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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 10 November

Cosmology and Nongalactic Astrophysics

Starobinsky Inflation and the Latest CMB Data: A Subtle Tension?

J. Bezerra-Sobrinho and L. G. Medeiros

We analyze the Starobinsky inflation model and the impact of curvature corrections, particularly a cubic $R^3$ term, to assess their behavior in light of the latest observational results from the Atacama Cosmology Telescope (ACT). With the recent sixth data release (DR6), the scalar spectral index was measured to be $n_s=0.9743 \pm 0.0034$, which appears to exclude the pure Starobinsky model at approximately the $2\sigma$ level. In this paper, we implement the Starobinsky inflationary potential directly into the CLASS code, without relying on the slow-roll approximation, and we constrain the number of e-folds of inflation $N_k$ using a theoretically motivated range derived from reheating considerations and standard couplings between matter fields and gravity. We show that it is still possible to identify a significant region of parameter space where the Starobinsky model remains highly consistent with the latest observational data. While the pure Starobinsky model remains a compelling candidate for cosmic inflation, we explore how including a cubic $R^3$ term can shift its predictions to better align with the Planck and ACT measurements.
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Astrophysics of Galaxies

PHANGS-JWST: the largest extragalactic molecular cloud catalog traced by polycyclic aromatic hydrocarbon emission

Z. Bazzi, D. Colombo, F. Bigiel et al. (+25 more)

High-resolution JWST images of nearby spiral galaxies reveal polycyclic aromatic hydrocarbon (PAH) emission structures that trace molecular gas, including CO-dark regions. We identify ISM cloud structures in PHANGS-JWST 7.7 $\mu$m PAH maps for 66 galaxies, smoothed to 30 pc and at native resolution, extracting 108,466 and 146,040 clouds, respectively. Molecular properties were inferred using a linear conversion from PAH to CO. Given the tendency for clouds in galaxy centers to overlap in velocity space, we opted to flag these and omit them from the analysis in this work. The remaining clouds correspond to giant molecular clouds, such as those detected in CO(2-1) emission by ALMA, or lower surface density clouds that either fall below the ALMA detection limits of existing maps or genuinely have no molecular counterpart. Cross-matching with ALMA CO maps at 90 pc in 27 galaxies shows that 41 % of PAH clouds have CO associations. The converted molecular properties vary little across environments, but the most massive clouds are preferentially found in spiral arms. Fitting lognormal mass distributions down to $2\times10^{3} M_{\odot}$ shows that spiral arms host the highest-mass clouds, consistent with enhanced formation in arm gravitational potentials. Cloud molecular surface densities decline by a factor of $\sim 1.5-2$ toward $2 - 3 R_{e}$. However, the trend largely varies in individual galaxies, with flat, decreasing, and even no trend as a function of galactocentric radius. Factors like large-scale processes and morphologies might influence the observed trends. We publish two catalogs online, one at the common resolution of 30 pc and another at the native resolution. We expect them to have broad utility for future PAH clouds, molecular clouds, and star formation studies.
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All authors Z. Bazzi, D. Colombo, F. Bigiel, A. K. Leroy, E. Rosolowsky, K. Sandstrom, A. Duarte-Cabral, H. Faustino Vieira, M. I. N. Kobayashi, H. He, S. E. Meidt, A. T. Barnes, R. S. Klessen, S. C. O. Glover, M. D. Thorp, H.-A. Pan, R. Chown, R. J. Smith, D. A. Dale, T. G. Williams, A. Amiri, S. Dlamini, J. Chastenet, S. K. Sarbadhicary, A. Hughes, J. C. Lee, L. Hands, the PHANGS collaboration

Astrophysics of Galaxies

Globular clusters of the Gaia Enceladus/Sausage – I. Orbital and dynamical evolution on cosmological timescales

Mykyta Bilodid, Maryna Ishchenko and Peter Berczik

We investigated Gaia-Enceladus/Sausage globular cluster samples and studied their orbital and dynamical evolution over cosmological timescales in external time-variable potential. We estimated the limits of distribution of the escaped stars from the globular clusters' orbital evolution in energy angular momentum space. To reconstruct the orbital evolution of the known globular clusters of the dwarf galaxy Gaia-Enceladus/Sausage, we used the parallel $N$-body code $\varphi$-GPU. We investigated the relationship between globular clusters and their progenitor by analysing their orbital parameters and phase-space distribution during 9 Gyr of evolution in the past. We created a $N$-body model of Gaia-Enceladus/Sausage globular clusters and analysed their dynamical evolution and distribution of the escaped stars today. We summarised the samples of the Gaia-Enceladus/Sausage globular clusters and created two main categories: `most probable' and `tentative', with 15 and 9 clusters, respectively. We analysed the evolution of their kinematic, orbital, and phase-space parameters in the external time-variable potential. We defined phase-space distribution limits of stars that escape from globular clusters during 9 Gyr of evolution: a specific energy from -18 to -12.2 $\times10^4$ km$^2$ s$^{-2}$, L$_{\rm z}$ from -0.98 to 0.72 $\times10^3$ kpc km s$^{-1}$, and L$_{\rm perp}$ from 0 to 1.8 $\times10^3$ kpc km s$^{-1}$. The limits of the GE/S debris in Galactic area based on orbital parameters of the GC's escaped stars are: for apocentre and pericetre distances of 10–28 and 1–4 kpc, < 18 kpc in Galactocentric radius and < |15| kpc in the Z direction. Generally we compared the phase-space distribution of escaped stars from the GCs GE/S debris energy-angular momentum limits with the observed very metal-poor stars, which belong to the GE/S itself and produce consistent results.
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Sunday 9 November

Earth and Planetary Astrophysics · Cross-listed from physics.bio-ph

Abiogenesis on Different Star Types; a Dissipative Photochemical Perspective

Andrés Ledesma and Karo Michaelian

From the non-equilibrium thermodynamic perspective of the origin of life as a photochemical dissipative structuring (entropy driven) process, we assess the probability of carbon-based life arising on Earth-like analogues orbiting different main-sequence stellar types (O7 V to M2 V). Using black-body spectra normalized to Earth's solar constant, we calculate surface photon fluxes for an atmosphere like early Archean Earth's in the productive dissipative structuring (P, soft UV-C + UV-B, 205-320 nm) and destructive ionization (D, hard UV-C + EUV, <205 nm) regions. Stationary concentrations of fundamental molecules and times to reach 99% of these are computed for different chemical degradation (e.g., deamination, hydrolysis, oxidation, etc.) rate constants of k = 10^{-7}, 10^{-6}, and 10^{-5} s^{-1}. For a nominal chemical degradation rate constant of k = 10^{-6} s^{-1} (t_{1/2}= 8 days), results show F-, G-, and K-type stars provide the highest stationary concentrations of fundamental molecules and short rise times (weeks to months), while quiescent M-type stars yield extremely low concentrations (~10^{-7} relative to G stars) and require years to reach even these values. Flaring M stars improve stationary concentrations by about an order of magnitude (~10^{-6} relative to G stars) but produce adverse planet surface environments for complex evolution through dissipative structuring. From this non-equilibrium thermodynamic perspective, carbon-based life like Earth's is to be found most probably on F-, G-, and high-mass K-type stars, with intelligent life arising only on G-type stars. Low mass K- and M-dwarfs are highly unlikely to harbor life unless seeded via panspermia. Biosignatures related to the thermodynamic imperative of photon dissipation are proposed.
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High Energy Astrophysical Phenomena

Formation Channels of Magnetars

Rui-Chong Hu and Bing Zhang

The formation channels of magnetars remain an open question. Although core collapse supernovae of isolated massive stars are important, binary interactions – such as tidal interaction, common envelope evolution, and stellar mergers – may also play a significant role in making magnetars. Understanding the relative contributions of these channels is crucial for linking magnetars to their observed properties and host environments. In this paper, we investigate potential magnetar formation channels using population synthesis simulations, considering both single-star and isolated binary system evolution. By conducting simulations with different parameters, we compare the effects of various evolution processes on magnetar formation. Additionally, we study the delay times and kick velocities across all formation channels, analyze the orbital properties and companion types of surviving magnetar binaries. We find that the majority of magnetars are observed as single objects ($\geq 90\%$), although a large fraction of them were originally in binary systems and experienced either kick disruption or merger. Surviving binaries are most likely to host main-sequence companions and exhibit different distributions of eccentricities due to different supernova mechanisms. These findings show the critical role of binary evolution in magnetar formation and provide predictions for the properties of magnetar populations that can be tested with future observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Stochastic Limit of Growing Gravitational Wave Memory from Sources in the Early Universe and Astrophysical Sources

Lydia Bieri

We show that the stochastic background of gravitational wave memory of growing type leads to a fractional Brownian motion increasing at the order of $t^{H}$ for large $t$ where $\frac{1}{2} < H <1$. This beats the scaling law of Brownian motion. In this article we investigate sources of gravitational waves in the early universe as well as in astrophysical settings. Cosmological sources may include primordial black holes or other sources immediately after the Big Bang when there were pockets of hot material, and large density fluctuations. Gravitational waves from mergers of primordial black holes produce memory. We show that due to the conditions in which these are taking place the gravitational wave memory will be increasing in time following a certain power law. Corresponding results hold for any gravitational wave memory from a cosmological source where the surrounding conditions are similar. The stochastic limit of these memories is a stochastic process growing in time faster than the $\sqrt{t}$ scaling law of Brownian motion. The latter is also typical for noise and for the limit of memory events as they have been mostly considered in the literature. In an expanding universe, the memory is enhanced by the expansion itself. Our results provide a tool to extract gravitational wave sources of this type from data using this memory signature. This would be particularly useful for the PTA data that has been already observed, answering the long-standing question on how to extract memory signals from the data. Further, the new results open up a new door to explore the conditions right after the Big Bang using the long-range dependence and further probability analysis.
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Solar and Stellar Astrophysics

LRPayne: Stellar parameters and abundances from low-resolution spectra

Nagaraj Vernekar, Lorenzo Spina, Sara Lucatello et al. (+4 more)

Aims. This paper introduces LRPayne, a novel algorithm designed for the efficient determination of stellar parameters and chemical abundances from low-resolution optical spectra, with a primary focus on data from large-scale galactic surveys such as WEAVE. Methods. LRPayne employs a model-driven approach, utilising a fully connected artificial neural network (ANN), trained on a library of 70,000 synthetic stellar spectra generated using iSpec with 1D MARCS model atmospheres and the Turbospectrum synthesis code. The network is trained to predict normalized flux given stellar labels (Teff, log(g), [Fe/H], vmic, vmax and v sin i, and 24 individual elemental abundances). Stellar parameters are subsequently derived from observed spectra by finding the best-fit synthetic spectrum from the ANN using a chi-squared minimisation technique. The method operates on spectra degraded to a resolution of R=5000 covering the wavelength range 4200-6900 Å. Results. Internal accuracy tests on synthetic spectra show a median interpolation error of less than 0.13 % for 90 % of the validation sample. The method accurately recovers most input labels from synthetic spectra, even at a signal-to-noise ratio (S/N) of 20, with some expected challenges for elements like Li, K, and N. Validation on observed spectra of 25 Gaia FGK benchmark stars and 42 metal-poor stars reveals good agreement with literature values. For stellar parameters, mean differences are 22+-87 K for Teff , 0.19+-0.23 dex for log(g), and 0.01+-0.17 dex for [Fe/H]. Abundances for elements like Na, Mg, Si, and most Fe-peak elements (Cr, Ni, V, Sc) are well-recovered. Challenges are noted for oxygen, manganese in metal-rich giants, aluminium in metal-poor stars and dwarfs, and for deriving log g in hot metal-poor dwarfs, partly due to non-local thermodynamic equilibrium effects and line characteristics.
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All authors Nagaraj Vernekar, Lorenzo Spina, Sara Lucatello, Carmelo Arcidiacono, Luca Cortese, Matteo Simioni, Andrea Balestra

Astrophysics of Galaxies

Resolved Schmidt-Kennicutt relation in a binary hyperluminous infrared galaxy at $z=2.41$

Jonathan S. Gómez, Hugo Messias, Neil M. Nagar et al. (+3 more)

Hyperluminous infrared galaxies (HyLIRGs; SFRs up to about 1000 Msun yr-1), though rare, provide key constraints on galaxy evolution. H-ATLAS J084933.4+021443, a z = 2.41 binary HyLIRG (galaxies W and T) with two additional luminous companions (C and M), offers an ideal laboratory for studying star formation during "cosmic noon". We use ALMA to obtain resolved imaging and kinematics of CO J:7-6, [C I] 2-1, H2O, and rest-frame 340-1160 GHz continuum emission in all four galaxies. Each system is spatially resolved within ~0.3 arcsec (2.5 kpc) apertures. Gas kinematics in W and T are rotation-dominated, with galaxy T showing emission extended along its kinematic minor axis due to lensing magnification. Spatially resolved SEDs indicate that W is well fitted by single-temperature greybody dust despite hosting a luminous AGN, while T requires an additional hot-dust component and extra millimetre emission. We confirm [C I] J:2-1 as a tracer of warm/dense molecular gas in these extreme systems, though its luminosity ratio with CO J:7-6 rises sub-linearly. We derive resolved (2.5 kpc-scale) Schmidt-Kennicutt (SK) relations for W and T using both cold and warm/dense gas, finding depletion times of about 50-100 Myr (W) and about 100-500 Myr (T). Both galaxies follow a steep SK relation with power-law index n ~ 1.7, significantly above the n ~ 1 observed in normal star-forming galaxies.
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All authors Jonathan S. Gómez, Hugo Messias, Neil M. Nagar, Gustavo Orellana-González, R. J. Ivison, Paul van der Werf

Solar and Stellar Astrophysics

Total solar eclipse 2024 modelling with COCONUT

Tinatin Baratashvili, Haopeng Wang, Daria Sorokina et al. (+2 more)

Coronal modelling is crucial for a better understanding of solar and helio-physics. Due to the strong brightness of the Sun and the lack of white light observations of the solar atmosphere and low corona (1-1.5R$_\odot$), total solar eclipses have become a standard approach for validating the coronal models. In this study, we validate the COCONUT coronal model by predicting the coronal configuration during the total solar eclipse on April 8, 2024. We aim to predict the accurate configuration of the solar corona during the total solar eclipse on April 8, 2024. We utilise the full 3D MHD model to reconstruct the solar corona from the solar surface to $30\;R_\odot$. The upcoming total solar eclipse predictions were conducted in three different regimes: quasi-steady driving of the inner boundary conditions (BCs) with a daily cadence and dynamic driving of the inner BCs with both daily and hourly cadences. The results from all the simulations are compared to the total solar eclipse images. Additionally, the synthetic white-light (WL) images are generated from the STEREO-A field of view and compared to COR2 observed images. Normalised polarised brightness is compared in the COR2 and synthetic WL images. The predicted solar corona does not vary significantly in the first half of the prediction window. The dynamic simulations yielded better results than the quasi-steady predictions. The west limb was reconstructed better in the simulations than the east limb. We have predicted the total solar eclipse coronal configuration 18 days before the total solar eclipse. We can conclude that the dynamic simulations produced more accurate predictions. The availability of comprehensive observations is crucial, as the emergence of the active region on the east limb made it difficult to accurately predict the east limb coronal configuration due to incorrect input of magnetic field data.
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All authors Tinatin Baratashvili, Haopeng Wang, Daria Sorokina, Andrea Lani, Stefaan Poedts

Solar and Stellar Astrophysics

Investigating the impact of the dynamic solar wind on the propagation of a coronal mass ejection with two models and multi-spacecraft measurements

Tinatin Baratashvili, Emma Davies, Eva Weiler et al. (+3 more)

Coronal mass ejections (CMEs) are the main drivers of disturbances in the solar heliosphere because they propagate and interact with the magnetic field of the solar wind. It is crucial to investigate the evolution of CMEs and their deformation for understanding the interaction between the solar wind and CMEs. We quantify the effect of the dynamic solar wind on the propagation of a CME in the heliosphere with a hydrodynamic plasma cloud-cone model and a linear force-free spheromak model at various locations in the heliosphere. We chose a CME event that launched on SOL2021-09-23T04:39:45 and was observed by multiple spacecraft, namely BepiColombo, Parker Solar Probe, Solar Orbiter, Stereo A and ACE. The solar wind was modelled in the steady and dynamic regimes in the Icarus model. The CME parameters were approximated for the selected event, and two CME models (spheromak and cone) were launched from the inner heliosphere boundary. The obtained synthetic in situ measurements were compared to the observed in situ measurements at all spacecraft. The internal magnetic field of the flux rope was better reconstructed by the spheromak model than by the cone CME model. The cone CME model maintained a nearly constant longitudinal angular extension while somewhat contracting in the radial direction. In contrast, the spheromak model contracted in the longitudinal direction while expanding in the radial direction. The CME sheath and magnetic cloud signatures were better reproduced at the four spacecraft clustered around the CME nose by the spheromak CME model. The dynamic solar wind caused a greater deceleration of the modelled CME than the steady-state solar wind solution. Because the background was homogeneous, the modelled CME properties were only mildly affected by the solar wind regime, however.
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All authors Tinatin Baratashvili, Emma Davies, Eva Weiler, Brigitte Schmieder, Pascal Démoulin, Stefaan Poedts

Earth and Planetary Astrophysics

Building Wet Planets through High-Pressure Magma-Hydrogen Reactions

Harrison Horn, Allona Vazan, Stella Chariton et al. (+2 more)

Close-in transiting sub-Neptunes are abundant in our galaxy \cite{fulton2017california}. Planetary interior models based on their observed radius-mass relationship suggest that sub-Neptunes contain a discernible amount of either hydrogen (dry planets) or water (wet planets) blanketing a core composed of rocks and metal \cite{bean2021nature}. Water-rich sub-Neptunes have been believed to form farther from the star and then migrate inward to their present orbits \cite{bitsch2021Dry}. Here, we report experimental evidence of reactions between warm dense hydrogen fluid and silicate melt that releases silicon from the magma to form alloys and hydrides at high pressures. We found that oxygen liberated from the silicate melt reacts with hydrogen, producing a significant amount of water up to a few tens of weight percent, which is much greater than previously predicted based on low-pressure ideal gas extrapolation \cite{misener2023Atmospheresa,schlichting2022Chemical}. Consequently, these reactions can generate a spectrum of water contents in hydrogen-rich planets, with the potential to reach water-rich compositions for some sub-Neptunes, implying an evolutionary relationship between hydrogen-rich and water-rich planets. Therefore, detection of a large amount of water in exoplanet atmospheres may not be the optimal evidence for planet migration in the protoplanetary disk, calling into question the assumed link between composition and planet formation location.
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All authors Harrison Horn, Allona Vazan, Stella Chariton, Vitali Prakapenka, Sang-Heon Shim

High Energy Astrophysical Phenomena

Sub-GeV dark matter in neutron stars: halo morphologies and their suppression by vacuum-like pressure

Loreany F. Araújo, Germán Lugones and José Ademir S. Lima

We investigate neutron stars that contain a unified dark sector composed of cold, degenerate fermionic dark matter and a vacuum-like dark-energy component. Within a general-relativistic two-fluid framework that allows a covariantly conserved, gradient-driven energy exchange between baryons and the dark sector, we quantify how dark microphysics reshapes global structure when the total gravitational radius need not coincide with the luminous baryonic radius. Using a state-of-the-art baryonic equation of state, we explore the halo-forming mass range for fermionic dark matter with particle masses of 400 MeV and 1 GeV, and we characterize sequences by the difference between the total and luminous radii and by the fractional difference between the total and baryonic masses. We confirm established trends: lighter fermions typically support low-density halos that increase the total radius by several kilometers at nearly fixed mass, whereas masses near 1 GeV tend to shrink halos and make the two radii appreciably closer. Our central new result is that a percent-level vacuum-like admixture markedly reduces halo formation, shrinking the radius difference from several kilometers to sub-kilometer scales and the fractional mass difference to $\lesssim 1\%$. Combined gravitational-wave and X-ray observations offer a practical route to bound the halo size and the allowed vacuum-like fraction.
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Astrophysics of Galaxies

The Calibration of Short Wavelength Polycyclic Aromatic Hydrocarbon Emission as Star Formation Rate Indicators with JWST

Benjamin Gregg, Daniela Calzetti, Angela Adamo et al. (+18 more)

We use JWST/NIRCam and MIRI imaging acquired by the Feedback in Emerging extrAgalactic Star clusTers (FEAST) program along with archival HST imaging to map ionized gas (Pa$\alpha$, Br$\alpha$, and H$\alpha$) and Polycyclic Aromatic Hydrocarbon (PAH) emission (3.3 and 7.7 $\mu$m) across a sample of four nearby galaxies (NGC 5194, 5236, 628, and 4449). These maps are utilized to calibrate the PAH features as star formation rate (SFR) indicators in 40 pc size regions around massive emerging young star clusters (eYSCs). We find a tight, sub-linear (power-law exponent, $\alpha{\,}{\sim}{\,}0.8$) relation between the PAH luminosities (3.3 and 7.7 $\mu$m) and SFR (extinction corrected Pa$\alpha$) in near solar metallicity environments. PAH destruction in more intense ionizing environments and/or variations in the age of our sources may drive the deviation from a linear relation. In the metal-poor environment of NGC 4449 (${\sim}$1/3 Z$_{\odot}$), we see substantial deficits in the PAH feature strengths at fixed SFR and significantly higher scatter in the PAH-SFR relations. We determine that the 3.3/7.7 $\mu$m PAH luminosity ratio increases towards lower metallicity environments. This is interpreted as a result of a shift in the size distribution towards smaller PAHs at lower metallicities, possibly due to inhibited grain growth. Focusing on the regions in NGC 4449, we observe a decreasing 3.3/7.7 $\mu$m ratio towards higher SFR, which could indicate that small PAHs are preferentially destroyed relative to larger PAHs in significantly sub-solar metallicity conditions. We estimate that ${\sim}$2/3 of the PAH emission in typical local star-forming galaxies is excited by older stars and unrelated to recent ($<$10 Myr) star formation.
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All authors Benjamin Gregg, Daniela Calzetti, Angela Adamo, Alex Pedrini, Sean T. Linden, Varun Bajaj, Jenna E. Ryon, Arjan Bik, Giacomo Bortolini, Matteo Correnti, Bruce T. Draine, Bruce G. Elmegreen, Helena Faustino Vieira, John S. Gallagher, Kathryn Grasha, Kelsey E. Johnson, Thomas S.-Y. Lai, Matteo Messa, Göran Östlin, Linda J. Smith, Monica Tosi

Solar and Stellar Astrophysics

Multiperiodic pulsations of the unique DAQ white dwarf J0551+4135: insights into a merger remnant

Murat Uzundag, Mukremin Kilic, Francisco C. De Gerónimo et al. (+7 more)

2MASS J05513444+4135297 (herafter J0551+4135) is the only pulsating DAQ white dwarf known with a carbon and hydrogen atmosphere. Its unusual atmospheric composition and kinematics indicate a white dwarf merger origin. We present time-series photometry of J0551+4135 obtained using the Apache Point Observatory 3.5m, Gemini North 8m, and Gran Telescopio Canarias 10m telescopes. J0551+4135 exhibits variations in pulsation amplitude and frequency over time. We detect ten significant recurring peaks across different subsets of observations, with frequencies ranging from 987 to 1180~$\mu$Hz, consistent with non-radial gravity ($g$)-mode oscillations. We present new evolutionary models suitable for spectroscopic characterization of DAQ white dwarfs, and derive a mass of $1.13 \pm 0.01\,M_\odot$ and a cooling age of $1.7 \pm 0.1$ Gyr for a CO core, and $1.12 \pm 0.01\,M_\odot$ and $1.6 \pm 0.1$\,Gyr for an ONe-core white dwarf, respectively. However, detailed asteroseismology of this unique pulsator has to wait until fully-consistent DAQ evolutionary models are available. Further observations, including multi-site campaigns to reduce daily aliasing and to improve the signal-to-noise ratio would be helpful for identification of additional modes and constraining the internal structure of this unique pulsator.
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All authors Murat Uzundag, Mukremin Kilic, Francisco C. De Gerónimo, Alejandro H. Córsico, Gracyn Jewett, Adam Moss, Alberto Rebassa-Mansergas, Alex J. Brown, Maria Camisassa, Pierre Bergeron

High Energy Astrophysical Phenomena

Kerr Black Hole Shadows in Dispersive Plasma: Frequency-Dependent Geodesics and Shadow Distortions

Sai Karan Mukthapuram and Sandeep Kumar Kataria

The black hole shadow, a direct probe of the event horizon's gravitational influence, has been observationally confirmed by the Event Horizon Telescope (EHT). While theoretical models of shadows in vacuum are mature, real astrophysical black holes like M87* and Sgr A* are enveloped in plasma, which can alter photon trajectories through dispersion. Current understanding, based on foundational work, indicates that only specific plasma distributions allow for an analytical treatment via the separation of the Hamilton-Jacobi equation. In this work, we build upon this framework to systematically investigate the propagation of light rays in Kerr spacetime surrounded by a pressureless, non-magnetized cold plasma. We explicitly derive the separability condition, identifying the exact class of plasma densities that permit a generalized Carter constant. For these models, we compute the photon regions and shadow boundaries, characterizing how the shadow's size and shape deviate from the vacuum case in a frequency-dependent manner. Our results provide analytical benchmarks for the distortion of shadows in dispersive media and determine the critical plasma frequency beyond which the shadow is erased, offering a direct link between observable shadow features and the properties of the ambient plasma environment and providing a foundation for studying more dynamic, non-separable plasma distributions.
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Earth and Planetary Astrophysics · Cross-listed from physics.hist-ph

Alexander Dalgarno and the development of astrochemistry

John H. Black

The interdisciplinary field of astrochemistry arose during the 1970s as observations in previously unexplored parts of the electromagnetic spectrum began to reveal the extent of a molecular component of interstellar matter with a surprisingly rich chemistry. Astrochemistry expanded further in order to explain the role of atomic and molecular processes in a broad range of phenomena in the universe. It is instructive to describe the current scope of astrochemistry using the career and accomplishments of Alexander Dalgarno as an organizing principle. Dalgarno helped to establish a self-sustaining community of astrochemists around the world. His own research interests highlight the early development of astrochemistry and anticipate much of its later evolution. His theoretical investigations of fundamental atomic and molecular processes lie at the heart of the subject.
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Solar and Stellar Astrophysics

A TESS View of Post-Eruption Variability in the Novae V1405 Cas,V1716 Sco, and V1674 Her

G. J. M. Luna, A. Dobrotka and M. Orio

We analyzed TESS archival data of three novae after recent outbursts, searching the orbital and white dwarf (WD) rotation period and possible variations of these periods. In V1405 Cas, we detected a period of $\sim$116.88 seconds, which we identified as due to the WD spin, and measured a rate of increase of 0.00165$\pm0.000006\, {\rm s\, d}^{-1}$, one of the fastest spin-down rates ever recorded. The rapid spin-down coupled with an X-ray luminosity several orders of magnitude lower than the available spin-down power, strongly indicates that the system is in a magnetic “propeller” state, namely the rotational energy powers the system's X-ray luminosity. We measured a previously unknown orbital period of 1.357$\pm0.005\,{\rm days}$ for V1716 Sco. If the X-ray flux modulation with a period of 77.9 s detected in outburst for this nova is due to the rotation of an strongly magnetized white dwarf as in other novae with similar modulations of the supersoft X-ray source in outburst, the system is in a parameter space that challenges standard models of cataclysmic variable evolution. For V1674 Her, which has already been classified as an intermediate polar (IP), we confirm the known spin period of 501.328$\pm0.024\,{\rm s}$ and the orbital period of $0.15293 \pm 0.00004$ days, suggesting that the spin modulation was also the root cause of the periodicity in X-rays in outburst, and that the WD atmosphere in the supersoft X-ray phase was not thermally homogeneous. Our results highlight the power of high-cadence, continuous observations in revealing extreme and unexpected characteristics of accreting white dwarfs.
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High Energy Astrophysical Phenomena

Accretion Geometry of the New Galactic Black Hole Candidate AT2019wey in the Hard State

Pragati Sahu, Swadesh Chand, Gulab C. Dewangan et al. (+3 more)

We perform broadband spectral and timing studies of the Galactic low-mass black hole candidate AT2019wey using quasi-simultaneous NICER, Swift, and NuSTAR observations obtained in 2022. The long-term MAXI light curve, along with the hardness-intensity diagram (HID), indicates that the source remained in the hard state and did not switch to the soft state. Spectral modeling using two different model combinations reveals that the broadband spectrum is best described by two distinct Comptonizing regions, associated reflection components, and thermal emission from the disk. The harder Comptonizing region dominates ($\gtrsim80\%$) the total flux and is primarily responsible for the observed reflection features from the distant part of the disk. We find that the accretion disk is truncated at a radius of $\sim16-56~r_{\rm{g}}$, while the luminosity is $\sim1.9\%$ of the Eddington limit, assuming a black hole mass of $10 ~ M_\odot$ and distance of 8 kpc. Our spectral results also show consistency in the estimated inner disk radius obtained through two independent methods: modeling the disk continuum and the reflection spectrum. The variability studies imply the presence of intrinsic disk variability, likely originating from an instability in the disk. We also detect hard time lags at low frequencies, possibly arising from the inward propagation of mass accretion rate fluctuations from the outer to the inner regions of the accretion disk. Moreover, an observed deviation of the lag-energy spectrum from the log-linear trend at $\lesssim 0.7$ keV is most likely attributed to thermal reverberation, arising from the reprocessing of hard coronal photons in the accretion disk.
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All authors Pragati Sahu, Swadesh Chand, Gulab C. Dewangan, Andrzej A. Zdziarski, Vivek K. Agrawal, Parijat Thakur

Astrophysics of Galaxies

MeerKAT observations of the spiral galaxy NGC 2997 in the S band. Detection of high dynamo modes

A. Damas-Segovia, R. Beck, S. A. Mao et al. (+18 more)

We seek to exploit the expanded observational range of the MeerKAT radio telescope with the new S-band receivers (2.0-2.8 GHz). To showcase its enhanced capabilities, we conducted new S-band observations of the galaxy NGC 2997 in full polarization. The S band is ideal for studying magnetic fields in spiral galaxies due to the weak Faraday depolarization. Performing a rotation measure (RM) synthesis allowed us to measure Faraday RMs in the galaxy, a signature of regular magnetic fields. A fast Fourier transform (FFT) algorithm was used to study the various azimuthal modes found in the RM data of the galaxy. The RM synthesis analysis indicates the direction of the magnetic field along the line of sight throughout the entire disk. Leveraging the sensitivity and high resolution provided by MeerKAT's S-band capability, this study achieves an unprecedented level of detail of the magnetic field structure. Our sector-based analysis of the RMs across azimuthal regions reveals the existence of modes of the large-scale magnetic field in NGC 2997. The variations in the RM values along the azimuthal angle reveal smoothly changing phase shifts between the rings, without the previously reported field reversal at about 3 kpc radius between the central region and disk. In this work, for the first time, a Fourier analysis has been applied to RM data averaged in sectors of rings in the disk plane of a spiral galaxy. Our Fourier analysis of the RM map shows three different large-scale field modes detected in the disk of NGC 2997. After applying a geometric modification, even multiples of the first mode were detected, as predicted from theoretical studies of dynamo action in a spiral galaxy with symmetric spiral structure. Our new method opens up new possibilities for investigating magnetic fields in spiral galaxies.
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All authors A. Damas-Segovia, R. Beck, S. A. Mao, A. Basu, S. Sridhar, E. Barr, A. Brunthaler, S. Buchner, F. Camilo, W. Cotton, A. M. Jacob, C. Kasemann, H.-R. Klöckner, M. Kramer, I. Rammala-Zitha, S. Ranchod, M. R. Rugel, O. Smirnov, J. D. Wagenveld, G. Wieching, O. Wucknitz

Cosmology and Nongalactic Astrophysics

Precision Cosmology with the Lightest Elements

Max Pettini and Ryan Cooke

This is a transcript of the joint talk we gave at the Sixth Gruber Cosmology Conference at Yale University on 3 October 2025. We describe the key role played by Big Bang Nucleosynthesis (BBN) in today's `Precision Cosmology', focusing in particular on the precise determination of the primordial abundance of deuterium. We describe the development of the ideas and methods of BBN research from their beginnings more than 75 years ago to the latest developments, and conclude with a forward look to likely advances expected towards the end of the current decade.
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Solar and Stellar Astrophysics

Cepheid Metallicity in the Leavitt Law (C–MetaLL) survey: VIII. High-Resolution IGRINS Spectroscopy of 23 Classical Cepheids: Validating NIR Abundances

G. Catanzaro, A. Bhardwaj, V. Ripepi et al. (+8 more)

Context. While most chemical abundance studies of Cepheids rely on optical spectroscopy, near-infrared (NIR) observations offer advantages in terms of reduced extinction and access to new elemental tracers. Aims. We aim to validate NIR-based abundance determinations against optical results and to explore the diagnostic power of spectral lines inaccessible in the optical domain. The H and K bands allow us to trace elements such as P, K, and Yb, while also probing obscured Galactic regions and more distant Cepheids. Methods. We obtained high-resolution (R=45000) H- and K-band spectra for 21 Galactic and 2 LMC Classical Cepheids using IGRINS. Atmospheric parameters were derived from photometry and line-depth ratios (Teff), empirical calibrations (log g), and spectral fitting. Abundances of 16 elements were determined via LTE full spectral synthesis and compared with optical literature values. Results. We find excellent agreement between NIR and optical abundances, confirming the reliability of IGRINS-based measurements. The Fe, Mg, and Si gradients match previous optical determinations. We provide the first homogeneous NIR-based measurements of P, K, and Yb in Cepheids, consistent with chemical evolution models. The two LMC Cepheids in our sample, also studied optically, serve as extragalactic benchmarks for validating NIR abundances in low-metallicity regimes. Conclusions. High-resolution NIR spectroscopy yields accurate chemical abundances in Cepheids, consistent with optical results, and grants access to additional nucleosynthetic tracers. These results support future large NIR spectroscopic surveys with instruments such as MOONS, ELT, and JWST for Galactic and extragalactic archaeology.
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All authors G. Catanzaro, A. Bhardwaj, V. Ripepi, E. Trentin, M. Marconi, M. Romaniello, N. Matsunaga, G. De Somma, T. Sicignano, I. Musella, Y. Soung-Chul

Cosmology and Nongalactic Astrophysics

Particle loads for cosmological simulations with equal-mass dark matter and baryonic particles

Shihong Liao, Yizhou Liu, Haonan Zheng et al. (+5 more)

Traditional cosmological hydrodynamical simulations usually assume equal-numbered but unequal-mass dark matter and baryonic particles, which can lead to spurious collisional heating due to energy equipartition. To avoid such a numerical heating effect, a simulation setup with equal-mass dark matter and baryonic particles, which corresponds to a particle number ratio of $N_{\rm DM}:N_{\rm gas} = \Omega_{\rm cdm} / \Omega_{\rm b}$, is preferred. However, previous studies have typically used grid-based particle loads to prepare such initial conditions, which can only reach specific values for $N_{\rm DM}:N_{\rm gas}$ due to symmetry requirements. In this study, we propose a method based on the glass approach that can generate two-component particle loads with more general $N_{\rm DM}:N_{\rm gas}$ ratios. The method simultaneously relaxes two Poisson particle distributions by introducing an additional repulsive force between particles of the same component. We show that the final particle load closely follows the expected minimal power spectrum, $P(k) \propto k^{4}$, exhibits good homogeneity and isotropy properties, and remains sufficiently stable under gravitational interactions. Both the dark matter and gas components individually also exhibit uniform and isotropic distributions. We apply our method to two-component cosmological simulations and demonstrate that an equal-mass particle setup effectively mitigates the spurious collisional heating that arises in unequal-mass simulations. Our method can be extended to generate multi-component uniform and isotropic distributions. Our code based on Gadget-2 is available at https://github.com/liaoshong/gadget-2glass .
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All authors Shihong Liao, Yizhou Liu, Haonan Zheng, Ming Li, Jie Wang, Liang Gao, Bingqing Sun, Shi Shao

Astrophysics of Galaxies

NbodyCP:A direct N-body simulation code for composite stellar populations of single and binary star clusters

Zhongmu Li and Rainer Spurzem

It is well-known that some star clusters contain composite stellar populations (CSPs), in which the metallicities or (and) ages of stars are different. The formation and evolution of such clusters and their stellar populations remain unclear. Both single and binary cluster channels may lead to such CSPs. In order to simulate the formation and evolution of such CSPs in star clusters, this work develops a code of direct N-body simulation of CSPs, NbodyCP. It is applied to different clusters, in particular, to binary clusters. It shows that CSPs and different kinds of cluster pairs can be formed via dynamical processes. This will help to partially explain the formation of CSPs and various clusters. Some special cluster structures, e.g., two cores or bar-like shape, are shown to be the results of evolution of some binary clusters. The simulation also shows that the separation between the members of a binary cluster affects the time of two member clusters to combine or move away significantly.
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Saturday 8 November

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

A synchronization-free one-way ranging observable for detecting and characterizing coherent orbital-period systematics in GRACE-FO laser ranging data

S. H. Wassegh

We present a synchronization-free differential observable for one-way inter-satellite laser ranging, designed to suppress first-order Doppler effects without requiring clock synchronization between spacecraft. The observable is constructed from successive pulse-interval differences, which isolate time-varying signatures while eliminating static and slowly varying biases. Applied to GRACE-FO Laser Ranging Interferometer (LRI) Level-1B data over four seasonal epochs in 2019, the method reveals a stable, spectrally narrow modulation at the orbital frequency. The amplitude and phase of the detected signature remain consistent across all datasets, demonstrating a deterministic, mission-internal origin. The detection is independently confirmed through synthetic-signal injection, shuffle-based significance testing, and cross-comparison with K-band ranging data. These results show that the proposed observable provides a sensitive diagnostic for identifying coherent orbital-period systematics that may remain hidden in conventional range-rate analysis. The method offers a pathway toward improved characterization of instrument and dynamical effects in current and future satellite gravity missions.
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Instrumentation and Methods for Astrophysics

A Firefly-inspired Model for Deciphering the Alien

Cameron Brooks, Estelle Janin, Gage Siebert et al. (+3 more)

The Search for Extraterrestrial Intelligence (ETI) is, historically, a search for aliens like us, inspired by human centric ideas of intelligence and technology. However, humans are not the only instance of an intelligent, communicating species on Earth, and thus not guide to how we might think about ETI. Here, we explore the potential for the study of non-human species to inform new approaches in SETI research, using firefly communication patterns as an illustrative example. Fireflies communicate their presence through evolved flash patterns distinct from complex visual backgrounds. Extraterrestrial signals may also be identifiable not by their complexity or decodable content, but by the structural properties of the signal, as currently being explored in efforts to decode communication in non-human species across our biosphere. We present a firefly-inspired model for detecting potential technosignatures within environments dominated by ordered astronomical phenomena, such as pulsars. Using pulsar data from the Australia Telescope National Facility, we generate simulated signals that exhibit evolved dissimilarity from the surrounding pulsar population. This approach shifts focus from anthropocentric assumptions about intelligence toward recognizing communication through its fundamental structural properties, specifically, evolutionarily optimized contrast with natural backgrounds. Our model demonstrates that alien signals need not be inherently complicated nor need we decipher their meaning to identify them; rather, signals might be distinguishable as products of selection. We discuss implications for broadening SETI methodologies, leveraging the diverse forms of intelligence found on Earth.
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All authors Cameron Brooks, Estelle Janin, Gage Siebert, Cole Mathis, Orit Peleg, Sara Imari Walker

Astrophysics of Galaxies

Damping of dynamical friction force in self-interacting ultralight dark matter and Fornax timing problem

E.V. Gorbar, O.V. Barabash, V.M. Gorkavenko et al. (+3 more)

The dynamics of globular clusters in the Fornax dwarf galaxy pose a challenge for the standard cold dark matter and can be used to test other models of dark matter. We study this dynamics in the context of an ultralight bosonic dark matter model, accounting for the damping term in a generalized Gross-Pitaevskii equation. Employing analytic formulas for the dynamical friction force, the infall time and evolution of globular clusters are compared in the cases with and without the damping term. It is argued that the damping term plays an important role in the Fornax timing problem in ultralight dark matter (ULDM) models. We found that the ULDM model with repulsive self-interaction can solve the Fornax timing problem in the absence of or with very small self-interaction, even if the initial position of the globular cluster is not far from the center of the galaxy. Still, the problem is resolved for strongly interacting repulsive ULDM, even for the most pressing case of globular cluster GC3, if its starting position exceeds 1.5 kpc.
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All authors E.V. Gorbar, O.V. Barabash, V.M. Gorkavenko, K. Korshynska, A.I. Momot, A.O. Zaporozhchenko

High Energy Astrophysical Phenomena

Probing a cosmogenic origin of astrophysical neutrinos and cosmic rays using gamma-ray observations of TXS 0506+056

A. Acharyya, A. Archer, P. Bangale et al. (+58 more)

In September 2017, a high-energy neutrino event detected by the IceCube Neutrino Observatory (IceCube-170922A) was associated, at the $3\sigma$ level, with a gamma-ray flare from the blazar TXS 0506+056. Cosmic rays that are accelerated in astrophysical sources can escape from their jets and interact with background radiation fields. Interactions with the extragalactic background light can produce pions and hence neutrinos, while interactions with the cosmic microwave background predominantly drive inverse Compton scattering, contributing to electromagnetic cascades in intergalactic space. The resulting secondary gamma-ray emission can be detected with high-energy gamma-ray telescopes. Here, we report on a new search for such cosmogenic cascade emission from the blazar TXS 0506+056, using a combined data set from the Fermi-Large Area Telescope and VERITAS. We compare the gamma-ray spectrum and neutrino observations with the predictions of cosmic-ray induced cascades in intergalactic space. The observed gamma-ray spectrum is modeled as a combination of the primary spectrum and the cascade spectrum. We apply a Monte Carlo simulation with a $\Delta\chi^2$-based likelihood analysis to jointly determine the best-fit parameters of a proton emission spectrum describing the data and derive constraints on the proton escape luminosity. Assuming a log-parabola primary photon spectrum, we find consistency with a proton injection spectral index of $\alpha_{p} \simeq 2.0$ and a cutoff energy of $E_{p,\text{max}} \simeq 1.3 \times 10^{16}$ eV, and constrain the isotropic proton escape luminosity to $1 \times 10^{44}$ erg s$^{-1}$ $\lesssim L_{p, esc} \lesssim 3 \times 10^{45}$ erg s$^{-1}$ at the 90 % confidence level.
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All authors A. Acharyya, A. Archer, P. Bangale, J. T. Bartkoske, W. Benbow, J. H. Buckley, Y. Chen, J. L. Christiansen, A. Duerr, M. Errando, M. Escobar Godoy, A. Falcone, S. Feldman, Q. Feng, S. Filbert, L. Fortson, A. Furniss, W. Hanlon, O. Hervet, C. E. Hinrichs, J. Holder, Z. Hughes, M. Iskakova, W. Jin, P. Kaaret, M. Kertzman, M. Kherlakian, D. Kieda, T. K. Kleiner, N. Korzoun, M. J. Lang, M. Lundy, G. Maier, C. L. Mooney, R. Mukherjee, W. Ning, R. A. Ong, A. Pandey, M. Pohl, E. Pueschel, J. Quinn, P. L. Rabinowitz, K. Ragan, P. T. Reynolds, D. Ribeiro, E. Roache, I. Sadeh, A. C. Sadun, L. Saha, G. H. Sembroski, R. Shang, M. Splettstoesser, D. Tak, A. K. Talluri, J. V. Tucci, J. Valverde, D. A. Williams, S. L. Wong, T. Yoshikoshi, M. Meyer, J. Müller

Astrophysics of Galaxies

A JWST/NIRSpec Integral Field Unit Survey of Luminous Quasars at z ~ 5-6 (Q-IFU): Rest-frame Optical Nuclear Properties and Extended Nebulae

Weizhe Liu, Xiaohui Fan, Richard Green et al. (+10 more)

It remains debatable how billion-solar-mass supermassive black holes (SMBHs) form and evolve within the first billion years. We report results from a James Webb Space Telescope (JWST)/NIRSpec integral field unit (IFU) survey of 27 luminous quasars at $z \sim 5$-$6$, enabling a systematic investigation of their key physical properties and the associated, extended line emission. Our sample hosts SMBHs with $\log(M_{\mathrm{BH}}/M_\odot) \sim 8.6$-$9.7$ and Eddington ratios of $\sim 0.1$-$2.6$ based on H$\beta$, and the H$\beta$-based and H$\alpha$-based BH mass are broadly consistent with each other. Our sample may have a slightly smaller median BH mass and larger median Eddington ratio than lower-redshift quasars within the same luminosity range, although the difference could still be explained by statistical uncertainties. They generally follow the empirical correlations between [O III] $\lambda$5007 equivalent width and bolometric luminosities or Eddington ratios formed by lower-redshift quasars. The majority of them fall within the Eigenvector~1 planes formed by lower-redshift quasars. Nevertheless, a subset of the sample shows enhanced, blueshifted [O III] emission associated with fast outflows. Spatially extended [O III] line emission is detected in 6 objects and shows morphologies and kinematics consistent with merging activities and/or turbulent and clumpy interstellar media (ISM). Tentative evidence of quasar radiative feedback shaping the ISM of a merging companion galaxy is seen in the object with the most extended [O III] emission. Our results provide crucial insight into the rapid growth of SMBHs and the gaseous environments they reside in at z$\sim$5-6.
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All authors Weizhe Liu, Xiaohui Fan, Richard Green, Jaclyn B. Champagne, Xiangyu Jin, Jianwei Lyu, Maria Pudoka, Wei Leong Tee, Feige Wang, Jinyi Yang, Yongda Zhu, Nayera Abdessalam, Haowen Zhang

High Energy Astrophysical Phenomena

AthenaK Simulations of Magnetized Binary Neutron Star Mergers

Jacob Fields and David Radice

We present new numerical-relativity simulations of a magnetized binary neutron star merger performed with AthenaK. The simulations employ a temperature- and composition-dependent tabulated nuclear equation of state, with initially dipolar fields with a maximum initial strength of ${\sim}10^{16}\ {\rm G}$ which extend outside the stars. We employ adaptive mesh refinement and consider three grid resolutions, with grid spacing down to $\Delta x_{\rm min} \simeq 92\ {\rm m}$ in the most refined region. When comparing the two highest resolution simulations, we find orbital dephasing of over 7 orbits until merger of only $0.06$ radians. The magnetic field is amplified during the merger and we observe the formation of a magnetized funnel in the polar region of the remnant. Simulations are continued until about $30$ milliseconds after merger. However, due to significant baryonic pollution, the binary fails to produce a magnetically-dominated outflow. Finally, we discuss possible numerical and physical effects that might alter this outcome.
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Earth and Planetary Astrophysics

Dust distribution in circumstellar disks harboring multi-planet systems. I. Sub-thermal mass planets

V. Roatti, G. Picogna and F. Marzari

We investigate the formation of dust gaps in circumstellar disks driven by the presence of multiple low-mass planets, focusing on the distinct physical mechanisms that operate across different gas-dust coupling regimes. We performed 2D hydrodynamical simulations of multiple planets embedded in a circumstellar disk using the PLUTO code, with the addition of dust treated as Lagrangian particles with a multi-size distribution. We carried out a large parameter space analysis to check the influence of disk and planetary properties on the dust component. Planets with $m \gtrsim 1 \, M_{\oplus}$ can open dust gaps for small grains in dense and warm disks (strong coupling) and for large grains in thin and cold disks (weak coupling), without significantly perturbing the gas. In the strong coupling regime, rapid Type I migration can shift the gap location inward or outward with respect to the planetary orbit, depending on the direction of migration. We also find dust gaps that overlap with Lindblad resonances. In the weak coupling regime, planets can create an inner dust cavity, multiple dust rings, or hide inside a common gap. Our results show how low-mass multi-planet systems perturb the dust distribution, which cannot be explained by considering each planet in isolation and has a crucial dependence on local disk conditions and dust grain sizes.
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