Testing the "no-hair" property of black holes with X-ray observations of accretion disks

TL;DR

This paper investigates whether X-ray emissions from accretion disks can be used to test the no-hair theorem of black holes by analyzing spectral features in various gravitational theories.

Contribution

It introduces a method to use X-ray spectral data from accretion disks to test the no-hair property of black holes within different gravity models.

Findings

Spectral features vary with black hole spacetime parameters.

Potential to distinguish Kerr black holes from alternative theories.

Constraints on black hole metrics using X-ray observations.

Abstract

Accretion disks around black holes radiate a significant fraction of the rest mass of the accreting material in the form of thermal radiation from within a few gravitational radii of the black hole ($ r \lesssim 20 G M / c^{2}$). In addition, the accreting matter may also be illuminated by hard X-rays from the surrounding plasma which adds fluorescent transition lines to the emission. This radiation is emitted by matter moving along geodesics in the metric, therefore the strong Doppler and gravitational redshifts observed in the emission encode information about the strong gravitational field around the black hole. In this paper the possibility of using the X-ray emission as a strong field test of General Relativity is explored by calculating the spectra for both the transition line and thermal emission from a thin accretion disk in a series of parametrically deformed Kerr metrics. In addition the possibility of constraining a number of known black hole spacetimes in alternative theories of gravity is considered.