Astrophysics and Space Science最新文献

In this work, we investigate the thermodynamic properties of a non-rotating hairy Bardeen black hole, highlighting deviations from the predictions of standard general relativity due to the presence of additional parameters. Specifically, we analyze the influence of the electric charge (Q ), the coupling constant (beta ), and the model parameter (eta ) on the black hole’s mass, temperature, sparsity parameter and entropy. While the overall qualitative behavior of these quantities remains consistent, we find that both (Q ) and (eta ) tend to decrease the mass and temperature, whereas (beta ) exerts an opposite effect by increasing them. Furthermore, using the entropic force approach, we derive a novel expression for the black hole entropy, which encapsulates the modifications to the underlying gravitational interaction. We then examine how the parameters (Q ), (beta ), and (eta ) affect the circular motion of photons. Our results show that the radius of stable circular orbits increases with (Q ) and (eta ), while the radius of unstable circular orbits decreases with (Q ) and increases with (beta ). Additionally, the critical impact parameter is found to grow with increasing (Q ), but diminish with increasing (beta ). We also study the variations in the Keplerian frequency of photons orbiting the black hole under the influence of these parameters. For small radial distances (r ), the charge (Q ) reduces the frequency, while for intermediate and large (r ), it causes an increase. A similar trend is observed for the model parameter (eta ) for small values of (r), whereas the coupling constant (beta ) produces the opposite effect across these regimes. At the end of the paper, we derive the modified Friedmann equation from the entropy of the studied black hole.

The origin of the hard, bright X-ray emission that defines the (gamma ) Cas analog class of Be stars remains an outstanding question in Be star literature. This work explores the possibility that the X-ray flux is produced by accretion onto a white dwarf companion. We use three-dimensional smoothed particle hydrodynamics simulations to model the prototype (gamma ) Cas system assuming a white dwarf companion and investigate the accretion of the circumstellar material by the secondary star. We contrast these results to a model for 59 Cyg, a non-(gamma ) Cas Be star system with a stripped companion. We find that the secondary stars in both systems form disk-like accretion structures with Keplerian characteristics, similar to those seen in the Be decretion disks. We also find that white dwarf accretion can produce X-ray fluxes that are consistent with the observed values for (gamma ) Cas, while the predicted X-ray luminosities are significantly lower for the non-degenerate companion in 59 Cyg. In addition, using the three-dimensional radiative transfer code, hdust, we find that these models produce H(alpha ) emission consistent with the observations for both (gamma ) Cas and 59 Cyg, and that the predicted polarization degrees across optical and UV wavelengths are at detectable levels. Finally, we discuss the impact that future UV spectropolarimetry missions could have on our understanding of these systems.

In this paper, we explore the cosmological evolution of a viscous dark energy model within the framework of (f(Q, C)) gravity, employing a two-fluid approach. The model incorporates non-metricity and boundary contributions to the total action, represented by the scalar quantities (Q) and (C). The viscosity in the dark energy fluid is introduced to investigate the impact of bulk viscosity on cosmic expansion and late-time acceleration. Field equations are derived in a modified FLRW background, and the dynamics of key cosmological quantities such as energy density, pressure, and the effective equation of state (EoS) parameter are analyzed. Observational constraints on (H(z)) are imposed using DESI BAO Measurements, Pantheon+ (without SHOES), and cosmic chronometer datasets. Results indicate that the model effectively captures the universe’s expansion history, including the deceleration–acceleration transition, consistent with observations. This framework provides an alternative explanation for late-time cosmic acceleration without invoking a cosmological constant.

The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) is set to revolutionize astronomy by generating an unprecedented petascale dataset. However, the success of its primary science goals, such as precision cosmology with weak lensing, is critically threatened by atmospheric turbulence, which blurs images and can systematically corrupt the faint cosmological signals. The sheer volume of LSST data—approximately 20 terabytes per night—renders classical iterative deconvolution methods computationally infeasible, while generic deep learning approaches often lack the physical guarantees necessary for high-precision science. This creates an urgent need for a fast, robust, and physically-grounded deconvolution framework. To meet this challenge, we introduce a deep learning model that synergistically combines a dual-domain architecture with physics-informed learning. Our U-Net model incorporates a Fast Fourier Transform (FFT) layer at its input, enabling it to directly “see” and correct the frequency-dependent signature of atmospheric blurring. We train the model with a hybrid loss function that enforces both structural realism, via a Point Spread Function (PSF) consistency term, and photometric accuracy, through a flux conservation constraint. Our final model, HF-UNet, produces good reconstructions on realistically degraded images, accurately recovering key galaxy morphological parameters with exceptional fidelity, achieving low Root Mean Square Error (RMSE) values, for instance, 0.05 for ellipticity and 3.37 for half-light radius with the proposed HF-UNet model. Crucially, it exhibits superior robustness when tested on data with mismatched PSF profiles and varying noise levels. This work presents a scientifically reliable deconvolution framework, offering an enabling technology essential for realizing the full scientific potential of the LSST.

The Viking mission identified both cold and hot electron populations in the auroral zone, enabling electron acoustic waves (EAWs) whose nonlinear dissipative interactions are believed to contribute significantly to broadband electrostatic noise (BEN). In this study, we examine the dissipative dynamics of EAWs in collisionless, unmagnetized plasmas using an effective viscosity model. The wave evolution is governed by a Higher Order Boussinesq–Burgers (HOBB) equation that incorporates enhanced nonlinear and dispersive effects. Analytical and numerical investigations reveal that when dissipation dominates over dispersion, the soliton structure transitions into a shock wave. In the weakly dissipative regime, the HOBB equation is solved using the Hirota bilinear method to obtain multi-soliton solutions. A detailed phase-space analysis, Poincaré sections, and near-zero Lyapunov exponents confirm the presence of quasiperiodic behaviour. Energy-based stability criteria show that the solutions remain stable when dissipative effects outweigh dispersive and nonlinear steepening influences. The bipolar electric potential structures predicted by the HOBB equation are analyzed for auroral plasma parameters relevant to Viking observations. The calculated amplitudes and durations of solitary structures show good agreement with measured BEN waveforms. These results demonstrate that the HOBB model successfully captures the interplay of nonlinearity, dispersion, and dissipation, offering a plausible mechanism for the generation of BEN in space plasmas.

While trying to arrive at the four-picket pulse shape, the author of this work accidently found a very interesting result. Specifically, it is found that not only four-picket pulse can be formed from combination of two or more Maxwell distributions but additionally several non-Maxwellian distributions can be generated. This result is very attractive and physically acceptable. Because, systems having two types of distributions will go to a third state that is non-equilibrium state, meaning that two Maxwellian distributions will give a third distribution and so on. Our results are significant for plasma systems connected to external energy source such as solar wind.

This research investigates the geoeffectiveness of interplanetary magnetic field configurations by analyzing 203 geomagnetic storm events recorded between 1995 and 2015. The study systematically categorizes events into five intensity levels: quiet, weak, moderate, intense, and severe, to evaluate how different polarity configurations and flux rope configurations influence geomagnetic activity. Utilizing an extensive methodology, we employed correlation analysis and superposed epoch analysis on 17 parameters extracted from OMNI/NASA hourly datasets. The investigation focused on identifying how specific magnetic configurations impact geomagnetic storm characteristics, with special attention to the Disturbance Storm-Time Index (Dst). The findings reveal nuanced variations in geoeffectiveness across magnetic configurations. Configurations were stratified into two primary groups, with Group 1 (S, SN, SNN, SNS) demonstrating notably higher geomagnetic responsiveness. Notably, the SNS configuration emerged as the most geoeffective, accounting for 37% of intense storms and exhibiting an extended main phase lasting 48 hours. Conversely, Group 2 configurations (N, NS, NSS, NSN) generally displayed reduced geoeffectiveness, contributing to 30% of quiet storms and merely 3% of severe storms. However, the NSS configuration presented an intriguing anomaly, characterized by the lowest negative Dst value and an unprecedented 96-hour recovery phase, attributed to its distinctive two-step main phase storm. Flux rope configurations also demonstrated differential impacts, with the (F^{+}) rotation being particularly geoeffective, contributing to 11% of severe storms. We further uncovered a remarkably strong correlation between the dawn-dusk electric field (Ey) and (Dst_{min}) in the NSS configuration, registering a correlation coefficient of -0.95.

The triple collision represents a fundamental singularity in the equations of motion for the three-body problem. Building upon previously identified triple collision orbits with equal masses, we employ the Clean Numerical Simulation (CNS) and the numerical continuation method to compute triple collision orbits for the free-fall three-body system with unequal masses. We first identify triple collision orbits for the three-body system where two bodies have unit mass, while the third body has various masses. Additionally, we extend our computation to obtain the triple collision orbits for the three-body problem with different masses. Numerical evidence is presented to demonstrate the asymptotic behavior of triple collision orbits with unequal masses. Our findings have potential inspiration for the study of the dynamical characteristic around the singularity of three-body systems.