Probes and Tests of Strong-Field Gravity with Observations in the Electromagnetic Spectrum

TL;DR

This paper reviews how electromagnetic observations of neutron stars and black holes can test key predictions of General Relativity in strong gravitational fields, focusing on stable orbits, event horizons, and current observational constraints.

Contribution

It highlights the importance of developing a theoretical framework for testing gravity theories and summarizes current observational constraints on deviations from General Relativity.

Findings

Current observations constrain deviations from GR in neutron stars.

Electromagnetic signals can probe the presence of event horizons.

Future observations can test strong-field predictions of gravity theories.

Abstract

Neutron stars and black holes are the astrophysical systems with the strongest gravitational fields in the universe. In this article, I review the prospect of probing with observations of such compact objects some of the most intriguing General Relativistic predictions in the strong-field regime: the absence of stable circular orbits near a compact object and the presence of event horizons around black-hole singularities. I discuss the need for a theoretical framework within which future experiments will provide detailed, quantitative tests of gravity theories. Finally, I summarize the constraints imposed by current observations of neutron stars on potential deviations from General Relativity.