Testing Gravity with Black Hole X-Ray Data

TL;DR

This paper reviews how X-ray emissions from black hole accretion disks are used to test Einstein's General Relativity, focusing on the Kerr hypothesis and current observational constraints.

Contribution

It provides a comprehensive overview of the current methods and results in testing gravity with black hole X-ray data, emphasizing the constraints on deviations from Kerr geometry.

Findings

X-ray data currently support Kerr black hole models.

No deviations from General Relativity have been detected.

X-ray observations provide stringent tests of strong-field gravity.

Abstract

The analysis of the properties of the X-ray radiation emitted from geometrically thin accretion disks around black holes can be a powerful tool to test General Relativity in the strong field regime. This chapter reviews the state-of-the-art of gravity tests with black hole X-ray data. So far, most efforts have been devoted to test the Kerr hypothesis - namely that the spacetime around astrophysical black holes is described by the Kerr solution - and X-ray data can currently provide among the most stringent constraints on possible deviations from the Kerr geometry. As of now, all X-ray analyses are consistent with the predictions of General Relativity.