Adiabatic inspirals under electromagnetic radiation reaction on Kerr spacetime

Abstract

A compact body in orbit about a black hole loses orbital energy and angular momentum through radiation-reaction processes, inspiralling towards the black hole until a final plunge. Here we consider a scenario with a charged compact body in which fluxes of electromagnetic radiation drive this inspiral. We calculate trajectories in the $(p,e)$ plane for inspirals in the equatorial plane of a rotating black hole within the adiabatic (orbital-averaged-dissipative) approximation. We make comparisons with a non-relativistic Keplerian approximation based on the Abraham-Lorentz force law, and with standard gravitational-wave driven scenarios. We find that EM-driven inspirals are less efficiently circularized (i.e. orbits remain more eccentric at the point of plunge) than their gravitational counterparts, and we quantify the effect of black hole spin.