Astrophysics and Space Science最新文献

This article explores the late-time acceleration phase of the universe through a novel (f(R,L_{m},T)) gravity model, particularly, (fleft (R,L_{m},Tright ) = R + alpha T + 2beta L_{m} ), where (alpha ) and (beta ) are free parameters of the model, in the presence of viscous fluid. We obtain the corresponding analytical solution and then we establish the constrain on arbitrary parameters of the solution by considering the Cosmic chronometers and Panthoen+SH0ES data. Further, we analyze the behavior of the obtained constrained solution through the deceleration, effective equation of state, and the Om diagnostic test. We find that the present (fleft (R,L_{m},Tright ) ) gravity model in the presence of viscous cosmic fluid successfully describe the late-time evolution phase of the universe with proper transition from the decelerated epoch to the accelerated one.

In this work, Infrared and Raman spectroscopic investigations on a new Turkish lunar regolith simulant (TBG-1), Chinese (own product), and Japanese simulants are presented for the first time. Our Raman spectroscopic investigation on TBG-1 simulant implies that it is mainly forsteritic olivine. Moreover, the Chinese sample produced by our group in Türkiye showed carbonate peaks at 712 cm⁻¹ and 878 cm⁻¹ in the IR spectra, which were attributed as calcium or sodium carbonates which could be a result of terrestrial weathering. Here, we propose that TBG-1 is close to the composition of lunar highland impact glass in terms of its (Mg, Ca)/Al₂O₃ ratios. Our effort suggested that our recently produced Turkish simulant is similar to the Apollo 11 lunar soil sample in terms of its Al₂O₃ and TiO₂ composition. Some of the samples we collected to simulate lunar regolith also show similarities to the Apollo 14 samples and JSC-1A simulant produced by NASA.

This study focuses on the porosity of the Didim H3−5 chondrite, providing insights into its physical and structural properties. Using the 3D laser scanning, we determined, that the bulk volume and the bulk density of Didim are 17.15 cm³ and 3.16 g/cm³, respectively. Through helium pycnometry, we found thatthe grain volume and the grain density of Didim chondrite are 1.41 cm³ and 3.64±0.001 g/cm³. We calculated that Didim has a porosity of 13.28±0.024%, which is consistent with similar chondrites, such as Fermo, but higher than Acfer 166 and Oum Dreyga. To establish robust links between meteorites and their possible parent bodies, further systematic and multi-analytical efforts, such as those used in this study, are requiredto accurately characterize meteorites’ porosities. Among the primary minerals in H3−5 chondrites, iron-nickel metals and iron-sulfides are also distributed heterogeneously in these ordinary chondrites. Using a combined approach of pycnometry and 3D laser scanning, we can further interpret shock processes from impacts on the parent body and weathering on Earth can be further interpreted in terms of their geologic history and the environmental conditions experienced by these chondrites both in parent bodies and after landing on Earth.

Based on modern observations on central S-stars by Gillessen et al. and hypervelocity stars (HVS) by Brown et al. the question is raised whether it is possible to establish the genetic duality of these stars? Could they belong in the past to a common parent binary star until it was captured and then gravitationally ruptured by a supermassive black hole (SMBH) within the Hills scenario? A cross-analysis of these observational data is carried out to obtain reliable evidence for the possible quantitative relationship of the stars under consideration. Three key issues are considered: 1. reconstruction of the trajectory of HVS ejection from the SMBH neighborhood by the method of backward integration in the Galaxy potential; 2. estimation of the dynamical stability of the S-star orbits by the (N)-body method — direct integration of their motion in the central field of the SMBH, taking into account the perturbing potential created by the S-cloud members; 3. checking of the coplanarity of orbits of a central S-star and an HVS; For nine HVSs it is possible to reconstruct the central trajectory of the ejection (at a distance less than a parsec from the SMBH) within the uncertainty of the observational proper motion values. For S2 star the timescale of the dynamical stability of its spatial orbital configuration in the S-cloud is evaluated as ∼ 100,000 years. This requires an additional comment on the criterion of the coplanarity of the orbits of paired S-HVS. The problem of identifying tidally decoupled components (S-HVS pairs) by the SMBH field poses a challenge to modern astrometric observations, and not only. This problem may provide an independent test of our knowledge of the distribution of baryon and dark matter, as well as the Galactic gravitational potential constructed on their basis, which is important in cosmological and evolutionary interpretations.

In this paper, we compute the structural composition of a static spherically symmetric regime configured with anisotropic distribution in the context of (f(G,T)) gravity. To accomplish this, we adopt the model (f(G,T)=G^{2}+varpi T), where (varpi ) denotes the coupling constant. We establish the modified field equations and utilize the MIT bag model equation of state to determine the graphical analysis of Her X-I, LMC X-4, 4U1820-30, and PSR J1614-2230 compact bodies. The Tolman IV solution is employed to study the above-mentioned structures. We check the graphical behavior of energy density, pressure components, anisotropy, and energy conditions by keeping the coupling constant fixed. We also study the behavior of mass, compactness, and redshift factors. Finally, we discuss the stability of the resulting solution through two different criteria. It is found that all the star candidates portray viable and stable behavior, except PSR J1614-2230, which is viable but not stable.

In the dynamic and complex environment of the solar corona, the interaction between kinetic Alfvén waves (KAWs) and magnetic null points might play a significant role in understanding various plasma processes. Recognizing the potential role of reconnection in coronal heating, our study aims to delve into how different types of null points affect KAW dynamics and ultimately contribute to heating. We investigate the behavior of nonlinear KAWs near the more frequently occurring components-null point with a mean magnetic field in the solar corona. The nonlinearity is attributed to the ponderomotive effects due to density perturbations. We used a three-dimensional model equation that describes the dynamics of KAWs in the presence of components-null point. Numerical methods are employed to solve the model equation for solar coronal parameters. Our simulations reveal that the nonlinear interaction between KAWs and magnetic null points can lead to the generation and amplification of turbulent and chaotic structures. This formation of localized structures, progressively exhibit more chaotic behavior over time, which may efficiently contribute to energy transfer. The power spectrum analysis of these turbulent structures shows a steeper spectrum with a pronounced cascade. Turbulence implies the presence of localized plasma heating, particle acceleration, and magnetic reconnection. These phenomena have significant implications for understanding the energy transport, particle dynamics, and magnetic topology in the solar corona. We also address nonlinearity’s role in promoting turbulence. This research offers insights into the dynamics of nonlinear KAWs near null points in the solar corona, suggesting their potential role in energy transfer and current sheet formation.

This work focuses on developing an analytical method for constructing images in gravitational lenses. Building on our previously proposed elimination method, which utilized algebraic geometry for constructing images from circular sources, this study emphasizes images from elliptical sources using axially symmetric gravitational lenses. We detail the rational parameterization of an arbitrarily located source and use our algorithm to derive an expression that determines all images for an arbitrary axially symmetric gravitational lens. To validate this expression, we considered several limiting cases leading to well-known results. Specifically, we examined two simple models: a single-point lens and a homogeneous disk lens. By placing an elliptical source at the origin of the source plane and reducing it to a circle, we reproduced all previously known images, such as the Einstein ring for a single-point lens, and a double Einstein ring for a disk lens. Additionally, we demonstrated the Construction of images in other arbitrary lens-source configurations.

The formation of the Magellanic Stream has puzzled astronomers for decades. In this review, we outline the history of our understanding of the Magellanic System highlighting key observations that have revolutionized thinking of its evolution. We also walk through the major models and theoretical advances that have led to our current paradigm − (1) the LMC and SMC have just had their first pericentric passage around the Milky Way, having approached recently as a bound pair; (2) the LMC and SMC have had several tidal interactions in which material has been stripped out into the Trailing Stream and Leading Arm; (3) the LMC hosted an ionized gas circumgalactic medium which envelops the Clouds and the neutral Stream today, providing the bulk of the associated mass; and (4) the Milky Way’s circumgalactic gas provides strong ram pressure and hydrodynamic forces to shape the morphology of the Magellanic System including the formation of a bow shock due to the LMC’s supersonic approach.

Pi2 magnetic pulsations have been observed to occur at low latitudes when the magnetosphere is in a near ground state and substorm activity would be expected to have ceased. In the present study, we report a global non-substorm Pi2 magnetic micro-pulsations occurred, for the first time, during a solar flare event. We investigate this Pi2 at two different locations: in the inner magnetosphere using Van Allen Probe A (VAP-A) satellite, and ground-based magnetic stations located in Japan-Korea, Africa, and America sectors. By comparing the horizontal component of ground stations with the electric and magnetic components within the magnetosphere, we report a global Pi2 starting nearby at 12:05 UT lasting to 12:11 UT during the ejection of a solar flare with X9.3-class that have had its peak flux at 12:02 UT on 6 September 2017. We study the Pi2 oscillations at Kakioka (KAK) station and VAP-A satellite through wavelet analysis. By analyzing the high-latitude stations, we find that the Pi2 event has a good correlation with a Poleward Boundary Intensification (PBI).

We provide highlights of research investigations over the last five decades in the area of resolved stellar populations. After discussing the early work on the state of blue straggler stars in Galactic globular clusters, we broaden our gaze to include all of the stellar systems in the Local Volume with the overall goal of understanding the formation and evolution of galaxies. More specifically, we focus on the stellar constituents (e.g. star clusters and RR Lyrae variables) of the Milky Way, the Magellanic Clouds, the Andromeda galaxy (M31), the Triangulum galaxy (M33), as well as several dwarf galaxies in the Local Group and two dwarfs in the Sculptor group. Because of the available instrumental capabilities, work on resolved stars in galaxies has been largely focused on stellar systems in the Local Group and nearby galaxy groups. The big picture of galaxy formation and evolution that emerges from an analysis of all these constituents is largely consistent with the dwarf galaxy fragmentation and accretion scenario first put forth by Leonard Searle and Robert Zinn in 1978.