Innermost stable circular orbit of Kerr-Bertotti-Robinson black holes and inspirals from it: Exact solutions

TL;DR

This paper derives exact solutions for stable circular orbits and inspiral trajectories of test particles around Kerr-Bertotti-Robinson black holes, revealing parallels with Kerr black holes and providing a foundation for future astrophysical studies.

Contribution

It presents the first exact analytical expressions for innermost stable circular orbits and inspiral solutions in Kerr-Bertotti-Robinson spacetime, extending understanding beyond Kerr black holes.

Findings

Innermost stable circular orbit radii are expressed similarly to Kerr black holes.

Closed-form solutions for inspiraling test particles are provided.

Results facilitate future astrophysical modeling of such black holes.

Abstract

For an uncharged test particle in the Kerr-Bertotti-Robinson spacetime, solutions of two major types of orbits are presented, both in exact forms. First, for both prograde and retrograde motions, the radii of innermost stable circular orbits are expressed fully in terms of the outer and inner horizon radii just in the same form as Kerr black holes, despite the fact that Kerr-Bertotti-Robinson black holes have three parameters. Second, closed analytic solutions are given to the problem of a test particle inspiraling toward the Kerr-Bertotti-Robinson black hole from innermost stable circular orbits at the infinitely distant past. These exact solutions can serve as a springboard for more general solutions and astrophysical applications in the future.