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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 2 January

High Energy Astrophysical Phenomena

Eccentric Disks from Gaseous Rings around Equal-Mass, Circular Binaries

Leonardo Betancourt, Andrew MacFadyen and Jonathan Zrake

We perform high-resolution, grid-based hydrodynamics simulations of gaseous rings viscously spreading into disks around equal-mass, circular binaries. We find that all systems suppress accretion onto the binary when the gas is relatively cold. Circumbinary rings (CBRs) display weak variability above the binary orbital frequency $\Omega_b$ and a dominant spectral peak at $\sim0.1\Omega_b$ (half the fiducial lump frequency of $\sim0.2\Omega_b$). The evolution of CBR eccentricity depends strongly on both the initial ring radius and gas temperature, with smaller, colder rings exhibiting higher eccentricity up to $e \simeq 0.7$. Cold, compact rings develop nearly radius-independent eccentricity profiles, maintaining large $e$ out to several times the initial gas semimajor axis. We find that eccentricity growth favors a stream impact mechanism, in which gas torqued by the binary at pericenter passage exerts a perturbative force on the cavity wall. We consider inefficiently-accreting, intermediate-mass ($\sim10^4 M_\odot$) black hole binaries as sources of quasi-periodic eruptions when rejected streams shock the cavity wall and radiate in the UV or soft X-ray. We discuss the implications of eccentric disks evolved from CBRs for quasar light curves and asymmetric, time-variable double-peaked line emission from disks in galactic nuclei. If binaries drive asymmetry in accretion disk line profiles, our study suggests that the progenitor CBR must have been very compact.
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Astrophysics of Galaxies

One-dimensional and time-dependent modelling of complex organic molecules in protostars

Le Ngoc Tram, Serena Viti, Katarzyna M. Dutkowska et al. (+5 more)

Complex organic molecules (COMs), the building blocks of life, have been extensively detected under various physical conditions, from quiescent clouds to star-forming regions. They therefore serve as excellent tracers for the local physical and chemical properties of these environments. Proper models that are capable of grasping the formation and destruction of COMs are crucial to understanding observations. However, given that distinct COMs may be detected from different locations and at varying times, we improve UCLCHEM - a gas-grain chemical code - to a one-dimensional, time-dependent model, tailored to protostars. In this update, we examine two stages of a protostar: the prestellar and heating stages, incorporating a simple radiative mechanism for both the internal and external radiation fields of the cloud. This approach relies on the key assumption that the dust and gas temperatures are completely coupled. Ultimately, we implement an updated version of our model to interpret observations obtained through both single-dish and interferometry under varying conditions, including a SgrB2(N1) hot core, massive Galactic clumps and a hot core in Orion. We show that our model could reproduce these observations well, highlighting that some COMs are positioned at a higher temperature in the envelope, whereas others are from the lower temperature, potentially leading to misinterpretation when using a single-point model. In a particular case of SgrB2(N1), the best model indicates that the cosmic-ray ionisation rate significantly exceeds the value typically used for the standard interstellar medium. Our model shows as an efficient computational tool particularly useful for better insights into observations of COMs.
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All authors Le Ngoc Tram, Serena Viti, Katarzyna M. Dutkowska, Gijs Vermariën, Tobias Dijkhuis, Audrey Coutens, Timea Csengeri, Thiem Hoang

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

Gravitational instability in partially ionized plasmas: A two-fluid approach

A. P. Misra and V. Krishan

We propose a new two-fluid model for a partially ionized magnetoplasma under gravity, in which electrons and neutrals are treated as a single fluid, while singly charged positive ions are a separate fluid. We observe that the classical result of gravitational instability (also known as Rayleigh-Taylor instability) in fully ionized plasmas becomes significantly modified by the influence of ion-neutral collisions (with frequency $\nu_{\rm{in}}$) and transverse wave numbers ($k_x$ and $k_y$). The instability growth rate can be enhanced or decreased depending on the values of the ratios $\kappa\equiv k_x/k_y$ and $f\equiv\nu_{\rm{in}}/\Omega_{\rm{ci}}$, where $\Omega_{\rm{ci}}$ is the ion-cyclotron frequency. We also estimate the growth rates relevant to the ionospheric E-region and solar atmosphere, noting that such growth rates can have a maximum for $\kappa,~f\ll1$, or for $\kappa>1$ and $f\sim0.64$, and minimized for $f\gg1$ irrespective of the value of $\kappa$. Furthermore, the timescale of instability ranges from $1$ minute to $2$ minutes in the solar atmosphere, while in the E region, it ranges from $1$ minute to $80$ minutes. The latter can be a satisfactory result for the reported lifetime of solar prominence threads.
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Solar and Stellar Astrophysics

Near-Contact Binaries on the Path to Contact Binaries

K. Stȩpień

A comprehensive evolution study was conducted on a carefully selected sample of near-contact binaries (NCBs) with more massive components filling the Roche lobes, utilizing the best-known basic parameters and indications of ongoing mass transfer. The results and discussion highlight that several NCBs with total masses exceeding 2 solar masses survive only a short time after mass exchange as contact binaries (CBs), with both components eventually merging to form a rapidly rotating giant, akin to FK~Com. Less massive NCBs transition into typical CBs and remain in this phase for up to 2 Gyr before ending their binary evolution as systems with extremely low mass ratios, susceptible to Darwin instability. However, this does not fully explain the existence of low-mass CBs with masses in the range of 1-1.5 solar masses. It is noted that there exists a population of low-mass binaries, nearly filling their Roche lobes. Their overall properties suggest that they could be progenitors of low-mass CBs.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Exceptional Lines and Excitation of (Nearly) Double-Pole Quasinormal Modes: A Semi-Analytic Study in the Nariai Black Hole

Nao Nakamoto and Naritaka Oshita

We show that quasinormal modes (QNMs) of a massive scalar field in Kerr-de Sitter and Myers-Perry black holes exhibit an exceptional line (EL), which is a continuous set of exceptional points (EPs) in parameter space, at which two QNM frequencies and their associated solutions coincide. We find that the EL appears in the parameter space spanned by the scalar mass and the black hole spin parameter, and also in the Nariai limit, i.e., $r_{\rm c} - r_{\rm h} \to 0$, where $r_{\rm c}$ and $r_{\rm h}$ denote the radii of the cosmological and black hole horizons, respectively. We analytically study the amplitudes or excitation factors of QNMs near the EL. Such an analytic treatment becomes possible since, in the Nariai limit, the perturbation equation reduces to a wave equation with the Pöschl-Teller (PT) potential. We discuss the destructive excitation of QNMs and the stability of the ringdown near and at the EL. The transient linear growth of QNMs – a characteristic excitation pattern near an EP or EL – together with the conditions under which this linear growth dominates the early ringdown, is also studied analytically. Our conditions apply to a broad class of systems that involve the excitation of (nearly) double-pole QNMs.
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High Energy Astrophysical Phenomena

Hadronic Origin of Sub-PeV Gamma-Ray Emission from LHAASO J0621+3755

Sonali Sahoo, Ankan Roy, Kritika Yadav et al. (+1 more)

Very High Energy (VHE) gamma-rays in pulsars, and their surrounding halos, are interpreted to originate from the leptonic channel, electromagnetic interactions through electron inverse Compton (IC) scattering. In the hadronic scenario, TeV-PeV gamma-rays are generated from the decay of neutral pions, which are produced from cosmic rays(CR) protons interacting with the ambient medium. Recent observations of sub-PeV gamma-rays from the halo of the pulsar PSR J0622+3749 by the Large High Altitude Air Shower Observatory Kilometer-Square Array (LHAASO-KM2A) provide an opportunity to investigate the underlying emission mechanisms. Previous studies have shown that the observed emission can be consistently explained within a leptonic framework by the slow diffusion of electrons. In this work, we explore an alternative explanation based on the hadronic scenario through the proton-proton ($pp$) interaction channel, incorporating the observation of VHE gamma-rays at 7 TeV by the High-Altitude Water Cherenkov detector (HAWC). To model the observed gamma-ray spectrum, ranging from $\sim 7~\mathrm{TeV}$ up to $200~\mathrm{TeV}$, the required CR proton luminosity is found to be $\eta_p \sim 0.14$ of the spin-down luminosity of PSR J0622+3749. This scenario assumes that protons propagate in a one-zone superdiffusive environment, characterized by a diffusion index $\alpha = 1.05$, within an ambient of density, $1~\mathrm{cm}^{-3}$.
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All authors Sonali Sahoo, Ankan Roy, Kritika Yadav, Reetanjali Moharana

High Energy Astrophysical Phenomena

Spectral Shapes of Pair Annihilation Line Emission in Magnetar Giant Flares

Tomoki Wada and Shigeo S. Kimura

We investigate the gamma-ray spectrum in the MeV range arising from electron-positron pair annihilation in fireballs associated with magnetar giant flares (MGFs), motivated by the recent observation of a MeV gamma-ray line feature in a bright gamma-ray burst, GRB~221009A. We develop an analytic model of line emission, demonstrating that relativistic beaming results in a broadened, power-law spectral feature with photon index -1. We then perform Monte Carlo radiative transfer simulations incorporating electron-positron pair production, annihilation, and Compton scattering. The dependence of the emergent spectrum on the baryon loading is also examined, showing that a baryon-poor fireball is more favorable for the detection of MeV gamma rays. We further assess the detectability of the line component. The simulation results indicate that a power-law MeV component from the initial spike of a Galactic MGFs could be observed with current instruments, such as Fermi/GBM, and will be well within the reach of upcoming MeV gamma-ray satellites, which are expected to detect O(100) photons from such events.
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Solar and Stellar Astrophysics

Activity correlation and temporal variation of small-scale magnetic fields on young Sun-like stars

A. Hahlin, B. Zaire, C. P. Folsom et al. (+2 more)

We aim to evaluate how well the variation of small-scale magnetic fields on the stellar surface can be monitored with time-series observations. Further, we aim to establish to what extent the measured total unsigned magnetic field traces other activity indicators. We measured the total unsigned magnetic field on four young, stars using Zeeman splitting of magnetically sensitive spectral lines from high-resolution spectra obtained with the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL. We then characterised the magnetic field variations using both sinusoidal variation and Lomb-Scargle periodograms. We evaluated how the rotational variation of the total unsigned magnetic field strength correlates with the activity indicators S-index, H$\alpha$-index, Ca IRT-index, and the large-scale magnetic field obtained from ZDI maps obtained in earlier studies. We find clear signals of rotational modulation of the total magnetic field on HIP 76768 and tentative detection on Mel 25-5. This is supported both by the sinusoidal fitting and the periodogram. For the other stars, we find no modulation signals of the total magnetic field. We find positive correlations between the total magnetic field and activity indices on all four stars, indicating that indirect magnetic activity indicators trace the underlying magnetic field variability. However, comparing the activity-magnetic field relationship between the stars in our sample shows a significant deviation between activity level and measured magnetic field strength. Small-scale magnetic field variability can be traced using the Zeeman effect on magnetically sensitive lines, provided that the star is sufficiently active. It is also possible to self-consistently recover rotational periods from such measurements. The primary limit for the detection of magnetic field variations is the precision of Zeeman broadening and intensification measurements.
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All authors A. Hahlin, B. Zaire, C. P. Folsom, K. Al Moulla, A. Lavail

Cosmology and Nongalactic Astrophysics

Dissecting the Hubble tension: Insights from a diverse set of Sound Horizon-free H0 measurements

Ioannis Pantos and Leandros Perivolaropoulos

The Hubble tension is commonly framed as a discrepancy between local, late-time measurements favoring $H_0 \approx 73$ km s$^{-1}$ Mpc$^{-1}$ and early-time, Sound-Horizon-based measurements favoring $H_0 \approx 67$ km s$^{-1}$ Mpc$^{-1}$. We challenge this viewpoint by analyzing 88 Sound Horizon Free $H_0$ measurements, categorized into four classes: Distance Ladder measurements using local calibrators; Local $\Lambda$CDM measurements assuming the standard expansion history; Pure Local measurements independent of $H(z)$ shape; and CMB Sound–Horizon–Free measurements using CMB data without the Sound Horizon scale. Our analysis reveals that the 30 Distance Ladder measurements yield $H_0 = 72.73 \pm 0.39$ km s$^{-1}$ Mpc$^{-1}$ ($\chi^2_\nu = 0.72$), while the 58 Distance Ladder-Independent/Sound Horizon Free measurements collectively yield $H_0 = 69.37 \pm 0.34$ km s$^{-1}$ Mpc$^{-1}$ ($\chi^2_\nu = 0.95$), a $6.5\sigma$ tension exceeding the Planck–SH0ES discrepancy. This tension remains significant at a minimum value of $3.9\sigma$ after accounting for correlations. Among categories, Local $\Lambda$CDM measurements favor the lowest value ($H_0 = 67.61\pm 0.96$ km s$^{-1}$ Mpc$^{-1}$), Pure Local yield an intermediate value ($H_0 = 71.03 \pm 0.69$ km s$^{-1}$ Mpc$^{-1}$), and CMB Sound Horizon Free measurements give $H_0 = 69.07 \pm 0.44$ km s$^{-1}$ Mpc$^{-1}$. We conclude that the Hubble tension is better characterized as a discrepancy between the Distance Ladder and all other methodologies, rather than an early-vs-late-time split. We also identify a $2.9\sigma$ internal tension among Distance Ladder Independent/Sound Horizon Free measurements: analyses assuming $\Lambda$CDM systematically recover lower $H_0$ values compared to cosmological-model-independent methods. This suggests either unrecognized systematics in the Distance Ladder or deviations from $\Lambda$CDM or both.
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2601.00650 · 2 Jan · 31 pages 4 figures. Added 5 new measurents. Added comments and references. Main conclusions unchanged. The numerical analysis files used for the construction of the figures may be found at https://github.com/ipantos/Dissecting-the-Hubble-Tension

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Earth and Planetary Astrophysics

Evidence for a Nonzero Eccentricity Superpuff Exoplanet WASP-107 b Using JWST Occultation Observation

Yunke Wu, Zixin Zhang, Xinyue Ma et al. (+6 more)

WASP-107~b is an extremely low-density super-puff exoplanet whose inflated radius and evidence of strong internal heating make it a key target for understanding planetary structure and evolution. Its orbital eccentricity is a critical parameter for testing mechanisms such as tidal heating and high-eccentricity migration, yet previous measurements have remained inconclusive. Due to the large radial velocity jitter caused by stellar activity, and the presence of at least one additional planet in the system, previous radial velocity measurements could not robustly determine the eccentricity of WASP-107~b. Here we combine the new JWST secondary eclipse data with transit timing data from HST, TESS, and JWST to measure the eccentricity of WASP-107~b. Our joint analysis shows that WASP-107~b has an eccentricity of $0.09\pm0.02$, a mass of $0.096\pm0.005 \, M_J$, and an orbital period of $5.721487\pm0.000001$~days. We find the $99.7\%$ lower limit of the eccentricity is about 0.04. These new measurements are consistent with the scenario in which WASP-107~b is in the final stage of high-eccentricity migration. Preliminary estimate shows that eccentricity-driven tidal dissipation can provide a significant contribution to the energy required to sustain the observed radius inflation of WASP-107~b. Our results establish the dynamical status of one of the most intriguing low-density exoplanets known, and offer new insights into its formation and evolution history.
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All authors Yunke Wu, Zixin Zhang, Xinyue Ma, Zhangliang Chen, Wenqin Wang, Shang-Fei Liu, Cong Yu, DiChang Chen, Bo Ma

Cosmology and Nongalactic Astrophysics

The SRG/eROSITA all-sky survey: The morphologies of clusters of galaxies: II. The intrinsic distributions of morphological parameters

J. S. Sanders, Y. E. Bahar, E. Bulbul et al. (+11 more)

X-ray selected surveys of clusters of galaxies have been reported to contain more regular cool core clusters compared to samples selected using the Sunyaev-Zel'dovich (SZ) effect. Morphology population studies on X-ray selected clusters will be biased without taking into account selection, as cool cores are more easily detected at low redshifts, but can be mistaken for point sources at high redshift. eROSITA, aboard SRG, found over 12000 optically-identified clusters in its first survey, eRASS1. Taking account of the selection function obtained from simulations, we obtain using a Bayesian framework the intrinsic distribution of morphological parameters, including the concentration, central density, cuspiness, ellipticity and slosh. We construct scaling relations for the parameters as a function of redshift (z) and luminosity (LX), and study their distribution within z or LX bins. We find that the concentration in a scaled aperture evolves positively with LX, similarly to the central scaled density, and negatively with z. When using a fixed aperture, its evolution with LX is lower, but also dependent on the choice of cluster centre. The mean ellipticity does not significantly evolve with z or LX. eRASS1 clusters show indications of higher concentrations compared to SZ-selected objects, even after taking account the selection; this suggests that if our X-ray selection model is correct SZ-selected clusters may also suffer from morphological selection effects. We compare different parameter distribution models in bins of z and LX. The distribution of concentration and ellipticity is generally consistent with a normal one, but other parameters such as the central density and cuspiness strongly favour more complex distributions. However, modelling of all clusters as a single population generally prefers non-normal distributions. [abridged]
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All authors J. S. Sanders, Y. E. Bahar, E. Bulbul, N. Clerc, J. Comparat, M. Kluge, A. Liu, N. Malavasi, M. E. Ramos-Ceja, T. H. Reiprich, F. Balzer, V. Ghirardini, F. Pacaud, X. Zhang

Earth and Planetary Astrophysics

Irradiated Atmosphere V: Effects of Vertical-Mixing induced Energy Transport on the Inhomogeneity

Wei Zhong, Zhen-Tai Zhang, Bo Ma et al. (+3 more)

Atmospheric variations over time and space boost planetary cooling, as outgoing internal flux responds to stellar radiation and opacity. Vertical mixing regulates this cooling. Our study examines how gravity waves or large-scale induced mixing interact with radiation transfer, affecting temperature inhomogeneity and internal flux. Through the radiative-convective-mixing equilibrium, mixing increases temperature inhomogeneity in the middle and lower atmospheres, redistributing internal flux. Stronger stellar radiation and mixing significantly reduce outgoing flux, slowing cooling. With constant infrared (IR) opacity, lower visible opacity and stronger mixing significantly reduce outgoing flux. Jensen's inequality implies that greater spatial disparities in stellar flux and opacity elevate the ratio of the average internal flux in inhomogeneous columns relative to that in homogeneous columns. This effect, particularly pronounced under high opacity contrasts, amplifies deep-layer temperature inhomogeneity and may enhance cooling. However, with mixing, overall cooling is weaker than without, as both the averaged internal flux of the inhomogeneous columns and that of the homogeneous column decline more sharply for the latter. Thus, while vertical mixing-induced inhomogeneity can enhance cooling, the overall cooling effect remains weaker than in the non-mixing case. Therefore, vertical mixing, by regulating atmospheric structure and flux, is key to understanding planetary cooling.
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All authors Wei Zhong, Zhen-Tai Zhang, Bo Ma, Xianyu Tan, Dong-dong Ni, Cong Yu

Solar and Stellar Astrophysics

Asteroseismology study of a new faint ZZ Ceti J053009.62+594557.0 discovered in WFST

Yang Yonghui, Guo Jincheng, Lin Jie et al. (+16 more)

In this work, we present a detailed asteroseismological analysis of WFST J053009.62+594557.0, a newly discovered faint pulsating white dwarf by the Wide Field Survey Telescope (WFST) with a Gaia G magnitude of 19.13. Analysis of two nights of high-precision WFST g band photometry reveals three significant pulsation frequencies with high signal-to-noise ratios. Follow-up P200/DBSP spectroscopy classifies the object as a DA white dwarf with Teff=11,609 $\pm$ 605 K and M = 0.63$\pm$ 0.22 $M_{\odot}$. To probe its internal structure, we construct asteroseismological models with the White Dwarf Evolution Code (WDEC). After exploring sufficient matching models, best-fitting solutions yield Teff=11,850$\pm$ 10 K and M = 0.600 $\pm$ 0.005 $M_{\odot}$, consistent with independent constraints from Gaia color-magnitude diagram, Gaia XP spectrum, P200 spectral fitting, SED fitting, and Gaia parallax. It has shown that the asteroseismological distance agrees with the Gaia parallax to 1.45%.
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All authors Yang Yonghui, Guo Jincheng, Lin Jie, Wang Tinggui, Jiang Ning, Wang Yibo, Fan Lulu, Fang Min, Li Bin, Li Feng, Liu Hao, Liang Ming, Luo Wentao, Tang Jinlong, Wang Hairen, Wang Jian, Xue Yongquan, Yao Dazhi, Zhang Hongfei

Astrophysics of Galaxies

The impact of cosmic voids on AGN activity

Benedict Rouse, Patricia B. Tissera, Yetli Rosas-Guevara et al. (+1 more)

From the Eagle project, we study the properties of galaxies hosting AGN in cosmic voids and their surrounding structures, filaments and walls, at $z=0$, comparing them to non-AGN galaxies in similar environments. We found that the AGN fraction decreases as a function of void-centric distance, with void galaxies displaying the highest AGN fraction (12%), and galaxies in denser environments, showing the lowest AGN fraction (6.7%), consistent with observations. The AGN fraction is particularly high in most massive void galaxies when controlling for stellar mass. When comparing AGN host galaxies to inactive ones, we find that AGN galaxies tend to have slightly more massive SMBHs, higher specific star formation rates, and reside in higher-mass haloes at a given stellar mass than non-AGN galaxies. At $\rm M_{*} > \rm 10^{10.2} \rm M_{\odot}$, AGN hosts in voids tend to have slightly more massive SMBHs than those in denser environments. Otherwise, the AGN population does not show a clear trend in relation to the global environment. In contrast, non-AGN void galaxies host more massive SMBHs, slightly higher sSFRs, and are located in more massive haloes than those in denser environments. Analysing the recent merger histories of both AGN and non-AGN populations, we find that a larger fraction of massive AGN galaxies have undergone major mergers compared to non-AGN galaxies, regardless of environment. Notably, AGN galaxies in voids show a higher frequency of recent mergers, especially major mergers, than their counterparts in other environments, especially at high stellar mass. Our results suggest that the evolution of SMBHs in voids is closely related to that of their host galaxies and their surrounding environment, while the most recent AGN activity is more strongly linked to recent interactions.
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All authors Benedict Rouse, Patricia B. Tissera, Yetli Rosas-Guevara, Claudia del P. Lagos

Instrumentation and Methods for Astrophysics

ASCNet: Research on all-sky camera images classification at the Muztagh-ata site

Siqi Wang, Qi Fan, Wenbo Gu et al. (+6 more)

Cloud coverage is one of the crucial elements of site testing in astronomy. All-sky camera (ASC) images are beneficial for our research on cloud coverage. In this paper, we propose ASCNet, an innovative model specifically designed for classifying nighttime ASC images collected at the Muztagh-ata site from 2022 March to 2024 June. ASCNet integrates ResNet34 with an ASCModule, which employs Depthwise Dilated Convolution and embeds lightweight Squeeze-and-Excitation attention within its branches to extract fine-grained texture information from the luminance channel. The data set is partitioned by category, with 70% of images assigned to the training set and 30% to the test set. The model's performance is assessed by comparing its predictions on the test set with manually annotated labels, yielding a consistency rate of 92.7%. All evaluation metrics of ASCNet are as follows: Accuracy 92.66%, Precision 83.26%, Recall 84.25%, and F1-Score 83.67%, and both ablation and comparative experiments demonstrate significant superiority over other models. A confusion matrix is utilized to analyze the differences between manual classification and model classification. The statistical results demonstrate the model's excellent classification performance and its robust generalization ability, illustrating that ASCNet has potential for application in future astronomical image classifications.
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All authors Siqi Wang, Qi Fan, Wenbo Gu, Haozhi Wang, AYZADA Jumahali, Lixian Shen, Daiping Zhang, Liyong Liu, Ali Esamdin

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Taxonomy of periodic orbits and gravitational waves in a non-rotating Destounis-Suvorov-Kokkotas black hole spacetime

Zhutong Hua, Zhen-Tao He, Jiageng Jiao et al. (+2 more)

In this paper, we investigate periodic orbits of test particles around a non-rotating Destounis-Suvorov-Kokkotas black hole and the resulting gravitational waves. Firstly, we examine the properties of circular orbits and find that circular orbits could disappear when the deformation is large enough. Then, using an orbital taxonomy, we characterize various periodic orbits with a triplet of integers, which describes the zoom-whirl behaviours. We also calculate the gravitational waveform signals generated by different periodic orbits, revealing the influence of the deformation on the gravitational wave, which can be potentially picked up by future space-based detectors.
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All authors Zhutong Hua, Zhen-Tao He, Jiageng Jiao, Jing-Qi Lai, Yu Tian

Astrophysics of Galaxies

A New Empirical Fit to Galaxy Rotation Curves

David C. Flynn and Jim Cannaliato

We present a new empirical model for galaxy rotation curves that introduces a velocity correction term {\omega}, derived from observed stellar motion and anchored to Keplerian baselines. Unlike parametric halo models or modified gravity theories, this approach does not alter Newtonian dynamics or invoke dark matter distributions. Instead, it identifies a repeatable kinematic offset that aligns with observed rotation profiles across a wide range of galaxies. Using SPARC data [1], we demonstrate that this model consistently achieves high fidelity fits, often outperforming MOND and CDM halo models in RMSE and R-squared metrics without parametric tuning. The method is reproducible, minimally dependent on mass modeling, and offers a streamlined alternative for characterizing galactic dynamics. While the velocity correction {\omega} lacks a definitive physical interpretation, its empirical success invites further exploration. We position this model as a local kinematic tool rather than a cosmological framework, and we welcome dialogue on its implications for galactic structure and gravitational theory. Appendix B presents RMSE and R2 comparisons showing that this method consistently outperforms MOND and CDM halo models across a representative galaxy sample.
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High Energy Astrophysical Phenomena

High-energy Emission from Turbulent Electron-ion Coronae of Accreting Black Holes

Daniel Groselj, Alexander Philippov, Andrei M. Beloborodov et al. (+1 more)

We develop a model of particle energization and emission from strongly turbulent black-hole coronae. Our local model is based on a set of 2D radiative particle-in-cell simulations with an electron-ion plasma composition, injection and diffusive escape of photons and charged particles, and self-consistent Compton scattering. We show that a radiatively compact turbulent corona generates extended nonthermal ion distributions, while producing X-ray spectra consistent with observations. As an example, we demonstrate excellent agreement with observed X-ray spectra of NGC 4151. The predicted emission spectra feature an MeV tail, which can be studied with future MeV-band instruments. The MeV tail is shaped by nonthermal electrons accelerated at turbulent current sheets. We also find that the corona regulates itself into a two-temperature state, with ions much hotter than electrons. The ions carry away roughly two-thirds of the dissipated power, and their energization is driven by a combination of shocks and reconnecting current sheets, embedded into the turbulent flow.
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All authors Daniel Groselj, Alexander Philippov, Andrei M. Beloborodov, Richard Mushotzky

Thursday 1 January

High Energy Astrophysical Phenomena

Discovering pulsars in compact binaries with a hidden Markov model

Joseph O'Leary, Liam Dunn and Andrew Melatos

Discovering radio pulsars in compact binaries, whose orbital periods $P_{\rm b}$ satisfy $P_{\rm b} \lesssim 1 \, \rm{day}$, is computationally challenging, because the time-dependent pulse frequency $f_{\rm p}(t)$ is strongly Doppler modulated by the binary motion. Here we present a new, fast, semi-coherent detection scheme based on a hidden Markov model (HMM) combined with a maximum likelihood matched filter, the Schuster periodogram. The HMM scheme complements traditional acceleration searches by dividing $f_{\rm p}(t)$ into piecewise-constant blocks and tracking the block-to-block evolution efficiently using dynamic programming. Monte Carlo simulations show that the new method can detect compact binaries with flux densities $S \geq 0.50 \, \rm{mJy}$ and orbital periods $P_{\rm b} \geq 0.012 \, \rm{day}$ under observing conditions (e.g.\ cadence) typical of radio pulsar surveys, with and without impulsive, narrowband radio frequency interference. The new method is fast; it employs the classic Viterbi algorithm to solve the HMM recursively. The central processing unit run time scales nominally as $T_{\rm run} \approx 2.8 \, N_B (N_T/10^2) (N_Q \ln N_Q/10^4 \ln 10^4) \, {\rm s}$ for $N_B$ subbands, $N_T$ coherent segments, and $N_Q$ frequency bins.
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Cosmology and Nongalactic Astrophysics

Late-Time Alleviation of the Hubble Tension in CPL Cosmology with Massive Neutrinos via Bayesian Physics-Informed Neural Networks

Muhammad Yarahmadi

We present a Bayesian analysis of the Hubble constant using Physics-Informed Neural Networks (PINNs), applied to the standard wCDM model and its dynamical extension via the Chevallier–Polarski–Linder (CPL) parametrization, with and without a free summed neutrino mass $\Sigma m_\nu$. Embedding the background Friedmann equation into a Bayesian PINN, we reconstruct $H(z)$ in a data-driven, physically consistent way while propagating epistemic uncertainty. Combining Cosmic Chronometers, DESI DR2 BAO, and Pantheon+ supernovae with Planck 2018 CMB distance priors, we quantify the Hubble tension against Planck and SH0ES (R22). For wCDM, BAO-dominated combinations favor lower $H_0$, easing the Planck tension at the cost of a larger SH0ES discrepancy. Letting the equation of state evolve within CPL shifts $H_0$ upward and consistently favors a mildly quintessence-like $w_0 \gtrsim -1$ with negative $w_a$, pointing to a slowly evolving, non-phantom dark energy component. Adding a free $\Sigma m_\nu$ stabilizes $H_0$ between $69.7$ and $71.6~\mathrm{km\,s^{-1}\,Mpc^{-1}}$, bounds $\Sigma m_\nu \lesssim 0.16$–$0.28~\mathrm{eV}$ ($2\sigma$), and reduces the SH0ES tension below $1.8\sigma$ (down to $0.83\sigma$) while the Planck tension persists at $1.6$–$2.8\sigma$. AIC and BIC both favor CPL+$\Sigma m_\nu$ despite its extra parameters, arguing against overfitting. A full-CMB MCMC cross-check via Cobaya, including CMB lensing, reproduces the BPINN posteriors – including the neutrino-mass bound – within 1–2$\sigma$ at a fraction of the cost. A mildly evolving dark energy component combined with sub-eV neutrino masses thus substantially eases, though does not fully resolve, the Hubble tension, supporting Bayesian PINNs as an efficient, physically consistent tool for precision cosmology beyond $\Lambda$CDM.
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Instrumentation and Methods for Astrophysics

Spectral performance of single-channel plastic and GAGG scintillator bars of the CUbesat Solar Polarimeter (CUSP)

Nicolas De Angelis, Abhay Kumar, Sergio Fabiani et al. (+45 more)

Our Sun is the closest X-ray astrophysical source to Earth. As such, it makes a formidable case study to better understand astrophysical processes. Solar flares are in particular very interesting as they are linked to coronal mass ejections as well as magnetic field reconnection sites in the solar atmosphere. Flares can therefore provide insightful information on the physical processes at play on their production sites, but also on the emission and acceleration of energetic charged particles towards our planet, making it a formidable forecasting tool for space weather. While solar flares are critical to understanding magnetic reconnection and particle acceleration, their hard X-ray polarization – key to distinguishing between competing theoretical models – remains poorly constrained by existing observations. To address this, we present the CUbesat Solar Polarimeter (CUSP), a mission under development to perform solar flare polarimetry in the 25-100 keV energy range. CUSP consists of a 6U-XL platform hosting a dual-phase Compton polarimeter. The polarimeter is made of a central assembly of four 4x4 arrays of plastic scintillators, each coupled to multi-anode photomultiplier tubes, surrounded by four strips of eight elongated GAGG scintillator bars coupled to avalanche photodiodes. Both types of sensors from Hamamatsu are respectively read out by the MAROC-3A and SKIROC-2A ASICs from Weeroc. In this manuscript, we present the preliminary spectral performances of single plastic and GAGG channels measured in the laboratory using development boards of the ASICs foreseen for the flight model.
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All authors Nicolas De Angelis, Abhay Kumar, Sergio Fabiani, Ettore Del Monte, Enrico Costa, Giovanni Lombardi, Alda Rubini, Paolo Soffitta, Andrea Alimenti, Riccardo Campana, Mauro Centrone, Giovanni De Cesare, Sergio Di Cosimo, Giuseppe Di Persio, Alessandro Lacerenza, Pasqualino Loffredo, Gabriele Minervini, Fabio Muleri, Paolo Romano, Emanuele Scalise, Enrico Silva, Davide Albanesi, Ilaria Baffo, Daniele Brienza, Valerio Campomaggiore, Giovanni Cucinella, Andrea Curatolo, Giulia de Iulis, Andrea Del Re, Vito Di Bari, Simone Di Filippo, Immacolata Donnarumma, Pierluigi Fanelli, Nicolas Gagliardi, Paolo Leonetti, Matteo Mergè, Dario Modenini, Andrea Negri, Daniele Pecorella, Massimo Perelli, Alice Ponti, Francesca Sbop, Paolo Tortora, Alessandro Turchi, Valerio Vagelli, Emanuele Zaccagnino, Alessandro Zambardi, Costantino Zazza

Solar and Stellar Astrophysics

Betelgeuse: Detection of the Expanding Wake of the Companion Star

Andrea K. Dupree, Paul I. Cristofari, Morgan MacLeod et al. (+1 more)

Recent analyses conclude that Betelgeuse, a red supergiant star (HD 39801), likely has a companion object with a period of about 2000 days orbiting at only 2.3 stellar radii, deep in the chromosphere of the supergiant. A probable detection of such a companion, named Siwarha, has just occurred from speckle imaging. This study finds that Betelgeuse spectra in the optical region and ultraviolet exhibit signatures of variable circumstellar absorption and chromospheric outflows. These variations are consistent with the ~ 2000-day period of the companion object. Circumstellar absorption evident in optical Mn I lines, and mass outflow marked by ultraviolet Fe II, Si I, and Mg I lines increase after the transit of the companion across the disk of Betelgeuse. Following the eclipse of the companion, the absorption and outflow slowly decrease in advance of the next transit. The occurrence and variation of this plasma appear consistent with the presence of a trailing and expanding wake caused by a companion star orbiting within the atmosphere of Betelgeuse.
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All authors Andrea K. Dupree, Paul I. Cristofari, Morgan MacLeod, Kateryna Kravchenko

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

Terrestrial Test of Shapiro Time Delay: Forth test of Einstein General Theory of Relativity

Farhad Hakimi and Hosain Hakimi

The Shapiro time delay is one of the four classical tests of Einstein general theory of relativity and is commonly interpreted as a constrain on the parametrized post Newtonian (PPN) parameter gamma, which is exactly unity in general relativity. To date all measurement of the Shapiro time delay have been confined to astrophysical and solar system observations, yielding constrains on the PPN parameter gamma at the 10-5 level. In this work, we propose a fiber based Sagnac interferometer for precision terrestrial measurements of the Shapiro time delay, enabling a laboratory scale determination of gamma with an intrinsic sensitivity approaching 10-9. This approach provides an independent test of general relativity in a previously unexplored regime.
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Solar and Stellar Astrophysics

The Solar Neighborhood LV: Spectral Characterization of an Equatorial Sample of 580 K Dwarfs

Hodari-Sadiki Hubbard-James, Sebastian Carrazco-Gaxiola, Todd J. Henry et al. (+5 more)

We present a spectroscopic characterization of 580 K dwarfs within 33 pc, observed with the CHIRON echelle spectrograph (R=80,000) on the SMARTS 1.5m telescope. This volume-limited sample is part of the RKSTAR survey of $\sim$4400 K dwarf primaries within 50 pc. Using Empirical SpecMatch and the diagnostic lines H-alpha (6562.8 Angstrom) and Li I (6707.8 Angstrom), we derive stellar properties, activity status, and age indicators calibrated against 35 benchmark K dwarfs with ages from 20 Myr to 5 Gyr. We find that 7.4% (43 stars) exhibit signatures of youth and/or chromospheric activity: 19 stars show lithium absorption indicating ages $<$1 Gyr, and 36 display H$\alpha$ emission. Kinematic analysis using BANYAN $\Sigma$ identifies 8 additional young stars through membership in the AB Doradus moving group and the Hyades cluster, bringing the total young/active population to 8.8% (51 stars). Stellar parameters span 3600–5500 K in \teff, $-$0.60 to $+$0.55 dex in [Fe/H], and $<$10 to $>$25 km s$^{-1}$ in $v\sin i$. A metal-poor population ([Fe/H] $\leq -$0.50 dex) comprises 4% of the sample. Galactic kinematics place 80% in the thin disk and 18.4% in the thick disk, with one halo member (HD 134439). Young and active stars are predominantly thin disk members, with two thick disk exceptions. Cross-matching with NASA's Exoplanet Archive reveals only 7.5% (44 stars) host confirmed planets as of July 2025. Our results identify 529 mature, inactive K dwarfs as prime targets for terrestrial planet searches, providing a crucial resource for exoplanet habitability studies in the solar neighborhood.
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All authors Hodari-Sadiki Hubbard-James, Sebastian Carrazco-Gaxiola, Todd J. Henry, Leonardo A. Paredes, Azmain H. Nizak, Xavier Lesley-Saldaña, Wei-Chun Jao, Abigail Arbogast

Cosmology and Nongalactic Astrophysics

Late Time Magnetogenesis from Ultralight Scalar Dark Matter

V. Kamali and R. Brandenberger

Assuming that Dark Matter is an ultralight scalar field which is coupled to electromagnetism via a gauge-kinetic function and which at the time of recombination is oscillating coherently over a Hubble patch, we show that there is a tachyonic instability for the gauge field modes which leads to the generation of magnetic fields on cosmological scales of sufficient amplitude to explain observations.
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High Energy Astrophysical Phenomena

Magnetic plasmoid explosions in the context of magnetar giant flares and fast radio bursts

Konstantinos N. Gourgouliatos

Magnetar flares are highly energetic and rare events in which intense X and {\gamma}-ray emission is released from strongly magnetised neutron stars. The events are also accompanied by mass ejection from the neutron star. Fast radio bursts are short and intense pulses of coherent radio emission. Their large dispersion measures support an extragalactic origin. While their exact origin still remains elusive, a substantial number of models associates them with strong magnetic field and high-energy relativistic plasma found in the vicinity of magnetars. There is growing evidence that some fast radio bursts are associated with flare-type events from magnetars. We provide a set of configurations describing a relativistic, spherical, magnetic plasmoid explosion. We proceed by solving the equations of relativistic magnetohydrodynamics for a system that expands while maintaining its internal equilibrium. We find the interdependent relation between pressure, mass density, Lorentz factor, and magnetic field that determines the detailed properties of the solutions. A dichotomy of solutions exists that correspond to higher and lower density and thermal pressure compared to the external one. For stronger toroidal magnetic fields, the maximum permitted expansion velocity becomes lower than the weaker toroidal fields. These solution classes can be applied to magnetar giant flares and fast radio bursts. Those that corresponding to over densities and higher pressure can be associated with magnetar flares, and those corresponding to underdensities can be relevant to fast radio bursts that correspond to magnetically dominated events with low mass loading. [Abridged]
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Solar and Stellar Astrophysics

A global view of post-interaction white dwarf-main sequence binaries

Cheyanne Shariat and Kareem El-Badry

Common-envelope evolution (CEE) is among the most uncertain phases in binary evolution. To empirically constrain CEE, we construct a uniformly selected sample of eclipsing post–common-envelope binaries (PCEBs). Starting from an unresolved white dwarf-main-sequence (WDMS) candidate sample within 200 pc selected from the Gaia color-magnitude diagram, we identify 39 detached eclipsing WDMS binaries using ZTF light curves. The binaries contain cool M dwarfs orbiting warm white dwarfs with orbital periods ($P_{\rm orb}$) of 0.1-2 d. The sample's simple selection function allows us to model observational incompleteness and infer intrinsic properties of the PCEB population. We find an orbital-period distribution consistent with being log-uniform over 0.1-2 d, contrary to recent reports of a bimodal distribution. The companion-mass distribution peaks around $0.25~{\rm M_\odot}$ and declines steeply toward larger masses. The estimated local space density is $7.2\times10^{-5}~{\rm pc^{-3}}$, corresponding to a Galaxy-wide birth rate of 0.01 per year. Combining our results with recent Gaia-based constraints on wider WDMS binaries, we construct an empirical period distribution of post-interaction WDMS binaries spanning 0.1-1000 d. The emerging period distribution is roughly log-flat (d$N/{\rm d}\log P_{\rm orb}\propto P_{\rm orb}^0$) at $P_{\rm orb} < 2$ d and log-increasing (d$N/{\rm d}\log P_{\rm orb}\propto P_{\rm orb}^1$) at $P_{\rm orb} = 100-1000$ d. The 10-100 d regime remains poorly constrained, but a few nearby systems suggest it is also well-populated. Short-period PCEBs ($P_{\rm orb}<2$ d) with M dwarf companions are roughly 2-3 times more common than wide ($P_{\rm orb} = 100-1000$ d) WDMS binaries with FGK companions, which likely formed through stable mass transfer. These results provide direct observational constraints on CEE and an empirical benchmark for binary-population models.
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Cosmology and Nongalactic Astrophysics

Fisher Forecasts for Cosmological Yields from $3\!\times\!2$pt Analysis of the Roman Space Telescope High Latitude Imaging Survey

Kaili Cao, David H. Weinberg, Vivian Miranda et al. (+5 more)

The High Latitude Imaging Survey (HLIS) of NASA's Nancy Grace Roman Space Telescope will provide powerful tests of cosmological models through sensitive measurements of cosmic shear, galaxy-galaxy lensing (GGL), and galaxy clustering. As part of the HLIS Project Infrastructure Team's Data Challenge 1 (DC1), we carry out Fisher forecasts of cosmological parameter constraints from combinations of these probes, focusing on inverse-variance figures of merit (FoMs) for the parameters $\sigma_8$ and $\Omega_{\rm{m}}$, which scale the amplitude of weak lensing signals. We find good agreement between Fisher analysis and Markov chain Monte Carlo (MCMC) analysis of the DC1 baseline data vector, and we investigate varied priors on cosmological parameters and on nuisance parameters describing unknown biases in photometric redshifts or shear measurements. The DC1 benchmark modeling assumes a “lens $=$ source” analysis with linear galaxy bias and no marginalization over baryonic physics. Under these assumptions, the forecast constraints from GGL+clustering are substantially stronger than those from cosmic shear, with the combination of all three probes (“$3\!\times\!2$pt”) providing moderate further improvement. Adding tight external priors on the power spectrum shape parameters $n_{\rm{s}}$, $\Omega_{\rm{b}}$, and $h_0$ can improve the $(\sigma_8, \Omega_{\rm{m}})$ FoMs by factors of $1.2$–$3.5$. The smallest scale angular bins provide much more information than the largest scale bins, and the highest redshift tomographic bins provide more information than the lowest redshift bins. Factor-of-two changes in the priors on photo-$z$ and shear biases, relative to the benchmark values based on anticipated calibration accuracy, produce changes of $\lesssim 20\%$ in FoMs.
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All authors Kaili Cao, David H. Weinberg, Vivian Miranda, Nihar Dalal, Tim Eifler, Jiachuan Xu, Haley Bowden, Katarina Markovič

Astrophysics of Galaxies

Low Metallicity Gas on the Outskirts of the Local Group: the Circumgalactic Medium of Sextans B

Andrew J. Fox, Sapna Mishra, Frances H. Cashman et al. (+6 more)

We present a UV absorption-line analysis of the circumgalactic medium (CGM) of Sextans B, a dwarf irregular galaxy at 1.3 Mpc distance on the outer frontier of the Local Group. Using HST/COS spectroscopy of two AGN sightlines passing through the Sextans B CGM at small impact parameters of 4 kpc and 8 kpc (0.04 and 0.08 r_vir), we detect the CGM in Si II, Si III, Si IV, and C II absorption. All four ions show a column-density profile that declines with radius. The profiles fall below the average CGM profiles of other nearby dwarfs (by 0.3-0.6 dex, depending on ion), likely due to the low halo mass and low metallicity of Sextans B. Using Cloudy photoionization models and interferometric measurements of the H I column density, we find low gas-phase silicon and carbon abundances in the Sextans B CGM, [Si/H]=-1.7+/-0.2 and [C/H]=-2.1+/-0.2, among the lowest gas-phase abundances anywhere in the Local Group. We calculate a cool CGM gas mass within 8 kpc of $\sim4\times10^7 M_\odot$, comparable to the H I mass and the stellar mass of Sextans B.
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All authors Andrew J. Fox, Sapna Mishra, Frances H. Cashman, David M. French, Philipp Richter, Rongmon Bordoloi, Nicolas Lehner, Jason Tumlinson, Sanchayeeta Borthakur

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Anatomy of RHN DM relic in the vanilla scotogenic neutrino mass model

Sujit Kumar Sahoo, Narendra Sahu and Vicky Singh Thounaojam

The scotogeneic neutrino mass models are very popular choices to generate light neutrino masses via radiative mechanism. In these models, the particles running in the loop are distinguished from the standard model due to an imposed $\mathcal{Z}_2$ symmetry under which the loop particles are odd. Therefore, the lightest particle running in the loop can be a viable dark matter candidate. In this paper, we revisit the minimal scotogenic neutrino mass model and study the anatomy of right handed neutrino (RHN) DM relic, taking into account contributions from self-annihilation, co-annihilation, conversion-driven processes, as well as production via the freeze-in mechanism. We impose the constraints from direct detection and collider searches of DM including anomalous magnetic moment of muon, charged lepton flavor violation and low-energy neutrino oscillation data to show that the lightest RHN can be a viable DM in the mass range: $M_{h}/2\lesssim M_{\rm DM}\lesssim2000 {\rm GeV}$ (thermal DM) and $0.1 ~{\rm GeV}\lesssim M_{\rm DM}\lesssim 1000 {\rm GeV}$ (non-thermal DM), where $M_h$ denotes the Standard Model Higgs mass and $M_{\rm DM}$ is the RHN dark matter mass. We also find the displaced vertex signatures of long lived particles which can be probed at future colliders.
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