Astrophysics and Space Science最新文献

A type of specialized fungi, lichens, are the pioneer and predominant life form in harsh land environments on Earth with strong tolerance to extreme environment, including both extant and fossilized materials. Multiple spectroscopic techniques have been widely used in extreme-environment and planetary detection and life detection. Herein, multiple spectral methods and Energy Dispersive Spectrometer (EDS) analysis were applied to test whether lichens could be the potential biomarkers and might contain the detectable biosignatures as life signal in extreme environments and on exoplanets (such as Mars). Our results indicated that Infrared spectroscopy (IR) and EDS techniques are effective for micro-region analysis of fossil components, which could distinguish fossil and rock substrates by characteristic spectral bands and elemental component contents. More importantly, C–O stretching in phenyl and C–H stretching were detected in both extant and the 165-million-year fossil lichens by IR, which are the basic skeleton constituting the characteristic lichen secondary metabolites. Raman spectroscopy successfully identified characteristic peaks corresponding to chlorophyll and carotenoids in extant lichen samples, but strong fluorescence interference hindered its application to fossil samples. Similarly, Laser-induced breakdown spectroscopy (LIBS) analysis detected emission peaks of CN and C₂ in extant lichen samples but failed to detect these organic components in fossil samples, likely due to the loss of organic materials during fossilization. Despite limitations, integrating multiple spectral techniques is crucial for comprehensive exoplanet and extreme environment life detection missions. This study suggested that lichen can be utilized as a potential biomarker for searching the Martian and extreme environmental life, as its characteristic aromatic compounds will be the practical biosignatures lasting 165 million years. Furthermore, our study emphasizes the potential of infrared spectroscopy, among other techniques, for in-situ biosignature detection in extreme environment and on exoplanets (such as Mars), offering valuable insights for future exploration.

We have studied the variations in stability, bifurcation, critical velocity, Lagrange points, and critical periodic orbits in the context of the transition from the Sitnikov four-body system (as analyzed by Soulis et al. (Celest. Mech. Dyn. Astron. 100:251–266, 2008)) to the Sitnikov five-body system. The incorporation of one primary body results in a reduction in critical velocity and an increase in the number of stability intervals. We applied Floquet’s theory to study the stability/instability of the motion of negligible mass. For this, we assume (z_{in}) as family parameter and vary it in the interval ([0, 10]). Upon slightly perturbing the negligible mass from the z-axis, we obtained 13 Lagrange points. We have determined three-dimensional families of periodic orbits which bifurcate from the critical points/bifurcation points. We observed that the bifurcation points lie within the interval ([1.0709360, 2.7944120]). We have discussed stability/instability of periodic orbits bifurcating from the critical points.

The accretion-ejection activities of black holes play a vital role in shaping the Universe. Bright and recurrent black hole X-ray binaries are ideal objects for studying accretion physics across a wide range of accretion rates, providing insights into the understanding of their supermassive counterparts. This short review summarizes X-ray techniques capable of measuring accretion geometry, our current understanding, and open questions. In particular, X-ray spectroscopic studies indicate that the accretion disk can extend close to the innermost stable circular orbit in the bright hard state. Some hints of disk-corona-jet connections are also discussed.

This study presents a comparative analysis of two modified theories of gravity, (f(R,T)) and (f(mathcal{T})), within the framework of a locally rotationally symmetric Bianchi type-I spacetime. The primary objective is to explore the role of curvature-matter coupling and torsional dynamics in explaining the universe’s late-time acceleration without invoking a cosmological constant. To solve the highly nonlinear field equations, a hyperbolic sine scale factor and a shear-expansion proportionality condition are employed. The resulting models are constrained using observational Hubble parameter data via a (chi ^{2}) minimization technique. Key cosmological quantities, including energy density, pressure, and the equation of state (EoS) parameter, are analyzed alongside geometrical diagnostics such as the (operatorname{Om}(z)) and statefinder parameters. Statistical tools like the Akaike and Bayesian information criteria (AIC/BIC) are used to assess model performance relative to (Lambda)CDM. Results show that both models capture the transition from decelerated to accelerated expansion, with the (f(mathcal{T})) model exhibiting a more dynamic dark energy behavior and an earlier onset of acceleration. These findings suggest that torsional-based gravity may provide a geometrically motivated and observationally consistent alternative to standard cosmology.

In this study, we investigate the global ionospheric response to the four most intense geomagnetic storms of Solar Cycle 25 (SC 25) by analyzing hourly averaged (Sigma mathrm{O}/mathrm{N}_{2}) ratios from the Global Ultraviolet Imager (GUVI) aboard the TIMED satellite, alongside 3D electron density profiles from the FORMOSAT-7/COSMIC-2 (F7/C2) constellation satellites. The analysis focuses on ionospheric behavior at low and mid-latitudes, with further evaluation across three longitudinal sectors: Asia (60°E–120°E), Africa (30°W–60°E), and the Americas (120°W–30°W). The negative effects at mid-latitudes started during the local nighttime in the main phase, prolonged into daytime in the early recovery phase, and continued into the following nighttime. These negative effects also reached low latitudes during similar local times. The extent, intensity, and equatorward expansion of these prolonged negative responses were strongly dependent on storm severity and duration. Short-term positive effects were observed at low latitudes during the early recovery phases of less intense storms. Moreover, positive ionospheric responses were recorded at low and mid-latitudes during daytime in the main phase, and long-lasting positive effects were evident at mid-latitudes during the late recovery phases. This study would be beneficial in enhancing space weather modeling and forecasting capabilities, particularly in understanding ionospheric variability during geomagnetic disturbances.

Using hourly data from the OMNIWeb database, we analyze key indices like F10.7 (solar radio flux), Ap, Kp, Dst, and PC (geomagnetic indices) for a few chosen months that represent the solar cycle’s various phases: solar minimum (October 2009), rising phases (August 2010 and December 2022), solar maximum (May 2012), and declining phase (September 2017). Each phase’s unique geomagnetic activity patterns are revealed by our analysis. Only slight disruptions were seen in the solar and geomagnetic activity during the solar minimum. During the rising phase, we saw a steady rise in solar activity, a significant geomagnetic storm in December 2022, and associated improvements in geomagnetic indices. Geomagnetic disruptions were frequent and severe during the solar maximum phase, which was marked by intense and extremely variable solar activity. Moderate geomagnetic activity was detected throughout the falling phase, most likely due to corotating high-speed solar wind streams. This study indicates the statistical analysis of solar parameters like F10.7 index, PC index, AP index, Dst index, KP index.

This paper aims to explore the impact of binary stars on the creation of second generation stellar populations using a model based on stellar collisions. This is accomplished by using a simple model of stellar collisions in which two first-generation stars collide and produce a product star belonging to the second-generation stellar population. Clusters are formed with single and binary stars having masses generated from a truncated Pareto distribution using Monte Carlo simulations and the split core pairing algorithm to form binary stars. No triples or further multiple stars are considered. We have considered single-single and single-binary collisions in our model. Then we studied the correlations between the fraction of second-generation stars and the slope of present-day mass function of the after-collision cluster and have compared those with observed data for 49 galactic globular clusters. We find that the fraction of second-generation stars is positively correlated to the slope of mass function for high-mass clusters and low-mass clusters separately. We additionally explore the possible values of the fraction of binary stars, the fraction of colliding single stars, the fraction of colliding binary stars as well as the slopes of the initial mass generating function that led to the formation of the present day observed high mass and low mass clusters.

We are discussing the capabilities of MASTER network of robotic telescopes to study variable red giant stars. We report the discovery and present archival light curves for three optical transients, connected with long period variable red giants, based on MASTER Robotic Net all-sky survey observations and archival MASTER light curves at Lomonosov database storage. We demonstrate transient detection frames and light curves for three Mira-type variables: MASTER OT ({J083717.54-573411.1}), MASTER OT ({J190436.33+192828.7}) and MASTER OT ({J07010810-6818548}). Spectroscopically validated carbon star MASTER OT ({J07010810-6818548}) shows mean magnitude growth but constant pulsation period which may indicate the presence of a long secondary period. As the result of MASTER wide-field images analysis at Lomonosov supercomputer data storage we present the 8-years historical light curves for all three objects with period calculations for all three Mira-type variables. We estimated fundamental astrophysical parameters for all three Mira-type variables: luminosities, radii, and zero age main sequence (ZAMS) masses.

The coupling is established analytically between the natural oscillations of stars normal to the mean horizontal plane and periodic changes in the excitation force in a rotationally flattened galactic disk using a linear perturbation framework. The nonaxisymmetric gravitational potential of a density-wave bar may cause these changes in this ‘pumping’ force. The excitation of out-of-plane oscillating motion with an amplitude exponentially increasing with time via parametric resonance interaction between stars and a bar is considered for the formation of the boxy/peanut-shaped bulges (an X-structure of stars crossing at the center of the system) often observed in disk galaxies, even in isolation, as well as in the Galaxy. A scenario involving this resonant interaction accounts for both the vertically short (lesssim 1) kpc boxy/peanut-shaped features and a (sim 1) Gyr time delay between when the bars form and vertically thicken.