Innermost stable circular orbits around a Reissner-Nordström-global monopole spacetime in a homogeneous magnetic field (2503.13683v1)

Abstract: We investigate the dynamics of charged particles in the spacetime of a global monopole swallowed by a Reissner-Nordstr\"om (RN) black hole in the presence of a external weak asymptotically homogeneous magnetic field. We carefully analyze and deduce the conditions to have such a magnetic field around this black hole and show that this is indeed possible in the small but nontrivial charge and monopole term limit. We obtain general equations of motion and analyze them for special cases of circular orbits, focusing on the inner-most stable circular orbit (ISCO) of this configuration. The richness of the parameters and complicated forms of the resulting equations of motion necessitate a numerical approach. Hence, we have presented our results with numerous graphs, which help to understand the evolution of ISCO as a function of the external test magnetic field and the monopole term depending on the parameters of the black hole, such as its electrical charge as well as the properties of the test particle such as its specific charge, angular momentum, and energy. We have also analyzed the effective potential that these fields generate and deduced results for the aforementioned values of external and internal parameters of spacetime.