Equilibrium configuration of perfect fluid orbiting around black holes in some classes of alternative gravity theories

Abstract

The hydrodynamic behaviour of perfect fluid orbiting around black holes in spherically symmetric spacetime for various alternative gravity theories has been investigated. For this purpose we have assumed an uniform distribution for the angular momentum density of the rotating perfect fluid. The contours of equipotential surfaces are illustrated in order to obtain the nature of inflow and outflow of matters. It has been noticed that, the marginally stable circular orbits originating from decreasing angular momentum density lead to closed equipotential surfaces along with cusp allowing existence of accretion disks. On the other hand, the growing part of angular momentum density exhibits central rings for which stable configurations are possible. However inflow of matter is prohibited. Among the solutions discussed in this work, the charged F (R) gravity and Einstein-Maxwell-Gauss-Bonnet solution exhibit inflow and outflow of matter with central rings present. These varied accretion disk structure of perfect fluid attribute these spacetimes astrophysical importance. The effect of higher curvature terms predominantly arises from region near the black hole horizon. Hence the structural difference of accretion disk in modified gravity theories with comparison to general relativity may act as an experimental probe for these alternative gravity theories.

Reissner–Nordstrøm–de Sitter manifold: photon sphere and maximal analytic extension

“…null geodesics orbiting the black hole at fixed r. It is known that this phenomenon is an important part of black hole spacetimes geometry. Discussions of photon orbits and there effects can be found in [6,7,8,13] for example. The effect of photon sphere concerning decay of test fields can be seen in [1,3,17] among others.…”

“…We showed that f has three positive zeros r 1 , r 2 , and r 3 if (5) holds. Note that f and P , given in (6), are both smooth and have the same sign over ]0, +∞[, and we know the sign of P everywhere. In a small interval around r 1 , f is decreasing since it is positive to the left of r 1 and negative to its right, thus f < 0 over this interval.…”

General relativistic polytropes with a repulsive cosmological constant

“…The cosmological constant can be relevant in both the geometrically thin Keplerian accretion disks [29,31,47,76,77] and geometrically thick toroidal accretion disks [76][77][78][79][80][81][82][83][84][85] orbiting supermassive black holes in the central parts of giant galaxies, or in the recently discussed ringed accretion disks [86,87]. Spherically symmetric, stationary polytropic accretion in the spacetimes with the repulsive cosmological constant has been studied in [88][89][90][91][92].…”

Strong gravitational lensing—a probe for extra dimensions and Kalb-Ramond field

“…where, f (r) and g(r) are arbitrary functions of the radial coordinate r with dΩ 2 2 being the line element on two sphere. (Some interesting features regarding this line element have been explored in [62][63][64][65]) We further assume that the spacetime is asymptotically flat, i.e., f (r → ∞) = 1 = g(r → ∞). We will be exclusively considering the trajectories of photons in this work and the single most important radius associated with those trajectories correspond to the radius of photon circular orbit r ph .…”