Influence of weak electromagnetic fields on charged particle ISCOs

TL;DR

This paper investigates how weak electromagnetic fields, specifically electric and magnetic test fields, influence the innermost stable circular orbits (ISCOs) of charged particles around a Schwarzschild black hole, revealing conditions for orbit stability and emergence.

Contribution

It provides a detailed analysis of the ISCO structure for charged particles in combined electric and magnetic test fields around a Schwarzschild black hole, highlighting new conditions for orbit stability.

Findings

Existence of four ISCO solutions depending on field strengths

Strong electric fields can prevent stable orbits of like-charged particles

Strong magnetic fields can restore stability and create static particle ISCOs

Abstract

Astrophysical black holes are often embedded into electromagnetic fields, that can usually be treated as test fields not influencing the spacetime geometry. Here we analyse the innermost stable circular orbit (ISCO) of charged particles moving around a Schwarzschild black hole in the presence of a radial electric test field and an asymptotically uniform magnetic test field. We discuss the structure of the in general four ISCO solutions for different magnitudes of the electric and the magnetic field's strength. In particular, we find that the nonexistence of stable circular orbits of particles with equal sign of charge as the black hole for sufficiently strong electric fields can be canceled by a sufficiently strong magnetic field. In this situation, we find that ISCOs made of static particles will emerge.