Inferring black hole charge from backscattered electromagnetic radiation

TL;DR

This paper analyzes how electromagnetic waves scatter off charged black holes, revealing that backward scattering patterns can indicate the black hole's charge, combining electromagnetic and gravitational effects.

Contribution

It introduces a method to infer black hole charge by analyzing electromagnetic scattering, highlighting the effects of charge-induced phase shifts and helicity reversal.

Findings

Backward scattering reveals black hole charge presence.

Charge affects electromagnetic to gravitational wave conversion.

Helicity-reversed scattering amplitude is non-zero in backward direction.

Abstract

We compute the scattering cross section of Reissner-Nordstr\"om black holes for the case of an incident electromagnetic wave. We describe how scattering is affected by both the conversion of electromagnetic to gravitational radiation, and the parity-dependence of phase shifts induced by the black hole charge. The latter effect creates a helicity-reversed scattering amplitude that is non-zero in the backward direction. We show that from the character of the electromagnetic wave scattered in the backward direction it is possible, in principle, to infer if a static black hole is charged.