Geodesics and Shadows of Rotating Black Holes

Abstract

We first investigate the consequences of running gravitational coupling on certain properties of rotating black hole. We are motivated by the functional form of gravitational coupling previously investigated in the context of infra-red limit of asymptotically safe gravity theory. In this approach, the involvement of a new parameter xËœ in this solution makes it different from Schwarzschild black hole. The Killing horizon, event horizon and singularity of the computed metric is then discussed. It is noticed that the ergosphere is increased as xËœ increases. Considering the black hole in equatorial plane, the geodesics of particlesare explored. The effective potential is computed and graphically analyzed for different values of parameter xËœ. Apart from the changes induced in the space-time structure of such black holes, we also study the implications to Penrose process and geodetic precession. The energy extraction from black hole is investigated via Penrose process. For the same values of spin parameter, the numerical results suggest that the efficiency of Penrose process is greater in asymptotically safe gravity than in Kerr Black Hole. At the end, a brief discussion on Lense-Thirring frequency is also done. A black hole’s spacetime is remarkably affected by presence of dark matter around it. We analyze the shadow of a new solution to Einstein Field Equations and consider the effects of dark matter on it. This solution describe a rotating black hole in the background of perfect fluid dark matter, along with its extension to nonzero cosmological constant L. Working in Boyer-Lindquist coordinates, we consider the effects of the perfect fluid dark matter parameter a on the shadow cast by a black hole with respect to an observer at position (ro, qo). Global monopoles are topological defects which may have been produced during the phase transitions in the early universe. In fact, global monopoles are just one type of topological defects. Other types of topological objects are expected to exist including domain walls and cosmic strings. A metric for rotating dyonic black hole with global monopole in presence of perfect fluid is computed in this work. We then discuss its surface topology at the event horizon using Gauss-Bonnet Theorem and also the ergoregion. We investigate the shadows of the rotating dyonic black hole. Choosing certain values of parameters, such as w = ð€€€1/3, 0, 1/3, we observe the effect of dark matter, dust and radiation on the silhouette of the black hole. Our findings lead us to conclude that the presence of parameters g and a, also deforms the shape of black hole’s shadow. These results have been depicted through graphical representation. We also analyze the two observables, radius Rs and distortion ds, related to black hole’s shadow. Energy emission rate of rotating dyonic black hole with global monopole surrounded by perfect fluid is also computed and graphically illustrated with respect to parameters.