High Energy Astrophysical Phenomena
The Role of the Core in Setting Massive Neutron-Star Radii
R.V. Lobato, J.E. Horvath and M. Malheiro
Recent observations by the
Neutron Star Interior Composition Explorer (NICER) indicate that the massive
pulsar PSR J0740+6620 ($2.08\,M_{\odot}$) has a radius comparable to those inferred for
stars near $1.4\,M_{\odot}$, as shown by PSR J0030+0451 and updated analyses. Such near-vertical mass-radius behavior is difficult to obtain unless the high-density equation of state (EOS) stiffens strongly. We show that, for massive
pulsars, the leading radial scale can be set by a relativistic, high-sound-velocity core beginning near twice the nuclear saturation scale, while the outer low-density layer, comprising the true crust and outer core, supplies only a subdominant correction. The key evidence comes from radius decomposition: replacing the low-density branch below the matching point with unified EOS models spanning a factor of two in transition pressure changes the $2.08\,M_{\odot}$ core radius by only $\sim160$ m, about half the variation of the total radius. This convergence is genuinely a high-mass phenomenon: at $1.4\,M_{\odot}$ the core radius remains more branch-sensitive, varying by about $0.5$ km. Fixed-fraction comparisons confirm that core dominance emerges systematically as the
star grows more massive, where the traditional separation between “radius physics” and “maximum-mass physics” breaks down. We establish this picture by combining analytical Tolman VII profiles and thin-crust matching, numerical Tolman-Oppenheimer-Volkoff integration with a piecewise EOS, and direct-grid
Bayesian inference using NICER and GW170817 constraints under causal and mass-support filters. Data modestly constrain the transition stiffness but leave the quadratic stiffening governed mainly by causality. A comparison with a constant-sound-speed core remains inconclusive: both descriptions produce comparable core-dominated radii, leaving a degeneracy that sub-kilometre radius measurements can break.
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Earth and Planetary Astrophysics
An Evolving Cosmic Shoreline and Sandbar Bounding the Rocky Airless Valley
Barron K. Nguyen, Laura K. Schaefer, Xuan Ji et al. (+7 more)
Recent JWST observations challenge the traditional '
cosmic shoreline' from both sides, revealing thick volatile atmospheres on the hottest close-in 'lava worlds,' where irradiation should drive the most extreme escape, and bare rocky surfaces on cooler terrestrial
planets around M dwarfs, where atmospheres would be expected to survive. Using a coupled atmosphere-interior
evolution model, we show that atmosphere retention is governed not by a single escape boundary but by two: a hot, outgassing-regulated '
cosmic sandbar' and a cooler, escape-regulated '
cosmic shoreline,' separated by an 'airless valley' that may mark a graveyard of stripped sub-Neptune cores. The sandbar arises because long-lived magma oceans, sustained further by tidal heating from secular eccentricity excitation in multi-
planet systems, keep most volatiles dissolved and expose only a small atmospheric reservoir to escape, whereas cooler
planets solidify, sequestering volatiles in the deep solid mantle while overexposing the rest to loss. This two-regime structure recasts the single
cosmic shoreline as two boundaries set by distinct physics: outgassing and escape. We provide time-evolving fits for both boundaries across G, K, and M stellar types as a function of volatile inventory, planetary mass, age, and tidal heating. Lava worlds with thick atmospheres are unlikely around
stars cooler than K-type unless sustained by extreme tidal and/or other interior heating. This framework links atmosphere survival from USP lava worlds to habitable zone
planets, informing target selection and interpretation for TRAPPIST-1 and JWST DDT characterization.
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All authors Barron K. Nguyen, Laura K. Schaefer, Xuan Ji, Christopher A. Theissen, Fei Dai, Bo Peng, Yao Tang, Andrea Zorzi, Michelle Hill, Megan Weiner Mansfield
Instrumentation and Methods for Astrophysics · Cross-listed from cond-mat.supr-con
Nonequilibrium pulse dynamics and metastable latching in nonlinear kinetic inductance detectors
M. Rouble, C. Albert, P. Day et al. (+3 more)
Microwave kinetic inductance detectors are typically operated at high readout power to raise the detector signal above system noise. At sufficiently large readout power, the current-dependent kinetic inductance couples the detector response to its readout bias. Using a nonlinear resonator framework and time-domain
circuit calculations, we show that the amplitude, shape, and relaxation time of the driven detector's response depend on both the absorbed energy and on the readout bias. Strongly driven bias points produce amplified, extended, and non-exponential pulse responses. Qualitative agreement between calculated and measured pulse responses indicates that these effects are dominated by the driven nonlinear resonator dynamics rather than by altered quasiparticle dynamics. Beyond resonance bifurcation, sufficiently large pulse events drive the resonator between stable branches, resulting in a metastable latched state which persists after the quasiparticle transient has decayed. The pulse energy required for branch switching is set by the readout bias, suggesting a mode of triggered detection with an in-situ tunable threshold. Although nonlinear operation requires calibration of the bias- and energy-dependent response, the enhanced pulse amplitude and duration, together with tunable latching and the ability to select these parameters via the readout operating state, are likely to be of interest for single-
photon and rare-event experiments, especially those limited by amplifier or system noise.
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All authors M. Rouble, C. Albert, P. Day, M. Dobbs, H. G. Leduc, J. Montgomery
Astrophysics of Galaxies
The Local Origin of a Host Dispersion Measure-Stellar Mass Relation in Fast Radio Bursts
Wasundara Athukoralalage, Liam Connor, Peter K. Blanchard et al. (+1 more)
The origin of fast
radio bursts (FRBs) and the relationship to their host
galaxy environments remain open questions. Using a sample of 37 FRBs with secure host associations at $z \lesssim 0.25$, and including dwarf, elliptical, and edge-on hosts, we examine the host dispersion measure ($\mathrm{DM_{host}}$) and its dependence on host stellar mass ($M_\star$). We find a statistically significant anti-correlation between the host dispersion measure and host stellar mass (the $\mathrm{DM_{host}}$-$M_\star$ relation; Pearson $r \approx -0.5$, $\log_{10} p \approx -2.8$) that extends across the full range of our sample, $\log_{10}(M_\star/M_\odot) \approx 8$-$11.4$. We find that the rest-frame Faraday rotation measure ($|\mathrm{RM}|_{\mathrm{host}}$) is largest in FRBs that reside in dwarf
galaxies, but there is no evidence for a correlation across the full mass range. We show that the $\mathrm{DM_{host}}$-$M_\star$ trend does not arise from the
galaxy-averaged interstellar medium (ISM) nor from the circumgalactic medium (CGM). Instead, we argue that the local ($\lesssim 100$ pc) environment is responsible. The spatial statistics of
star formation and
metallicity-dependent FRB progenitor channels plausibly lead to denser ionized environments in low-mass
galaxies and less nearby gas in massive hosts.
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All authors Wasundara Athukoralalage, Liam Connor, Peter K. Blanchard, Edo Berger
Astrophysics of Galaxies
The Evolution of Low-Ionization Electron Densities in Galaxies Across Cosmic Epochs
Mabel G. Stephenson, John Chisholm, Alberto Saldana-Lopez et al. (+12 more)
We investigate the low-ionization electron density in the interstellar medium of
galaxies across $0$$<$$z$$<$$8$, derived with the [O II]$\lambda\lambda3727,3730$ and [S II]$\lambda\lambda6718,6733$ doublets, using both deep JWST NIRCam/grism and NIRSpec/MSA spectroscopy. Along with ancillary density samples from the literature at $0$$<$$z$$<$$6$, we assemble three samples containing a total of 703
galaxies spanning $3.7$$<$$z$$<$$7.8$ at $\langle z\rangle\sim5.6$; 691
galaxies in the luminosity-complete NIRCam/grism programs CONGRESS and FRESCO at $\langle z\rangle \sim4.3$ and $\langle z\rangle\sim5.3$, respectively, and 12
galaxies with high-resolution NIRSpec/MSA spectra from the GO 1871 and GLASS programs. We find median electron densities of $n_{\rm{e}}$[S II]$=$$463^{+281}_{-203}~{\rm{cm}}^{-3}$ for CONGRESS, $n_{\rm{e}}$[S II]$=$$301^{+388}_{-206}~{\rm{cm}}^{-3}$ for FRESCO, and $n_{\rm{e}}$[O II]$=$$202^{+145}_{-102}~{\rm{cm}}^{-3}$ for the NIRSpec/MSA sample. The median low-ionization $n_{\rm{e}}$ increases from $z= 0$ to $z=4$, in agreement with previous studies and those using JWST observations. However, beyond $z\sim4$ median $n_{\rm{e}}$ begins to deviate from a monotonically increasing
evolution with $z$. We find a positive, but shallow, correlation between O$_{32}$ (a proxy for the ionization parameter) and $n_{\rm{e}}$, while also confirming a positive correlation between O$_{32}$ and $z$. We suggest that these trends are possibly due to an evolving ISM gas density and ionization structure, and propose a toy model where the gas clumping evolves with $z$ to explain the observed density and ionization variations.
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All authors Mabel G. Stephenson, John Chisholm, Alberto Saldana-Lopez, Jorryt Matthee, Alaina Henry, Rohan P. Naidu, Sophia R. Flury, Taylor A. Hutchison, Steven L. Finkelstein, Natalia G. Guseva, Yuri I. Izotov, Rui Marques-Chaves, Pascal A. Oesch, Naveen A. Reddy, Daniel Schaerer
Cosmology and Nongalactic Astrophysics
A New Probe of Dark Matter Subhalos: Stellar Aberration with TESS
Matthias Daniel, Xiao Xue, Kris Pardo et al. (+1 more)
Small-scale dark matter (DM) structure encodes key information about the particle nature of DM and therefore provides a sensitive test of competing models. Yet, it remains hidden from electromagnetic surveys and is instead inferred through its gravitational effects. Stellar aberration, the apparent shift in a light source's position induced by the observer's motion, offers a largely unexplored channel to access such signatures. DM subhalos can perturb the observer's motion, imprinting characteristic, spatially correlated shifts in stellar positions across the sky. We show that the Transiting
Exoplanet Survey Satellite (TESS), with its long temporal baseline, wide sky coverage, and high-cadence observations, is well suited to search for these aberration signals. We derive Fisher-
matrix-based sensitivity estimates for constant observer accelerations, forecasting a sensitivity down to $6.3\times 10^{-9}\,\mathrm{m/s^2}$ from the combined sample of TESS
stars with magnitude $\mathrm{Tmag}\leq 10$. This sensitivity allows TESS to probe concentrated DM subhalos over a broad parameter space, from $\gtrsim 10^{-6}\,\mathrm{M_{\odot}}$ at AU-scale distances to $\gtrsim 10^{7}\,\mathrm{M_{\odot}}$ at $\mathcal{O}(10\,\mathrm{pc})$. TESS's sector-based observing strategy further provides intrinsic temporal resolution of potential DM-induced aberration signals. Moreover, we briefly discuss challenges for future data analysis, including the modeling of instrumental systematics and stellar astrometric foregrounds, such as parallax and proper motion. Our results establish stellar aberration as a novel probe of DM substructure, paving the way for dedicated searches in TESS and next-generation wide-field surveys.
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All authors Matthias Daniel, Xiao Xue, Kris Pardo, Laura Sagunski
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Topics in the phenomenology of axions: the cases of cosmic strings and superradiance
Antonios Kyriazis
Originally proposed as a solution to the strong CP problem and later understood to be a good dark matter candidates,
axions have appeared in a variety of beyond-the-standard-model theories and are imbued with rich phenomelogical consequences. In this dissertation, we will examine two of these consequences: the emission of
axions from
cosmic strings and the superradiant mechanism in black hole physics. The spontaneous
symmetry breaking of a global
symmetry in the early universe can give rise to a network of
cosmic strings, which emit ultra light,
axion-like particles that can contribute to the dark matter density. We will discuss how the associated density fluctuations of these particles can be computed from first principles by treating them as a collection of plane waves. We will then calculate the density power spectrum and compare it to well-established cosmological observables, as well as to observables from future surveys, to derive constraints on the mass of the particles and the
symmetry breaking scale. These light
axion-like particles can also form a gravitational atom around a spinning black hole through the superradiance process. Considering the black hole to be part of a binary system, the tidal potential of the companion periodically perturbs the gravitational atom such that an atomic transition occurs between two of its energy states. Gravitational waves are emitted by the cloud during this transition. We will derive the analytical formulae of both the strain waveform and frequency spectrum of the signal and identify the systems that would be the most promising for detecting it in future, space-based gravitational wave observatories.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Defining higher memory signals and forecasting their observation prospects for binary-black-hole mergers with next-generation gravitational-wave detectors
Siddhant Siddhant, Alexander M. Grant and David A. Nichols
In asymptotically flat spacetimes far from an isolated source, gravitational waves (GWs) undergo nonlinear interactions with themselves and with the parts of the spacetime
curvature related to the time-dependent four-momentum and angular momentum of the spacetime. These spacetime nonlinearities produce distinctive offsets in the GW strain and its time integrals, which have been referred to as the displacement
memory effect for the strain and “higher” GW
memory effects for the integrals of the strain. There are existing data analysis pipelines that search for evidence for the displacement
memory effect in the population of binary-black-hole mergers observed by current GW detectors (though conclusive evidence for the effect has not yet been found). The first set of higher
memory effects include the
spin and center-of-mass effects (collectively, “drift”
memory), and the second is the “ballistic”
memory effect. Prior work has shown that next-generation, ground-based GW detectors could find evidence for the
spin memory effect in the large population of binary black holes that these detectors will be capable of observing. In this paper, we investigate how well a detector network of two
Cosmic Explorer detectors can measure the displacement through ballistic
memory signals. We first formulate what are appropriate notions of time-dependent GW signals associated with these
memory effects. With these definitions of displacement and higher
memory signals, we find that the
Cosmic Explorer network is capable of detecting the displacement
memory from tens of individual mergers per year and capable of finding evidence for the
spin and center-of-mass
memory effects in a population of mergers after a roughly one-year observation run at design sensitivity. [Abstract abridged]
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Earth and Planetary Astrophysics
An analysis of the Herbig star population and their protoplanetary disks within 1 kpc
L. M. Stapper, M. Vioque, A. J. Winter et al. (+6 more)
Herbig
stars are intermediate mass pre-main sequence
stars of 1.5 to $\sim15$~M$_\odot$ and are in between low and high-mass
star formation. This work provides a catalog of all 243 known bona-fide Herbig
stars with clear infrared excess and in many cases
accretion signatures within 1~kpc. It contains archival, recalibrated, and newly derived stellar parameters,
accretion rate properties, and disk dust mass measurements. We derive the latter by using newly obtained millimeter photometry and literature values. We find that 50% of Herbig dust disks are more massive than 10~M$_\oplus$, while this is only true for 20% and 5% of the T~Tauri disks in Lupus and Upper~Scorpius respectively. Furthermore, the Herbig disk dust mass distribution is bimodal, it consists of a high and low disk mass population with a mean dust mass of 21~M$_\oplus$ and 0.45~M$_\oplus$ respectively. We find that the catalog is near complete for within 300~pc, however, this decreases to 24% out to 1~kpc. We observe a flat relation for Herbig disks due to objects with short disk lifetimes, caused by a combination of low disk masses and high
accretion rates. Furthermore, we find the peak of the occurrence rate of massive (>10~M$_\oplus$) disks to occur at $\sim$1-2~M$_\odot$
stars, coinciding with the peak in occurrence rate of giant
exoplanets. The small number of Herbig
stars with low
accretion rates ($<10^{-8}$~M$_\odot$~yr$^{-1}$) or low disk dust masses ($\lesssim1$~M$_\oplus$), combined with the lack of an age dependence in the disk dust mass distribution, suggests that the observed Herbig
star population represents the surviving disk-hosting phase in the optically visible late stages of intermediate-mass
star formation. We argue that this is either due to the formation of deep dust traps in these disks or replenishment by late-infall, or a combination of the two.
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All authors L. M. Stapper, M. Vioque, A. J. Winter, D. J. Wilner, J. P. Williams, M. Benisty, A. S. Booth, S. L. Grant, M. R. Hogerheijde
Solar and Stellar Astrophysics
Periodic activity on the (sub)mm surface of the AGB star Mira A
M. Andriantsaralaza, B. Bojnordi Arbab, W. Vlemmings et al. (+7 more)
Evolved
stars on the asymptotic giant branch (AGB) lose mass through stellar winds launched from their dynamic extended atmospheres. Recent high-angular-resolution observations of the archetypal AGB
star Mira A (o Ceti) have revealed compact hotspots on its submillimetre (submm) surface, whose origin remains unclear. We aim to characterise the submm photosphere of Mira A and investigate the properties and temporal behaviour of the compact hotspots detected on its surface. We analysed 19 epochs of high-angular-resolution observations obtained with the Atacama Large Millimetre/submillimetre Array in Bands 4, 6, 7, and 9, ranging from 134.34 to 669.25 GHz. The complex visibilities were fitted with parametric models to derive the flux density, size, morphology, and brightness temperature of the stellar disc and an additional more compact component across multiple pulsation phases and observing frequencies.Our results show that the flux density of the stellar disc increases with frequency while its apparent size decreases, in agreement with the expected stratified
radio photosphere. In Band 6, both the flux density and the size of the stellar disc vary with pulsation phase, reaching maximum values close to optical maximum light and decreasing toward minimum light. Compact hotspots are detected in Bands~6 and 7 near maximum light, with their brightness temperatures exceeding those of the stellar disc by several thousand kelvins, reaching T>8600 K in Band 6. They are highly energetic and persist on timescales of weeks but evolve over longer timescales, showing changes in both position and intensity. Hotspot activity appears to occur repeatedly across multiple pulsation cycles and may be linked to strong shocks,
magnetic activity, and/or episodic mass ejections, and could therefore play an important role in the mass-loss process in AGB
stars.
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All authors M. Andriantsaralaza, B. Bojnordi Arbab, W. Vlemmings, T. Khouri, L. Planquart, J. Alcolea, E. Humphreys, S. del Palacio, M. Wittkowski, K. T. Wong
Earth and Planetary Astrophysics
GravDyn: A Python Framework for Gravitational Modeling of Irregular Celestial Bodies Using Polyhedral, mascon, and Series Expansion Methods
Safwan Aljbaae, valerio Carruba, Allan K. de Almeida Jr et al. (+4 more)
GravDyn is an open-source Python package for computing gravitational potentials and accelerations around irregular celestial bodies. It implements three approaches within the same workflow: the constant-density polyhedral method, a layered mascon approximation based on tetrahedral decomposition, and the Potential Series Expansion Method (PSEM). The package handles shape-model preprocessing, builds the selected
gravity representation, and evaluates potentials and accelerations efficiently. The three implemented methods serve different regimes: the polyhedral model provides a reference solution near the surface, the mascon model supports layered internal density structures, and PSEM offers fast evaluation outside the Brillouin sphere once the
polynomial coefficients have been generated. Validation tests against the polyhedral solution show that the mascon and PSEM models reproduce the reference potential with small relative errors while reducing evaluation costs. GravDyn is intended for mission design and studies of spacecraft motion, orbital stability, and gravitational modeling around asteroids and other small bodies.
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All authors Safwan Aljbaae, valerio Carruba, Allan K. de Almeida Jr, Gabriel Antonio Caritá, Antonio F. B. A. Prado, Marcelo L. Mota, Carlos E. Ferreira Lopes
High Energy Astrophysical Phenomena
Cows, Tasmanian Devils, and Other Mysteries: Diversity and Origins of Luminous Fast Blue Optical Transients
Anna Y. Q. Ho and Wenbin Lu
By repeatedly mapping the sky, optical
telescopes have unveiled a diverse landscape of transients, ephemeral celestial events arising from the destruction of
stars and stellar remnants. In this review, we focus on a recently identified phenomenon referred to as luminous fast blue optical transients (LFBOTs) and typified by the transient AT2018cow ("The Cow"). AT2018cow was distinguished by luminous emission at X-ray and
radio wavelengths in addition to luminous, rapidly evolving, and blue optical emission. Certain LFBOTs have properties that have not been seen in any other class of transients, such as minutes-duration optical flaring in AT2022tsd ("The Tasmanian Devil"). Determining the physical origin of LFBOTs is likely important for understanding stellar
evolution and the formation and growth of compact objects such as black holes. We describe how LFBOTs were discovered, their basic observational properties, and the models that have been proposed to explain them. We conclude by highlighting promising avenues for resolving the mystery of their origins.
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Cosmology and Nongalactic Astrophysics
Beyond $w_0-w_a$ and Phantom Crossing: Testing Models of Coupled Dark Sector
Kaynan R. de O. Pompeu, João Rebouças and Rogerio Rosenfeld
The combination of
cosmic microwave background (CMB) measurements with distance measurements from baryon acoustic oscillations (BAO) and type Ia
supernovae (SNIa) suggests that dark energy is dynamical, with an equation of state crossing the phantom divide at low
redshifts. This feature can not be described within canonically normalized, minimally coupled, self-interacting scalar field models. We investigate the possibility of achieving phantom crossing by introducing an interaction in the dark sector such that the dark matter particle mass is dependent on the dark energy field $\phi$ as $m \propto \phi^\alpha$. We consider a self-interacting potential of the inverse power-law form $V \propto \phi^{-\beta}$. We implement this model both at the background and perturbative levels in a Boltzmann solver and use a
bayesian framework to constrain its parameters using using CMB, BAO and SNIa data. We find best-fits that have similar goodness-of-fits as the commonly used phenomenological $w_0-w_a$ parameterization, providing a more fundamental understanding of the dark sector.
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High Energy Astrophysical Phenomena
Sub-Millisecond Pulsars: Missing or Impossible?
T.M. Tauris, V. Venkatraman Krishnan, R. Senzel et al. (+7 more)
The minimum
spin period attainable by a
neutron star has been debated since the discovery of the first millisecond
pulsar in 1982. A
neutron star rotating faster than 1 ms would have far-reaching implications for the dense-matter equation of state, gravitational-wave emission, and the physics of
accretion and
spin-up. Yet despite the discovery of over 700 millisecond
pulsars with
spin periods between 1.4 and 10 ms, no sub-millisecond
pulsar has been identified. Here we review the physical and observational constraints governing the formation, survival, and detectability of ultra-fast
neutron stars. We discuss physical constraints imposed by the
neutron star equation of state and their implications for the minimum attainable
spin period, and we summarise gravitational-wave emission from both accreting and rotation-powered millisecond
pulsars. We argue that sub-millisecond
spins are not primarily excluded by
equilibrium spin limits, magnetospheric physics, or selection effects, but instead by a combination of inefficient recycling, short mass-transfer lifetimes in the most favourable binaries, and rapid post-formation
spin-down unless
magnetic fields are exceptionally weak. Together, these effects make sub-millisecond
pulsars intrinsically rare. If they exist at all, they are most likely to be detected transiently during
accretion, rather than as long-lived
radio pulsars. Finally, we show that stellar-mass black holes can attain sub-millisecond horizon
spin periods, reflecting fundamentally different
spin constraints.
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All authors T.M. Tauris, V. Venkatraman Krishnan, R. Senzel, P.C.C. Freire, S.M. Ransom, A. Papitto, C.A.N. Biscio, N. Langer, E.P.J. van den Heuvel, M. Kramer
Earth and Planetary Astrophysics
The Highly Unusual Behavior and Chemical Composition of Interstellar Comet 2I/Borisov
Allison N. Bair, David G. Schleicher, Theodore Kareta et al. (+2 more)
We report on imaging, spectroscopy, and narrowband photometry of interstellar comet 2I/Borisov obtained at Lowell Observatory from 2019 September 13 to December 16. We measured chemical composition on four nights before perihelion, from October 4 to November 25 (2.466 to 2.028 au), with CN detections on all nights. Our measurements from October 27 represent the earliest reported detections of C$_2$ and C$_3$, where C$_2$-to-CN and C$_3$-to-CN log production rate ratios were $-$0.7 and $-$1.3, respectively. Both ratios increased by nearly 4$\times$ to $-$0.3 and $-$0.9 by November 25, an extremely large increase with heliocentric distance that is unprecedented in the Lowell Observatory comet database. We additionally observed OH and NH on November 25, with a derived H$_2$O production rate of 4.5$\times $10$^{26}$ mol s$^{-1}$ and very high log production rate ratios for CN-to-OH ($-$2.0) and NH-to-OH ($-$1.7). Monitoring from broadband $R$ images from September 13 to December 16 suggests dust ($A(0^{\circ})f\rho$) production peaked around October 19, 50 days before its December 8 perihelion passage. Narrowband images from October 4 and 27 reveal a nearly symmetric CN distribution in Borisov's coma, suggesting activity over its entire sunward hemisphere and possibly its entire
nucleus. Our results, combined with those from others, reveal a chemical composition and behavior with heliocentric distance unlike any other comet we have observed.
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All authors Allison N. Bair, David G. Schleicher, Theodore Kareta, Matthew M. Knight, Michael S.P. Kelley
Cosmology and Nongalactic Astrophysics · Cross-listed from nucl-th
Deuterium Production in an Effective Field Theory Constructed from On-Shell Amplitudes
Tim M.P. Tait
We compute the deuterium-production reaction $n+p \to d+\gamma$ in an effective field theory whose degrees of freedom are the nuclear states themselves: the amplitude is assembled from on-shell three-point vertices, glued across its factorization channels, and completed by the contact terms consistent with the
symmetries. The deuteron enters through the $d$-$n$-$p$ vertex, normalized to the measured asymptotic normalization coefficient. Rescattering of the nucleon pair is resummed dispersively, leaving two short-distance constants, an isovector
magnetic and an electric dipole contact interaction. A joint
Bayesian fit to the thermal capture measurements and the SLEGS photodisintegration data finds both of natural size and determines the thermonuclear rate to 0.22-0.24% across the nucleosynthesis window, including systematics spanning the defensible treatments of the SLEGS data and of the $P$-wave rescattering. Truncating the expansion is bounded separately at 0.12%, of which the next order of contact terms – degenerate with the two fitted constants – supplies 0.03%, for a total theory uncertainty of 0.25-0.27%. Propagated through a BBN network, the rate shifts the predicted primordial deuterium by -0.06% and cuts this reaction's contribution to the D/H uncertainty from 0.089% to 0.050%, retiring it from the primordial D/H error budget for practical purposes.
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Solar and Stellar Astrophysics
A giant magnetic eruption from the asymptotic giant branch star Mira A
W. Vlemmings, M. Andriantsaralaza, B. Bojnordi Arbab et al. (+14 more)
Mass loss during the advanced evolutionary stages of low- and intermediate-mass
stars is traditionally attributed to dust-driven winds, whereas the influence of
magnetic fields remains poorly constrained. However, recent observations show massive directional mass ejections from the nearby asymptotic giant branch (AGB)
star Mira~A that appear not to be driven by radiation pressure on the dust. We observationally investigate whether
magnetic fields are responsible for the mass loss ejections from Mira A. We obtained full-polarisation ALMA observations of the SiO $v=1$, $J=5\rightarrow4$ maser transition at 215 GHz with angular resolutions of 1.5-2.6 au. The observations reveal a highly magnetized loop-like mass ejection traced by strongly polarised SiO masers extending to approximately eight stellar radii. The morphology, polarisation pattern, energetics, and kinematics indicate a magnetically driven eruption analogous to a stellar coronal mass ejection. The observations demonstrate that
magnetic eruptions can dominate mass loss from evolved
stars and imply that
magnetic fields must become an integral component of future models of AGB, and potentially other cool giant, winds.
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All authors W. Vlemmings, M. Andriantsaralaza, B. Bojnordi Arbab, T. Khouri, B. Lankhaar, L. Planquart, E. De Beck, S. Del Palacio, E. Humphreys, D. Jadlovsky, M. Maercker, H. Olofsson, M. Saberi, M. Siebert, R. Unnikrishnan, S. Wedemeyer, M. Wittkowski
Instrumentation and Methods for Astrophysics
A General Response Theory for Closure Phases through Visibility Nulls and Image Structure
Shokoufe Faraji and Avery E. Broderick
Closure phase is robust to station based phase errors, yet its connection to image structure is often interpreted only qualitatively and a nonzero closure phase is still interpreted mainly through qualitative
symmetry arguments or source specific models. We develop, to our knowledge, the first unified response theory for an arbitrary brightness distribution and an arbitrary zero free observing triangle. Away from visibility zeros, closure phase is naturally a log-visibility observable. This structure yields an exact first order master kernel for image perturbations and a Cartesian moment hierarchy that separates the spatial content of the source change from the sensitivity of the sampled triangle. For a fixed image, the same framework gives a local expansion in
Fourier plane displacement, providing a direct description of closure phase
evolution along observing tracks. We then identify the boundary of this regular regime: at a true visibility null, the log-visibility expansion fails and the phase behavior is controlled by the local properties of the null, including its order and winding charge, distinguishing removable phase wraps, non-null visibility minima, and nulls for which the visibility phase is multivalued. We validate these expansions using structured ring models. We then apply both branches of the theory to EHT data of M87*, and demonstrate the ability to measure asymmetric image structure associated with higher image moments directly from the
evolution of the closure phase. Finally, we show that the same formalism extends naturally to Phase Closure Nulling in optical and infrared interferometry. The resulting framework turns closure phase structure into a quantitative probe of faint and asymmetric source features across interferometric regimes.
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Solar and Stellar Astrophysics
Agentic Active Learning Meets Visual Embeddings: Finding Anomalies among 370 000 Variable Stars from ASAS-SN
Milan Pesta and Yuan-Sen Ting
Unusual light-curve morphologies can point to rare physical configurations or new phenomena, but automatic searches for anomalies are often dominated by artifacts. Separating genuine anomalies from false positives has traditionally required manual vetting, which does not scale to modern surveys. We present an active learning framework for detecting anomalies in samples of periodic variable
stars, with the vetting delegated to
multimodal large
language model
agents. The initial ranking comes from isolation forests trained on DINOv2 ViT-g/14
embeddings of phase-folded light curves. The
agents iteratively review the light-curve images of the top-ranked candidates and assign relevance scores, which are propagated through the
embedding space to prioritize the next targets. A logistic regression step then extends the search beyond label propagation, and a multi-
agent consensus review filters false positives. Using Gemini~3 Flash
agents, we applied the pipeline to $373\,646$ periodic variables from ASAS-SN Sky Patrol V2.0. Across $51$ iterations, the
agents labeled ${\sim}1\%$ of the sample in roughly $3$ hours at a cost of ${\approx}$ $$40$, yielding our final catalog of $24$ anomalies ($18$ newly reported) and $153$ potentially interesting objects. The anomalies include eclipsing binaries with extremely deep primary eclipses, high-amplitude contact binaries and pulsators, and a symbiotic nova in outburst for over two decades. At the same labeling budget, the initial ranking would have recovered only $30%$ of our catalog, while reaching its lowest-ranked anomaly would have required ${\sim}70$ times the budget. These results demonstrate the feasibility of agentic active learning for anomaly detection in existing and upcoming photometric surveys.
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Astrophysics of Galaxies
Cool CGM MgII Absorption Across the Star-Forming, Green Valley, and Quiescent Transition
Simon Xinlin Wu, Rongmon Bordoloi, Robert A. Simcoe et al. (+4 more)
We investigate the distribution and kinematics of cool circumgalactic medium (CGM) gas across the
star-forming to quiescent transition using MgII absorption for 716
galaxies spanning $0.07<z<2.7$ (169 new and 547 archival
galaxies). To compare
galaxies uniformly across 10 billion years of
cosmic time, we introduce a
star-formation offset metric ($\sigma_{\mathrm{SFO}}$), which measures a
galaxy's deviation from the
star-forming main sequence of its epoch. A key advantage of $\sigma_{\mathrm{SFO}}$ is its ability to identify transitional green valley
galaxies as a distinct population across
redshift, which would otherwise be obscured by binary
star-forming-passive classifications. We fit a virial-radius-normalized radial profile and find that the MgII absorption strength declines with increasing projected distance from the host
galaxy. The scatter around this mean profile correlates strongly with
star-formation activity: radial profile residuals correlate positively with $\log sSFR$ and $\sigma_{\mathrm{SFO}}$, with
star-forming
galaxies showing excess absorption above the profile, green-valley
galaxies showing intermediate residuals, and quiescent
galaxies falling preferentially below it. The MgII covering fraction in the inner CGM ($R/R_{200} < 0.25$) follows the same sequence, declining monotonically from
star-forming through green-valley to quiescent systems. MgII absorption kinematics are consistent with a predominantly bound cool CGM.
Star-forming
galaxies further exhibit a bimodal azimuthal dependence, with MgII absorption enhanced along both the polar and disk directions, consistent with bipolar outflows and co-planar
accretion. Together, these results indicate that the cool CGM tracks the quenching of
star-formation in
galaxies, with $\sigma_{\mathrm{SFO}}$ revealing a gradual decline in cool gas across the green valley rather than an abrupt
star-forming-to-passive transition.
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All authors Simon Xinlin Wu, Rongmon Bordoloi, Robert A. Simcoe, Andrew J. Fox, Jessica K. Werk, Jason Tumlinson, J. Xavier Prochaska
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Color-Kinematics Duality and the Double Copy in Curved Spacetimes
Mariana Carrillo González
The double copy relates gravitational data to gauge-theory data, most sharply through color-kinematics duality for flat-space scattering amplitudes. This review surveys the extent to which this idea can be formulated beyond asymptotically flat backgrounds. After recalling the flat-space ingredients needed for comparison, we describe curved-space constructions for boundary correlators and scattering observables in AdS, dS, and other non-trivial backgrounds. We then review classical and field-level maps, including Kerr–Schild, Weyl, Cotton, twistor, and convolutional double copies. A separate part is devoted to self-dual sectors. Throughout, we emphasize both the common structures that survive from flat space and the obstructions introduced by
curvature.
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Cosmology and Nongalactic Astrophysics
Exact Equivalence of the Observed Redshift and the Pulsar Timing Modulation in the Infinitesimal-Pulse Limit
Matteo Magi and Jaiyul Yoo
The
pulsar timing arrays (PTA) collect the times of arrival of
radio signals from the millisecond
pulsars, and gravitational waves can modulate their arrival times. Although the PTA observable involves successive
radio pulses propagating along different light paths, its standard theoretical description at linear order in perturbations is equivalent to the Sachs-Wolfe formula for the observed
redshift, which describes the fractional change in
photon frequency along a single geodesic. While this equivalence is well known at linear order, its validity beyond first order has not been systematically addressed in the PTA literature. Here we show that, in the limit of vanishing proper-time separation between successive emission events, the timing modulation is exactly equal to the observed
redshift, without expanding the spacetime geometry. For a finite emission interval, we derive the exact relation between the timing modulation and the observed
redshift, and show that their difference is controlled by the ratio between the emission interval and the characteristic timescale over which the observed
redshift varies.
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Earth and Planetary Astrophysics
Quantitative Links between Formation and Atmospheric Composition for Giant Planets
Yayaati Chachan, Ruth Murray-Clay and Jonathan J. Fortney
Precise atmospheric abundances of giant
exoplanets are becoming increasingly prevalent and there is a need to systematically convert these measurements into metrics that inform us about the
planets'
accretion history. We present a quantitative framework for relating atmospheric composition to the
accretion of metals and primordial gas. This includes i) new relations that simplify and generalize the connection between atmospheric
metallicity and metal mass fraction, ii) methods for inferring the source of the metals and quantifying the quantity of metals accreted via different sources, and iii) relating the derived quantities to expectations from formation models. We also derive a new estimate of the minimum disk mass needed to form a planetary system based on the amount of excess metals accreted by a
planet, assuming that this excess originates from the drift and evaporation of pebbles at condensation fronts. This paper is accompanied by an open-source code that implements the methods presented herein.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
When the HL-LHC is blind, LISA is deaf (but not vice versa): 2HDM collider-cosmology synergies
Stefano Moretti, André Pousette and Carlo Tasillo
Extensions of the Standard Model scalar sector can render the electroweak phase transition first-order and thereby provide the departure from thermal
equilibrium required for electroweak baryogenesis, while at the same time sourcing a
stochastic gravitational wave (GW) background in the milli-Hertz range. In this work, we investigate electroweak phase transitions in the CP-conserving type-I two-
Higgs-doublet model (2HDM), focusing on the interplay between
collider constraints at the HL-LHC and the projected sensitivity of LISA. We compute the expected GW background due to strong first-order electroweak phase transitions and perform extensive Monte Carlo scans over the
collider-viable model parameter space. We find that GW signals within reach of LISA arise almost exclusively in regions of parameter space that necessarily predict observable deviations at the HL-LHC, in particular through the $H \to ZZ$ decay channel of the heavy CP-even and neutral
Higgs state with $m_H \simeq 180\text{--}250 \, \text{GeV}$. Our results highlight the decisive complementarity between
collider and GW probes and show that the largest parts of the 2HDM parameter space relevant for phase transition signals at LISA can already be tested by HL-LHC. A possible future discovery of 2HDM states at the HL-LHC, however, would not allow conclusive statements about LISA being able to find a GW background due to the amount of parameter tuning required for an observable GW signal. In order to evaluate possible caveats of this statement we study the theoretical uncertainties related to the GW predictions in a two-fold approach using both state-of-the-art tools, BSMPT and TransitionListener, and also allow for model realizations in which the electroweak
symmetry is not restored in the high-temperature limit, which are the ones combining the loudest GW signals with the weakest
collider coverage.
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Earth and Planetary Astrophysics
WASP-12b Exhibits Persistent In-Transit H$\alpha$ Absorption
Shreyas Vissapragada, Fabienne Nail, Morgan MacLeod et al. (+6 more)
High-resolution H$\alpha$ and He 10830 Å transit spectroscopy can trace the extended upper atmospheres of
exoplanets, typically revealing excess in-transit absorption that occurs in the
planet's rest frame. However, hydrodynamical simulations predict that absorption should not strictly follow the
planet's orbital motion if gas quickly escapes the planetary Roche lobe and shears into tidal tails. The ultra-hot Jupiter WASP-12b fills an exceptionally large fraction of its Roche lobe ($R_p/R_\mathrm{Roche} = 0.55$), and in this paper we present evidence for tidally-modulated outflow kinematics on this unique
planet. We observed a transit of WASP-12b with MMT/Hectochelle and found an excess H$\alpha$ absorption of $3.29^{+0.35}_{-0.36}\%$ (9.3$\sigma$) during the transit and extending at least 30~min post-egress. The signal does not follow the
planet's orbital motion and instead appears largely in the stellar rest frame, similar to the extended helium outflows in HAT-P-32b and HAT-P-67b, and is slightly redshifted ($+5.4_{-1.7}^{+1.5}$ km s$^{-1}$). We demonstrate that a similar signal appears across previous high-sensitivity observations dating back to 2012 once the atypical signal kinematics and baseline self-subtraction are taken into account. Finally, we present a three-dimensional Athena++ model of WASP-12b's outflowing atmosphere that simultaneously exhibits the observed extended morphology and lack of
planet-aligned velocity gradient. Our study highlights the necessity of three-dimensional simulations for interpreting absorption lines formed in strong outflows, where gas may not simply follow the
planet's Doppler signature.
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All authors Shreyas Vissapragada, Fabienne Nail, Morgan MacLeod, Adam Jensen, Stefan Czesla, Mercedes Lopez-Morales, Jea Adams Redai, Kevin N. Ortiz Ceballos, Jaehyon Rhee
High Energy Astrophysical Phenomena
Signatures of Compact Object Mergers Inside Stars in AGN Disks
Matteo Cantiello, Alexander J. Dittmann, Saavik Ford et al. (+4 more)
Disks of gas accreting onto supermassive black holes, powering active galactic
nuclei (AGN), can capture
stars from nuclear
star clusters or form
stars in situ via gravitational instability. The dense, hot disk environment can drive rapid
accretion onto embedded
stars, dramatically altering their
evolution. Models predict that, for sufficiently rapid
accretion, fresh gas replenishes hydrogen in stellar cores as quickly as it is burned, and the
stars reach a quasi-steady state. Here we study encounters of such massive, long-lived (”immortal”)
stars with compact objects in AGN disks. We estimate the encounter rate and the timescale for a single compact remnant to spiral into an AGN
star; depending on how strongly feedback regulates the ensuing
accretion, the
star is either consumed in a collapsar-like, engine-driven transient or converted into a long-lived, quasi-
star-like object hosting a central black hole. We then study the merger of a binary black hole (BBH) inside the AGN
star, and show that gas drag hardens the binary to merger far faster than gravitational-wave emission alone. The resulting merger is a loud LIGO-Virgo-KAGRA (LVK) source, but the characteristic imprint of the dense environment -a strong suppression and dephasing of the inspiral relative to
vacuum- falls in the deci-Hz band rather than the milli-Hz LISA band, and is best resolved by next-generation detectors such as DECIGO. We estimate that this channel could contribute a BBH merger rate of up to $\sim8\,{\rm Gpc^{-3}\,yr^{-1}}$ in favorable scenarios, and discuss the model uncertainties and directions for future work.
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All authors Matteo Cantiello, Alexander J. Dittmann, Saavik Ford, Barry McKernan, Carlos Palenzuela, Rosalba Perna, Taeho Ryu
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Wilsonian Cosmology: de Sitter (in)Stability
Jean Alexandre, Lucien Heurtier and Silvia Pla
We develop a (Wilsonian) functional-renormalisation-group framework for scalar cosmology in which
quantum fluctuations of a scalar field are coarse-grained on cosmological spacelike hypersurfaces. Integrating out
quantum fluctuations with wavelengths smaller than the Hubble radius $H(t)^{-1}$, we obtain an effective scalar potential $U(\phi(t),H(t))$ that evolves in time. We derive a non-perturbative flow equation for this potential, together with the coupled set of (modified) Friedmann equations. We then apply this formalism to the simplest possible case of a de Sitter
vacuum when the scalar field is at rest, in two situations which satisfy exactly our flow equation: $(i)$ A flat potential, for which we find that the only pure de Sitter solution is unstable and corresponds to a saddle point. $(ii)$ A quadratic potential with
curvature $m^2>0$, for which we find that the presence of the mass term stabilises the system. The latter case leads to a de Sitter attractor either at the Hubble scale when the mass is larger than the Hubble scale at initial time, or by introducing a new attractor located at $H=m$ in the case the mass is smaller, which may be particularly relevant to the phenomenological study of dark energy and inflation theories.
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Astrophysics of Galaxies
A simulation-based quality-control framework for the broad-line region radius-luminosity relation
Juri Wladimir Seib, Francisco Pozo Nuñez and Sarah Elena Ivana Bosman
The broad-line region (BLR) radius-luminosity (R-L) relation underpins single-epoch black hole mass estimates in active galactic
nuclei (AGN). The published H\beta sample is heterogeneous in observational quality, and it remains unclear how much of its scatter is intrinsic rather than caused by systematics in lag recovery. We quantify the contribution of unreliable lag recovery to the observed scatter of the H\beta R-L relation and provide tools for quality control. We compile a publicly available database of reverberation mapping measurements for ~1200 AGN from 32 campaigns spanning more than three decades, including lags, luminosities, line widths, black hole masses, and observational metadata. We develop a simulation-based consistency framework in which damped random walk light curves are sampled according to each campaign's baseline, cadence, and signal-to-noise ratio, and lags are recovered with the interpolated cross-correlation function (ICCF). Comparing expected, reported, and simulation-retrieved lags defines a four-tier flagging scheme. We refit the R-L relation with UltraNest for progressively cleaner samples and construct consensus samples across three reference slopes to reduce model dependence. Of 248 H\beta sources, ~40% show discrepancies between reported and simulation-retrieved lags, while ~5% show direct inconsistencies between expected and retrieved lags. Excluding flagged sources and correcting for model bias reduces the inferred intrinsic scatter from \sigma = 0.26^{+0.02}_{-0.01} dex to 0.11\pm0.01 dex, with a corrected slope of \alpha = 0.48\pm0.02. Our results indicate that a substantial fraction of the observed H\beta R-L scatter arises from observational limitations and lag-recovery biases rather than intrinsic AGN diversity. The database, simulation code, and RM-Scout campaign-planning tool are publicly available.
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Astrophysics of Galaxies
Spin inference with the Black Hole Explorer. I. Fisher information matrix forecast
Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson et al. (+1 more)
General relativity predicts the presence of a thin, bright ring of light superimposed on the image of a black hole (the “
photon ring”), whose geometry is sensitive to the
spin of the black hole. Detecting this
photon ring in observations of nuclear supermassive black holes would yield insight into
gravity in the strong-field regime as well as their growth histories. The Black Hole Explorer (BHEX) is a mission being developed to detect the
photon ring for the first time, raising the question of how precisely we can constrain
spin from its observations. We use the method of Fisher information
matrices (FIMs) along with a simple dual-cone semi-analytic emission model to forecast BHEX
spin posterior widths for the primary science targets (M87* and Sgr~A*) in a variety of configurations. We find that BHEX can constrain the dimensionless
spin of its targets to a precision of $\sigma_{a_*} \ll 0.1$ after 30 orbits, even in the presence of significant systematic errors. We validate our results via numerical checks for stability and robustness, as well as synthetic data cross-validation to assess handling of covariances and prior information in the FIM against a full posterior exploration.
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All authors Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson, Dominic O. Chang
Astrophysics of Galaxies
More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at $>3\sigma$, Hinting at Synchronized Black Hole Seed Formation
Fabio Pacucci and C. Megan Urry
The Little Red Dots (LRDs) are compact, red sources at $4 \lesssim z \lesssim 9$, likely powered by accreting massive black holes. Multiple studies have detected blue companions in their vicinity: we compare $253$ LRDs, uniformly selected across several JWST deep fields, against $>7000$ matched controls in the same mosaics. We find that $27.7\%$ of the brightest LRD quartile (in F444W) hosts a blue ($\beta<-1$) companion at $0.5-2$ kpc, versus $11.6\%$ of
redshift-matched controls: a $\times 2.39$ excess, significant at $3.3\sigma$. Against controls additionally matched in brightness and compactness, the excess ratio is similar ($\times 2.17$), although constrained only at $1.4\sigma$ by the small size of that control pool. This phenomenon is limited to the brightest LRDs, as the full LRD sample pairs at a rate indistinguishable from controls. Moreover, the excess is confined to the close-pair window ($< 2$ kpc), outside which LRD environments are ordinary. Their companions are overwhelmingly ($92\%$) blue and significantly bluer than those of controls ($\beta\approx-2.32$ versus $-1.92$), rejecting a common parent distribution at $3.4\sigma$. The signal is thus directional in brightness, separation, and companion color, as expected for synchronized-pair seed formation. Therefore, we conclude that the association between the brightest LRDs and their close blue companions is physical, i.e., the two phenomena are causally connected: either one drives the other, or both emerge from the same synchronized formation event. A natural explanation is that the radiation from these young,
star-forming neighbors enabled the direct collapse of the massive black holes powering the LRDs themselves.
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