QPOs analyses and circular orbits of charged particles around magnetized black holes in Bertotti-Robinson geometry

Abstract

Analyses of astrophysical observations, such as quasiperiodic oscillations (QPOs), combined with theoretical studies, help to understand the deeper properties of black hole spacetime and obtain parameters of black holes and alternative gravity theories. In this study, we investigate the dynamics of charged particles orbiting magnetized black holes within the Bertotti-Robinson (BR) geometry, also known as the electromagnetic universe (EU). We study the circular motion and oscillations of charged particles around a black hole in the presence of a magnetic field, focusing on their applications to QPOs. First, we obtain solutions for the Maxwell equations for orthonormal components of magnetic fields around the black holes in radial and angular directions and analyze the dependence on the EU field and magnetic interactions. The effective potential, specific angular momentum, energy, and innermost stable circular orbits (ISCOs) of charged particles are analyzed to demonstrate how the black hole spacetime, in conjunction with magnetic interaction and EU parameters, affects particle dynamics. Then, we calculate the Keplerian, radial, and vertical epicyclic frequencies, providing insight into the orbital and oscillatory behavior of particles near the black holes. Furthermore, we investigate twin-peak QPOs using the relativistic precession (RP) model and compare the main results with those of the standard Schwarzschild limit. Finally, we employ Monte Carlo Markov Chain (MCMC) simulations to obtain constraint values for black hole mass, the EU, and magnetic interaction parameters, using QPO frequency data observed in microquasars (as an example, XTE J1550-564, GRO J1655-40, GRS 1915+105) and galactic centers (in cases of M82 and Milky Way). Our findings may provide valuable insights into understanding the combined effects of RB spacetime and electromagnetic interactions around black holes on astrophysical observations of QPOs and testing gravity theories in a strong gravity regime.