Dynamics, ringdown, and accretion-driven multiple quasi-periodic oscillations of Kerr–Bertotti–Robinson black holes

Abstract We study the motion of test particles around the Kerr–Bertotti–Robinson (KBR) black hole (BH) and explore how the three defining parameters, the mass M , rotation parameter a , and magnetic parameter B influence their dynamics. We derive analytical expressions for the energy and angular momentum of stable equatorial circular orbits, along with the corresponding radial and latitudinal oscillation frequencies, as functions of M , a , and B . We also examine the key features of the quasi-periodic oscillations (QPOs) of test particles near stable circular orbits, including the precession effects such as periastron precession and the Lense-Thirring effect. We compare our results with those corresponding to the Kerr BH. We find that the particle motion is strongly shaped by the BH parameters. Using a WKB approach, we also study scalar quasinormal modes of rotating KBR BH in an external magnetic field and show that the magnetic field increases damping, while rotation and angular momentum mainly set the oscillation frequencies. Alternatively, general relativistic modeling of Bondi-Hoyle-Lyttleton (BHL) accretion onto rapidly rotating KBR BH shows that two distinct physical structures emerge and cyclically transform into one another over time. These processes produce either a strongly oscillating flip–flop shock cone or a nearly stationary toroidal structure, with their formation governed by the BH spin and magnetic curvature. Power spectral analysis shows that these configurations give rise to low- and high-frequency QPO, providing a unified theoretical framework to understand how multiple QPO–like features can arise in rapidly spinning accreting systems.