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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 1 January

High Energy Astrophysical Phenomena

The Double-Peaked Calcium-Strong SN 2025coe: Progenitor Constraints from Early Interaction and Ejecta Asymmetries

Aravind P. Ravi, Sahana Kumar, Raphael Baer-Way et al. (+47 more)

Supernova (SN) 2025coe at a distance of $\sim$25 Mpc is the second-closest calcium-strong (CaST) transient. It was discovered at a large projected offset of $\sim$34 kpc from its potential host galaxy NGC 3277. Multiband photometry of SN 2025coe indicates the presence of two peaks at day $\sim$2 and day $\sim$11 after explosion. Modeling the bolometric light curve, we find that the first peak can be reproduced either by shock cooling of a compact envelope ($R_\mathrm{env}$ $\approx $6-40 $R_{\odot}$; $M_\mathrm{env}$ $\approx $0.1-0.2 $M_{\odot}$) or by interaction with close-in circumstellar material (CSM; $R_{\mathrm{CSM}} \lesssim 6 \times10^{14}$ cm), or a combination of both. The second peak is dominated by radioactive decay of $^{56}$Ni ($M_{\mathrm{ej}} \approx $0.4-0.5 $M_{\odot}$; $M_{^{56}\mathrm{Ni}} \approx 1.4 \times 10^{-2}$ $M_{\odot}$). SN 2025coe rapidly evolves from the photospheric phase dominated by He I P-Cygni profiles to nebular phase spectra dominated by strong [Ca II] $\lambda \lambda$7291, 7323 and weak [O I] $\lambda \lambda$6300, 6364 emission lines. Simultaneous line profile modeling of [Ca II] and [O I] at nebular phases shows that an asymmetric core-collapse explosion of a low-mass ($\lesssim$3.3 $M_{\odot}$) He-core progenitor can explain the observed line profiles. Alternatively, lack of local star formation at the site of the SN explosion combined with a low ejecta mass is also consistent with a thermonuclear explosion due to a low-mass hybrid He-C/O white dwarf + C/O white dwarf merger.
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All authors Aravind P. Ravi, Sahana Kumar, Raphael Baer-Way, Stefano Valenti, Maryam Modjaz, Bart F. A. van Baal, Anders Jerkstrand, Yize Dong, Lindsey A. Kwok, Jeniveve Pearson, David J. Sand, Daichi Hiramatsu, Alexei V. Filippenko, Jennifer Andrews, Moira Andrews, Prasiddha Arunachalam, K. Azalee Bostroem, Thomas G. Brink, Collin Christy, Liyang Chen, Kyle W. Davis, Ali Esamdin, Joseph Farah, Ryan J. Foley, Emily Hoang, Griffin Hosseinzadeh, D. Andrew Howell, Brian Hsu, Ruifeng Huang, Abdusamatjan Iskander, Daryl Janzen, Saurabh W. Jha, Ravjit Kaur, Michael J. Lundquist, Curtis McCully, Darshana Mehta, Yuan Qi Ni, Nicolas Meza Retamal, Kishore C. Patra, Conor Ransome, Manisha Shrestha, Nathan Smith, Bhagya Subrayan, Kirsty Taggart, Xiaofeng Wang, Kathryn Wynn, Yi Yang, Shengyu Yan, Weikang Zheng, Dan Coe

Cosmology and Nongalactic Astrophysics

Constraining Primordial Black Holes via p-wave annihilation in light of CMB Spectral Distortion and 21-cm global signal

Shibsankar Si, Pravin Kumar Natwariya and Alekha C. Nayak

Primordial black holes (PBHs) can form spike density halos through the accretion of weakly interacting massive particles (WIMPs). In these halos, the enhanced density significantly boosts the annihilation rate of WIMPs. For Majorana dark matter annihilation into light fermions, the s-wave part of the annihilation cross section is helicity-suppressed, making the p-wave contribution dominant. We study the velocity-dependent p-wave annihilation case, whose resulting energy injection can modify the thermal and ionization history of the Universe, leaving observable imprints on the cosmic microwave background (CMB) spectrum and the global 21-cm signal. From the predicted energy injection into the plasma, we derive stringent upper limits on the fraction of dark matter in form of PBHs for p-wave annihilation models, based on the observational constraints of the CMB spectral distortions ($y$-type), and from the measurement of the 21-cm absorption signal at cosmic dawn. Our results highlight that accounting for the p-wave nature of annihilation is crucial for deriving robust constraints on the PBH abundance.
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Earth and Planetary Astrophysics

The Persistent Thermal Anomalies in Rocky Worlds

Zifan Lin and Tansu Daylan

Observing the dayside thermal emissions of rocky exoplanets provides essential insights into their compositions and the presence of atmospheres. Even though no conclusive evidence has been found for atmospheres on small rocky exoplanets orbiting M dwarfs, recent JWST observations identified puzzling thermal emission excesses. Some rocky exoplanets orbiting M dwarfs have dayside emission temperatures higher than the theoretical maximum temperatures, which are calculated assuming stellar irradiation as the sole energy source. Therefore, the observed thermal emission excesses imply that these planets may have internal heat sources. In this work, we simulate three possible internal planetary processes that may generate excess heat in addition to stellar irradiation: residual heating from formation, tidal heating, and induction heating due to interactions with the stellar magnetic field. We found that these mechanisms, even when combined, cannot explain the observed thermal emission excesses, nor can they account for a tentative positive trend in the brightness temperature scaling factor with irradiation temperature. Our results imply that planetary internal processes are unlikely to generate remotely detectable heat, so the observed thermal excesses, if astrophysical, are likely caused by stellar contamination, surface processes, geometric effect, or other internal processes not considered in this study. The ongoing JWST-HST Rocky Worlds Director's Discretionary Time Program and the upcoming Nancy Grace Roman Space Telescope will provide more insights into the thermal emission of rocky exoplanets.
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High Energy Astrophysical Phenomena

Ring Asymmetry and Spin in M87*

Vadim Bernshteyn, Nicholas S. Conroy, Michi Bauböck et al. (+261 more)

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring's peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin $a_{*}$. We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor $|a_{*}| \lesssim 0.2$. This is consistent with the Blandford-Znajek model for M87's jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints, and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.
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All authors Vadim Bernshteyn, Nicholas S. Conroy, Michi Bauböck, Paul Tiede, Abhishek V. Joshi, Ben S. Prather, Charles F. Gammie, the Event Horizon Telescope Collaboration: Kazunori Akiyama, Ezequiel Albentosa-Ruíz, Antxon Alberdi, Walter Alef, Juan Carlos Algaba, Richard Anantua, Keiichi Asada, Rebecca Azulay, Anne-Kathrin Baczko, David Ball, Bidisha Bandyopadhyay, John Barrett, Bradford A. Benson, Dan Bintley, Lindy Blackburn, Raymond Blundell, Katherine L. Bouman, Geoffrey C. Bower, Michael Bremer, Roger Brissenden, Silke Britzen, Avery E. Broderick, Dominique Broguiere, Thomas Bronzwaer, Sandra Bustamante, Douglas F. Carlos, John E. Carlstrom, Andrew Chael, Chi-kwan Chan, Dominic O. Chang, Koushik Chatterjee, Ming-Tang Chen, Yongjun Chen, Xiaopeng Cheng, Paul Chichura, Ilje Cho, John E. Conway, Thomas M. Crawford, Geoffrey B. Crew, Alejandro Cruz-Osorio, Yuzhu Cui, Brandon Curd, Rohan Dahale, Jordy Davelaar, Mariafelicia De Laurentis, Roger Deane, Jason Dexter, Vedant Dhruv, Indu K. Dihingia, Sheperd S. Doeleman, Sergio A. Dzib, Razieh Emami, Heino Falcke, Joseph Farah, Vincent L. Fish, Edward Fomalont, H. Alyson Ford, Marianna Foschi, Raquel Fraga-Encinas, William T. Freeman, Per Friberg, Christian M. Fromm, Antonio Fuentes, Peter Galison, Roberto García, Olivier Gentaz, Boris Georgiev, Ciriaco Goddi, Roman Gold, Arturo I. Gómez-Ruiz, José L. Gómez, Minfeng Gu, Mark Gurwell, Kazuhiro Hada, Daryl Haggard, Ronald Hesper, Dirk Heumann, Luis C. Ho, Paul Ho, Mareki Honma, Chih-Wei L. Huang, Lei Huang, David H. Hughes, Shiro Ikeda, C. M. Violette Impellizzeri, Makoto Inoue, Sara Issaoun, David J. James, Buell T. Jannuzi, Michael Janssen, Britton Jeter, Wu Jiang, Alejandra Jiménez-Rosales, Michael D. Johnson, Svetlana Jorstad, Adam C. Jones, Taehyun Jung, Tomohisa Kawashima, Garrett K. Keating, Mark Kettenis, Dong-Jin Kim, Jae-Young Kim, Jongsoo Kim, Junhan Kim, Motoki Kino, Jun Yi Koay, Prashant Kocherlakota, Yutaro Kofuji, Patrick M. Koch, Shoko Koyama, Carsten Kramer, Joana A. Kramer, Michael Kramer, Thomas P. Krichbaum, Cheng-Yu Kuo, Noemi La Bella, Deokhyeong Lee, Sang-Sung Lee, Aviad Levis, Shaoliang Li, Zhiyuan Li, Rocco Lico, Greg Lindahl, Michael Lindqvist, Mikhail Lisakov, Jun Liu, Kuo Liu, Elisabetta Liuzzo, Wen-Ping Lo, Andrei P. Lobanov, Laurent Loinard, Colin J. Lonsdale, Amy E. Lowitz, Ru-Sen Lu, Nicholas R. MacDonald, Jirong Mao, Nicola Marchili, Sera Markoff, Daniel P. Marrone, Alan P. Marscher, Iván Martí-Vidal, Satoki Matsushita, Lynn D. Matthews, Lia Medeiros, Karl M. Menten, Hugo Messias, Izumi Mizuno, Yosuke Mizuno, Joshua Montgomery, Kotaro Moriyama, Monika Moscibrodzka, Wanga Mulaudzi, Cornelia Müller, Hendrik Müller, Alejandro Mus, Gibwa Musoke, Ioannis Myserlis, Hiroshi Nagai, Neil M. Nagar, Dhanya G. Nair, Masanori Nakamura, Gopal Narayanan, Iniyan Natarajan, Antonios Nathanail, Santiago Navarro Fuentes, Joey Neilsen, Chunchong Ni, Michael A. Nowak, Hiroki Okino, Héctor Raúl Olivares Sánchez, Feryal Özel, Daniel C. M. Palumbo, Georgios Filippos Paraschos, Jongho Park, Harriet Parsons, Nimesh Patel, Ue-Li Pen, Dominic W. Pesce, Vincent Piétu, Alexander Plavin, Aleksandar PopStefanija, Oliver Porth, Giacomo Principe, Dimitrios Psaltis, Hung-Yi Pu, Alexandra Rahlin, Venkatessh Ramakrishnan, Ramprasad Rao, Mark G. Rawlings, Luciano Rezzolla, Angelo Ricarte, Luca Ricci, Bart Ripperda, Jan Röder, Freek Roelofs, Cristina Romero-Cañizales, Eduardo Ros, Arash Roshanineshat, Helge Rottmann, Alan L. Roy, Ignacio Ruiz, Chet Ruszczyk, Kazi L. J. Rygl, León D. S. Salas, Salvador Sánchez, David Sánchez-Argüelles, Miguel Sánchez-Portal, Mahito Sasada, Kaushik Satapathy, Saurabh, Tuomas Savolainen, Karl-Friedrich Schuster, Zhiqiang Shen, Sasikumar Silpa, Randall Smith, Bong Won Sohn, Jason SooHoo, Kamal Souccar, Joshua S. Stanway, He Sun, Alexandra J. Tetarenko, Remo P. J. Tilanus, Michael Titus, Kenji Toma, Pablo Torne, Teresa Toscano, Efthalia Traianou, Sascha Trippe, Matthew Turk, Ilse van Bemmel, Huib Jan van Langevelde, Daniel R. van Rossum, Sebastiano D. von Fellenberg, Jesse Vos, Jan Wagner, Derek Ward-Thompson, John Wardle, Jasmin E. Washington, Jonathan Weintroub, Maciek Wielgus, Kaj Wiik, Michael F. Wondrak, George N. Wong, Jompoj Wongphexhauxsorn, Qingwen Wu, Paul Yamaguchi, Aristomenis Yfantis, Doosoo Yoon, André Young, Ziri Younsi, Wei Yu, Feng Yuan, Ye-Fei Yuan, Ai-Ling Zeng, J. Anton Zensus, Shuo Zhang, Guang-Yao Zhao

Solar and Stellar Astrophysics

Molecular hydrogen controls the temperatures of flares on TRAPPIST-1

Alexander I. Shapiro Nadiia Kostogryz Sara Seager Veronika Witzke Julien de Wit Valeriy Vasilyev Astrid M. Veronig Robert Cameron Hardi Peter Sami K. Solanki

Early JWST observations of TRAPPIST-1 have revealed an unexpected puzzle: energetic white-light flares ($\rm{E} > 10^{30}$ erg) reach temperatures of only ${\sim}$3500–4000\,K, nearly three times cooler than typical solar flares, which peak around 9000–10000\,K. Here we explain this difference by identifying the physical mechanism that regulates flare temperatures on late M-dwarfs. The key factor is that in the cool, dense atmosphere of TRAPPIST-1, magnetic heating is strongly moderated by the dissociation of molecular hydrogen (H$_2$) into atomic hydrogen. This "H$_2$ dissociation thermostat" acts as an efficient energy sink, preventing flare regions from heating above ${\sim}4000$\,K. Our chemical equilibrium and heat capacity calculations show that this effect depends sensitively on stellar atmospheric pressure and the local abundance of H$_2$. In hotter stars, from early M dwarfs to solar-type stars, the scarcity of molecular hydrogen renders this mechanism ineffective; instead, atomic hydrogen ionization limits flare temperatures near ${\sim}$9000\,K.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

High Frequency Spectrum of Primordial Gravitational Waves

Kamil Mudrunka and Kazunori Nakayama

During inflation long wavelength gravitational waves are produced, which form stochastic background in the present universe with very wide range of frequencies. Higher frequency gravitational waves never experience super-Hubble-radius regime, but they are also amplified after inflation due to the inflaton oscillation. Taking account of the inflaton dynamics after inflation, the spectrum of such quantum-mechanically produced gravitational waves may extend to much higher frequencies than previously thought. In this paper we calculate the spectrum of high frequency gravitational waves produced during and after inflation in detail, in particular focusing on the connection between the low and high frequency regime, and show that the detailed spectrum can distinguish inflation models.
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Solar and Stellar Astrophysics

Open Questions in Massive Star Research across Cosmic Scales

Andreas A.C. Sander

Massive stars are the engines of the Cosmos, shaping their environments and driving galaxy evolution across cosmic time. Yet, this general textbook picture faces many challenges when trying to turn abstract insights into quantitative predictions. Recent discoveries, such the surprisingly high metallicity and early nitrogen enrichment in high-redshift galaxies discovered by JWST, are challenging current descriptions of massive star evolution and add new pieces to a puzzle that is yet everything but complete. The oncoming era of large surveys and advances in computational modeling create the potential to reach breakthroughs in our understanding. Yet, to resolve current problems and conflicting conclusions, we will also need to reconsider what we think we know. Are the objects we observe what we think they are? Are the models we use describing what is actually going on? And what can we learn from previous misconceptions? This short review highlights major open questions from individual stars and stellar systems back to the first galaxies while also discussing two examples - the weak-wind problem as well as the different flavours and impact of Wolf-Rayet stars - where recent discoveries might point in a new direction.
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Solar and Stellar Astrophysics

On the Theory of Absorption of Sound Waves via the Bulk Viscosity in the Partially Ionized Solar Chromosphere

Albert M. Varonov and Todor M. Mishonov

Bulk viscosity and thermodynamic variables of a hydrogen-helium cocktail: internal energy, enthalpy, pressure, their derivatives, heat capacities per constant density and pressure are obtained using temperature and density height profiles of the solar atmosphere [Avrett & Loeser, ApJS Vol. 175, 229 (2008)]. The qualitative evaluation for the necessary sound wave energy flux to heat the solar chromosphere is determined to be 320 kW/m$^2$. It is concluded that the bulk viscosity creates the dominating mechanism of acoustic waves damping and it is not necessary to introduce artificial viscosity or to conclude that shear viscosity is not sufficient for chromosphere heating; the volume viscosity induced wave absorption is sufficient.
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Astrophysics of Galaxies

Asymmetric torus variability in active galactic nuclei driven by global brightening and dimming

Suyeon Son, Minjin Kim and Luis C. Ho

Temporal asymmetry in the flux variability of active galactic nuclei (AGNs) offers key insights into the physical mechanisms driving AGN variability. In this study, we investigated the variability of the torus by analyzing temporal asymmetry in the mid-infrared (MIR) continuum. We compared ensemble structure functions between the brightening and dimming phases for AGNs at $0.15<z<0.4$, using monitoring data in the optical from the Zwicky Transient Facility and in the MIR from the Near-Earth Object Wide-field Infrared Survey Explorer. We found that AGNs with bluer optical-to-MIR colors exhibit positive temporal asymmetry in the MIR, indicating that their variability amplitude is larger when brightening. Conversely, those with redder colors show negative asymmetry, exhibiting larger variability amplitude when decaying. However, there is no significant temporal asymmetry in the $g$-band variability driven by the accretion disk, suggesting that the temporal asymmetry in the MIR continuum primarily originates from intrinsic processes in the torus instead of the reflection of the ultraviolet-optical variability from the accretion disk. Analysis of the composite light curves revealed that AGNs with bluer optical-to-MIR colors tend to brighten gradually in the MIR, leading to the observed temporal asymmetry. This finding suggests that hot-dust-rich AGNs evolve with a gradual decline in hot dust emission, while hot-dust-poor AGNs are associated with a steady increase.
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Earth and Planetary Astrophysics

KMT-2024-BLG-0816/OGLE-2024-BLG-0519 – A Microlensing Event with Candidate Free-Floating Planet Lens and Blended Light

R. Poleski, Y.-H. Ryu, A. Udalski et al. (+27 more)

We present the discovery of a free-floating planet microlensing event KMT-2024-BLG-0816. The event shows finite-source effect, significant blending light, and no microlensing signal from a putative planet host. Among the free-floating planet events with finite source effects, this is the only event with unresolved blending light. We discuss how follow-up observations can be used to determine whether the blending light originates from a putative planet host.
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All authors R. Poleski, Y.-H. Ryu, A. Udalski, W. Zang, M. D. Albrow, S.-J. Chung, A. Gould, C. Han, K.-H. Hwang, Y. K. Jung, I.-G. Shin, Y. Shvartzvald, J. C. Yee, H. Yang, D.-J. Kim, C.-U. Lee, B.-G. Park, M. K. Szymański, I. Soszyński, K. Ulaczyk, P. Pietrukowicz, J. Skowron, D. Skowron, P. Mróz, K. Rybicki, P. Iwanek, M. Wrona, M. Gromadzki, M. Mróz, M. Ratajczak

Earth and Planetary Astrophysics · Cross-listed from nlin.PS

Self-assembled versus biological pattern formation in geology

Julyan H. E. Cartwright, Charles S. Cockell, Julie G. Cosmidis et al. (+11 more)

Both abiotic self-organization and biological mechanisms have been put forward as the origin of a number of geological patterns. It is important to comprehend the formation mechanisms of such structures both to understand geological self-organization and in order to differentiate them from biological patterns – fossils and bio-influenced structures – seen in geological systems. Being able to distinguish the traces of biological activity from geological self-organization is fundamental both for understanding the origin of life on Earth and for the search for life beyond Earth.
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All authors Julyan H. E. Cartwright, Charles S. Cockell, Julie G. Cosmidis, Silvia Holler, F. Javier Huertas, Sean F. Jordan, Pamela Knoll, Electra Kotopoulou, Corentin C. Loron, Sean McMahon, Anna Neubeck, Carlos Pimentel, C. Ignacio Sainz-Díaz, Piotr Szymczak

Cosmology and Nongalactic Astrophysics

Measurement of the extragalactic background light at 8600Å using dark cloud shadow and the CaII-triplet lines

Lauri K. Haikala, Kalevi Mattila and Petri Väisänen

We present results of a measurement of the near infrared Extragalactic Background Light using the dark-cloud method. Long-slit spectra covering the opaque core of the intermediate–latitude globule DC303.8-14.2 and the almost unobscured off area were measured using nodding-along-the-slit measuring technique providing a differential spectrum free of most of the foreground components. A template for the only remaining major foreground component, the scattered integrated starlight dominated by the strong Ca II triplet lines at 8498, 8542, 8664$\r{A}$, from the dark core itself was constructed using the GAIA RVS spectral database. The derived EBL intensity is $1.62\pm 0.76(\sigma_{stat})\, 10^{-9} erg\, cm^{-2} s^{-1}\r{A}^{-1} sr^{-1}$ or $13.8\pm6.5(\sigma_{stat})$nW m$^{-2}$sr$^{-1}$; this represents a tentative detection at $2.1\sigma$, level.
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Astrophysics of Galaxies

Comparison of Static and Evolving Potentials in the Orbital Dynamics of Globular Clusters in the Central Region of the Galaxy

Anisa Bajkova, Anton Smirnov and Vadim Bobylev

A comparative analysis of the dynamics of the orbital motion (regular or chaotic) of 45 globular clusters in the central region of the Galaxy with a radius of 3.5 kpc is carried out. The static and evolving (based on the semi-analytical cosmological model of Gomez et al. (2010) and Hagi et al. (2015)) potentials of the Galaxy are considered both in the form of an axisymmetric and non-axisymmetric potential of the Galaxy with a rotating elongated bar with the following parameters at the present time: mass $10^{10} M_\odot$, length of the major semi-axis 5 kpc, rotation angle of the bar axis 25$^o$, angular velocity of rotation 40 km s$^{-1}$ kpc$^{-1}$ . To form the 6D-phase space required for integrating the orbits, the most accurate astrometric data to date from the Gaia satellite (Vasiliev & Baumgardt, 2021), as well as new refined average distances (Baumgardt & Vasiliev, 2021) were used. We used a frequency method for analysis of the chaotic/regular orbital motion of all 45 GCs. The results are summarized in the table, which provides an overview of each GC in our sample, the degree of chaotization in both the static and evolving potentials, and the influence of the central rotating bar on the degree of orbital chaotization in both cases. It is shown that the orbital dynamics have undergone minor changes during the transition from the static to the evolving potential. This confirms our previously obtained result that changes in the masses and sizes of the gravitational potential components act on orbital parameters in opposite ways, and at small galactocentric distances this influence is maximally compensated, while the orbits of distant objects and objects with large apocentric distances experience the greatest influence.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Revisiting p-$^{11}$B Fusion: Updated Cross-sections, Reactivity, and Energy Balance

Hong-Yi Wang, Yu-Qi Li, Qian Wu et al. (+1 more)

Recent experimental progress has substantially improved the available cross-section data for the p-$^{11}$B fusion reaction, particularly in energy regions that previously lacked direct measurements. In this study, we develop a high-precision analytical parameterization of the p-$^{11}$B reaction cross-section over the 0–10 MeV energy range, incorporating the new experimental data into a continuous and numerically efficient representation. Using this parameterization, we evaluate the thermonuclear reactivity of the p-$^{11}$B reaction and examine the effects of the dominant resonance at 0.6 MeV and a newly observed resonance around 4.7 MeV. Furthermore, we assess the energy balance by analyzing the fusion power density and the electron bremsstrahlung power density. Our results indicate that p-$^{11}$B fusion is not precluded by bremsstrahlung constraints when contemporary cross-section data and self-consistent thermal modeling are employed.
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All authors Hong-Yi Wang, Yu-Qi Li, Qian Wu, Zhu-Fang Cui

Solar and Stellar Astrophysics

Detailed Investigation of a W UMa Contact Binary with an Ultralow Mass Ratio and a Third-Body as a Potential Merger Candidate

Atila Poro, Ehsan Paki, Fahri Alicavus et al. (+1 more)

The lower limit of the mass ratio in contact binaries remains uncertain, with observations suggesting systems exist below theoretical predictions. The stability of such very low mass ratio systems is still debated. Based on our review of systems within the mass ratio cutoff range, we reanalyzed TYC 3801-1529-1 and found it to have the lowest known mass ratio, $q = 0.024_{-(1)}^{+(2)}$, among analyzed contact binaries. The reanalysis of this target was carried out using the BSN application and the MCMC method. We then compared our light curve solution obtained from TESS observations with the results of a previous study. We studied the period variations of this system and identified a cyclic trend over the past six years. After the third-body contribution has been removed, the system's period variations can be described either by a linear trend with a negative slope or by a quadratic trend with a downward curvature. These results indicate that it is still not possible to definitively determine whether the orbital period is increasing or decreasing, underscoring the importance of future observations. By considering the challenges of detecting the faint secondary in extremely low mass ratio systems, we estimated the absolute parameters of the target. Based on our analysis, the secondary component of the binary is likely a brown dwarf, while the third body appears to be a low-mass M-type dwarf. According to our analysis, TYC 3801-1529-1 is dynamically unstable and thus represents a remarkable candidate for a binary merger.
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All authors Atila Poro, Ehsan Paki, Fahri Alicavus, Raul Michel

Cosmology and Nongalactic Astrophysics

Isotropic stochastic gravitational wave background reconstruction for Taiji constellation

Yang Jiang and Qing-Guo Huang

The stochastic gravitational wave background is a broadband target from diverse astrophysical and cosmological sources. The background falls within the mHz frequency band could become a potential observable for future space-based interferometers. Taiji, a proposed space mission slated for launch in the 2030s, will enable the study of such a background. However, the unique characteristics of space missions pose distinctive challenges for separating the stochastic background from instrumental noise. To address the data analysis requirements, we develop a preliminary pipeline to search for the SGWB and evaluate its performance with Taiji simulation datasets. At present, we demonstrate that the algorithm can successfully recover the parameters of injected background with a known spectral density after setting aside the complication of galactic binaries foreground. Furthermore, by employing the trans-dimensional Markov Chain Monte Carlo method, we extend the analysis to reconstruct the background with unknown spectral morphology.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gravitational Wave Tails and Transient Behaviors of Quantum-Corrected Black Holes

Rong-Zhen Guo and Qing-Guo Huang

Gravitational wave astronomy plays a pivotal role in testing the dynamics of gravity in strong-field regimes and probing the nature of black holes. Motivated by recent studies on late-time tails in gravitational waves, we examine the gravitational wave tails of black holes incorporating quantum corrections within the framework of effective Loop Quantum Gravity. Our findings indicate that both the amplitudes and the intermediate behavior of these tails are influenced by quantum corrections. We demonstrate that the amplitude and transient characteristics of the tail are sensitive to the specific details of the black hole's dynamics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Metric Reconstruction and Second Order Perturbation for Generic Spherically Symmetric spacetime

Rong-Zhen Guo and Qing-Guo Huang

Higher-order perturbations during the ringdown phase are essential for testing gravitational theories. This requires a perturbation framework that extends beyond General Relativity, as well as an appropriate method for reconstructing the spacetime metric. In this work, we address these challenges within the context of general spherically symmetric spacetimes. We introduce a modified Teukolsky equation for perturbative calculations in asymptotically flat, spherically symmetric spacetimes. The metric reconstruction method, which does not rely on the Hertz potential, is extended to $tr$-symmetric spacetime, allowing for the calculation of metric components under specific gauge conditions. Additionally, we present a second-order perturbation theory applicable to generic spherically symmetric spacetimes.
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Earth and Planetary Astrophysics · Cross-listed from math.DS

A new fast multiple-shooting method for computing periodic orbits in symplectic maps leveraging simultaneous Floquet vector computation to avoid large linear systems

Bhanu Kumar

Given a 4D symplectic map $F_0$ that has a normally hyperbolic invariant cylinder foliated by invariant tori, those with rational rotation numbers are themselves foliated by subharmonic periodic orbits (SPOs). If $F_0$ is part of a perturbative family $F_\varepsilon$, one is often interested in computing those SPOs which persist for $\varepsilon >0$. Assuming that a persisting SPO of $F_0$ has been identified, in this paper, we develop a quasi-Newton method which solves for the SPO simultaneously with its Floquet vectors and multipliers. This in turn enables continuation by the perturbation parameter $\varepsilon$. The resulting SPO and Floquet vectors are then used to compute Taylor parameterizations of the SPO's weak stable and unstable manifolds, if they exist. Our quasi-Newton method is based on an adaptation of the parameterization method for invariant tori, with this paper being the first-ever to apply such a framework to directly compute periodic orbit points themselves. The new algorithm improves on efficiency compared to prior multi-shooting methods for SPOs, and notably applies to the case of stroboscopic maps of 2.5 DOF Hamiltonian flows resulting from periodic perturbations of 2 DOF systems. The tools have been successfully used for studies of resonant orbits in perturbed real-life celestial systems, the results of which are summarized as a demonstration of the methods' utility.
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Instrumentation and Methods for Astrophysics

Combining datasets with different ground truths using Low-Rank Adaptation to generalize image-based CNN models for photometric redshift prediction

Vikram Seenivasan, Srinath Saikrishnan, Andrew Lizarraga et al. (+3 more)

In this work, we demonstrate how Low-Rank Adaptation (LoRA) can be used to combine different galaxy imaging datasets to improve redshift estimation with CNN models for cosmology. LoRA is an established technique for large language models that adds adapter networks to adjust model weights and biases to efficiently fine-tune large base models without retraining. We train a base model using a photometric redshift ground truth dataset, which contains broad galaxy types but is less accurate. We then fine-tune using LoRA on a spectroscopic redshift ground truth dataset. These redshifts are more accurate but limited to bright galaxies and take orders of magnitude more time to obtain, so are less available for large surveys. Ideally, the combination of the two datasets would yield more accurate models that generalize well. The LoRA model performs better than a traditional transfer learning method, with $\sim2.5\times$ less bias and $\sim$2.2$\times$ less scatter. Retraining the model on a combined dataset yields a model that generalizes better than LoRA but at a cost of greater computation time. Our work shows that LoRA is useful for fine-tuning regression models in astrophysics by providing a middle ground between full retraining and no retraining. LoRA shows potential in allowing us to leverage existing pretrained astrophysical models, especially for data sparse tasks.
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All authors Vikram Seenivasan, Srinath Saikrishnan, Andrew Lizarraga, Jonathan Soriano, Bernie Boscoe, Tuan Do

Wednesday 31 December

Instrumentation and Methods for Astrophysics

Predictability of bursts of a recurrent nova using topological data analysis and machine learning

Ignacio Morales-Gil

RS Oph is a recurrent nova, a kind of cataclismic variable that shows bursts in a period approximately shorter than a century. Persistent homology, a technique from topological data analysis, studies the evolution of topological features of a simplicial complex composed of the data points or an embedding of them, as some distance parameter is varied. For this work I trained a supervised learning model based on several featurizations, namely persistence landscapes, Carlsson coordinates, persistent images, and template functions, of the persistence diagrams of sections of the lightcurve of RS Oph. A tenfold cross validation of the model based on one of the featurizations, persistence landscapes, consistently shows high recalls and accuracies. This method serves the purpose of predicting whether RS Oph is bursting within a year.
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Instrumentation and Methods for Astrophysics

Light-tight skipper-CCDs for X-ray detection in space

Ana M. Botti, Yikai Wu, Brenda Cervantes et al. (+6 more)

Skipper Charge-Coupled Devices (skipper-CCDs) are pixelated silicon detectors with deep sub-electron resolution. Their radiation hardness and capability to reconstruct energy deposits with unprecedented precision make them a promising technology for space-based X-ray astronomy. In this scenario, optical and near-infrared photons may saturate the sensor, distorting the reconstructed signal. We present a light-tight shield for skipper-CCDs to suppress optical backgrounds while preserving X-ray detection efficiency. We deposited thin aluminum layers on the CCD surface using an e-beam evaporator and evaluated their blinding performance across wavelengths from 650 to 1000 nm using a monochromator, as well as the X-ray transmission using an $^{55}$Fe source. We find that 50 and 100 nm layers provide >99.6% light suppression, with no efficiency loss for 5.9 and 6.4 keV X-rays. In addition, we used Geant4 simulations to extend these results to a broader energy range and quantify the efficiency loss for different aluminum thicknesses. Results show that thin aluminum coatings are an effective, low-cost solution for optical suppression in skipper-CCDs intended for X-ray detection and space instrumentation.
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All authors Ana M. Botti, Yikai Wu, Brenda Cervantes, Claudio Chavez, Juan Estrada, Stephen E. Holland, Nathan Saffold, Javier Tiffenberg, Sho Uemura

Astrophysics of Galaxies

Evolution of bar formation in galaxies over the last 6 giga-years

M.A. Chacón

This work examines the evolution of bar formation in disk galaxies over the last 6 giga-years by analyzing the barred galaxy fraction as a function of key structural parameters. A representative sample of local and distant field galaxies was studied using bar detection techniques based on elliptical isophotes and Fourier decomposition. The analysis focuses on the dependence of bar formation on stellar mass, color index, and bulge-to-total ratio (B/T). In the local universe, the bar fraction increases with stellar mass and is higher in red, more evolved galaxies, suggesting that disk stability plays a fundamental role in bar formation. In contrast, distant galaxies exhibit a significantly lower bar fraction, indicating that dynamically unstable disks in earlier cosmic epochs limited both the formation and persistence of bars. Bars are more frequent in galaxies with disk-dominated structures (low B/T) at all redshifts; however, even these systems show a reduced bar fraction at higher redshift. Overall, the results highlight the importance of disk stabilization in driving the morphological evolution of galaxies across cosmic time.
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Astrophysics of Galaxies

Little Red Dots: The Assembly of Early Supermassive Black Holes in the JWST Era

David D Vaida and Ryan Jeffrey Farber

Since the launch of James Webb Space Telescope (JWST) in late 2021, our understanding of high-redshift objects has faced several upheavals. JWST has discovered much more massive galaxies and supermassive black holes (SMBH) than cosmological models had expected. Furthermore, JWST observations have revealed an entirely novel population of high-redshift objects. Characterized by a dominant red rest-frame component and point-like morphology, these “little red dots” (LRD) have set off a flurry of observational and theoretical follow-up. The current identity of LRD is highly debated, yet falling into two main scenarios: active galactic nuclei (i.e., SMBH) or compact star-forming regions. If star-forming, LRD would represent the highest stellar densities ever observed. If SMBH, their high Eddington fractions, and already high masses, help elucidate the growth of the most massive SMBH found by JWST in the early Universe ($z \gtrsim4)$. In this mini-review, we present the observational evidence accumulated to date, including sub-millimeter probes of LRD dust masses, constraints on radio and X-ray emission from stacking, and rest-frame ultraviolet & optical measurements provided by JWST. Furthermore, we highlight how identifying additional LRD that are truly primarily SMBH-driven may help to shed light on the formation of `overly massive' SMBH discovered by JWST within the first billion years since the Big Bang.
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High Energy Astrophysical Phenomena

The propagation of long GRB jets through and beyond its progenitor star

Gerardo Urrutia and Agnieszka Janiuk

Long gamma-ray bursts (lGRB) are produced by relativistic jets arising from the collapse of massive stars. Such progenitor environments present complex physical conditions that are challenging to model by numerical simulations. The difficulty increases when solving the accretion process and propagation of the outflows, as it requires covering distances from the black hole horizon to beyond the progenitor star. General Relativistic Magnetohydrodynamic (GRMHD) simulations provide a convenient framework to study high-luminosity jets, where magnetic flux plays an important role in the process of jet launching from the central engine. To follow the propagation of the jet through and beyond its progenitor environment, we use multi-scale simulations (i.e., AMR-based). In this work, we report results of 2.5-dimensional GRMHD simulations of a lGRB progenitor. We present highly magnetized, weakly magnetized, and non-magnetized pre-collapse stars, and discuss the observational implications for lGRB jets.
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Solar and Stellar Astrophysics

Forging neon-distilling white dwarfs in the stellar engulfments of helium white dwarfs

Nicholas Z. Rui and Jim Fuller

Once carbon–oxygen white dwarfs cool sufficiently, they crystallize from the inside out. If the white dwarf is rich enough in ${}^{22}\mathrm{Ne}$, these crystallized solids are buoyant and rapidly rise, efficiently liberating potential energy which may halt the cooling of the white dwarf or power magnetic phenomena. Although this ${}^{22}\mathrm{Ne}$ distillation process may explain the cooling anomaly in Q-branch white dwarfs and anomalous emission lines in DAHe white dwarfs, its operation demands unusually high ${}^{22}\mathrm{Ne}$ abundances not generically predicted by isolated stellar evolution. We show that the engulfments of helium white dwarfs by both main-sequence and red giant stars can result in carbon–oxygen white dwarfs with ${}^{22}\mathrm{Ne}$ abundances high enough to distill ${}^{22}\mathrm{Ne}$. This enhancement occurs because carbon dredged up following an especially energetic and off-center helium flash can be processed into ${}^{22}\mathrm{Ne}$ by subsequent hydrogen shell burning and helium shell burning. ${}^{22}\mathrm{Ne}$-distilling white dwarfs from these merger channels are predicted to be somewhat more massive than typical white dwarfs (up to $\simeq0.7M_\odot$) and may have anomalous rotation rates, consistent with DAHe white dwarfs. These binary formation channels for ${}^{22}\mathrm{Ne}$-rich white dwarfs reveal new connections between binary interactions and white dwarf cooling phenomena.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Freeze-in leptogenesis without the need for right-handed neutrino oscillations

Martin A. Mojahed and Sascha Weber

We present an experimentally testable leptogenesis mechanism based on the standard type-I seesaw model that successfully operates at right-handed-neutrino (RHN) masses around the GeV scale. The mechanism takes place in a cosmological background with an asymmetry between right-handed electrons and left-handed positrons generated at high temperatures, and does not require oscillations between RHNs or any CP violation in the RHN sector. In contrast to standard leptogenesis via freeze-in, our mechanism works even in the presence of a single RHN around the GeV scale. The mechanism is illustrated for the minimal type-I seesaw with two RHNs, where we show that successful baryogenesis via leptogenesis is viable in large regions of parameter space even without a small mass splitting between the RHNs.
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Astrophysics of Galaxies

Exploring the Structure and Evolution of Four Young Open Clusters Near the Galactic Mid-plane via Gaia DR3

W. H. Elsanhoury, S. Taşdemir, D. C. Ç{\i}nar et al. (+3 more)

We present a comprehensive analysis of four young open clusters, NGC 663, NGC 2301, NGC 2384, and NGC 7510, utilizing high-precision astrometric and photometric data from Gaia DR3. Cluster membership was determined using the UPMASK algorithm, resulting in probable member counts ranging from 337 to 1498 across the clusters. Bayesian MCMC isochrone fitting yielded cluster ages in the range $\log t \sim 7.0$ -$8.15$, with uncertainties of $\sim 0.11$-$0.18$. Reddening values ranged from $E(B-V)=0.093$ mag in NGC 2301 to $1.24$ mag in NGC 7510, consistent with their positions near the Galactic plane. The stellar mass function slopes ($\alpha \approx 2.00$-$2.26$) closely match the Salpeter IMF, with total stellar masses spanning nearly an order of magnitude, from $\sim 486\,M_\odot$ in NGC 2301 to $\sim 3584\,M_\odot$ in NGC 663. Dynamical relaxation times indicate that only NGC 2301 ($\tau \approx 10.00$) and NGC 2384b ($\tau \approx 2.03$) are dynamically relaxed; the others remain dynamically evolving. Orbital integrations in the MWPotential2014 model reveal nearly circular Galactic orbits with very low eccentricities ($e \approx 0.003$-$0.014$) and small vertical distances ($Z_{\rm max} < 0.142$ kpc), confirming their confinement to the thin disk. SED and kinematic analysis show that NGC 2384a and NGC 2384b are separated by $\sim 0.55$ kpc, indicating an optical pair.
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All authors W. H. Elsanhoury, S. Taşdemir, D. C. Ç{\i}nar, R. Canbay, A. A. Haroon, A. Ahmed

Earth and Planetary Astrophysics

Covertly Active Comet (139359) 2001 ME1

Qicheng Zhang, Quanzhi Ye, Karl Battams et al. (+3 more)

On 2018 November 18, coronagraphs onboard the Solar and Heliospheric Observatory (SOHO) captured an unrecognized comet crossing its fields of view. We identified this comet to be the minor planet (139359) 2001 ME1 whose previously unnoticed dust activity near perihelion became optically amplified by efficient forward scattering of sunlight as the comet crossed between the Sun and SOHO/Earth at up to 175.6 deg phase angle. Simultaneous backscattering observations by the Solar Terrestrial Relations Observatory (STEREO) precisely constrain the comet's ~7 mag forward scattering brightening, enabling a direct comparison with the ~3 mag brightening of the more active but optically dust-poor comet 2P/Encke seen by SOHO and STEREO under similar geometry in 2017. Earlier STEREO observations from 2014 additionally show the newly recognized activity to be recurrent – consistent with a reanalysis of the comet's associated meteor activity – and has likely only been previously overlooked due to the comet's faintness and proximity to the Sun while active. Orbital integrations show the comet has likely followed a near-Earth orbit for at least the past 10 kyr, suggesting that the weakness of its observed activity evolved through its continued depletion of accessible volatiles.
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All authors Qicheng Zhang, Quanzhi Ye, Karl Battams, Matthew M. Knight, Worachate Boonplod, Rainer Kracht

Earth and Planetary Astrophysics

Sub-Neptune Memories I: Implications of Inefficient Mantle Cooling and Silicate Rain

Roberto Tejada Arevalo, Akash Gupta, Adam Burrows et al. (+3 more)

We explore the evolution of sub-Neptune (radii between $\sim$1.5 and 4 R$_\oplus$) exoplanet interior structures using our upgraded evolution code, APPLE, which self-consistently couples the thermal and compositional evolution of the whole structure. We incorporate stably stratified regions with convective mixing and, for the first time, ab initio results on the phase separation of silicate-hydrogen mixtures to model silicate rain in sub-Neptune envelopes. We demonstrate that inefficient mantle cooling can retain sufficient heat to Gyr ages: inefficient heat transport from mantle to envelope alone keeps radii $\sim$10% larger than predicted by adiabatic models at late times. Silicate rain can contribute an additional $\sim$5% to the radius, depending on envelope mass and initial metal abundance. The silicate-hydrogen immiscibility region may lie in the middle or even upper envelope, far above the envelope-mantle boundary layer, and bifurcates the envelope into two an upper, hydrogen-rich region and a lower, metal-rich region above the mantle. If silicate rain occurs, atmospheres should appear depleted of silicates while radii remain inflated at late ages. To demonstrate the effects of inefficient mantle cooling, we present interior evolution models for GJ 1214 b, K2-18 b, TOI-270 d, and TOI-1801 b, showing that hot, liquid silicate mantles with thin envelopes reproduce their radii and mean densities, providing an alternative to water-world interpretations. These results imply that bulk compositions inferred from mean density must account for the mantle thermal state and the envelope mixing/phase-separation history; such thermal “memories” may constrain formation entropies and temperatures when metallicities are more precisely measured.
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All authors Roberto Tejada Arevalo, Akash Gupta, Adam Burrows, Donghao Zheng, Yao Tang, Jie Deng