Astrophysics最新文献

Temperature effect in proto neutron star (PNS) PSR J0740+6620 is studied by using relativistic mean field theory and considering baryon octet. The nucleon coupling constant is chosen as GM1, and the temperature of the PNS is set as T = 7, 14, 21, 28, 35 MeV, respectively. Our results show that under the constraint of mass M = 2. 08 M_⨀ of the PNS PSR J0740+6620, the radius R increases with increasing temperature T. With respect to the same baryon density ρ, the field strength of mesons σ, ω, ρ and the chemical potential of neutrons μ_n decrease while the field strength of σ^* and ϕ increase with the increase of temperature T. The chemical potential of electron μ_e increases when the baryon density is less than ρ = 0.3 fm^-3, but decreases when the baryon density is greater than ρ = 0.3 fm^-3, companying with the increase of temperature T. Relative to the same baryon density ρ, the relative density of neutrons decreases while those of proton, Λ, Σ⁺, Σ⁰, Σ^–, Ξ⁰, and Ξ^– all increases with increasing temperature T. The central relative densities of neutrons decrease, while those of protons, hyperons Σ⁺, Σ⁰, Σ^–, Ξ⁰, and Ξ^– all increase with increasing temperature T. As for the relative density of hyperon Λ, it increases firstly, reaching a maximum value when the temperature is about T = 20 MeV, and then decreases with the increase of temperature T.

The SiCSi is considered as one of the important molecules responsible for the production of dust around the carbon-rich stars. First detection of the SiCSi has been in the envelope of red supergiant star IRC+10216. Cabrera-Gonzalez et al. (2023) have calculated collisional rate coefficients for the disilicon carbide (SiCSi) colliding with para-H₂ (j = 0), in the CC (Close-Coupling) approximation, between 31 rotational levels, having energy up to 23. 844 cm^-1. Though the calculations are performed for the kinetic temperature of 50 K, but they are found useful for the calculations with the temperature up to 30 K. For more reliable analysis of the molecule and for large kinetic temperature in an object, the data for large number of levels are essentially required. Thus, one needs to extend the calculations for a large number of rotational levels. In the present investigation, the work of Cabrera-Gonzalez et al. (2023) has been extended for 78 rotational levels, having energy up to 61. 746 cm^-1. The present calculations however have been performed in the CS (Coupled-States) approximation.

We performed a search for new dwarf galaxies in a direction towards the southwestern part of the Local Void using the data on DESI Legacy Imaging Surveys. In a sky area of ~1000 square degrees, we discovered 12 candidates to nearby dwarfs with a high confidence. Four of them are probable new companions to the nearby galaxy M83 and others are isolated objects. We found also 20 nearby dwarf candidates with a low confidence. Almost all of the detected galaxies are classified as late type dwarfs. A new cluster of bluish stars with an angular diameter of 0'. 9 is revealed by us at a high galactic latitude, b = 29°. Being at a distance of ~70 kpc, it can be a globular cluster associated with the Milky Way stellar stream Sagittarius dSph or a new ultra-faint satellite of the Milky Way.

In this study, we considered plane-symmetric space-time in the presence of string clouds coupled with perfect fluid in f (R, T) theory of gravitation. Here, R is the Ricci scalar and T is the torsion scalar of space-time. The simple functional forms of the function f (T), such f (R, T) = R + 2f (T) is chosen for the investigation. Exact solutions of the field equations were obtained by considering the average scale factor. Different types of strings are discussed. Different forms of energy conditions are considered to obtain the exact solution of the nonlinear field equation. The following parameters were studied: i) average scale factor (t² + λ/μ)^1/2μ ii) shear scalar σ, iii) expansion scalar θ and iv) deceleration parameter q. Some of the physical and geometrical features of the model are represented using graphs.

We consider general scalar-tensor theories in (D +1)-dimensional spacetime. The interplay between the Jordan and Einstein frame representations is explored. As a specific illustration of the general frame-work, we examine higher-dimensional generalizations of the Jordan-Brans-Dicke theory, theories with non-minimally coupled scalar fields, f (R) gravity and low-energy string effective gravity. The properties of the Einstein frame scalar field effective potentials are discussed.

This paper is the second part of "A study on geodesics and lifespan of the Rindler-modified Schwarzschild black hole" [1] where we have investigated the time-like geodesics in the Rindler-modified Schwarzschild black hole (RMSBH) spacetime. In this part, we continue to study the null geodesics around the RMSBH. Based on this, we further explore the lifespan of the black hole. For the radial null geodesics, the relationship between the coordinate distance and the coordinate time is obtained. In addition, the expressions for the radius of the circular orbit formed by photons around the RMSBH and the impact parameter of the null geodesics are also derived. Meanwhile, we calculate the deflection angle of light rays grazing around the RMSBH and find that the cosmological constant does not affect the deflection angle of photons passing by the black hole, but the Rindler acceleration will reduce the deflection angle. In the thermodynamics part, our primary focus is on the radiation lifespan of the black hole. Our calculations reveal that both the Rindler acceleration and the cosmological constant can reduce the lifespan of the black hole.

This manuscript’s primary object is to investigate and study the anisotropic universe in terms of f (G) gravity. Kantowski-Sachs spacetime is considered for this evolution, in a modified theory of gravity. The exact solutions of modified theory field equations are investigated using a viable f (G) model choice. We considered two bouncing scenarios described by exponential and power law scale factors, these non-singular bouncing models also accommodate a transition cosmic acceleration phenomenon. Specific significant cosmological parameters are estimated and discussed for the obtained models.