Instrumentation and Methods for Astrophysics
The Role of Artificial Intelligence in the SKA Era
Philipp Denzel, Frank-Peter Schilling and Elena Gavagnin
The Square Kilometre Array Observatory (SKAO) will usher in an era of unprecedented data complexity and scientific opportunity in
radio astronomy, producing petabyte-scale
datasets and terabit-per-second streams that challenge traditional analysis paradigms. Artificial Intelligence (AI) stands at the forefront of this transformation, offering scalable, adaptive solutions to the most pressing problems in
radio astronomy and astrophysics. This chapter explores the pivotal role of AI in the SKA era, from real-time operations to scientific discovery. We examine how deep learning models enable automated source detection,
radio-frequency interference mitigation, anomaly detection, and parameter inference, while generative approaches accelerate sky simulations, calibration, and imaging. Reinforcement learning promises dynamic scheduling and autonomous system control, and
federated learning could address the distributed nature of SKA data. Beyond performance, we emphasize the necessity of explainability, uncertainty quantification, and physics-informed inductive biases to ensure scientific integrity. By mapping SKAO's core challenges - data volume, complexity, and interpretability - onto modern AI methodologies, we review how deep learning, self-supervised frameworks, and probabilistic models can unlock new frontiers in cosmology,
galaxy evolution, and time-domain astrophysics. AI is not merely an automation tool for coping with scale. It is a catalyst for discovery, redefining how we observe, model, and understand the Universe.
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Astrophysics of Galaxies
pop-cosmos: Galaxy size evolution across structural and star-formation classifications in COSMOS-Web
Madalina N. Tudorache, Hiranya V. Peiris, Stephen Thorp et al. (+7 more)
Galaxy sizes are correlated with
stellar mass and
redshift, as characterised by size scaling relations. The inferred forms of these scaling relations are sensitive to how
galaxies are classified – either by their
star formation activity (e.g. specific
star-formation rate, sSFR) or by their morphology markers (e.g. bulge-to-total ratio, Sérsic index). We combine
stellar mass and sSFR estimates from pop-cosmos (a generative model trained on COSMOS2020 Spitzer IRAC $\textit{Ch.1} <26$) with size and morphology measurements from COSMOS-Web, obtaining $99,369$
galaxies. By investigating the size-mass and the size-
redshift relations, we show that: (i) the sSFR/morphology splits give quantitatively different slopes, intercepts, and intrinsic scatter behaviour; (ii) intrinsic scatter depends on structural morphology but not on sSFR, which constrains the
galaxy-
halo connection; (iii) the quiescent and bulge-dominated size-mass relations both show double-power law breaks, but at different pivot masses, indicating that quenching and structural transformation occur on different time-scales; (iv) the morphology-dependent trends are only recoverable from space-based imaging. Further, the quiescent pivot mass $M_{\ast} \sim 10^{10.7}~\mathrm{M}_{\odot}$ coincides with the mass scale at which AGN (infrared
torus) bolometric luminosity fraction peaks in transitioning
galaxies, while the bulge-dominated pivot mass $M_{\ast} \sim 10^{11.1}~\mathrm{M}_{\odot}$ coincides with the
halo mass at which AGN-driven baryonic redistribution peaks, tracing the interval over which AGN feedback ramps from quenching onset to structural transformation.
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All authors Madalina N. Tudorache, Hiranya V. Peiris, Stephen Thorp, Sinan Deger, Daniel J. Mortlock, Gurjeet Jagwani, Anik Halder, Boris Leistedt, Benedict Van den Bussche, Joel Leja
Cosmology and Nongalactic Astrophysics
Dark energy from neutrino interactions in Unimodular Gravity
Alejandro Gil-Ocaranza, Josue De-Santiago, Mauricio Lopez-Hernandez et al. (+1 more)
We investigate a dark energy scenario generated by
neutrino interactions mediated by a light scalar field, in which finite-temperature corrections induce an effective
neutrino mass that evolves with the thermal history of the Universe. Within the framework of Unimodular
Gravity, these interactions give rise to a non-conservation current, leading to dynamical dark energy. We study one- and two-
neutrino realizations of the model. In the one-
neutrino case, the dark energy density evolves monotonically, whereas in the two-
neutrino scenario it can reach a maximum at intermediate
redshifts before decreasing at late times. Using late time cosmological
datasets, we constrain the effective interaction strength for lightest-
neutrino masses in the range $0.05 \,{\rm meV}\le m_1 \le 1 \,{\rm meV}$. We find preferred interaction scales of order $G_s\sim10^{12} \, {\rm eV}^{-2}$ with a significance of $2 \sigma$, with the inferred coupling decreasing as the assumed
neutrino mass increases. Assuming
neutrino couplings of order unity, this $G_s$ value corresponds to an ultralight mediator with mass $m_\phi\sim10^{-6} \, {\rm eV}$. We further assess the impact of Planck distance-prior, finding a noticeable reduction in parameter degeneracies and a reconstructed dark energy
evolution closer to that of a cosmological constant. Our results show that
neutrino interactions can generate both monotonic and non-monotonic dark energy evolutions while remaining compatible with current cosmological observations. The inferred interaction strengths remain consistent with non-zero values for part of the explored
neutrino-mass range, supporting
neutrino-induced dark energy dynamics as a viable phenomenological extension of $\Lambda$CDM at the background level.
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All authors Alejandro Gil-Ocaranza, Josue De-Santiago, Mauricio Lopez-Hernandez, Jorge L. Cervantes-Cota
Cosmology and Nongalactic Astrophysics
Strongest constraints on dark acoustic oscillations from the Lyman-alpha forest
Zhihan Yuan, Caleb Gemmell, Keir K. Rogers et al. (+4 more)
We set the first constraints on a small-scale dark acoustic oscillation (DAO) in the linear matter power spectrum arising from dark sector interactions, with a full forward model of the Ly-$\alpha$ forest. No more than 30% of dark matter can form DAOs if they peak at wavenumbers $< 50\,h\,\mathrm{Mpc}^{-1}$ (95% c.l.), probing scales $25 \times$ smaller than the
cosmic microwave background (CMB). Given the complex covariance of DAO and nuisance parameters, we use a deep kernel learning emulator of hydrodynamical simulations to capture imprints of linear oscillations in the Ly-$\alpha$ forest.
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All authors Zhihan Yuan, Caleb Gemmell, Keir K. Rogers, Jared Barron, Sandip Roy, David Curtin, Norman Murray
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Background-Induced Forces from Quadratically Coupled Ultralight Dark Matter
Thomas Bouley, Xucheng Gan, Hailin Xu et al. (+1 more)
Quadratically coupled ultralight scalar dark matter behaves as a coherent classical field whose interactions with matter can induce a composition-dependent force through the dark matter background. We present a complete calculation of this background-induced force beyond the spherically symmetric approximation. Using a partial-wave treatment of dark-matter scattering, we determine its angular dependence and derive an analytic description valid even when the dark-matter wavelength is much smaller than the Earth's radius. We show for the first time that Earth screening generates a characteristic frequency-band structure, splitting the signal into multiple sidebands that provide a distinctive experimental signature. We further show that the relative amplitudes of these sidebands vary annually due to the Earth's motion through the dark-matter
halo, enabling the construction of a complete signal template. As an application of these results, we re-evaluate constraints from the MICROSCOPE mission, which currently provides the strongest laboratory limits on equivalence-principle violations from ultralight dark matter. We further show that proposed space-based equivalence-principle experiments, such as Galileo Galilei and STE-QUEST, can significantly enhance their sensitivity to ultralight scalar dark matter by incorporating the full frequency-band information.
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All authors Thomas Bouley, Xucheng Gan, Hailin Xu, Tien-Tien Yu
Instrumentation and Methods for Astrophysics
Domain-Informed Multi-View Self-Distillation for Astronomical Light-Curve Representation Learning with JEPA
Yicheng Rui
Light curves describe temporal variations in the brightness of celestial objects. Learning robust representations of light curves is essential for large-scale automatic discovery in the dynamic universe, but existing time-series foundation models often struggle with the uneven sampling, complex noise, and wide range of physical timescales that characterize astronomical observations. We propose a domain-informed representation learning framework for irregular astronomical time series with Joint-
Embedding predictive architecture (JEPA), combining semantics-preserving views, uncertainty-aware tokenization, and multi-view self-
distillation. The encoders are trained with multi-view self-
distillation using LeJEPA regularization on the LEAVES
dataset and evaluated on the StarEmbed classification
benchmark. On StarEmbed, our model outperforms hand-crafted features on 15 of 16 classification metrics. In few-shot linear probing, it achieves macro-F1 scores of 42.56 $\pm$ 7.21 with one sample per class and 63.58 $\pm$ 1.20 with 100 samples per class, consistently improving over hand-crafted features. Beyond variable-
star classification, the learned representation supports similarity search, parameter estimation, and photometric zero-point drift detection. We further evaluate cross-domain adaptation on 12 heterogeneous irregular time-series
datasets from PYRREGULAR, where the adapted variant matches or exceeds previous state-of-the-art performance on 5
datasets, compared with at most 3 wins by any single prior baseline. These results demonstrate that domain-informed multi-view self-
distillation is an effective strategy for learning representations of irregular time series, while also highlighting that successful time-series representation learning requires domain-specific inductive biases rather than a universally optimal architecture.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.pop-ph
Signs and Signatures of Intelligence
Julia DeMarines
Research into the emergence and
evolution of intelligence is underrepresented in astrobiology. I propose noosemiotics, the study of noosignatures, to address this gap. Noosignatures are the structured traces that minds leave on a medium, whether physical (tools, etchings, architecture) or signal-based (encoded transmissions, complex animal communication), that remain detectable as the products of intelligence regardless of whether their meaning can be recovered. Where biosignatures mark life and technosignatures mark technology, noosignatures mark the space between. This paper defines noosemiotics, situates it within astrobiology, and proposes a research program for empirical metrics, with material culture as the primary test bed.
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High Energy Astrophysical Phenomena
Continuation of Force-Free Electrodynamics upon the loss of magnetic dominance
Morifumi Mizuno
Force-Free Electrodynamics (FFE) describes the
evolution of the electromagnetic field in magnetically dominated
plasmas, but ceases to be
hyperbolic once the
magnetic dominance condition $F^{ab}F_{ab}>0$ is lost. We demonstrate that, after the loss of
magnetic dominance, FFE may be replaced by a theory of null fields, $F^{ab}F_{ab}=0=F^{ab}\tilde{F}_{ab}$, characterized by the condition that its principal null direction is tangent to a geodesic congruence. In flat spacetime, this theory may be equivalently stated as the condition that the field satisfies $\vec{B}^2-\vec{E}^2=0=\vec{E}\cdot\vec{B}$ and the integral curves of the drift velocity $\vec{E}\times\vec{B}/\vec{B}^{2}$ are straight lines. We develop the general structure and the properties of this theory and test it against 1D PIC simulations using the collision of planar symmetric Alfvén waves. We find that the force-free combined with the null continuation shows remarkable macroscopic agreement with PIC simulations, including the birth and
evolution of the null region ($F^{ab}F_{ab}=0$) and the formation of a current sheet. As an independent test, we apply the null continuation to Adhikari's type-changing solution, an exact FFE solution exhibiting finite-time loss of
magnetic dominance, and also find macroscopic agreement with 1D PIC simulations.
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High Energy Astrophysical Phenomena
The Role of Scintillation in Detecting HI Absorption in FRB Spectra
Om Gupta, Pawan Kumar, Paz Beniamini et al. (+1 more)
The 21-cm absorption line of neutral hydrogen has been a long hypothesized observational feature of the spectra of Fast
Radio Bursts (FRBs). The difficulties associated with detector noise in extracting HI absorption have been previously studied. We test the role that scintillation plays in the HI absorption line's detectability, and characterize the regimes where a realistic FRB may yield the 21-cm line. We build an efficient model to simulate diffractive scintillation arising from FRB passage through a thin scattering screen. We find that the absorption profile is detectable in a scintillation-dominated high signal-to-noise spectrum if the scintillation decorrelation bandwidth differs significantly in scale from the width of the absorption profile. Active repeaters also enable favorable conditions as the absorption signal improves when repeat bursts are stacked. Repeat bursts must be separated in time by more than the diffractive scintillation timescale, otherwise flux modulations with frequency are correlated. By cross-referencing repeating FRB positions with an observational catalog of Milky Way molecular clouds detected in CO, we find that the sightline to FRB 20180916B may intersect a
Galactic molecular cloud. For currently operating and planned sensitive
telescopes, the presence of both scintillation and noise requires $\gtrsim 1000$ bursts to be stacked to detect the HI absorption line at a $5\sigma$ significance. Improvement in detector sensitivities will help probe HI clouds intersected by FRBs in the host or intervening
galaxies, or in high-
redshift minihalos.
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All authors Om Gupta, Pawan Kumar, Paz Beniamini, Edward L. Robinson
Astrophysics of Galaxies
Kinematic detection of dusty outflows from active galactic nuclei: Polycyclic aromatic hydrocarbon kinematics of type 2 quasars with JWST/MIRI spectroscopy
Fergus R. Donnan, Cristina Ramos Almeida, Omaira González Martín et al. (+5 more)
Active
galactic nuclei (AGN) are thought to have dusty
outflows, but unlike in the gas phase, it is challenging to measure the kinematics of
dust. We present the detection and analysis of the kinematics of
dust in five type 2
quasars at $z\sim0.1$ from the
Quasar Feedback (QSOFEED) sample observed with JWST/MIRI spectroscopy. We used principal component analysis
tomography to produce velocity maps of polycyclic aromatic hydrocarbon (PAH) features, which are the smallest carbonaceous
dust particles. We were then able to compare velocity maps of the PAHs with emission lines of ionised and molecular gas. We produced velocity maps of the 11.3 $\mu$m PAH feature, which traces large and neutral PAHs, for three out of the five objects, where all three show an
outflow in the PAH kinematics. This becomes particularly clear after we subtracted disk kinematics, where the H$_2$ rotational transitions also show residuals consistent with an
outflow. Compared to previous work with Seyfert
galaxies, this work suggests that dusty
outflows are more common at higher Eddington ratios, $\lambda_{\rm Edd}\gtrsim0.1$, in agreement with previous suggestions, although the sample size is small. We were unable to produce velocity maps for the 6.2 $\mu$m PAH, which traces ionised PAHs, potentially due to differences in the intrinsic profile and/or suppression of the feature in AGN, which was seen previously in Seyfert
galaxies. This reflects studies of PAH band ratios where AGN
outflows have more neutral PAHs. This work demonstrates that dusty
outflows may be common, particularly at high Eddington ratios, and it therefore plays a key role in the
evolution and life cycle of AGN.
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All authors Fergus R. Donnan, Cristina Ramos Almeida, Omaira González Martín, Karin Sandstrom, Anelise Audibert, Marina Bianchin, Miguel Pereira-Santaella, Ismael García-Bernete
Cosmology and Nongalactic Astrophysics
Constraining primordial oscillations and inflationary particle production with Planck, ACT DR6, and DESI DR2
Simran K. Nerval, Renee Hlozek, Hidde T. Jense et al. (+1 more)
Non-standard inflationary models often predict oscillatory features in the
primordial power spectrum. We present constraints on general oscillatory templates for
primordial power spectra, including those that vary linearly and logarithmically with wavenumber, as well as oscillations induced by inflationary particle production. We utilize the Planck 2018 and Atacama Cosmology
Telescope Data Release 6
cosmic microwave background data as well as large-scale structure data from the Dark Energy Spectroscopic Instrument Data Release 2. To efficiently explore the
multimodal posteriors for these models as well as performing mode comparisons, we integrate the preconditioned sequential Monte Carlo sampler, pocoMC, into the widely used sampling code, Cobaya. We find that the combined
dataset tightens the 95% CL upper bounds on the general oscillation amplitudes to $A_{\text{lin}} < 0.021$, $A_{\text{log}} < 0.022$, and $A_{\text{log rf}} < 0.023$, restricting the amplitude to $\sim 2\%\, A_s$. For the inflationary particle production model, our analysis places a maximum a posteriori constraint on the coupling constant of $g = 0.034$. While these models all provide an improved fit to the data compared to the concordance $\Lambda$CDM model, the
Bayesian evidence still reveals a moderate preference for $\Lambda$CDM compared to models with general oscillations and is inconclusive regarding the particle production model, suggesting that the added complexity of these models beyond the standard model is not statistically justified by current data.
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All authors Simran K. Nerval, Renee Hlozek, Hidde T. Jense, J. Richard Bond
Astrophysics of Galaxies
SKA$-$VLBI view of AGN jets in the early Universe
C. Spingola, M. Mezcua, Y. Liu et al. (+33 more)
Active
Galactic Nuclei (AGN) are among the brightest sources in the Universe, and those that are also jetted are uniquely valuable at the earliest epochs, because their relativistic
outflows can regulate the gas supply of their host
galaxies, potentially affecting both early
star formation and the rapid growth of supermassive black holes (SMBHs). Their compact, high-brightness-temperature
radio cores provide the sharpest beacons for very long baseline interferometry (VLBI), enabling direct constraints on Doppler boosting, jet duty cycles, and jet$-$environment coupling at extreme
redshifts. In this White Paper, we discuss how the SKA-VLBI will provide sub-$\mu$Jy sensitivity together with milliarcsecond (mas) angular resolution to image and characterise jetted AGN at $z>6$ across SKA-Mid and SKA-Low frequencies. These observations can directly test SMBHs ($>10^6$ M$_{\odot}$) formation/
evolution models (including jet-assisted super-Eddington phases) and infer the geometry of the Universe, directly probing the cosmological framework at high precision. Synergies with current and next-generation multi-band facilities will also be crucial to fully understand their host
galaxies and their environment, providing an unprecedented panchromatic knowledge of the first jetted AGN.
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All authors C. Spingola, M. Mezcua, Y. Liu, S. Frey, S. Belladitta, T. An, M. Giroletti, A. Caccianiga, A. Moretti, L. Ighina, T. Sbarrato, G. Migliori, D. Dallacasa, L. I. Gurvits, K. É. Gabányi, K. Perger, Z. Paragi, R. D. Baldi, E. Bañados, G. Bernardi, M. Bondi, E. De Rubeis, F. D'Ammando, F. De Gasperin, I. Delvecchio, F. Vito, K. Rubinur, M. Krezinger, R. Lico, E. Momjian, M. Orienti, J. Hodgson, C. Stanghellini, A. Wang, M. Latif, H. Cao
Cosmology and Nongalactic Astrophysics
First results of sub-arcsecond scale objects identified with ASKAP using interplanetary scintillation
R. Chhetri, J. S. Morgan, R. D. Ekers et al. (+4 more)
We present a catalogue of 131 compact $(\lesssim 0.1 \,arcsec)$ sources detected at 823 MHz via their Interplanetary Scintillation (IPS). These measurements were made with the ASKAP
telescope, across its full field of view of 35 square degrees, utilising all 36 Phased Array Feed (PAF) beams. To bypass ASKAP's standard correlator's minimum integration limit of 10 s, we used the CRAFT data capture system (CRACO), with visibilities sampled every 110 ms. Here we present the data processing steps, the sources detected, and their IPS-inferred properties. ASKAP IPS cleanly separates two populations: compact hot spots embedded in extended lobes and IPS-unresolved sources which are AGN or CSO sources associated with the
galactic nucleus. We also compare these results with the results from observations of IPS at 162 MHz with the Murchison Widefield Array, providing the spectra of compact components between 162 MHz and 888 MHz. These measurements further re-enforce the dominance of peaked-spectrum SEDs in the compact-source population at frequencies below 1 GHz. This pilot study using test data is a pathfinder for a more comprehensive ASKAP IPS survey which is underway.
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All authors R. Chhetri, J. S. Morgan, R. D. Ekers, E. M. Sadler, V. A. Moss, A. Waszewski, P. E. Gordon-Hall
High Energy Astrophysical Phenomena
The impact of stellar binaries and star cluster dynamics on pair-instability supernovae
Francesco Gabrielli, Cristiano Ugolini, Lavinia Paiella et al. (+12 more)
Pair-instability
supernovae (PISNe) are among the most luminous transients in the Universe. However, they have never been confidently observed. Solving this puzzle would have key implications for several astrophysical topics, including
galaxy chemical enrichment, the interpretation of gravitational waves from binary black hole mergers, and the nature of red dropout sources seen by JWST. With this aim, we present the first in-depth study of PISN occurrence in binary
stars, both in isolation and in dense
star clusters. We employ the SEVN code, with PARSEC
stellar tracks, to evolve a suite of 35 synthetic binary populations, including variations on formation channels, cluster properties, and upper limit of the
stellar initial mass function. We find that binary interactions can boost the PISN rate by up to threefold, relative to single
stars, whereas binary hardening can either enhance or suppress PISN production, depending on whether the progenitors are
primordial or dynamically formed. Moreover, we showcase how our comprehensive framework for the
cosmic PISN rate can be used to constrain uncertain aspects of
stellar and
galaxy evolution models, via comparison with observations, including the recipes for
stellar-wind mass loss in very-massive
stars, and the
galaxy metallicity distribution throughout the Universe.
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All authors Francesco Gabrielli, Cristiano Ugolini, Lavinia Paiella, Benedetta Mestichelli, Manuel Arca Sedda, Lumen Boco, Kendall Shepherd, Giuliano Iorio, Guglielmo Costa, Giovanni Gandolfi, Andrea Lapi, Erik Zackrisson, Thomas Nordlander, Alessandro Bressan, Mario Spera
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Particle Production from Inhomogeneities: the off-shell side of gravitational waves
Michele Redi and Andrea Tesi
We continue the study of particle production from gravitational inhomogeneities in the early Universe. Focusing on sources active on sub-horizon scales, we derive general expressions relating particle production to the unequal-time two-point function of the stress-energy tensor sourcing scalar, vector and tensor metric perturbations. The resulting particle yield probes the time-like support of this correlator, and in the tensor case the same object controls gravitational wave emission when evaluated on the light-like support. This establishes a phenomenological link between dark matter production and gravitational wave signals, allowing the dark matter mass to be related to the amplitude of the
stochastic gravitational wave background. Our results show that, on sub-horizon scales, particle production from inhomogeneous metric backgrounds practically reduces to gravitational scattering. This directly connects the formalism to gravitational freeze-in from the Standard Model thermal bath, while extending it to non-thermal and out of
equilibrium sources. We apply the formalism to first order phase transitions and discuss the associated production from scalar and tensor perturbations. The mechanism can efficiently populate gravitationally coupled dark sectors, especially when the perturbations are generated shortly after inflation.
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Cosmology and Nongalactic Astrophysics
Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes
S. Allegrini, A. J. Iovino, G. Perna et al. (+1 more)
The curvaton provides a simple mechanism for generating strongly non-Gaussian
curvature perturbations after inflation, with potentially important consequences on small scales. We study curvaton dynamics beyond the standard quadratic potential and construct the local non-Gaussian map $\zeta=F(\zeta_{\rm G})$ relating the
curvature perturbation to an auxiliary Gaussian field $\zeta_{\rm G}$. Curvaton self-interactions make the onset of oscillations field dependent and modify the effective equation of state once the curvaton enters the adiabatic regime. We incorporate these effects using the abbreviated action, which provides a compact way to connect the frozen and oscillatory regimes and exposes sources of non-Gaussianity absent in the purely quadratic case. We apply the formalism to quadratic, monomial, quartic, and cosine potentials, for which we derive the mapping $F(\zeta_{\rm G})$ and show that self-interactions can either enhance or suppress the resulting non-Gaussianity depending on the potential and initial conditions. We consider non-perturbative aspects in the strongly non-Gaussian regime, and show how strong non-Gaussianity can suppress the power spectrum. As an application, we provide a bottom-up scenario in which strongly positive curvaton non-Gaussianity allows
primordial supermassive black hole seeds at peak amplitudes $\mathcal{A}_{\rm pk}\sim10^{-5}$, which are compatible with the COBE/FIRAS $\mu$-distortion bounds. This opens a new
primordial scenario for the Little Red Dots observed by the JWST. The
axion-like curvaton provides a particularly natural setting for this mechanism.
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All authors S. Allegrini, A. J. Iovino, G. Perna, H. Veermäe
High Energy Astrophysical Phenomena
Accretion-Driven Evolution of Compact-Object Populations in Gas-Rich Environments and the Origin of Massive Gravitational-Wave Sources
Mor Rozner, Alejandra Rosselli-Calderon and Enrico Ramirez-Ruiz
The origin of the most massive gravitational-wave sources remains elusive. We show that gas
accretion can be understood as a transport process in mass space, causing compact objects to migrate through a population at rates determined by the underlying growth law. Using a continuity-equation framework, we demonstrate that population
evolution is governed primarily by the mass dependence of the
accretion rate, $\dot m \propto m^\beta$.
Accretion laws with $\beta>1$ naturally produce divergent
evolution and generate extended high-mass tails, whereas $\beta<1$ leads to convergent
evolution and compresses the population toward a narrower range of masses. We apply this framework to physically motivated
accretion regimes and explore their consequences using analytical calculations and Monte Carlo population models. We show that sustained gas
accretion can substantially broaden compact-object mass distributions, populate the high-mass end of gravitational-wave catalogs, and alter the mass-ratio distribution of compact-object binaries. In particular, collective
accretion within compact binaries drives their mass ratios toward unity. Our results suggest that gaseous environments act as transport media that continuously reshape compact-object populations, providing a natural pathway toward the formation of massive mergers such as GW231123 and the high-mass tails increasingly revealed by gravitational-wave observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Generalizing the interacting dilatonic ghost condensate as a dark energy model
Manuel Gonzalez-Espinoza, Ramon Herrera and Johan Casimiro
In this article, we study the
cosmic evolution of a generalized dilatonic ghost condensate field as a dark energy candidate, formulated from a Lagrangian density with two dominant kinetic terms; one linear and one of arbitrary integer $n>2$ in combination with an exponential potential, which interacts with dark matter through a source term. We analyzed three scenarios: the non-interacting situation $Q=0$ and two different interaction models, $Q\propto\rho_m\dot{\phi}$ and $Q\propto \rho_m H$ to describe the
evolution of the present universe. For each interaction $Q$, we perform a detailed phase-space analysis to obtain stability conditions and identify critical points. In all situations, the system reproduces the standard cosmological dynamics and evolves toward late-time dark energy-dominated attractors, with quintessence or phantom features depending on the sign of the coupling parameter $\alpha$ associated with the standard kinetic term. Furthermore, a joint likelihood analysis with
Cosmic Chronometers, PantheonPlus, and DESI observations is performed for two values of power $n$ ($n=3$ and $n=5$) to determine marginalized parameter constraints at the confidence levels of 68$\%$ and 95$\%$ for the different $Q-$models. For the interaction term $Q\propto \dot{\phi}\rho_m$, we find that the direction of the flow of energy depends on the sign of the coupling parameter $\alpha$ associated with the standard kinetic term. However, for the interaction $Q\propto H\,\rho_m$, the direction of the energy flow is independent of the sign of the coupling parameter $\alpha$ and always remains negative, corresponding to an energy transfer from dark matter to dark energy.
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High Energy Astrophysical Phenomena
JWST observations support the jittering-jets explosion mechanism (JJEM) for the core-collapse supernova remnant SNR 0540-69.3
Dmitry Shishkin and Noam Soker
We examine published JWST observations of the core-collapse
supernova (CCSN) remnant SNR 0540-69.3 and identify a point-symmetric morphology in its inner ejecta. Within the framework of the jittering jets explosion mechanism (JJEM), we interpret this morphology as evidence that the ejecta were shaped by two, and likely three or more, pairs of jets during the explosion process. Both visual inspection and a recently developed quantitative
symmetry-identification method for astrophysical imaging reveal an approximate rotational
symmetry between the northeastern redshifted ejecta and the southwestern blueshifted ejecta. Each side contains clumps (
knots) surrounding a previously identified cavity, with the best quantitative correspondence obtained for a rotation of 189{\deg}. We further identify a
symmetry center that is offset from the current
pulsar position, strengthening an earlier claim for a
pulsar kick. We interpret the pair of cavities and their surrounding clumpy structures as having been shaped by multiple jet-launching episodes. In addition, we identify a pair of opposing nozzles at a large angle to the cavities, which we attribute to another jet pair. Guided by the similarities to point-symmetric planetary nebulae shaped by jets and by recent three-dimensional hydrodynamical simulations of the JJEM, we conclude that the inner ejecta were shaped by at least three jet pairs launched by the
neutron star after it acquired its kick velocity, consistent with the JJEM.
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High Energy Astrophysical Phenomena
Early Optical Follow-up of Gamma-Ray Bursts: The Critical Role of Robotic Telescopes
Rahul Gupta, Judith Racusin, Gor Oganesyan et al. (+26 more)
Gamma-ray bursts (GRBs) are the most luminous electromagnetic explosions in the Universe, and offer unique laboratories for studying relativistic jets, compact-object formation, particle acceleration, and the high-
redshift Universe. The early optical emission of GRBs, particularly within seconds to minutes after the burst, carries crucial information about the central engine, jet magnetization, bulk Lorentz factor, and circumburst environment. We present a comprehensive review of the early optical phenomenology of GRBs and the essential role played by ground-based robotic optical
telescopes to observe the fleeting early-time phenomena through rapid, automated responses to real-time GRB alerts and high-cadence photometry. We examine the key early optical features of GRBs, including
prompt optical emission coincident with the $\gamma$-ray phase, bright reverse shock optical flashes, the onset of external forward shock afterglow, and superimposed optical
flares, plateaus, and discuss the diagnostic power of each in constraining jet physics. We discuss the physical mechanisms underlying these phenomena and their implications for GRB physics (e.g., estimating the initial Lorentz factor $\Gamma_0$, magnetization, and the density profile). Early optical observations have constrained the initial bulk Lorentz factor $\Gamma_0 \sim 100$–$1000$, weak-to-moderate ejecta magnetization for events with prominent reverse shocks, the circumburst density profile, and the geometry of the
magnetic field in the ejecta through polarimetry. We also provide the technical capabilities and landmark contributions of major robotic facilities, and discuss future prospects in the era of SVOM, Einstein Probe, Rubin/LSST, ULTRASAT, TeV observatories, and multi-messenger alerts.
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All authors Rahul Gupta, Judith Racusin, Gor Oganesyan, Ramandeep Gill, Sergey Karpov, Samantha R. Oates, Maria Gritsevich, Alberto J. Castro-Tirado, Vladimir Lipunov, Benjamin P. Gompertz, Maria Giovanna Dainotti, S. Bradley Cenko, Bing Zhang, Toktarkhan Komesh, Martin Jelínek, Stéphane Basa, Takanori Sakamoto, Carl W. Akerlof, Antonio Martin Carrillo, Sam Shilling, Ryan Seeb, Shashi B. Pandey, Varun Bhalerao, M. D. Caballero-Garcia, Ivan Panchenko, Pavel Balanutsa, Artem Kuznetsov, Kirill Zhirkov, Natalia Tyurina
High Energy Astrophysical Phenomena
Numerical model of fast electron energy deposition in interstellar molecular gas
Aleksandr Nesterenok
The energy deposition of fast electrons in interstellar molecular gas is considered. We use the rotationally resolved cross sections for electron-impact excitation of H$_2$ molecule that were calculated using the adiabatic-
nuclei molecular convergent close-coupling method. The initial electron energy distribution is assumed mono-energetic, and the differential equation for electron energy distribution is solved. We compare calculated energy deposition parameters with the results of similar studies in which the Monte Carlo approach was used. It is shown that about 11 per cent of the initial energy of fast electrons goes into direct ro-vibrational excitation of energy levels of H$_2$ molecule including pure rotational excitation in neutral molecular gas. About 7 per cent of initial electron energy goes into the excitation to $v=1$ vibrational state of H$_2$ molecule, most of this energy eventually converts into emission of transitions at near-infrared wavelengths. For ro-vibrational levels with $v \geq 3$, the electron-impact excitation to electronic states followed by downward radiative transitions to the ground electronic state is the dominant mechanism of excitation. The yields for excitation to vibrational states via radiative cascading from excited electronic states are found to be $1.5-2$ times higher than were obtained in previous studies.
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Earth and Planetary Astrophysics
Reflective-Sail Weak Stability Boundary Structure with the Locally Optimal Control Law
Shuyue Fu, Jinkai Zhang, Di Wu et al. (+2 more)
Escaping from the Earth is the first step of interplanetary transfers. Traditional ballistic escape trajectories in the Sun-Earth circular restricted three-body problem face limitations in relatively long time of flight and low
hyperbolic excess velocity. To augment the construction of escape trajectories from the Earth, this Note proposes the concept of reflective-sail weak stability boundary structures and accordingly constructs and analyzes escape trajectories from the Earth in the context of the Sun-Earth planar circular restricted three-body problem with a reflective sail. Using an ideal reflective sail, the locally optimal control law to maximize the time derivative of the Keplerian energy with respect to the Earth is adopted. Levi-Civita regularization about the Earth is derived to address the singularity caused by the Earth. The configurations of reflective-sail weak stability boundary structures are calculated to provide initial states for constructing escape trajectories and information about regions where escape is facilitated. Then, the escape trajectories using a reflective sail are constructed based on the proposed weak stability boundary structures. The escape performance, including time of flight and estimated
hyperbolic excess velocity, is analyzed. Comparison with ballistic escape trajectories in the Sun-Earth PCR3BP is also performed, indicating improved escape performance characterized by shorter time of flight and higher
hyperbolic excess velocity.
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All authors Shuyue Fu, Jinkai Zhang, Di Wu, Shengping Gong, Peng Shi
Astrophysics of Galaxies
When Jets Don't Quench: Near-Infrared H$_{2}$ in Star Forming Low-Excitation Radio Galaxies
Swetha Sankar, Andreea O. Petric, Debora Pelliccia et al. (+11 more)
We present new Gemini/GNIRS near-infrared spectroscopic observations of eight low-
redshift ($z < 0.1$) blue low-excitation
radio galaxies (BLERGs), a rare subset ($\sim 2.5\%$ of low-excitation
radio galaxies; LERGs) that complicate the classical jet-mode AGN picture by combining
radio activity with
star-forming, gas-rich hosts. These
star-forming BLERGs exhibit significant warm H$_2$ emission traced via ro-vibrational transitions at $T \sim 2000$–$4000$ K. We find that BLERGs span a broad range of mass-normalized warm H$_2$ luminosities ($L_{\rm H_2}/M_\star$), comparable to
radio-emitting early-type
galaxies, yet without a clear positive dependence on
radio power. Instead, the strongest H$_2$ emission preferentially occurs in morphologically disturbed and advanced-merger systems, while compact
radio sources ($\lesssim 20$ kpc) remain plausible sites of localized jet-ISM interaction. Together, these results suggest that merger-driven processes, including
tidal shocks, gas inflows, and disturbed interstellar medium conditions, are the dominant drivers of warm molecular gas excitation in BLERGs, although localized jet-driven heating may contribute in individual systems. The compact
radio morphologies, gas-rich hosts, and rarity of BLERGs are consistent with a short-lived evolutionary phase in which
radio AGN activity coexists with an interaction-driven, molecular-rich interstellar medium prior to the onset of large-scale maintenance-mode feedback. Spatially resolved spectroscopy and higher-resolution
radio imaging will be essential to disentangle the relative roles of mergers and jets in regulating the molecular gas of jet-mode AGN.
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All authors Swetha Sankar, Andreea O. Petric, Debora Pelliccia, Timothy M. Heckman, Reiner M. J. Janssen, Mark Lacy, Nicole P. H. Nesvadba, Kate Rowlands, Pallavi Patil, Brian C. Lemaux, Maya Skarbinski, Annie Giman, Justin A. Otter, Katherine Alatalo
Cosmology and Nongalactic Astrophysics
Cancellation of one-loop time dependence in superhorizon curvature perturbations from all scales
Keisuke Inomata
We show the conservation of the superhorizon
curvature perturbations at one-loop level in spatially-flat gauge, including contributions from loop wavenumbers on all scales. In contrast to previous works, we do not assume a hierarchy $k \gg q$ between the wavenumber of the loop integral, $k$, and that of the power spectrum, $q$, and we explicitly include the regime $k \lesssim q$. Taking into account the nonlinear relation between the inflaton fluctuation and the
curvature perturbation with the $\delta N$ formalism, we show that the apparent time dependence of the one-loop
curvature power spectrum cancels once all contributions, including boundary terms, are combined consistently.
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Instrumentation and Methods for Astrophysics
Faraday Tomography with the SKA: A New Era of Cosmic Magnetism Studies
Miguel Carcamo, Anna M. M. Scaife, Jeroen Stil et al. (+3 more)
The Square Kilometre Array (SKA) represents a significant advancement in
radio astronomy, enabling detailed study of
cosmic magnetism through Faraday Rotation and Faraday Measurement Synthesis. This chapter provides a comprehensive review of these techniques, tracing their development and illustrating their crucial role in investigating
magnetic fields across different
cosmic environments. We focus on Array Assembly 4 (AA4), the final deployment stage, featuring 197 dishes (133 SKA, 64 MeerKAT) with 40 km maximum baselines and frequency coverage from 350 MHz to 15.4 GHz (goal: 24 GHz). These capabilities enable high-resolution Faraday
tomography of
magnetic structures in
galaxies, clusters, and the
cosmic web. We also highlight the earlier AA* stage with 144 dishes (80 SKA, 64 MeerKAT). Band 1 (350–1050 MHz) offers the finest Faraday depth resolution among the dish bands (full resolution $\sim$2.5 rad m$^{-2}$) with a maximum observable depth around 174,708 rad m$^{-2}$. Other bands (Band 2, Band 5a, Band 5b) enable multi-scale studies, probing larger structures with lower resolution but higher maximum depths. We discuss synergies between Faraday Measurement Synthesis and Image Synthesis techniques, showing how they complement each other in reconstructing
magnetic field structures. Simulation results demonstrate the SKA's potential for high-resolution observations. We explore possible enhancements beyond the baseline configuration and synergies with other observatories, emphasizing multi-wavelength astronomy. This chapter aims to provide a thorough account of how the SKA's phased deployment from AA* to AA4 will transform our understanding of
cosmic magnetic fields and drive new discoveries in astrophysics.
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All authors Miguel Carcamo, Anna M. M. Scaife, Jeroen Stil, Russ Taylor, Jennifer L. West, Tessa Vernstrom
High Energy Astrophysical Phenomena
SKAO and Gamma-Ray Synergies
Gianluca Castignani, Gavin Rowell, Arnau Aguasca-Cabot et al. (+26 more)
A wide variety of
Galactic and extragalactic sources are known to emitradiation across the entire electromagnetic spectrum, including both transient and steady-state phenomena. A few hundred of these sources (~300) have been detected even at the highest energies, in the TeV range. The number of known TeV emitters is expected to increase substantially in the coming years with the operation of current and next-generation Cherenkov detectors, such as the Large High Altitude Air Shower Observatory (LHAASO) and the Cherenkov
Telescope Array Observatory (CTAO). These sources typically exhibit broad, non-thermal, spectral energy distributions. Explaining such emission requires efficient particle acceleration mechanisms (e.g.
Fermi processes, shock acceleration) and radiative processes involving
magnetic fields (e.g. synchrotron and inverse Compton radiation), often accompanied by polarization signatures. However, the relative contribution of these emission mechanisms and the underlying physical processes are still debated. In this work, we present an overview of the scientific potential arising from the synergy between the Square Kilometre Array (SKA) and current and upcoming gamma-ray facilities. Combined observations across these energy bands will provide crucial insights into the physical mechanisms driving emission from GeV-TeV sources of both
Galactic and extragalactic origin. These include transient events (e.g. gamma-ray bursts,
supernovae, fast
radio bursts,
tidal disruption events,
neutrino and gravitational-wave counterparts), variable sources (e.g. blazars, active
galactic nuclei), and steady emitters (e.g. the
Galactic centre,
supernova remnants,
radio galaxies, and
galaxy clusters). We discuss the prospects for coordinated SKA-gamma-ray observations, including wide-field surveys, monitoring of variable sources, and target-of-opportunity follow-ups.
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All authors Gianluca Castignani, Gavin Rowell, Arnau Aguasca-Cabot, Gemma E. Anderson, Csaba Balazs, Pol Bordas, Andrea Botteon, Jess W. Broderick, Gianfranco Brunetti, Ettore Carretti, Roland M. Crocker, Shi Dai, Filippo D'Ammando, Philip G. Edwards, Sabrina Einecke, Miroslav D. Filipovic, Marcello Giroletti, Adelle J. Goodwin, James A. Green, Sanja Lazarevic, Giulia Migliori, Monica Orienti, Josep M. Paredes, Elena Pian, Alak Ray, Lauren Rhodes, Zachary J. Smeaton, Nick Tothill, Martin White
Solar and Stellar Astrophysics
An Adjoint Projection Formulation for Enforcing the divergence-free Constraint in Smoothed Particle Magnetohydrodynamics
Yusuke Tsukamoto
We present a projection method for controlling numerical \(\nabla\cdot\B\) errors in smoothed particle magnetohydrodynamics (SPMHD). The method corrects the
magnetic field after an MHD update by solving an
elliptic projection problem constructed from the same discrete divergence operator used to measure the error. A key ingredient is to use the adjoint gradient associated with a volume-weighted metric. With this choice, the projection gives an energy-minimizing correction, does not increase the discrete
magnetic energy, and leads to a symmetric positive semidefinite linear system that can be solved by the conjugate-gradient method without explicitly assembling the
matrix. We test the method using two-dimensional Dedner-type divergence tests and three-dimensional magnetized collapse calculations. With sufficiently many iterations, the projection reduces the divergence error to the floating-point roundoff level in both test problems. In realistic collapse runs, practical stopping criteria designed to reduce the divergence error generated by the underlying SPMHD update suppress the normalized divergence error well below that obtained in the divergence-cleaning run, with a projection cost of only about \(1\)–\(10\%\) of the SPMHD update cost. The density and
plasma-\(\beta\) structures remain consistent when the projection interval is varied, whereas the divergence-cleaning run shows quantitative differences. These results indicate that the projection method is a robust and attractive alternative to divergence cleaning for controlling \(\nabla\cdot\B\) errors in SPMHD and related particle or meshless MHD schemes.
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Astrophysics of Galaxies
J. Moldon, A. Alberdi, M. Perez-Torres et al. (+11 more)
The appearance of
galaxies is strongly dominated by two physical phenomena:
star formation and
accretion of material onto compact objects, primarily supermassive black holes. Nearby
galaxies offer a unique window to study these processes in detail and with high spatial resolution. The $\mu$Jy sensitivity, sub-arcsecond angular resolution and broadband coverage provided by SKA AA4 configuration will enable us to separate morphologically and spectrally the contribution from SMBH
accretion and
star formation processes, from the most compact
nuclear region out to the most diffuse,
galaxy-wide components. Disentangling thermal and non-thermal emission using multi-scale spectral index maps (traced by SKA-Mid) and absorption processes (traced mainly by SKA-Low) will allow us to account for the present and past
star-formation rate, the AGN activity and the ISM properties. SKA observations of a wide range of
galaxy types in the nearby Universe, including quiescent, AGN-dominated and starburst
galaxies, will provide a broad view of how
star formation and
accretion regulate
galaxy evolution, while time-domain and spectral-variability information further isolate compact
accretion and transient phenomena.
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All authors J. Moldon, A. Alberdi, M. Perez-Torres, G. Lucatelli, R. Beswick, M. Sargent, E. Brinks, R. D. Baldi, S. Dey, F. S. Tabatabaei, K. Rubinur, N. Seymour, M. Pandey-Pommier, C. Bot
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Universal EOS-Radius Inverse Mappings Govern Precision-Dependent Inference of the Neutron Star Equation of State
Bao-An Li
Bayesian inference of the
neutron star (NS) equation of state (EOS) generally assumes that improved observations primarily reduce posterior uncertainties while leaving inferred EOS parameters unchanged. Using mock measurements of the radius of a canonical $1.4\,M_\odot$ NS with identical central values but varying observational precisions, we show that the inferred posterior means of EOS parameters can shift systematically as the measurement uncertainty changes. We demonstrate that this behavior originates from previously unidentified nearly universal inverse mappings between the NS radius $R_{1.4}$ and empirical EOS parameters. Across a broad range of observational precisions, posterior samples collapse onto nearly unique functions. These mappings are largely independent of observational precision and define a low-dimensional EOS
manifold underlying
Bayesian inference. We show that the precision dependence of inferred EOS parameters arises from nonlinear filtering of the posterior radius distribution through these mappings. In the narrow-distribution limit this effect reduces to a Jensen-type correction proportional to the local
curvature of the inverse mapping, while for presently realistic uncertainties the full nonlinear-filtering relation accurately reproduces the posterior means. Our results reveal a
geometric origin of precision-dependent inference in NS EOS studies and provide a new framework for connecting astrophysical observations directly to microscopic
nuclear many-body theories.
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Instrumentation and Methods for Astrophysics
Radiation tolerance of a diamond radiation detector for space use
Yoshiyuki Ando, Shutaro Ueda, Ryota Heibatake et al. (+13 more)
We present a study of the radiation tolerance of two types of diamond radiation detectors for space use. We plan to launch a 3U-size CubeSat, KSAT3-X, developed by Kanazawa University in 2027. The KSAT3-X mission is aimed to observe inflows and
outflows of charged particles such as electrons and
protons, particularly in the 10 - 40 keV energy range, in the Earth's magnetosphere. As the mission instrument, we have developed two diamond radiation detectors. The first is composed of a microwave
plasma chemical vapor deposition (MPCVD) diamond fabricated by Element Six, and the second is based on a MPCVD diamond produced in-house at Kanazawa University. We irradiate both diamonds with 100 MeV
protons and evaluate their spectroscopic performance as an indicator of radiation tolerance using characteristic X-rays from radioisotope sources. We find no significant degradation in their spectroscopic performance up to at least the 10-year equivalent irradiation under the orbital environments of KSAT3-X. We additionally irradiate the Element Six diamond with 100 MeV
protons up to the 100-year equivalent. As a result, no significant degradation in the spectroscopic performance is observed. These results indicate that the two diamond radiation detectors have sufficiently high radiation tolerance. We also discuss possible physical origins of the observed difference in the spectroscopic performance between the two detectors.
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All authors Yoshiyuki Ando, Shutaro Ueda, Ryota Heibatake, Kaito Ozawa, Makoto Arimoto, Tatsuya Sawano, Daisuke Yonetoku, Kimiyoshi Ichikawa, Norio Tokuda, Taichi Miyazaki, Shoya Matsuda, Yasuhiro Shoji, Satoshi Hatori, Kyo Kume, Shinko Sando, Satoshi Mizushima