سیاهچاله

In this paper, we apply the Newtonian limit to the general relativistic magnetohydrodynamic (GRMHD) equations that govern the motion of magnetoplasma accreting onto a static black hole. We study the time evolution of a non-viscous, magnetized, thick accretion disk in the presence of the central black hole's dipolar magnetic field. With the presence of finite electrical conductivity in the fluid, the magnetic stress effectively replaces the viscous shear stress in the standard disk model and is responsible for the transfer of angular momentum. All physical quantities of the system are functions of three variables: t, r, and θ. We determine the time dependence of the system's physical functions using the self-similar method. With suitable physical assumptions, we derive the spatial dependence of the functions as accurately as possible through analytical solutions, and, when necessary, through numerical methods. Self-similar solutions indicate that over time, the accretion and rotation of the fluid slow down, the disk becomes less dense, cooler, and less pressurized, and the electrical conductivity of the fluid also decreases. As the electrical conductivity of the fluid increases, the accretion and rotation of the fluid slow down, and the disk becomes denser and cooler, but the mass accretion rate increases. The azimuthal electric current density generated by the motion of the magnetofluid determines the magnetic field structure within the disk and results in a polar component for the disk's magnetic field. Due to the finite electrical conductivity of the fluid, at the boundary surface of the disk, the constant magnetic field lines of the disk connect to the dipolar magnetic field lines of the central black hole. Over time, this configuration remains stable because the time dependence of the magnetic field components of the disk is similar.

In this paper, a charged AdS black hole is considered and exponential corrections on entropy ‎are studied for it. Next, thermodynamic quantities of this black hole, including mass, ‎temperature, heat capacity, as well as pressure and Gibbs free energy, are investigated. Then, ‎the thermodynamic geometry of this black hole is investigated using the geometric methods of ‎Weinhold, Ruppeiner, Quevedo, HPEM and NTG. In addition, the correspondence between ‎singularities of the scalar curvature of these metrics and the black hole phase transition points ‎is investigated. It has been observed that Quevedo (II), HPEM and NTG formalisms provide ‎more information about the phase transition of this black hole compared with Weinhold, ‎Ruppeiner and Quevedo (I) formalisms.‎

In recent years, modified gravity models have played an important role in the cosmological structures. One of these models is F(R) gravity theory which opened a new insight in the context of black hole thermodynamics. Some of interesting consequences of the black hole thermodynamics resulted into investigation of thermal properties of different black holes. In this paper, first we investigate topological Lifshitz-like black hole solutions of F(R) gravity in d-dimensions and then study thermodynamic properties of such special class of F(R) gravity. Finally, we examine thermal stability and possible phase transition with respect to the heat capacity and Gibbs free energy.

In this paper, the second and third order corrections of the curvature tensor to the holographic complexity of a temperature state in the coherent field theory are studied. Dual geometry of  this  temperate state  is Schwarzschild's anti deSitter black hole geometry. The calculations made in this paper show that considering these new sentences will only appear as a constant coefficient in the final result, that is the rate of complexity growth over long periods of time.

In this paper، we considered cosmological constant as a variable and studied properties and the thermodynamics stability of BTZ black hole from a geometric perspective. Also، we examined the correspondence between thermodynamic curvature singularities and phase transitionpoints with different thermodynamic metrics. We found that theQuevedo metric cannot predict the phase transition points in two ensembles. This result is also valid for the kerr-de sitter spacetime.

In this paper, the rotating black brane solutions with zero curvature horizon of classical gravity with first order string corrections are introduced. Although these solutions are not asymptotically anti de Sitter, one can use the counterterm method in order to compute the conserved quantities of these solutions. Here, by reviewing the counterterm method for asymptotically anti de Sitter spacetimes, the conserved quantities of these rotating solutions are computed. Also a Smarr-type formula for the mass as a function of the entropy and the angular momenta is obtained, and it is shown that the conserved and thermodynamic quantities satisfy the first law of thermodynamics. Finally, a stability analysis in the canonical ensemble is performed, and it is shown that the system is thermally stable. This is in commensurable with the fact that there is no Hawking-Page phase transition for black object with zero curvature horizon.