Test particles dynamics around deformed Reissner-Nordström black hole

Abstract

In this paper we study the dynamics of neutral, electrically charged and magnetized particles around deformed electrically and magnetically charged Reissner-Nordstr\"om black holes. For the neutral test particles motion, it is shown that the radius of the innermost stable circular orbits (ISCOs) decrease with the increase in both the black hole charge and positive spacetime deformation. It reaches up to $3.85M$ at the value of deformation parameter $\ensuremath{\epsilon}=20.45$ in Schwarzschild spacetime case ($Q=0$). In the extreme charged Reissner--Nordstrom black hole case, the ISCO decreases up to $2.26M$ at the value of deformation parameter $\ensuremath{\epsilon}=6.17$. Moreover, the negative deformation results in an increase in the ISCO radius. Comparing effects of positive deformation and the Reissner-Nordstr\"om black hole charge with spin of rotating Kerr black holes, it is shown that the extremely charged Reissner-Nordstr\"om black hole can mimic rotating Kerr black hole up to the spin parameter $a/M=0.48$, while for the positive deformation with $\ensuremath{\epsilon}=6.17$ the mimic value increases up to $a/M=0.88$ implying that the supermassive black hole M87 cannot be considered as Reissner-Nordstr\"om black hole. Using this comparison, we estimate charge of the supermassive black hole Sagittarius A* as $Q/M\ensuremath{\simeq}0.8287$ without deformation which can mimic the spin of the black hole. When the deformation $\ensuremath{\epsilon}=1$, the mimic charge increases up to $Q/M\ensuremath{\simeq}0.8926$. Our study of the energy extraction from the accretion disk shows that the maximum energy efficiency increases up to 20.02%, which is almost the same for extreme Kerr black hole case (20.6%). We have also considered the behaviour of ISCO of electrically charged particles showing that the attractive (repulsive) electrostatic interactions cause rapid increase (slightly decrease) of the ISCO radius. Finally, we have explored the dynamics of magnetized particles around deformed magnetically charged Reissner-Nordstr\"om black hole. By treating the magnetar PSR J1745-2900, orbiting the supermassive black hole Sagittarius A* as a magnetized particle, showing that the magnetic charge of pure Reissner-Nordstr\"om black hole can mimic spin of a rotating Kerr black hole up to $a/M\ensuremath{\simeq}0.82$ for the value to be in the range ${Q}_{m}/M\ensuremath{\in}(0,0.692)$. Moreover, we find that the positive values of the deformation parameter lead to shift the ISCO for the magnetized particles toward the central object.