Cosmology and Nongalactic Astrophysics
A model-independent measurement of the Hubble constant from gravitational-wave standard sirens and electromagnetic observations
Gaurav N. Gadbail and Kazuharu Bamba
The Hubble tension is one of the most significant challenges in modern cosmology. Developing new approaches to estimate the Hubble constant is therefore crucial, and in this work, we employ a Gaussian process, a fully model-independent method that relies solely on observational data. To determine the Hubble constant, we use not only electromagnetic observations but also include gravitational-wave standard siren data from GWTC3. Our measurements of the Hubble constant are strongly consistent with the SH0ES result, with tensions less than $2\sigma$, indicating no statistically significant discrepancy. This approach quantifies the impact of gravitational-wave data on the determination of the Hubble constant, examines its consistency with electromagnetic measurements, and explores its potential role in addressing the Hubble tension.
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Cosmology and Nongalactic Astrophysics
Large-scale halo velocity correlations and the impact of finite simulation volumes
Yao-Tsung Chuang, Teppei Okumura and Takahiro Nishimichi
The velocity correlation functions directly measured from the peculiar velocity field of dark matter in numerical simulations are known to have an amplitude lower than that predicted by theoretical models at large scales. The trend persists for dark-matter
halos or
galaxies that are more closely related to the observables. We investigate the impact of the finite simulation box sizes on the measured velocity correlation functions of
halos, utilizing N-body simulations with different box sizes. We measure the
halo velocity correlations from N-body simulations with side lengths of $1{\rm Gpc}/h$ and $2{\rm Gpc}/h$, confirming the former is more suppressed compared to the linear theory prediction on large scales due to the lack of large-scale modes beyond the box size. In contrast, even though we subdivide the larger-box simulations into those with side lengths of $1{\rm Gpc}/h$, the amount of the suppression is the same as that from the original boxes, as the large-scale modes are already imprinted. Introducing the lower limit of the integral in the Hankel transform, $k_{\rm min}$, as a free parameter and marginalizing it over, we find that the constrained growth rate parameter, $f(z)\sigma_8(z)$, returns the correct value assumed in the simulations. However, when we ignore the effect and set $k_{\rm min}=0$, the constraint on $f\sigma_8$ is significantly biased if the correlation between different separation bins is also ignored. Furthermore, we find that the suppression of the velocity correlation amplitude on large scales depends on
halo mass, with more massive
halos exhibiting a systematically stronger suppression. These results highlight the importance of accounting for missing long-wavelength modes when developing simulation-based modeling of velocity statistics, such as emulators.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Neutron Dark Decay and Exotic Compact Objects
M. Vikiaris, V. Petousis, M. Veselsky et al. (+1 more)
Recent measurements of the compact
star XTE J1814-338, with a mass of $M=1.2_{-0.05}^{+0.05}\ M_{\odot}$ and a radius of $R=7_{-0.4}^{+0.4} \ {\rm Km}$ alongside those of HESS J1731-347, which has a mass of $M=0.77_{-0.17}^{+0.20}\ M_{\odot}$ and a radius of $R=10.4_{-0.78}^{+0.86} \ {\rm Km}$, provide compelling evidence for the potential existence of exotic matter in
neutron star cores. These observations offer important insights into the equation of state of dense
nuclear matter. Recently, Fornal and Grinstein, in order to overcame the discrepancy between the
neutron lifetime measured in beam and bottle experiments, proposed the existence of
neutron dark decay. In the present work, an effort is made to connect the interpretation of the above exotic compact objects with the possible existence of dark particles, assumed to be products of
neutron dark decay. Our hypothesis offers an advantage over comparable proposals, as the coexistence of dark matter and hadronic matter within
neutron stars emerges from an intrinsic mechanism, thereby obviating the need to invoke external merger-related processes. It is still unclear to what extent the proposed dark decay of the
neutron is affected by the extreme environment within
neutron stars. Within this framework, we examined the case in which a mechanism suppressing the dark
neutron decay becomes operative at densities few times above
nuclear saturation density. We found that the proposed alternative explanation accommodates the simultaneous existence of
neutron dark decay while consistently predicting both the two
solar mass limit and the presence of compact objects with subsolar masses.
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All authors M. Vikiaris, V. Petousis, M. Veselsky, Ch.C. Moustakidis
Solar and Stellar Astrophysics
SN 2017ati: A luminous type IIb explosion from a massive progenitor
Z.-H. Peng, S. Benetti, Y.-Z. Cai et al. (+21 more)
We present optical photometric and spectroscopic observations of the Type~IIb
supernova (SN)~2017ati. It reached the maximum light at about 27~d after the explosion and the light curve shows a broad, luminous peak with an absolute $r$-band magnitude of $M_{r} = -18.48 \pm 0.16$~mag. At about 50~d after maximum light, SN~2017ati exhibits a decline rate close to that expected from the $^{56}$Co $\rightarrow$ $^{56}$Fe radioactive decay, at 0.98 mag per 100 days, as usually observed in SNe IIb. However, it remains systematically brighter at late times by about 1–2~mag, exceeding the usual upper luminosity range of this class. As a result, modelling the light curve of SN~2017ati with a standard $^{56}$Ni decay scenario requires a large nickel mass of up to $\sim0.37\,M_{\odot}$ and still fails to reproduce the early-time light curve adequately. In contrast, incorporating additional energy input from a magnetar yields a significantly improved fit to the light curve of SN~2017ati, which would reduce the nickel mass to $\sim0.21\,M_{\odot}$, still close to the upper end of the range typically inferred for SNe~IIb. Comparing the fitted results of SN~2017ati with the known sample of SNe~IIb indicates that its luminosity
evolution is best explained by a combination of
neutron star spin-down energy and radioactive nickel deposition. From late-time nebular spectra of SN~2017ati, the luminosity of the [\Oi]~$\lambda\lambda6300,6364$ doublet implies an oxygen mass of $\sim1.82-3.34\,M_{\odot}$, and the combination of a [\Caii]/[\Oi] flux ratio of $\sim0.5$ with nebular spectral model comparisons favours a progenitor zero-age main-sequence mass of $\geq17\,M_{\odot}$.
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All authors Z.-H. Peng, S. Benetti, Y.-Z. Cai, A. Pastorello, J.-W. Zhao, A. Reguitti, Z.-Y. Wang, E. Cappellaro, N. Elias-Rosa, Q.-L. Fang, M. Fraser, T. Kangas, E. Kankare, Z. Kostrzewa-Rutkowska, P. Lundqvist, S. Mattila, T. M. Reynolds, M. D. Stritzinger, A. Somero, L. Tomasella, S.-P. Pei, Y.-J. Yang, J.-J. Zhang, Y. Pan
Solar and Stellar Astrophysics
Cosmic Ray Inter-Station Correlation Variations as Precursors of Geomagnetic Storms: A Statistical Study and Multi-Parameter Early Warning Framework
Haoyang Li, Zongyuan Ge and Zhaoming Wang
The modulation of
galactic cosmic rays (GCRs) by interplanetary disturbances, manifested as Forbush decreases (FDs), has long been recognized as a signature of coronal mass ejection (CME) passages through the heliosphere. While individual FD events have been extensively studied, systematic investigations of how GCR inter-station correlation variations relate to geomagnetic storm (GS) intensity have not been established. Here we analyze the relationship between GCR characteristics (from a global NM network) and GSs, aiming to understand the physical mechanisms of heliospheric disturbances and to develop complementary predictive capabilities beyond existing L1
solar wind monitoring. By applying a newly introduced anisotropy characteristic method alongside correlation analysis to 25 years of hourly NM data (1995-2020, seven stations), we demonstrate significant correlations between GCR parameters and geomagnetic activity. Inter-station relative differences and anisotropy enhancements show distinct precursor signatures depending on storm intensity, with extreme events displaying detectable signals 48-96 hours in advance. Based on these intensity-dependent response patterns, we propose a "two-stage multi-level" early warning framework: mid-term identification (48-96 hr) triggered by sustained anisotropy increases, followed by short-term grading (0-48 hr) based on inter-station relative difference variations and high-latitude flux changes. Validated on the extreme November 2003 and severe August 2018 geomagnetic storms, our approach successfully identifies precursor signals, providing a potential means to extend GS prediction windows.
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Solar and Stellar Astrophysics
From Main Sequence Binary to Blast: MESA Modeling of the Double-Detonation Progenitor PTF1~J2238+7430
Mercedes S. Hernandez, Thomas Kupfer, Diogo Belloni et al. (+1 more)
Hot subdwarf B (sdB)
stars in close binaries with white
dwarf (WD) companions are potential progenitors of double-detonation thermonuclear
supernovae. The recently discovered system PTF1 J2238+7430 is a candidate for this evolutionary channel, hosting a low-mass sdB and a comparatively massive WD in a compact orbit. We aim to reproduce the evolutionary history of PTF1 J2238+7430, in which the sdB forms first via stable mass transfer, followed by the formation of the WD through a subsequent common-envelope (CE) phase. Additionally, we seek to constrain the range of initial binary parameters that can lead to such double-detonation progenitors. Using the Modules for Experiments in
Stellar Astrophysics (MESA), we performed detailed binary
evolution simulations from the zero-age main sequence to the present-day configuration. We explored initial
stellar masses, orbital periods, and mass-loss fractions, including the effects of angular momentum transfer,
tidal synchronization, and gravitational-wave-driven orbital
evolution. The post-CE binary properties were derived using the standard energy formalism. Our models successfully reproduce the observed properties of PTF1 J2238+7430, consisting of a 0.406
solar-mass sdB and a 0.72
solar-mass WD in a 76.34-minute orbit. Stable Roche-lobe overflow of an approximately 2.7
solar-mass donor produces the sdB, while the WD forms from the initially less massive companion during an episode of CE
evolution. We find that the CE ejection efficiency must be high to match the observed orbit, exceeding canonical values for similar systems. We further delineate the allowed parameter space for initial binaries that can evolve into sdB+WD systems consistent with double-detonation progenitors. These limits are preliminary; a systematic exploration of all parameters is needed for robust constraints, but our results provide a useful starting point for future work.
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All authors Mercedes S. Hernandez, Thomas Kupfer, Diogo Belloni, Matthias R. Schreiber
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ed-ph
Lessons Learned from Integrating Generative AI into an Introductory Undergraduate Astronomy Course at Harvard
Christopher W. Stubbs, Dongpeng Huang, Jungyoon Koh et al. (+2 more)
We describe our efforts to fully integrate generative artificial intelligence (GAI) into an introductory undergraduate astronomy course. Ordered by student perception of utility, GAI was used in instructional Python notebooks, in a subset of assignments, for student presentation preparations, and as a participant (in conjunction with a RAG-encoded textbook) in a course Slack channel. Assignments were divided into GAI-encouraged and GAI-discouraged. We incentivized student mastery of the material through midterm and final exams in which electronics were not allowed. Student evaluations of the course showed no reduction compared to the non-GAI version from the previous year.
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All authors Christopher W. Stubbs, Dongpeng Huang, Jungyoon Koh, Madeleine Woods, Andrés A. Plazas Malagón
Astrophysics of Galaxies
Atom Addition Formation of Thionylimide (HNSO) on Interstellar Dust Grains: Chemical routes requiring oxygen and nitrogen atom surface diffusion
Juan Carlos del Valle, Miguel Sanz-Novo, Johannes Kästner et al. (+4 more)
We investigate the formation of the recently detected HNSO molecule using
quantum chemical calculations on ices and astrochemical models in tandem. Our results indicate that HNSO is efficiently produced on grain surfaces through reactions involving atomic oxygen and nitrogen atoms with the radicals NS and SO, forming NSO as a key intermediate. Subsequent hydrogenation of NSO leads to HNSO, with a clear preference for the lowest energy cis conformer, while the trans form is metastable and may be short-lived under typical interstellar conditions. The models predict that solid HNSO can reach abundances comparable to icy OCS, placing it among the major sulfur-bearing species in interstellar ices. Gas-phase abundances, in contrast, remain lower than those of OCS. The implementation of a multibinding scheme in our models clarifies the role of diffusive chemistry in the production of HNSO at early times, improving agreement with observations. These findings suggest that reactions involving diffusing O and N atoms on icy grains contribute significantly to sulfur chemistry and beyond in dense clouds and motivate further searches for molecules containing simultaneously H, N, O and S in other astronomical environments.
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All authors Juan Carlos del Valle, Miguel Sanz-Novo, Johannes Kästner, Kenji Furuya, Víctor M. Rivilla, Rafael Martín-Domńech, Germán Molpeceres
Solar and Stellar Astrophysics
Stellar Interpretation of Meteoritic Data and PLotting for Everyone (SIMPLE): Isotope Mixing Lines for Six Sets of Core-Collapse Supernova Models
Marco Pignatari, Mattias Ek, Georgy V. Makhatadze et al. (+15 more)
Bulk meteorites and their inclusions exhibit, for many chemical elements, isotopic variability produced by nucleosynthetic events in
stars and
supernovae before the formation of the Sun. While the exact astrophysical origins of these variations are still a matter of debate, their identification provides insights on the environment of the Sun's birth and the formation of the
Solar System. Here we present a new Python tool called SIMPLE (
Stellar Interpretation of Meteoritic Data and Plotting for Everyone) designed to compare the isotopic composition of the ejecta from core-collapse
supernovae (CCSNe) with meteoritic data. In the present version, the SIMPLE toolkit includes a
dataset of 18 CCSN models, from 6 different published sets, with initial masses of 15, 20, and 25 M$_{\odot}$ and
solar metallicity. SIMPLE is designed to easily extract the isotopic abundances predicted by each CCSN model for any elements and post-process them into the format needed to compare to the meteoritic data, therefore, facilitating their interpretation. As an example of how to use SIMPLE, we analyze the composition of the Ni isotopes in the 18 models and confirm that bulk meteorite Ni anomalies are compatible with material from the innermost Si-rich region of CCSN ejecta. Designed as a collaborative platform, SIMPLE is open-source and welcomes community contributions to enhance its development and dissemination for
stellar nucleosynthesis and meteoritic studies. Future enhancements include addition of more model predictions and inclusion of mixing between different layers of
supernova ejecta.
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All authors Marco Pignatari, Mattias Ek, Georgy V. Makhatadze, Gábor G. Bálazs, Lorenzo Roberti, James M. Ball, Borbála Cseh, Alessandro Chieffi, Chris Fryer, Falk Herwig, Chiara Incollingo, Thomas Lawson, Marco Limongi, Thomas Rauscher, Maria Schönbächler, Andre Sieverding, Reto Trappitsch, Maria Lugaro
Astrophysics of Galaxies
BEACON: JWST NIRCam Pure-parallel Imaging Survey. IV. A Systematic Search for Galaxy Overdensities and Evidence for Gas Accretion Mode Transition
Ryo Albert Sutanto, Takahiro Morishita, Tadayuki Kodama et al. (+20 more)
We systematically search for
galaxy overdensities using 20 independent fields with a minimum of six filters (F090W, F115W, F150W, F277W, F356W, and F444W) from BEACON, the JWST Cycle 2 NIRCam pure-parallel imaging survey. We apply an adaptive kernel-density estimation method that incorporates the full photometric
redshift probability distribution function of each
galaxy to map
galaxy overdensities, and identify 207 significant ($>4\,\sigma$) overdensities at $1.5<z<5$. We measure the quenched-
galaxy fraction, the median specific
star formation rate (sSFR), the total
halo mass, and the local
galaxy density of each system. By investigating the correlation among these observables, we find that
galaxy quenching proceeds in two paths:($i$) Overdensities within more massive
halos exhibit higher quenched fractions and lower averaged sSFRs. This trend weakens at $z\gtrsim2$, consistent with cold gas streams penetrating shock-heated massive
halos and sustaining
star formation activity at early times. ($ii$) We also find a dependence of the same parameters on local densities at $z<2$, where the quenched fraction increases and the sSFR decreases toward higher densities. The environmental trend in sSFR weakens at $z\sim2$–$3$ and shows tentative evidence for a reversal at $z>3$, potentially due to a larger cold gas supply in earlier times. Our study reveals a complex interplay between individual
galaxies and large-scale environmental properties, marking the onset of environmental effects on
galaxy quenching in massive
halos at
cosmic noon.
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All authors Ryo Albert Sutanto, Takahiro Morishita, Tadayuki Kodama, Abdurro'uf, Larry D. Bradley, Andrew J. Bunker, Nima Chartab, Nuo Chen, Matthew J. Hayes, George Helou, Novan Saputra Haryana, Nicha Leethochawalit, Zhaoran Liu, Charlotte A. Mason, Marc Rafelski, Michael J. Rutkowski, Massimo Stiavelli, Kosuke Takahashi, Harry I. Teplitz, Michele Trenti, Tommaso Treu, Benedetta Vulcani, Yechi Zhang
High Energy Astrophysical Phenomena
SN 2024abfl: A Low-Luminosity Type IIP Supernova in NGC 2146 from a Low-Mass Red Supergiant Progenitor
Xiaohan Chen, Ning-Chen Sun, Qiang Xi et al. (+44 more)
Type IIP
supernovae (SNe IIP) exhibit a significant diversity in their explosion properties, yet the physical mechanisms driving this diversity remain unknown. In this work, we present photometric and spectroscopic observations of SN 2024abfl, a SN IIP in NGC 2146 with a directly detected red supergiant (RSG) progenitor. We find it has a low plateau luminosity ($M_V \sim -15$ mag) and a relatively long plateau length ($\sim 126.5$ days). By fitting a semi-analytical model, we estimated a $^{56}$Ni mass of $\sim 0.009 M_\odot$, an initial kinetic energy of $\sim 0.42$ foe, an initial thermal energy of $\sim 0.03$ foe and an ejecta mass of $\sim 8.3 M_\odot$. The spectral
evolution of SN 2024abfl is similar to those of other SNe IIP, except for much lower ejecta velocities at similar epochs. At later epochs, we find a relatively high-velocity H$\alpha$ absorption feature at $\sim -4000$ km s$^{-1}$, possibly due to a fast-moving plume of matter in the inner ejecta, and two emission features at $\pm 2000$ km s$^{-1}$, possibly caused by CSM interaction. We estimate the progenitor mass to be $\le 15 M_\odot$ based on nebular spectra. We conclude that SN 2024abfl is a low-luminosity SN IIP originating from a low-mass RSG progenitor.
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All authors Xiaohan Chen, Ning-Chen Sun, Qiang Xi, Chun Chen, Yu Zhang, Zexi Niu, Junjie Jin, Yiming Mao, Beichuan Wang, Samaporn Tinyanont, Krittapas Chanchaiworawit, Kanthanakorn Noysena, David Aguado, Ismael Perez-Fournon, Frédéric Poidevin, Justyn R. Maund, Xunhao Chen, Pengliang Du, David López Fernández-Nespral, Liguo Fang, Guolin Gao, Jiupeng Guo, Min He, Xinyi Hong, Zhigang Hou, Qingzheng Li, Wenxiong Li, Tongyu Liu, Alicia López-Oramas, Haiyang Mu, César Rojas-Bravo, Jianfeng Tian, Jinhui Wang, Lingzhi Wang, Rui Wang, Yanan Wang, Ziyang Wang, Klaas Wiersema, Ying Wu, Guo Zhen, Jie Zheng, Guoyin Zhu, Yinan Zhu, Zhou Fan, Jing Li, Hong Wu, Jifeng Liu
Cosmology and Nongalactic Astrophysics
Parametric Resonance and Backreaction Effects in Magnetogenesis from Ultralight Dark Matter
Nirmalya Brahma and Robert Brandenberger
We take a more detailed look at the recently proposed magnetogenesis mechanism triggered by ultralight dark matter coupled to electromagnetism. The proposed mechanism made use of a tachyonic resonance channel which leads to the exponential amplification of infrared modes. Here, we first investigate a possible narrow band parametric resonance channel which can produce
photons at higher frequencies. Secondly, we estimate the effects of back-reaction on terminating the resonance. We find that there is indeed a narrow resonance channel. It is characterized by a Floquet exponent which is slightly smaller than the corresponding exponent for the tachyonic resonance. However, there is a region of parameter space (corresponding to a very small coupling constant) for which the tachyonic resonance is ineffective. In this case, the narrow resonance will dominate, and it will still be sufficiently strong to generate the observed
magnetic fields on cosmological scales. Our analytical treatment of the back-reaction effects considered here indicates that a fraction of order one of the initial dark matter density can flow into the gauge fields. Hence, our magnetogenesis scenario appears to be robust to back-reaction effects.
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Solar and Stellar Astrophysics
Limb Shift of the Fe I 6569 Å line on the Sun
H. C. Yu, M. D. Ding, J. Hong et al. (+2 more)
The convective motions of
solar granules generate a center-to-limb variation of Doppler velocity in the photospheric lines, known as the limb shift effect. This study presents a comprehensive analysis of this effect for the Fe I 6569 Å line using both observational data from the CHASE mission and numerical simulations from the Bifrost code. We employ two independent methods to derive the limb shift curve: a spectral-averaging method (Method 1) and a velocity-averaging method (Method 2). By comparing synthetic and observed data, we determine the convective blueshift, which is not accounted for in the CHASE observations. The simulations reproduce the observed trends for both methods at the instrument's spatial resolution of 1.2 arcsec. However, at resolutions below 1 arcsec, Method 2 produces limb-shift curves that depart significantly from both Method 1 results and traditional limb-shift profiles, whereas Method 1 remains in agreement with classical behavior. Further analysis finds that the results from Method 1 comprise two distinct components: a contrast contribution caused by the correlation between velocity and line depth, and a Dopplergram contribution caused by density inhomogeneities and corrugation effects.
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All authors H. C. Yu, M. D. Ding, J. Hong, Y. K. Wang, Z. Li
Astrophysics of Galaxies
Variable Modified Newtonian Mechanics VIII: Ultra faint dwarfs in Milky Way
James Chi Chung Wong
Velocity dispersions of Ultra faint
dwarf (UFD)
galaxies are observed to deviate significantly from the
Baryon Tully Fisher Relation of the massive
galaxies (BTFR). We propose a solution with Variable Modified Newtonian dynamics model, which could explain this deviation.
Instrumentation and Methods for Astrophysics
A Quantum Computing Framework for VLBI Data Correlation
Lei Liu
We present a
quantum computing framework for VLBI data correlation. We point out that a classical baseband time series data of length $N$ can be embedded into a
quantum superposition state using amplitude encoding with only $\log_2 N$
qubits. The basic VLBI correlation and fringe fitting operations, including fringe rotation,
Fourier transform, delay compensation, and cross correlation, can be implemented via
quantum algorithms with significantly reduced computational complexity. We construct a full
quantum processing pipeline and validate its feasibility and accuracy through direct comparison with a classical VLBI pipeline. We recognize that amplitude encoding of large data volumes remains the primary bottleneck in
quantum computing; however, the quantized nature of VLBI raw data helps reduce the state-preparation complexity. Our investigation demonstrates that
quantum computation offers a promising paradigm for VLBI data correlation and is likely to play a role in future VLBI systems.
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Cosmology and Nongalactic Astrophysics
From Nonparametric Distance Reconstruction to Testing the Etherington Relation and Cosmic Curvature Using 2D and 3D BAO Measurements
Darshan Kumar, Jie Zheng, Zhi-Qiang You et al. (+1 more)
We present a joint test of
cosmic curvature, $\Omega_{k0}$, and the
cosmic distance-duality relation (CDDR) using the Etherington relation, which connects the luminosity and angular diameter distances at the same
redshift. In this work, we combine the angular diameter distance measurements from recent
Baryon Acoustic Oscillation (BAO) observations with luminosity distances reconstructed from
Cosmic Chronometers data of Hubble parameter $H(z)$ using a non-parametric technique, Gaussian Process. A key part of our analysis is the systematic comparison of different BAO measurements (2D BAO, 3D BAO, and 3D DESI BAO) to determine whether any potential tension between angular and anisotropic BAO data affects constraints on the distance duality parameter $\eta(z)$ and $\Omega_{k0}$. We adopt four representative parameterizations of $\eta(z)$ to examine the correlation between $\eta(z)$ and $\Omega_{k0}$. Our results show no evidence for violation of the CDDR, with $\eta(z)$ consistent with unity at the 99% confidence level for all BAO
datasets and parameterizations. In all scenarios, the best-fit values of $\Omega_{k0}$ mildly favor a non-flat universe, although a spatially flat universe remains compatible at the 95% confidence level. The constraints on $\eta_1$ and $\Omega_{k0}$ indicate slight variations across different BAO
datasets, but the discrepancies between the 2D and 3D BAO measurements do not introduce any significant bias, and no statistically meaningful tension is observed. Our work provides robust constraints on
cosmic curvature and the validity of the CDDR based on non-parametric distance reconstruction.
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All authors Darshan Kumar, Jie Zheng, Zhi-Qiang You, Da-Chun Qiang
Earth and Planetary Astrophysics
Propulsion Trades for a 2035-2040 Solar Gravitational Lens Mission
Slava G. Turyshev
The
Solar Gravitational Lens (SGL) enables resolved imaging and spectroscopy of nearby terrestrial
exoplanets, but useful science begins only after a spacecraft reaches roughly 650-900 astronomical units (AU). A 20 yr lower-bound trip to 650 AU requires an average radial speed of 32.5 AU per year, or 154 km/s, before launch, targeting, steering, and operations margins. We compare close-perihelion
solar sailing, fission-electric
nuclear electric propulsion (NEP), and high-thrust Oberth injection followed by NEP cruise using common lower-bound outbound-leg architecture envelopes, not closed end-to-end trajectories. For an ideal sail passing 0.05 AU from the Sun, total sailcraft areal density must be about 4.9 grams per square meter to reach 105 km/s, and 2.3 grams per square meter to reach 155 km/s. Thus sub-20 yr sail-only access requires ultra-low areal density plus deep-perihelion thermal qualification. For a 20 t NEP spacecraft with 800 kg payload and Isp=9000 s, optimized constant-power transfers reach 650 AU in t_rep ~ 27-33 yr when the integrated power-plus-propulsion specific mass is 10-20 kg per electric kilowatt, requiring 0.18-0.30 megawatt-electric (MWe) and few-newton thrust. NEP-only t_rep <20 yr requires <3 kg per electric kilowatt, while hybrid architectures can approach t_rep ~ 20 yr if an upstream injection stage supplies 50-70 km/s. Thus sail-first is the nearer-term lightweight-access path; hybrid injection+NEP is higher-capability but requires prior high-energy-injection and 0.2-0.4 MWe integrated NEP demonstrations.
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Instrumentation and Methods for Astrophysics
GASV: A New VLBI analysis software for Geodesy and Astrometry
Dang Yao, Yuan-wei Wu and Xu-hai Yang
We present GASV, a novel Python-based software package specifically designed for the analysis of Very Long Baseline Interferometry (VLBI) data. Developed with ease of installation and user friendliness in mind, GASV supports both pipeline and interactive processing modes. The software processes VLBI baseline delays and rates in standard formats such as HOPS outputs and NGS card files to estimate key geodetic and astrometric parameters, including station coordinates, Earth Orientation Parameters, source coordinates, clock parameters, and atmospheric models. We evaluate the capabilities and performance of GASV, demonstrating that its parameter estimation accuracy for IVS INT, Regular, and CONT sessions is comparable to that achieved by the VLBI analysis centers at BKG and USNO. As a state-of-the-art tool, GASV not only enables high-quality single-session data processing but also but also supports global analyses of long-term SINEX files, generating Celestial Reference Frame and Terrestrial Reference Frame solutions with reliable accuracy.
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Astrophysics of Galaxies
A high rate of foreground contaminants toward high-redshift galaxies resolved by JWST
Weiyang Liu and Linhua Jiang
We present a study of high-
redshift Ly$\alpha$ emitters (LAEs) with multiple components using HST and JWST. High-
redshift galaxies are mostly point-like objects on ground-based images, but they often exhibit multiple components in higher spatial resolution images. JWST for the first time allow detailed analyses on these individual components. We collect 840 spectroscopically confirmed LAEs at $z=2\sim7$ from the literature and nearly 50% of them appear to have multiple components in JWST images. We further construct a sample of 248 LAEs that have two or more relatively isolated components in a circular aperture of 2$\arcsec$ in diameter. We estimate photometric
redshifts for all 593 components of the 248 LAEs, and find that 68% of them are `real components' with photometric
redshifts consistent with the spectroscopic
redshifts of the LAEs. The remaining components are mostly foreground objects. The fraction of the `real components' decreases rapidly with the projected distance to the LAE centers from $\sim80\%$ at $0\farcs2-0\farcs4$ to $\sim30\%$ at $0\farcs8-1\farcs0$. Our SED modeling results suggest that the majority of the LAEs are young, low-mass, low extinction starburst
galaxies (partly due to a selection effect), and their `real components' have stronger
star-forming activities than main-sequence
galaxies. We investigate the potential impact of the high foreground contamination rate on previous studies based on ground-based images that often use a 2$\arcsec$ aperture for photometry, and find that some of key parameters such as
stellar mass would have been largely affected.
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Astrophysics of Galaxies
Kinematic-Distance Biases in the Inner Milky Way from a Stellar-Dynamically Constrained Bar
Junichi Baba
We quantify how bar-driven non-circular motions bias Milky-Way gas maps inferred with the kinematic-distance (KD) method. KD reconstructions of H\,i and CO surveys assume circular rotation in an axisymmetric potential, an assumption that is strongly violated in the barred inner Milky Way. We use high-resolution hydrodynamical simulations of gas flow in an observationally constrained barred Milky Way potential. From a quasi-steady snapshot we generate synthetic longitude–velocity data and apply a standard axisymmetric KD inversion using the circular-speed curve derived from the $m=0$ component of the same potential. To isolate non-circular effects, we remove the near–far ambiguity by selecting, for each gas element, the KD branch closest to its true distance. We find that the KD method reproduces the gas distribution reasonably well outside the bar-dominated region ($R \gtrsim 5$~kpc), but fails systematically in the bar region ($R \sim 0.5$–3~kpc). There the KD-reconstructed face-on map exhibits anisotropic, quadrant-dependent artifacts, including arc-like overdensities and LOS-elongated low-density cavities. In azimuthally averaged profiles, these anisotropic misassignments translate into net radial mixing: the axisymmetric KD inversion substantially fills in the true bar-induced depression (hereafter, the “bar gap”) and yields a flatter inner profile. Distance-error maps show coherent structures with $|\Delta d| \sim 1$–2~kpc and relative errors of several tens of percent along the bar and inner ring, coincident with zones where the KD mapping is intrinsically ill-conditioned, quantified by a large
geometric sensitivity $S \equiv \left|\partial d/\partial V_{\rm LOS}^{\rm circ}\right|$. In these regions the error is well approximated to first order by $\Delta d \simeq S\,\Delta V_{\rm LOS}$, linking KD failures directly to bar-driven streaming velocities. ...
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Astrophysics of Galaxies
Intermediate-Mass Black Hole Formation from Hierarchical Mergers in Galactic Nuclei
Amanda Newton, Sanaea C. Rose, Fulya K{\i}roğlu et al. (+2 more)
Dense
stellar environments like
nuclear star clusters (NSCs) can dynamically assemble gravitational wave (GW) sources. We consider a population of single
stellar mass black holes (BHs) in the inner $0.1$~pc of a NSC surrounding a $4 \times 10^6$~M$_\odot$ supermassive black hole (SMBH). Using a semianalytic model, we account for direct collisions between BHs and
stars and GW capture between BHs. We explore the effect of the initial BH mass and
spin distributions on their final properties and the production of GW sources. Specifically, we consider upper and lower limits for the BH initial mass distribution, and we account for the possibility that a subset of our initial population are the merger products of
primordial BH binaries. We find that $\sim 500$ M$_{\odot}$ intermediate mass black holes (IMBHs) can form for our upper limit mass distribution, while our lower limit mass distribution forms none. Most IMBHs $\gtrsim 200$~M$_\odot$ eventually sink towards the center of the cluster and merge with the SMBH. We also find successive BH-
star collisions can produce low-spinning BHs with $\chi \lesssim 0.2$. Our results have implications for LIGO-Virgo-KAGRA sources. We find that the overall merger rate depends primarily on the initial BH mass distribution and is $\gtrsim 10^{-9}$~yr$^{-1}$ per Milky Way-like
galaxy for our range of initial conditions. However,
primordial binaries can change the number of GW mergers with second and higher generation progenitor BHs by an order of magnitude.
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All authors Amanda Newton, Sanaea C. Rose, Fulya K{\i}roğlu, Bao-Minh Hoang, Frederic A. Rasio
High Energy Astrophysical Phenomena
McFACTS. IV. Electromagnetic Counterparts to AGN-disk-embedded Binary Black Hole Mergers
Emily McPike, Rosalba Perna, K.E. Saavik Ford et al. (+10 more)
The
accretion disks of active
galactic nuclei (AGNs) are promising environments for producing binary black hole (BBH) mergers, which have been detected via gravitational waves (GWs) with the LIGO-Virgo-KAGRA (LVK) GW detector network. BBH mergers embedded in AGN disks are unique among GW formation channels in their generic ability to produce electromagnetic (EM) counterparts, via interactions between the merger remnant and the surrounding disk gas (though these are not always observable). While such mergers represent valuable multimessenger sources, the lack of predictive statistical models in existing literature currently limits our ability to select possible EM counterparts with GW detections in archival data and in real time using time-domain surveys such as the Zwicky Transient Facility or LSST. Here we employ the Monte Carlo For AGN Channel Testing and Simulation code (McFACTS, https://www.github.com/mcfacts/mcfacts) to predict the bolometric luminosities of jets and shocks associated with LVK-detectable BBH merger remnants in AGN disks. McFACTS predicts the distribution of GW observables for an underlying black hole population and disk model. In this work we present a new capability that simultaneously generates the distribution of bolometric EM luminosities corresponding to these predicted GW detections. Our results are consistent with current observational surveys and indicate that (i) migration in dense, Sirko-Goodman-like disks preferentially produces EM counterparts from high-mass ($\mathscr{M} > 40M_{\odot}$), high-
spin remnants across multiple merger generations and (ii) lower chirp mass mergers are more likely to contribute observable counterparts and with shorter emission breakout times in less dense, Thompson-Quataert-Murray-like disks.
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All authors Emily McPike, Rosalba Perna, K.E. Saavik Ford, Barry McKernan, Harrison E. Cook, Vera Delfavero, Miranda McCarthy, Kaila Nathaniel, Jake Postiglione, Nicolas Posner, Varun Pritmani, Shawn Ray, Richard O'Shaughnessy