposite rings. At high inclination angles of the jets' axis to the line of sight, the projection of each ring on the plane of the sky forms two bright zones, where the rings cross the plane of the sky. This morphology explains that of SNR G46.8-0.3. At intermediate inclination angles, the rings are fully visible as two opposite bright elliptical rims. Our simulations explain the two prominent rings on the outer shell of CCSNR G11.2-0.3. Our results strengthen the claim that the JJEM is the primary explosion mechanism of CCSNe.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Gravitational waves from gaps of neutron stars

Akira Dohi, Asuka Ito and Shota Kisaka

The pulsar magnetosphere is a potential source of continuous gravitational waves due to the rapid charge-discharge process in short timescale, varying the electric-field energy density. We estimate the strain of the continuous gravitational waves, considering relativistic effects and different gap regions. We find that the strain from the polar cap is too small, in contrast to previous results. On the other hand, the strain from the outer gap is as large as $\sim2\times10^{-24}$, enough for future gravitational-wave detection such as the Einstein Telescope. Our result presents a new approach for the future detection of gravitational waves to probe the physics in the magnetosphere.
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High Energy Astrophysical Phenomena

Anomaly detection in Fink. I. Discovery, follow-up, and classification of unusual sources

M. V. Pruzhinskaya, M. V. Kornilov, A. V. Dodin et al. (+19 more)

Modern wide-field time-domain surveys produce alert streams whose scientific potential is often concentrated in rare and unusual events. Efficient discovery therefore requires automated pipelines to be combined with rapid expert validation and follow-up. We present the first-year performance of the anomaly-detection (AD) pipeline operating within the Fink broker on the Zwicky Transient Facility alert stream, and assess its ability to identify scientifically valid outliers and enable discovery of rare phenomena. The pipeline transforms ZTF light curves into a compact set of features and ranks alerts using an Isolation Forest model trained on archival ZTF data. Each night, the 10 most anomalous candidates are distributed to experts via Slack/Telegram and exposed through an API. We also implement an expert-feedback loop using a public Telegram bot and retrain the model using the Active Anomaly Discovery algorithm. During the first year of operations (starting from 25 January 2023), the AD pipeline identified multiple high-interest sources and triggered dedicated photometric and spectroscopic follow-up. We report the discovery and multi-instrument (11-m SALT telescope, 2.5-m CMO telescope, 0.6-m ASA RC600, 0.25-m FRAM-ORM) follow-up of the rare AM CVn system Fink J062452.88+020818.3 of the WZ Sge type, UX Ori-type star Fink J222324.32+744222.0 and the unusual transient with precursor SN 2023mtp. In addition, the module triggered 33 supernovae, including 30 previously unreported ones, with candidates for superluminous and hostless events. Furthermore, nine new dwarf novae were discovered. These results show that broker-level anomaly detection, coupled with rapid dissemination, expert assessment, and follow-up observations, provide an effective bridge between large-scale survey streams and domain expertise, turning anomaly scores into astrophysical insights and concrete discoveries.
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All authors M. V. Pruzhinskaya, M. V. Kornilov, A. V. Dodin, A. Baluta, T. A. Pshenichniy, A. M. Zubareva, E. E. O. Ishida, J. Peloton, I. Beschastnov, I. Ippolitov, A. A. Belinski, P. Golysheva, N. P. Ikonnikova, V. A. Kiryukhina, V. V. Krushinsky, A. M. Tatarnikov, S. G. Zheltoukhov, D. A. Buckley, A. Kniazev, S. V. Karpov, A. Möller, Y. Tampo

Astrophysics of Galaxies

Milky Way evolution on a human timescale

Eugene and Neige

How do galaxies form and evolve? This is one of the most puzzling questions in astronomy. Galaxy assembly takes place throughout the entire history of the Universe, but our understanding of it is hampered by the unfortunate fact that we can only observe galaxies at a single moment in time. Here, we use archival data of decades-long monitoring of the Milky Way to examine some of its key characteristics, namely the mass of its central black hole, the pattern speed of the bar, and the distance from the Sun to the Galactic centre. We find a surprisingly fast evolution of these three properties on a timescale of only a few decades, and speculate that it might be driven by shared physical processes.
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