Papers for Friday, Aug 22 2025

Massive stars in the Hertzsprung gap are a mixed population of objects in short-lived evolutionary phases: yellow supergiants (YSGs) evolving towards the red supergiant (RSG) phase, partially-stripped post-RSGs, and other, rarer outcomes of stellar evolution. Studies of sufficiently large samples of these objects can constrain massive star structure and evolution during these poorly-understood phases. As part of our ongoing program searching for post-RSGs, we characterized the spectral line profiles of 32 YSGs in the Large Magellanic Cloud using high-resolution spectra obtained with the MIKE spectrograph on the Magellan 2/Clay telescope at Las Campanas Observatory. We find that the line profiles are strongly broadened by turbulent photospheric motion. After fitting the profiles to measure microturbulent and macroturbulent velocities, we identify two groups within our sample that are separated by the ratio of the two velocity scales. In both groups, the macroturbulent velocity scales with stellar properties such as effective temperature. Additionally, we find statistically-significant correlations between the macroturbulent velocity and other possible probes of large-scale photospheric motions: line profile asymmetry, as well as the amplitude and quality factor of the stochastic low frequency variability measured from {\it Transiting Exoplanet Survey Satellite} lightcurves. These correlations differ between the two groups of YSGs. Finally, we construct 1D evolutionary models of YSGs in both pre- and post-RSG phases, and find reasonable agreement between the convective velocities in these models and our measured microturbulent velocities. However, the macroturbulent velocities are much higher than the convective velocities in the models.

High-redshift galaxies exhibit compact regions of intense star formation, known as ``clumps,'' which are conspicuous in the rest-frame ultraviolet. Studying them can shed light on how they form and evolve and inform theoretical models of galaxy evolution. We examine the evolution of clumpy galaxies with redshift and stellar mass over $2<z<12$ with James Webb Space Telescope (JWST) imaging from the JWST Advanced Extragalactic Survey (JADES). Off-center clumps are detected in the rest-frame near-ultraviolet (NUV) using similar techniques to those in earlier studies based on Hubble Space Telescope (HST) images. This is done for a sample of 9,121 star-forming galaxies with stellar masses $\log\left(M_{\star}/M_{\odot}\right) \geq 8$. The fraction of clumpy galaxies, $f_{\rm{clumpy}}$, increases from $\sim20\%$ at $z>6.5$ to $\sim80\%$ at $z\sim2.75$ at $\log\left(M_{\star}/M_{\odot}\right) \geq 9$. Our $f_{\rm{clumpy}}$ values are generally higher at fixed redshift and increase faster with decreasing redshift than what studies based on HST data found, which we attribute largely to the higher sensitivity of JWST. Clumps make up $15-20\%$ of the NUV luminosity of clumpy galaxies, with little dependence on redshift or stellar mass. $f_{\rm{clumpy}}$ correlates with stellar mass and there is little correlation with specific star-formation rate. Our $f_{\rm{clumpy}}$ measurements are compared with those from simulations as well as other observations. At low redshifts ($z\lesssim5.75$) and intermediate-to-high stellar masses ($\log\left(M_{\star}/M_{\odot}\right) \geq 9$), our results suggest gas fragmentation due to violent disk instabilities to be the dominant mechanism for forming clumps. At high redshifts and low stellar masses, compression of gas during mergers appears to dominate.

Context: Recent studies using Gaia data have reported tidal tail detections for tens to hundreds of open clusters. However, a comprehensive assessment of the reliability & completeness of these detections is lacking. Aims: This work aims to summarise the expected properties of tidal tails based on N-body simulations, review the reliability of tidal tail detections in the literature, and grade them according to a set of diagnostic tests. Methods: We used a grid of 68-20000 Msun simulated clusters & analysed the formation & evolution of the tails. We compiled 122 catalogues (58 unique clusters) from literature, within 500 pc of the Sun. We employed tests based on photometric, morphological & dynamical signatures, & comparisons with simulations, to grade their tails. Results: Based on the simulations, we analysed the complex morphology of the tails & their properties (e.g., size, span, stellar types, number density, & mass function) at various cluster masses & ages. During the first 200 Myr of evolution, the tails typically form a characteristic S shape, with an amplitude that scales with cluster mass. The tail span increases at a rate of 4 times the initial velocity dispersion, & the near-tail is predominantly populated by recent escapees. Conclusions: In the 122 published tail catalogues, we found that 15 gold & 55 silver catalogues passed the majority of the tests. The remaining 51 were graded as bronze; care should be taken before using these for further analysis. The age, metallicity, binary fraction, & mass function of stars in the tails were generally consistent with those of their parent clusters. The gold/silver catalogues (69 catalogues of 40 clusters) represent reliable samples for detailed analyses of tails. Future data will be essential for further validation & for leveraging tidal tails as tracers of cluster dissolution & the Galactic potential.

Recent observations have revealed star-forming regions as possible origin sites of very-high-energy (TeV) cosmic rays, not associated with supernova remnants. Colliding-wind binaries (CWBs) are strong X-ray and radio synchrotron emitters and have been proposed as potential accelerators of such particles. We perform high-resolution three-dimensional magnetohydrodynamic simulations coupled with test-particle integration to investigate how local plasma conditions affect particle acceleration in CWBs. We find that the maximum particle energies and the hardness of the energy distributions depend on the shock magnetization and cooling efficiency. For moderate magnetization ($\gt$1 G), CWBs can accelerate hadronic particles up to hundreds of TeV or even PeV energies, with more than 1\% of particles reaching the very-high-energy range. By correlating the local acceleration rate with plasma quantities - \textit{magnetic field strength, current density, vorticity, and velocity divergence} - we show that turbulence and magnetic field complexity dominate the acceleration, while classical diffusive shock acceleration plays a limited role. These results suggest that turbulent, magnetically driven processes are key to producing relativistic particles in CWBs, with implications for future high sensitivity $\gamma$-ray observations (e.g. LACT and CTAO).

We present the first results from the COSINE (Cometary Object Study Investigating their Nature and Evolution) project, based on a uniformly processed dataset of 484 comets observed over the full 15-year duration of the WISE/NEOWISE mission. This compilation includes 1,633 coadded images spanning 966 epochs with signal-to-noise ratios (S/N) greater than 4, representing the largest consistently analyzed infrared comet dataset obtained from a single instrument. Dynamical classification identifies 234 long-period (LPCs) and 250 short-period comets (SPCs), spanning heliocentric distances of 0.996--10.804 au. LPCs are statistically brighter than SPCs in the W1 (3.4 um) and W2 (4.6 um) bands at comparable heliocentric distances. Cometary activity peaks near perihelion, with SPCs exhibiting a pronounced post-perihelion asymmetry. Multi-epoch photometry reveals that SPCs show steeper brightening and fading slopes than LPCs. The observing geometry of WISE/NEOWISE -- constrained to a fixed ~90-deg solar elongation from low-Earth orbit -- introduces systematic biases in the sampling of orientation angles for extended features. Collectively, the results reveal a continuous evolutionary gradient across comet populations, likely driven by accumulated solar heating and surface processing. This study establishes a foundation for subsequent COSINE analyses, which will separate nucleus and coma contributions and model dust dynamics to further probe cometary activity and evolution.

We present a comprehensive analysis of transit, eclipse, and radial velocity data of the hot Jupiter TrES-1 b and confirm evidence of orbital variations on secular timescales. Apparent variations due to systemic motion and light travel time effects have been ruled out, indicating that the observed changes are dynamical in origin. Joint modeling of the TrES-1 b data favors an apsidal precession model, but the rapid precession rate of $4^\circ$ yr$^{-1}$ cannot be explained without invoking an undetected close-in planetary companion, which remains unseen in the data. While radial velocity measurements reveal a previously undetected companion candidate on a wide, eccentric orbit, it is unlikely to drive the observed evolution of TrES-1 b. However, an orbital decay model provides a plausible alternative if the loss of orbital energy is driven by planetary obliquity tides. We find that the best-fit orbital decay rate of $-7.1^{ +1.5}_{-1.6}$ ms yr$^{-1}$ is aligned with theoretical predictions for modified tidal quality factors of hot Jupiters if TrES-1 b has a planetary obliquity $\varepsilon_p > 30^\circ$. We encourage follow-up observations of this system, particularly of eclipse timing and radial velocities, to further constrain the nature of the observed evolution. This paper provides a practical framework for studying secular variations and aims to accelerate future research on similar systems.

Type Ia supernovae (SNIa) are thermonuclear explosions of white dwarfs in binary systems. They are central to galactic chemical evolution and serve as standardizable candles in cosmology, yet their progenitors remain uncertain. In this work, we present a grid of five models detailing the evolution and nucleosynthesis of slowly merging carbon-oxygen white dwarfs approaching the Chandrasekhar mass. These models test a variety of physics input settings, including accretion rates, nuclear reaction rates, convection parameters, and the composition of the accreted material. During the merger process, as the mass of the primary white dwarf approaches the Chandrasekhar limit, carbon burning is initiated first on the surface before eventually igniting explosively at the center. As a consequence, the 22Ne(a,n)25Mg reaction activates in the outer layers of all models. The neutrons released in this way produce a weak s-process-like abundance distribution peaking at Kr, which is overproduced by more than a factor of 1000 compared to solar. The trans-Fe elements-enriched outer layer mass varies from 0.04 Msun to 0.11 Msun, depending on the accretion rate. Our explosion simulation of these progenitor models ejects significant amount of first-peak elements (e.g., Kr, Sr) as well as of some long-lived radioactive species, such as 60Fe. In a previous theoretical study, we found that a similar nucleosynthesis process during the progenitor phase may also occur on the surface of near-Chandrasekhar white dwarfs formed through the accretion of H-rich material via the single-degenerate scenario. Therefore, these results suggest trans-Fe enrichment might be a hallmark of near-Chandrasekhar SNIa ejecta, regardless of the specific progenitor channel, and could provide a new spectral signature distinguishing them from sub-Chandrasekhar explosions.

The potential presence of a magma surface below a thick atmosphere primarily composed of hydrogen in some sub-Neptune exoplanets suggests a strong link between the interior composition and atmosphere through chemical coupling of volatile and refractory species. In this study, we aim to model the possibility for mineral cloud formation in the atmosphere of sub-Neptunes from outgassing of refractory species at the magma surface. In our specific cases, we find that mineral clouds easily form near the magma-atmosphere boundary, but also higher in the atmosphere once vapour is mixed to the cooler atmospheric regions. We find that the vertical cloud structure depends on the mixing profile of the atmosphere, with stronger mixing allowing particles to remain lofted in the atmosphere, while weak to moderate mixing produces larger, more sedimented cloud particle profiles. We suggest that due to the strong thermal feedback from cloud opacity, clouds may play an important role in the overall structure of the interior-surface-atmosphere coupled system in sub-Neptunes, as well as affect their observed spectral properties, especially at near-infrared wavelengths.

Here we present an open-source cloud model for substellar atmospheres, called Virga. The Virga-v0 series has already been widely adopted in the literature. It is written in Python and has heritage from the Ackerman & Marley (2001) model (often referred to as eddysed), used to study clouds on both exoplanets and brown dwarfs. In the development of the official Virga-v1 we have retained all the original functionality of eddysed and updated/expanded several components including the back-end optical constants data, calculations of the Mie properties, available condensate species, saturation vapor pressure curves and formalism for fall speeds calculations. Here we benchmark Virga by reproducing key results in the literature, including the SiO2 cloud detection in WASP-17 b and the brown dwarf Diamondback-Sonora model series. Development of Virga is ongoing, with future versions already planned and ready for release. We encourage community feedback and collaborations within the GitHub code repository.

This study evaluates the performance of several machine learning models for predicting hazardous near-Earth objects (NEOs) through a binary classification framework, including data scaling, power transformation, and cross-validation. Six classifiers were compared, namely Random Forest Classifier (RFC), Gradient Boosting Classifier (GBC), Support Vector Classifier (SVC), Linear Discriminant Analysis (LDA), Logistic Regression (LR), and K-Nearest Neighbors (KNN). RFC and GBC performed the best, both with an impressive F2-score of 0.987 and 0.986, respectively, with very small variability. SVC followed, with a lower but reasonable score of 0.896. LDA and LR had a moderate performance with scores of around 0.749 and 0.748, respectively, while KNN had a poor performance with a score of 0.691 due to difficulty in handling complex data patterns. RFC and GBC also presented great confusion matrices with a negligible number of false positives and false negatives, which resulted in outstanding accuracy rates of 99.7% and 99.6%, respectively. These findings highlight the power of ensemble methods for high precision and recall and further point out the importance of tailored model selection with regard to dataset characteristics and chosen evaluation metrics. Future research could focus on the optimization of hyperparameters with advanced features engineering to further the accuracy and robustness of the model on NEO hazard predictions.

Flares from stars can significantly impact the atmospheres of their orbiting planets, yet the role of hard X-ray (HXR; 3-20 keV) emission in driving escape and tracing particle acceleration remains poorly constrained. With the aim of quantifying the HXR share of the total radiative budget, we obtained a NuSTAR observation, quasi-simultaneous with Swift and Einstein Probe observations, of the young M1Ve star AU Mic, detecting two flares. We build an empirical soft X-ray (SXR; 0.3-3 keV)-HXR scaling relation and, on that basis, quantify the HXR share of the total radiative budget, defined as the sum of extreme ultraviolet (EUV; 0.01-0.3 keV), SXR, and HXR, and assess its effect on atmospheric escape. We find that the HXR fraction is 1.7% in quiescence and rises to 3.3% at flare peaks; even adopting the EUV + SXR (collectively referred to as XUV) escape efficiency as an upper bound, HXR-powered mass loss amounts to only a few percent of the XUV-driven rate. High-energy spectral tails are detected in quiescence and in Flare 2. Both nonthermal and high temperature thermal models provide acceptable fits to the data; however, the presence of two localized Neupert effect episodes in Flare 2, combined with the implausibly large energy budget required for a 290 MK plasma, strongly favors a nonthermal interpretation. Consistent with this picture, spectral-timing analysis shows that the 6-20 keV share of the emission actually declines during flares, while heating is dominated by 3-6 keV photons-implying rapid thermalization of accelerated electrons and a predominantly thermal energy release. Overall, the flares are thermally dominated, nonthermal electrons can power chromospheric heating episodically, but HXR-induced escape appears to be marginal for the long-term atmospheric evolution of AU Mic's planets.

The prominent Thackeray's globules are a collection of cloudlets seen in silhouette against the bright emission of the IC 2944 HII region, ionized by the Collinder 249 cluster of early-type stars (placed at 2331$\pm$30 pc, derived from a Gaia DR3 analysis of the parallaxes of 11 massive stars). Here we present the analysis of Band 3 ALMA data that reveals the cold emission (continuum and molecular) associated with the neutral gas and its kinematic behavior. Many of the globules follow a linear velocity gradient that can be explained as the result of an acceleration process due to the rocket effect, where freshly ionized material streams away from the globule, compressing and accelerating it. We identified 46 globules (12 of which are new detections), measured their kinematics, and estimated their densities and masses. At least 5 of them are associated with emission of dense molecular tracers and/or millimeter continuum sources and have indications of possible gravitational collapse. We applied a simple model for the acceleration of the globules which accounts for the observed kinematics. In this scenario only the most massive of the globules will be able to gravitationally collapse before being completely destroyed, in the process reaching speeds of tens km/s, and potentially becoming low-mass walkaway/runaway protostars.

Many possible interior compositions exist for sub-Neptunes: ice-poor, ice-rich, and water-dominated interiors can all match the measured masses and radii. Motivated by recent theory of carbon-rich planet formation outside of the refractory organic carbon "soot line" and observations of carbon-rich protoplanetary disks around late M dwarfs, we propose another possible sub-Neptune composition: a carbon-rich composition consisting of an iron-silicate core, a carbon layer, and a hydrogen/helium-dominated envelope. We show that the interiors of three prototypical sub-Neptunes with high-quality spectral observations - TOI-270 d, GJ 1214 b, and K2-18 b - are consistent with carbon-rich compositions if they have $\leq100\times$ solar metallicity atmospheres. We further show that carbon-rich interiors lead to atmospheric compositions that match HST and JWST observations. Simulated carbon-rich TOI-270 d transmission spectra pass the $\chi^2$ test under a wide range of C/O, haze, and cloud scenarios. K2-18 b spectral models are broadly consistent with observation, but requires additional sources for carbon species to be fully compatible. GJ 1214 b models, however, are incompatible with observations, ruling out a carbon-rich interior composition, if the atmosphere of the planet is primordial and reflects interior C/O.

The Integrating Miniature Piggyback for Impulsive Solar Hard X-rays (IMPISH) is a solar X-ray spectrometer that features large-area scintillators, fast readout electronics, and good energy resolution in the hard X-ray band. IMPISH is a low-cost spectrometer designed to measure subsecond variation in hard X-ray time profiles from solar flares, with the goal of constraining particle acceleration timescales. To meet these requirements, we carried out a systematic optimization of the scintillation design, focusing on maximizing photon collection, reducing noise level, and improving energy resolution. We tested two high-yield scintillating crystals (LYSO, lutetium yttrium oxyorthosilicate, and GAGG, gadolinium aluminum gallium garnet), two reflector types (specular and lambertian), two kinds of surface finishes (all sides polished and readout face only polished), different optical coupling materials and thicknesses, multiple geometries, and readout face angles. Our studies show that light collection improves with increasing the crystal's effective area, breaking its symmetry, and reducing the photon's travel length. These minimize photon loss due to self-absorption and total internal reflection. Through combined simulation and laboratory tests, we achieved an optimal energy resolution with the LYSO trapezoid-shaped crystal coupled to a Broadcom NUV-MT SiPM with an approximately 0.25 mm thin Sylgard 184 optical pad.

We investigate whether an Early-Universe stochastic gravitational-wave background (SGWB) can account for the common spectrum process reported by NANOGrav, while also being consistent with current and projected CMB measurements of extra radiation. We compute the contribution of effective number of relativistic species, $\Delta N_{eff}$, for a number of Early-Universe models proposed to explain the pulsar timing array (PTA) spectrum. We demonstrate that models predicting $\Delta N_{eff}$ above the CMB limit would be firmly excluded, implying that the NANOGrav signal in tension with these bounds must instead arise from astrophysical sources. We find that current NANOGrav 15-year dataset, sensitive up to 60 nHz, gives a negligible contribution to $\Delta N_{eff}$ and remains well below the present and future CMB detection threshold. However, when we project future PTA capabilities reaching upto 1 $\mu$Hz, even with our conservative estimate we find that Inflation, Scalar Induced Gravitational Waves (SIGW), and metastable cosmic strings can induce a $\Delta N_{eff}$ large enough for $>3.5\sigma$ detection by the Simons Observatory.

Galaxy cluster mergers drive powerful shock fronts that heat the Intra-Cluster Medium (ICM) and accelerate particles, redistributing the energy in a merger. Abell 665 is one of only a few clusters with such a powerful shock ($M \sim 3$) and provides a unique opportunity to study the thermalization timescale of the ICM, particularly the electron-ion equilibration timescale. Understanding this timescale is crucial for determining how energy from the merger is distributed between thermal and non-thermal particle populations. Using $\sim$200 ks of NuSTAR observations, we measure the temperature distribution across the shock to distinguish between two heating models: (1) an instant, collisionless model where ions and electrons are immediately heated at the shock front, and (2) a collisional model where electrons are initially adiabatically compressed at the shock and subsequently equilibrate with the ions over $\sim$100 Myr. Our measurements favor the delayed equilibration model, suggesting that electrons do not immediately reach thermal equilibrium with the ions at the shock front and instead equilibrate over $t_{eq} = (4.0 \pm 3.4) \times 10^8$ yrs. Additionally, our temperature measurements indicate that the Mach number may be lower than previously estimated ($M = 2.8 \pm 0.7$), suggesting that the shock strength has been overestimated in past studies. These results add to our understanding of the microphysics governing how thermal energy is distributed in diffuse plasmas like the ICM, with implications for galaxy cluster evolution, large scale structure formation, and cosmology.

We present a pseudo-Newtonian stationary circumbinary slim disk model. We extend the slim disk formalism by including the binary tidal torque and solve the resulting steady-state equations to determine the circumbinary disk structure. We compare the binary slim disk solutions with corresponding binary thin disk solutions, calculate the disk spectrum, explore the impact of different parameters on the system, and estimate the binary shrinkage timescale. We find that; (1) due to the different disk density profiles, the integrated tidal torque exerted on the disk is significantly smaller for the slim disk than for the thin disk; as a result thin disks onto binary black holes can be radiatively significantly more efficient than slim disks; (2) The presence of the secondary alters the emission of the circumbinary disk, making it different from the spectrum of a single black hole Active Galactic Nuclei (AGN); (3) The tidal torque boosts the viscous torque in the outer part of the disk (radii greater than the binary separation), which is strongly dependent on the disk parameters, including the binary mass ratio $q$, the orbital separation $a$, the viscous parameter $\alpha$ and the accretion rate $\dot M$; (4) The vertical component of the potential of the secondary slightly decreases the integrated tidal torque. However, both the vertical and radial components of the potential of the secondary have small impact on the disk radiative flux; (5) Using the integrated disk tidal torque backreacting on the secondary at different orbital separations, we find that the disk provides an efficient way to shrink the binary orbital separation.

The young neutron star (NS) in the Cassiopeia A (Cas A) supernova remnant is a fascinating test for theories of NS cooling. Chandra observations have indicated that its surface temperature is declining rapidly, about 2% per decade, using 20 years of data, if a uniform carbon atmosphere is assumed for the NS. This rapid decline may be caused by the neutrons in the NS core transitioning from a normal to a superfluid state. However, most of the Cas A NS observations were performed by the Chandra ACIS detectors, which suffer complicated systematic effects. Here, we test the cooling of the Cas A NS with Chandra HRC data over 25 years. The Chandra HRC detector has independent systematics, serving as a cross-check. Assuming a fixed hydrogen column density ($N_{\rm H}$), we infer the cooling rate of the Cas A NS to be 0.57$^{+0.26}_{-0.27}$% per decade. Allowing the $N_{\rm H}$ to vary with time (as estimated using ACIS data), the cooling rate is 1.11$^{+0.25}_{-0.28}$% per decade. These cooling rates are smaller than measured using ACIS data, implying systematic uncertainties have not been eradicated from either or both datasets. However, we have verified the decline in the absorbed flux from the Cas A NS using an independent instrument, at $>3\sigma$ level (4.7%$\pm$1.5% over 10 years). Additionally, the weaker cooling rate of Cas A NS inferred from HRC datasets eliminates the tension with the theoretically predicted cooling, and can be explained by the reduced efficiency of the neutrino emission accompanying the Cooper pair breaking and formation process in neutron triplet-state superfluid.

Several models have been proposed to explain the formation of solar prominences, among which the evaporation--condensation model and the direct injection model are the most popular ones. In our previous study we proposed to unify these two models, namely, both are due to localized heating in the chromosphere, presumably via magnetic reconnection. When the localized heating is located in the upper chromosphere, the cold in-situ plasmas are heated to coronal temperatures, then evaporated to the corona, and finally condensate to form a prominence. Such a process is manifested as the evaporation-condensation model. When the localized heating is located in the lower chromosphere, the enhanced in-situ pressure would push the cold plasmas in the upper chromosphere to the corona directly, which is manifested as the direct injection model. While the idea was confirmed by the one-dimensional hydrodynamic simulations, the heating was imposed ad hoc. In order to simulate the localized heating more self-consistently, we perform two-dimensional magnetohydrodynamic simulations in this paper, where the localized heating is naturally realized by magnetic reconnection at different heights. The simulations further validate our model. Besides, mass circulation in the solar atmosphere is also briefly discussed.

We investigate an interacting polytropic dark energy (PDE) model characterised by the equation of state $p_{d} = \alpha \rho_{d}^{\,1+\frac{1}{\beta}}$, where the interaction between dark energy and pressureless matter is modelled via a linear coupling term $Q = 3\eta H\rho_{d}$. The background dynamics are formulated by deriving the Hubble parameter in the interacting scenario, and the model parameters are constrained through a Markov Chain Monte Carlo (MCMC) analysis using three joint observational data sets: Hubble77+BAO26, Hubble77+Pantheon$^+$, and Hubble77+BAO26+DESI DR2. The resulting best-fit values of $(H_0, \Omega_{d0}, \eta) $ are $(69.22^{+1.27}_{-1.24},\,0.73^{+0.02}_{-0.02},\,-0.22^{+0.10}_{-0.12})$, $(69.23^{+1.27}_{-1.22},\,0.73^{+0.02}_{-0.02},\,-0.34^{+0.15}_{-0.17})$, and $(67.77^{+1.26}_{-1.24},\,0.73^{+0.02}_{-0.02},\,\\-0.02^{+0.10}_{-0.11})$ respectively for the respective data combinations. Our results indicate a positive energy density and negative pressure over the full redshift range, with the evolution of the equation-of-state parameter and state finder parameters placing the model firmly within the Quintessence regime. The study of the deceleration parameter also reveals a shift from a decelerating to an accelerating cosmic expansion. The estimated present age of the Universe is $14\,\mathrm{Gyr}$, consistent with recent observational data. Furthermore, the sign of $Q$ implies a current energy transfer from dark energy to matter. These findings support the interacting PDE framework as a viable candidate for explaining late-time cosmic acceleration and related large-scale dynamics.

The first direct detection of the gravitational wave (GW) event GW170817 and its electromagnetic (EM) counterpart open a new window for studying of multi-messenger astronomy. However, how to identify the remnant of binary neutron star (NS) merger via EM radiation remain an open question. In this paper, we propose a method of color evolution of kilonova emission to identify its progenitors. We assume that the energy of the kilonova is contributed from radioactive decay, magnetar spin-down, and pulsar wind nebula (PWN). The color evolution of kilonova emission associated with short GRB is significant when the spectrum is thermal emission, while it tends towards a constant when the spectrum is non-thermal radiation. On the other hand, if the central engine is a black hole (BH) which is promptly generated by the NS-NS merger or NS-BH merger, then the kilonova is powered only by the radioactive decay. There is no color evolution at the beginning before the peak of kilonova emission, but is significantly and rapidly increasing after the peak. On the contrary, if the central engine is a magnetar or stable NS, the kilonova emission is contributed from radioactive decay, magnetar, and PWN. The color evolution after the peak of kilonova emission is complex behavior which depends on the rotational energy and spin-down time-scale of magnetar, and finally tend to a constant in the late state.

Understanding the evolution of pulsar dispersion measures is vital to high precision timing experiments, as well as astrometric experiments to determine pulsar positions and proper motions. In this work, we present a novel approach to measuring dispersion measure gradients using pulsar scintillometry. This approach makes use of the multipath propagation through the interstellar medium to simultaneously probe dispersion measures along multiple sight lines from a single observation. Using existing data of PSR B0834+06, we are able to measure gradients of $9.7\pm0.3\times10^{-6}~\rm{pc}~\rm{cm}^{-3}~\rm{mas}^{-1}$.

We present a novel host galaxy subtraction technique in longslit spectroscopy for extragalactic transients. Unlike classic methods which generally estimate the background using a simple linear interpolation of local galaxy flux in the 2D spectrum, our approach leverages multi-band archival images of the host galaxies to model the background emission from the galaxy in the 2D spectrum. Such imaging is readily accessible through wide-field imaging surveys. These images encode the wavelength-dependent galaxy profile along the slit. We construct a smooth prior for the 2D galaxy profile with a Gaussian process (GP) based on these reference images, and use another GP to model the correlated deviations from the prior in the observed spectrum. This enables accurate inference of the galaxy flux blended with the transient. On synthetic longslit data of a spiral galaxy extracted from a Multi Unit Spectroscopic Explorer (MUSE) hyper-spectral cube, the GP method remains robust as long as the host galaxy is spatially resolved and consistently outperforms the classic method. We apply the method to archival Keck spectra of two real transients, SN 2019eix and AT 2019qiz, to further demonstrate how the method uniquely recovers weak spectral features amid strong galaxy contamination, enabling refined constraints on the properties of both transients. We have released the software implementation, $\texttt{HostSub_GP}$, a scalable toolkit that leverages $\texttt{JAX}$, with an MIT license.

SCUPOL, the polarimeter for SCUBA on the James Clerk Maxwell Telescope (JCMT), was used for polarization observations of 104 regions at 850 micron wavelength and 15 arcsec resolution in the mapping mode by Matthews et al. (2009). They presented the polarization values and magnetic field morphologies in these regions. In this work, we took the opportunity to use this big legacy survey data to investigate further the collective statistical properties of the measured polarization in different star-forming regions containing cores and filaments. We did not reproduce the polarization maps but used the polarization value catalogs to investigate the statistics of distributions. In some of these regions, the data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) polarization observation at 1.3 mm wavelength and 2.5 arcsec resolution were also available from the TADPOL survey (Hull et al., 2014). We used that data and compared it with JCMT/SCUPOL values. We also study how the direction of outflows appears to relate to the mean B-field direction from large scale (JCMT observation at 15 arcsec) to small scale (CARMA observation at 2.5 arcsec) for the nine core regions common in both.

Neutron star mergers produce $r$-process elements, with yields that are sensitive to the kinematic and thermodynamic properties of the ejecta. These ejecta properties are potentially affected by dynamically-important feedback from $r$-process heating, which is usually not coupled to the hydrodynamics in post-merger simulations modeling the ejecta launching and expansion. The multi-messenger detection of GW170817 showed the importance of producing reliable ejecta predictions, to maximize the diagnostic potential of future events. In this paper, we develop a prescription for including $r$-process heating as a source term in the hydrodynamic equations. This prescription depends on local fluid properties and on the $Y_{e}$ history as recorded by dedicated tracer particles, which exchange information with the grid using the Cloud-in-Cell method. The method is implemented in long-term viscous hydrodynamic simulations of accretion disk outflows to investigate its feedback on ejecta properties. We find that $r$-process heating can increase the unbound disk ejecta mass by $\sim 10\%$ relative to a baseline case that only considers alpha particle recombination. Nuclear heating also enhances the radial velocity of the ejecta with $Y_e < 0.25$ by up to a factor of two, while concurrently suppressing marginally-bound convective ejecta.

The diffuse Galactic $\gamma$-ray emission (DGE) provides a valuable probe for investigating the cosmic ray propagation and interactions within our Galactic environment. Recent observations have demonstrated systematic excesses of DGE compared with the conventional cosmic-ray propagation model predictions. While $\gamma$-ray emissions have been detected in a subset of globular clusters, their undetected populations may significantly contribute to the DGE. Motivated by this possibility, we present a comprehensive assessment of potential contributions from unresolved globular clusters to the DGE. In our analysis, a nonparametric method is employed to estimate the luminosity function and spatial distribution function of globular clusters using the Fermi-LAT fourth source catalog (4FGL) combined with a reference globular cluster catalog. Based on these distributions, we calculate the cumulative contribution of unresolved globular cluster populations to the DGE observed by Fermi-LAT and the Large High Altitude Air Shower Observatory (LHAASO). Our results reveal that globular clusters account for only $\sim$2\% of the DGE at the TeV range, and smaller than $1\%$ in the GeV regime, which is effectively negligible.

The search for large polycyclic aromatic hydrocarbons (PAHs) with over 100 carbon atoms is crucial to resolving the origin of unidentified infrared emission (UIE) bands. These bands are commonly observed in nebulae and the interstellar medium, yet their spectroscopic assignment has remained unknown for decades. Using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), the world's most sensitive instrument operating in the decimeter-wavelength range, we conducted a search for rotational transitions of large, quasi-symmetric PAHs. Our sample included two prototypical UIE sources, NGC 7027 and TMC-1, along with a non-UIE source, IRC+10216, for comparison. A matched filter technique was employed to isolate comb-like spectral features from quasi-symmetric PAHs containing 138 to 194 carbon atoms in the FAST spectra. This method significantly enhanced detection sensitivity to these astrophysically critical molecular signatures. Although no such features were detected, we derived upper limits on the abundance of large PAHs based on simplifying assumptions. These upper limits are lower than the values predicted by theoretical models, which might tentatively suggest that large PAHs may not be the primary carriers of UIE bands. However, this conclusion should be treated as tentative, given that it rests on simplistic assumptions which have not been empirically validated.

The dense and gaseous environments of active galactic nuclei (AGNs) can catalyze repeated mergers of stellar-mass black holes (BHs), potentially explaining the high-mass tail of binary black hole (BBH) mergers observed by LIGO-Virgo-KAGRA (LVK). We present a semi-analytical population synthesis framework that captures key physical processes in AGN disks, including gas capture, migration, binary pair-up, gas hardening, and dynamical binary-single interactions. Our simulations show that AGN disks can produce hierarchical mergers, especially near migration traps, and may contribute to the high-mass, high-spin BBH population. This work opens prospects for constraining both the AGN channel and supermassive black hole growth with future gravitational-wave detections.

A major aspect of the search for extraterrestrial intelligence (SETI) involves searching for electromagnetic transmissions from extraterrestrial sources, often using our own transmissions as a guide. Previous studies have suggested that humanity's most consistently detectable technosignatures were transmissions from our deep-space networks and interplanetary radar. In this study, we analyze NASA Deep Space Network logs to explore what strategies for selecting SETI targets and scheduling observations would enhance the chances of detecting such networks. Analyzing Deep Space Network uplink transmission logs over the last 20 yr, we find that these emissions were predominantly directed along the ecliptic plane, towards or directly away from the Sun, and towards other planets. The average duty cycle within the Earth Transit Zone is 20 times higher than that across all ecliptic latitudes. In the case of Mars, we find a species that is able to observe the Solar System for radio emission during an Earth-Mars conjunction in the past 20 yr would have had a 77% chance of observing during one of our transmissions, a $4\times10^5$-fold increase over intercepting our Deep Space Network transmission versus a random observer at a random time. These findings quantify how SETI searches might benefit from prioritizing edge-on exoplanet systems and aligning observation windows with exoplanetary conjunctions or planet-planet occultations because they significantly improve the likelihood of intercepting transmissions from any civilizations employing deep-space networks similar to our own.

Redback pulsars are a subclass of millisecond pulsar system with a low-mass non-degenerate companion star being ablated by the pulsar. They are of interest due to the insights they can provide for late-stage pulsar evolution during the recycling process. J0523.5-2529 is one such candidate where redback-like emission has been seen at multiple wavelengths except radio. It is a system with a binary orbit of 16.5 hours and a low-mass non-degenerate companion of approximately 0.8 solar masses. The aim of this work was to conduct follow-up radio observations to search for any exhibited radio pulsar emission from J0523.5-2529. This work employs a periodicity and single burst search across 74 percent of the system's orbital phase using a total of 34.5 hours of observations. Observations were carried out using the Murriyang Telescope at Parkes and the Robert C. Byrd Green Bank Telescope (GBT). Despite extensive orbital phase coverage, no periodic or single-pulse radio emission was detected above a signal-to-noise threshold of 7. A comprehensive search for radio pulsations from J0523.5-2529 using Parkes and GBT yielded no significant emission, likely due to intrinsic faintness, scattering, or eclipses by the companion's outflow. The results demonstrate the elusiveness of the pulsar component in some redback systems and highlight the need for multi-wavelength follow-up and higher-frequency radio observations to constrain the source nature and binary dynamics.

To directly image Earth-like planets, contrast levels of 10^-8 - 10^-10 are required. The next generation of instruments will need wavefront control below the nanometer level to achieve these goals. The Zernike wavefront sensor (ZWFS) is a promising candidate thanks to its sensitivity, which reaches the fundamental quantum information limits. However, its highly non-linear response restricts its practical use case. We aim to demonstrate the improvement in robustness of the ZWFS by reconstructing the wavefront based on multi-wavelength measurements facilitated by technologies such as the microwave kinetic inductance detectors (MKIDs). We performed numerical simulations using an accelerated multi-wavelength gradient descent reconstruction algorithm. Three aspects are considered: dynamic range, photon noise sensitivity, and phase unwrapping. We examined both the scalar and vector ZWFS. Firstly, we find that using multiple wavelengths improves the dynamic range of the scalar ZWFS. However, for the vector ZWFS, its already extended range was not further increased. In addition, a multi-wavelength reconstruction allowed us to take advantage of a broader bandpass, which increases the number of available photons, making the reconstruction more robust to photon noise. Finally, multi-wavelength phase unwrapping enabled the measurement of large discontinuities such as petal errors with a trade-off in noise performance.

In mid-August 2025, 0.75-5.0 micron SPHEREx imaging spectrophotometric and ancillary NASA-IRTF SpeX 0.7-2.5 micron low-resolution spectral observations of Interstellar Object 3I ATLAS were obtained. The combined spectrophotometry is dominated by features due to water ice absorption and CO2 gas emission. A bright, 3 arcmin radius CO2 gas coma was clearly resolved, corresponding to Qgas,CO2 = 9.4 x 10{^26} molec/sec. From the SPHEREx photometry, we put conservative, preliminary 3sigma upper limits on the gas production rates for H2O and CO of 1.5 x 10{^26} and 2.8 x 10{^26} molec/sec. No obvious jet, tail, or trail structures were found in SPHEREx images. Assuming all observed 1-um flux is scattered light from an pv = 0.04 albedo spherical nucleus, its radius would be 23 km. Compared to the nucleus size limit r = 2.8km of Jewitt+ 2025, this suggests that greater than 99 percent of the measured SPHEREx continuum flux is from coma dust.

Galaxies reside in extended dark matter halos, but their baryonic content, especially dust, remains less well understood. We aim to investigate the amount and distribution of dust in galactic halos by measuring shifts in the observed magnitudes of background galaxies. Dust absorbs and scatters shorter-wavelength light, reddening background sources. We quantify this effect using multi-band magnitude shifts in the Kilo-Degree Survey (KiDS) Data Release 4, distinguishing it from achromatic magnification. Our pipeline is validated using MICE2 mock catalogues, and we explore potential systematics arising from galaxy selection, in contrast to previous quasar-based studies. Simulations show that input halo and dust masses can be recovered independently and jointly using galaxy-galaxy lensing (GGL) and magnitude shifts. A minimum redshift separation of $\Delta z_{\mathrm B}\sim0.3$ and brightness cuts are required to minimise overlap effects and the effects of photometric noise, respectively. Applying our pipeline to KiDS data, we first confirm the achromaticity of magnitude shifts in five near-infrared filters ($ZYJHK_{\rm s}$). In optical bands ($ugri$), joint analysis constrains halo mass and dust mass to $0.2$ dex and $0.3$ dex, respectively, yielding $M_{\rm dust}=7.24^{+0.52}_{-0.64} \times 10^7\,M_\odot$ and $\log(M_{\rm halo}^{\rm DM}/M_\odot)=12.33^{+0.08}_{-0.04}$. These results agree with previous studies and represent the first successful measurement of magnitude shifts and halo extinction with KiDS, confirming that galaxies reside in extended baryonic halos enriched by gas and dust from feedback processes.

In this paper we present a major update to the general relativistic magnetohydrodynamics (GRMHD) code cuHARM, which adds fully covariant treatment of radiation transport and the subsequent radiation backreaction on the dynamics of the fluid. For the radiative calculations, we discretize and solve the radiation transfer equation on a geodesic grid, in order to resolve the angular distribution of the radiation field everywhere in space. This allows for detailed treatment of non-isotropic radiation fields, which is crucial for accurately resolving regions of intermediate optical depth. We present the equations solved, the numerical methods used, and standard tests used to verify the different aspects of a radiation hydrodynamics code, in particular radiation transport and radiation-fluid interaction. We present an application of the code to the case of black hole radiative accretion. This new radiation module is fully GPU-accelerated and represents a major advance in the capabilities of cuHARM.

Global lunar chemical maps are essential for understanding the origin and evolution of the Moon, its surface characteristics, and its potential for resource extraction. Lunar elemental abundance maps have been derived using X-ray and gamma ray spectroscopy previously but are limited in coverage or have coarse spatial resolution. Here we used X-ray fluorescence line intensity of O, Mg, Al, Si, Ca and Fe derived from five years of data from the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) to generate global O/Si, Mg/Si, Al/Si, Mg/Al, Ca/Si and Fe/Si line intensity ratio maps at a resolution of 5.3 km/pixel. We have developed an independent data analysis methodology for CLASS, based on open source Python packages. Our analysis shows that the Mg/Al map best represents the geochemical differences between the major terranes, consistent with the findings of the Apollo 15 and 16 X-ray Fluorescence Spectrometer (XRS) maps. We have also shown a good correlation of the line intensity ratios with the abundance ratios from CLASS using published elemental abundance maps. Further, we apply Gaussian mixture models to the Mg/Si vs Al/Si density maps to map geochemically distinct regions on the Moon that could be of interest for future investigations.

Binary black hole (BBH) mergers,, an important source of gravitational-waves(GWs), are assumed to be hosted in galaxies. The probability of a galaxy to host a BBH is related to its properties, for example stellar mass and star formation rate. These properties can be estimated from observables, such as the luminosity in certain observation bands. We refer to this description of host galaxy properties as host galaxy weighting models. However, the host galaxy weighting model for BBHs has yet to be accurately determined. Population synthesis has provided a variety of host galaxy weighting models. Here we investigate whether it is possible to distinguish different host galaxy weighting models using a data driven approach. We use the GW cosmology tool gwcosmo with a simulated IGO-Virgo-KAGRA (LVK) fifth observing run (O5)-like observing scenario. We also construct a mock spectroscopic galaxy catalogue from MICECATv2. Our analysis compares the Bayes factors among three simple luminosity weighting models, r-band, g-band, and uniform weighting. The Bayes factors among different host galaxy weighting models show a minor preference for the true model for a ~200-detection case, and a decisive preference for the true model over the uniform model for a ~1000-detection case, which is strongly driven by a small number of well-localised events.

We report on the simultaneous monitoring of the repeating fast radio burst (FRB) 20240114A at 2.25 and 8.60~GHz, conducted 66 times between 2024 January 29 and 2025 February 15 with the Shanghai Tianma Radio Telescope (TMRT). In about 180 hours of observation, we detected 155 bursts at 2.25~GHz above a fluence threshold of 0.72~Jy~ms, but none at 8.60~GHz above a fluence threshold of 0.27~Jy~ms. FRB~20240114A exhibited frequency-dependent activity, as evidenced by the non-detections in 14.3 hours of observations at 2.25~GHz prior to 2024 February 24, despite its reported activity below 2~GHz. In contrast to its low-activity state reported below 1.4~GHz between 2024 June and December, FRB~20240114A exhibited high activity at 2.25~GHz in 2024 July with a mean burst rate of $1.72^{+0.18}_{-0.16}~\rm{hr}^{-1}$, followed by a low-activity state. We also detected a short-term reactivation at 2.25~GHz around 2025 January 20, about two weeks after renewed activity was reported below 1.4~GHz by other telescopes. The median burst width at 2.25~GHz is 3~ms, which is narrower than that at lower frequencies. The waiting time distribution peaks at 1019~s, and burst arrivals on hourly timescales consistent with a Poisson process. The isotropic-equivalent energy of bursts spans $10^{37} -10^{39}$~erg. The distribution of burst energy above the completeness threshold ($7.5\times10^{37}$~erg) follows a power-law relation with an index of $\gamma=-1.20\pm0.03\pm0.02$. Finally, we find that FRB~20240114A is at least two orders of magnitude less active at 8.60~GHz than at 2.25~GHz, and we constrain the broadband spectra of the detected bursts.

More than 30 Galactic double neutron star (DNS) binaries have now been identified through radio pulsar timing. The 24 DNSs in the Galactic field with measured total masses lie in the narrow range of 2.3--2.9 $M_{\odot}$. In contrast, gravitational-wave observations have detected two DNS mergers: GW170817, with a total mass of 2.7 $M_{\odot}$, and GW190425, with a significantly higher mass of 3.4 $M_{\odot}$. The unusually high mass of GW190425 suggests a non-standard formation channel not represented in the known Galactic population. To investigate the origin of such a massive DNS system, we model the late evolutionary stages of helium stars with initial masses between 2.5 and 9.8 $M_{\odot}$ in binaries with 1.4 $M_{\odot}$ neutron star companions, using the 1D stellar evolution code MESA at solar metallicity. We test alternative formation pathways and calibrate our models to reproduce the observed Galactic DNS mass and orbital distributions. By incorporating a modified natal kick prescription, our population synthesis results are broadly consistent with the observed total mass distribution of known DNS systems. Only a small fraction of DNSs of our model have total masses $\geq$ 3 $M_{\odot}$, insufficient to explain the high rate of massive DNS mergers inferred from GW observations. However, our model rules out the formation of heavy DNS systems like GW190425 via the second unstable mass transfer.

Our understanding of the elusive radio-pulsar emission mechanism would be deepened by determining the locality of the emission. Pulsars in which the two poles interact can potentially help solve this challenge. We here report the discovery of interaction of emission between the main and the interpulse in two pulsars -- J1842+0358 and J1926+0737, based on FAST and MeerKAT data. When emission is bright in one pulse, it is dim in the other. Even when split in just 2 groups (strong versus weak) the anti-correlated brightness can change by a factor $\gtrsim$2. Both sources furthermore show the same quasi-periodic modulation from the main and interpulse, at timescales exceeding 100 pulse periods. The longitude stationary modulation from at least one pulse suggests that it is a key signature for interpulse pulsars showing main and interpulse interaction. If the interaction happens within an isolated magnetosphere, without external influences, either communication between the opposite poles is required, or global changes drive both. This detailed study of these two sources was only made possible by improved sensitivity. The fact that both show two-pole modulation strongly suggests this is a general phenomenon in interpulse pulsars. In regular pulsars only one pole is visible, and a number of these show correlated changes between the profile and spin-down rate, that are also thought to be caused by global magnetospheric changes. Our results strengthen the case that such interactive magnetospheres are common to all pulsars.

Subgiants and early red giants are crucial for studying the first dredge-up, a key evolutionary phase where the convective envelope deepens, mixing previously interior-processed material and bringing it to the surface. Yet, very few have been seismically characterized with Kepler because their oscillation frequencies are close to the 30 minute sampling frequency of the mission. We developed a new method as part of the new PyA2Z code to identify super-Nyquist oscillators and infer their global seismic parameters, $\nu_\mathrm{max}$ and large separation, $\Delta\nu$. Applying PyA2Z to 2 065 Kepler targets, we seismically characterize 285 super-Nyquist and 168 close-to-Nyquist stars with masses from 0.8 to 1.6 M$_\odot$. In combination with APOGEE spectroscopy, Gaia spectro-photometry, and stellar models, we derive stellar ages for the sample. There is good agreement between the predicted and actual positions of stars on the HR diagram (luminosity vs. effective temperature) as a function of mass and composition. While the timing of dredge-up is consistent with predictions, the magnitude and mass dependence show discrepancies with models, possibly due to uncertainties in model physics or calibration issues in observed abundance scales.

We aim to understand how landslides affect the shape and rotational motion of small rubble planetary bodies. We limit ourselves to axisymmetric global landslides, and take the primordial shape of the body to also be axisymmetric. The landslides are modeled through depth-averaging, while also incorporating the effect of the body's rotation, topographical changes due to multiple landslides, the body's non-uniform gravity field and possible surface mass shedding. The body's rotational dynamics is coupled to its shape change due to landsliding, and also includes the action of radiation torque. We utilize our model to investigate regolith motion on actual asteroids. We then study the evolution of the shape and spin state of an initially spherical rubble asteroid due to impact-induced global landsliding events over its lifetime. We find that rotational fission is suppressed by regolith redistribution to the body's equator by landsliding. Furthermore, top shapes are rapidly formed and this may explain the abundance of top-shaped asteroids in near-Earth orbits.

Calibrating the ages, masses, and radii of stars on the upper main sequence depends heavily on accurate measurements of the effective temperature ($T_\mathrm{eff}$) and surface gravity ($\log g$). These parameters are difficult to obtain meticulously due to the nature of hot stars, which exhibit features such as rapid rotation, atomic diffusion, pulsation, and stellar winds. We compare the $T_\mathrm{eff}$, and $\log g$, values of apparent normal B-F stars in four recent catalogues that employ different methods and pipelines to obtain these parameters. We derived various statistical parameters to compare the differences between the catalogues and discussed the astrophysical implications of these differences. Our results show that the huge differences in $T_\mathrm{eff}$, (up to $10^4$\,K) and $\log g$, (up to 2 dex) between the catalogues have serious implications on the determination of ages, masses, and radii of the stars in question. We conclude that there appears to be no homogeneous set of stellar parameters on the upper main sequence, and one must be cautious when interpreting results obtained from using only one of the catalogues. The homogenisation of said parameters is an essential task for the future and will have a significant impact on astrophysical research dealing with stars on the upper main sequence.

We investigate the role of fluctuations in the matter density on neutrino flavor evolution by studying their effects on the collision terms in the spherically symmetric quantum kinetics equations (QKEs). We solve the QKEs with varying radial resolution ($r_{\mathrm{bins}} = 150 \, , 1500 \, , 15000$) to assess numerical convergence in angular distributions, number densities, and energy spectra for four neutrino flavors ($\nu_e$, $\bar{\nu}_e$, $\nu_x$, $\bar{\nu}_x$). Our results demonstrate that the solutions are numerically converged already at the coarsest resolution, with higher resolutions yielding almost identical outcomes. We introduce random perturbations to each radial bin, thus adding perturbations with a length scale that is related to the radial resolution. We study both time-independent and time-dependent perturbations to the matter density that affect the collision term and analyze their effects on neutrino flavor evolution. We find that such fluctuations do not induce any significant instabilities or qualitative changes in flavor evolution. Angular structure remains robust, and flavor-dependent number densities and energy spectra show only minor deviations compared to the unperturbed case. These findings suggest that matter perturbations have a negligible effect on neutrino flavor evolution in spherically symmetric settings.

The detection and atmospheric characterization of potentially habitable, temperate terrestrial exoplanets using a space-based mid-infrared nulling interferometer is a major goal of contemporary astrophysics. A central part of the analysis of such an instrument are correlated errors arising from perturbations in the system. While previous studies have often treated their effects in a limited manner, we aim to treat them comprehensively here and argue that data whitening based on the covariance of these errors is a suitable method to mitigate their impact. We present a framework that quantitatively connects instrumental perturbations to performance metrics and develop two computational tools to support our analysis: PHRINGE, for the generation of synthetic nulling data, and LIFEsimMC, a new Monte Carlo-based end-to-end simulator for the Large Interferometer For Exoplanets (LIFE). Applying our framework to a reference observation of an Earth twin orbiting a Sun twin at 10 pc, we find that whitening is not only essential for a correct interpretation of the detection metric used in hypothesis testing, but also improves the estimates of the planetary properties. Moreover, our approach enables an estimation of the spectral covariance of the extracted planetary spectra, providing valuable additional input for future atmospheric retrievals. We therefore recommend incorporating the framework into performance assessments and requirement derivations for future nulling interferometers.

The interstellar object 3I/ATLAS (also C/2025 N1 (ATLAS), henceforth, 3I), discovered by the ATLAS Chile telescope on 2025 July 1, was rapidly revealed to be the third known interstellar object (ISO) transiting the solar system, with an incoming velocity at infinity of 57.9763 $\pm$ 0.0044 km s$^{-1}$. An examination of 3I's pre-encounter kinematics shows that it is likely to be an object from the galactic thick disk, and thus a remnant of the Galaxy's ``cosmic noon'' period of intense star formation $\sim$9 - 13 gigayears ago. This kinematic assignment of 3I to the thick disk can be tested observationally in the transit of 3I through the solar system. Unfortunately for terrestrial observers, the 3I perihelion will happen when it is on the other side of the Sun as seen from Earth, at a solar elongation of 12.80 degrees, rendering observation from Earth (or near-Earth space telescopes) hard or impossible. With a retrograde orbit inclined 175.114 degrees (only 4.886 degrees from the ecliptic plane), and a trajectory passing inside the orbit of Mars, 3I will pass relatively close to a number of already launched interplanetary spacecraft. We find a strong science case for observations in the periods of the close approaches of the Psyche spacecraft on 2025 September 4, at 0.302 AU, the martian spacecraft array on 2025 October 3, and the Juice spacecraft on 2025 November 4. In addition, the Europa Clipper, Hera and even the more distant Lucy spacecraft may pass through 3I's cometary tail in the period after its perihelion passage, potentially directly observing the conditions and composition there. Spacecraft observations could, to the extent they are possible, provide the only source of spectral and imaging data during the 3I perihelion passage.

Complex organic molecules (COMs) have been detected abundantly at various stages of star formation, particularly in the warm protostellar phase. The progress in gas-phase measurements has been accelerated by the advent of the Atacama Large Millimeter/submillimeter Array and in ice measurements by the James Webb Space Telescope. Particularly, the community has moved from single-source studies of COMs to statistical analyses because of these powerful instruments. In this article, I review surveys that consider COMs in the gas and ice. The two takeaways from this review include; 1. Gas-phase abundance ratios for some COMs show a small difference across many objects and the ice abundance ratios show similar or higher values to the gas, both pointing to the importance of ice chemistry in COM formation, 2. Some COM ratios show larger differences across many objects which could be due to either chemical or physical effects, thus both factors need to be considered when interpreting the data.

We study constant classical electric fields and the Schwinger effect in de Sitter space, with potential implications for magnetogenesis and inflationary dark matter production. Treating the photon as a dynamical field, we show that sustaining a constant electric field in de Sitter requires a tachyonic photon mass of order the Hubble scale. This observation has physical implications, as it alters the infrared behaviour of the induced Schwinger current. Using an on-shell renormalization condition consistent with a tachyonic photon, we recompute the current for charged fermions and scalars, finding it to be finite and positive even in the massless limit of the charge carriers-contrary to earlier results predicting a puzzling negative IR divergence. For scalars, we include a non-minimal coupling to the Ricci curvature, enabling us to analyze the conformal limit, where the current closely matches that of charged fermions.

We discuss new ideas that the Standard Model might be emergent with connection to electroweak vacuum stability and related consequences for cosmology. In this scenario, the gauge symmetries and particles of the Standard Model would be ``born'' in some phase transition at a large scale about $10^{16}$ GeV with the Standard Model parameters constrained by the requirement of vacuum this http URL gauge symmetries are well known in condensed matter physics. Perhaps the Standard Model might also be emergent. In this case the particles would be the stable long range excitations of degrees of freedom that operate above the scale of emergence. The dark energy scale comes out with similar size to the tiny masses of light Majorana neutrinos. The emergence scenario comes with interesting constraints on possible dark matter structure. New physics at energy scales around $10^{16}$ GeV might be explored through its effects in the neutrino mass matrix plus using high frequency gravitational waves and polarisation observables in the cosmic microwave background.

Black hole spectroscopy is an important pillar when studying gravitational waves from black holes and enables tests of general relativity. Most of the gravitational-wave signals observed over the last decade originate from binary black hole systems. Binary neutron star or black hole-neutron star systems are rarer but of particular interest for the next-generation ground-based gravitational-wave detectors. These events offer the exciting possibility of studying matter effects on the ringdown of "dirty black holes". In this work, we ask the question: Does matter matter? Using numerical-relativity, we simulate a wide range of collapsing neutron stars producing matter environments, both in isolated scenarios and in binary mergers. Qualitatively, the resulting ringdown signals can be classified into "clean", "modified", and "distorted" cases, depending on the amount of matter that is present. We apply standard strategies for extracting quasinormal modes of clean signals, using both theory-agnostic and theory-specific assumptions. Even in the presence of matter, possible modifications of quasinormal modes seem to be dominated by ringdown modeling systematics. We find that incorporating multiple quasinormal modes allows one to drastically reduce mismatches and errors in estimating the final black hole mass at early times. If not treated carefully, deviations in the fundamental quasinormal mode might artificially be overestimated and falsely attributed to the presence of matter or violations of general relativity.