فهرست مطالب

Astronomy and Astrophysic - Volume:6 Issue: 1, 2019
  • Volume:6 Issue: 1, 2019
  • تاریخ انتشار: 1397/12/10
  • تعداد عناوین: 5
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  • Mohammad Rostami, Jafar Sadeghi, Sedigheh Mirabotalebi *, Ami Ali Masoudi Pages 1-8

    In this letter, we consider static black hole in f(R) gravity.We take advantage from corrected entropy and temperature and investigate such black hole. Finally, we study the $ P - V $ critically and phase transition of corrected black hole with respect to entropy and temperature. Here also, we obtain the heat capacity for the static black hole in $ f(R) $ gravity. This calculation help us to investigate some singularity.We have shown that the corrections exist for any black hole, but they are important for a small black holes and negligible for the large black holes. The advantage of a static black hole in $ f(R) $ gravity is its holographic picture, which is a van der Waals fluid. Then, We have shown that in the presence of corrections there is still a van der Waals fluid as a dual picture.The critical values of event horizon radius for phase transitions are shown due to the corrections of entropy and temperature.We have some figures which show the phase transition and $ P - V $ critically.

    Keywords: The static black hole, Phase transition, Van der Waals behavior, corrected of entropy, temperature
  • Mina Zamani *, Mohsen Bigdeli Pages 9-23
    ‎In this work, we review the formalism which would allow us to model magnetically deformed neutron stars. We study the effect of different magnetic field configurations on the equation of state (EoS) and ‎the ‎structure of such stars. ‎For this aim‎, the EoS of magnetars is acquired by using the lowest order constraint variational (LOCV) method ‎‎and ‎employing‎ the AV18 potential‎.‎ We ‎show ‎how ‎the ‎magnetic ‎field ‎varies ‎from ‎the ‎‎surface ‎to ‎the ‎center ‎of ‎neutron‎ ‎star ‎by ‎using ‎various ‎exponential ‎and ‎polynomial ‎profiles ‎and ‎compare ‎their ‎results.‎‎In addition‎, ‎global properties of neutron stars ‎are‎ obtained within two formalisms‎. ‎The first formalism is described by considering the pressure into two directions and the deformation of neutron stars is governed by anisotropies in‎ ‎the equation of state‎‎. The second formalism for investigating macroscopic properties of magnetars is gained by treating the nonuniform pressure as a perturbation to the total pressure and expanding metric and pressure up to the quadrupole term in spherical ‎harmonics.‎Afterwards‎, ‎we include three nucleon interactions (TNI) to ‎the ‎EoS‎ and apply this model to represent our results for both exponential and polynomial magnetic field profiles.‎The maximum gravitational mass is obtained ‎in ‎the ‎range ‎of ‎(‎1.7‎1-1.80)‎ M. ‎and ‎(‎2.13‎‎-‎2.1‎9)‎‎‎ M.‎ for ‎the EoS without and with TNI ‎contribution‎, respectively.
    Keywords: magnetars‎‎, magnetic field ‎profiles‎‎, ‎deformed neutron stars‎ ‎
  • Omid Jalili *, Shahin Toni Pages 25-31
    The harmonic oscillator in anti de Sitter space(AdS) is discussed. We consider the harmonic oscillator potential and then time independent Schrodinger equation in AdS space. Then we apply the supersymmetric Quantum Mechanics approach to solve our differential equation. In this paper we have solved Schrodinger equation for harmonic oscillator in AdS spacetime by supersymmetry approach. The shape invariance, charge conjugation and other properties of supersymmetric Quantum Mechanics for our equation are discussed. We investigate the dynamical symmetry into definite group. We also obtain the Casimir operator and thermodynamics properties of harmonic oscillator in Anti de sitter space. We have discussed the corresponding algebra for the N=2 Supersymmetry. The energy spectrum of the harmonic oscillator is similar to the flat space but the constant terms of it are different, This constant terms depends to the geometrical parameter of the background. Finally we have obtained the various thermodynamics quantity of the system.
    Keywords: Harmonic Oscillator, Anti de Sitter space, Supersymmetry, Thermal Properties
  • E. A. Hegazy * Pages 33-44

    In the second self-creation theory of gravitation and in the general theory of relativity, Bianchi type VI0 cosmological model in the presence of viscous fluid is studied. An exact solution of the field equations is given by considering the cosmological model yields a constant decelerations parameter q=constant and the coefficients of the metric are taken as A(t)=[c1t+c2]3L/(q+1)(L+1), B(t)=[c1t+c2]3/2(q+1)(L+1),C(t)=[c1 t+ c2]3/2(q+1)(L+1),where c1,c2 and L are constants . Effect of the viscosity on the entropy of the universe is given by a composition of the second law of thermodynamics with the the energy momentum tensor Tji with bulk viscous term in a conservative manner. We obtained a formula for calculation the entropy of the universe in term of the viscosity and used it to study and compare the Entropy, Enthalpy, Gibbs energy and Helmholtz energy of the universe in the presence of viscosity term in the self-creation theory of gravitation and in the general theory of relativity. The physical and geometrical properties of the obtained models are discussed.the formila is not displayed correctly!

    Keywords: General theory of relativity, Einstein field equations, Bianchi type VI$, 0$ cosmological models, Viscosity, Entropy
  • Zahra Zali, Jafar Sadeghi, Behnam Pourhassan * Pages 45-52

    In this work, we consider a graphene-like background in braneworld scenario which is one of the interesting models in cosmology and theoretical physics. Indeed, this paper is an application of holography in condense matter. We use the geometric form of potential which help to obtain field equations and solve it to obtain the energy spectrum. In that case we calculate superpotential and energy density of this model. Thermodynamical study of this model suggest that the entropy should modified due to the large-scale corrections. An important point is stability of this model in braneworld scenario. We study model stability by two separated methods. We calculate heat capacity, Gibbs and Helmholtz free energy to analyze thermodynamics stability, then consider small perturbations in graphene like metric background to investigate gravitational stability. We find that the model is completely stable unless in very low temperatures where the graphene structure may break. Hence, we confirm that our braneworld model is thermodynamically stable and also small perturbations yields to an oscillation around the equilibrium point.

    Keywords: stability, Perturbations, Graphene, Thermodynamics, Braneworld