Testing the no-hair theorem with the continuum-fitting and the iron line methods: a short review

TL;DR

This paper reviews how the continuum-fitting and iron line methods are used to test the no-hair theorem around black holes, discussing models, assumptions, and observational constraints with current and future telescopes.

Contribution

It provides a comprehensive overview of the two leading techniques for testing the no-hair theorem, including their astrophysical models and observational capabilities.

Findings

Both methods effectively probe black hole spacetime geometry.

Current observations place constraints on deviations from the Kerr metric.

Future facilities will improve the precision of these tests.

Abstract

The continuum-fitting and the iron line methods are leading techniques capable of probing the spacetime geometry around astrophysical black hole candidates and testing the no-hair theorem. In the present paper, we review the two approaches, from the astrophysical models and their assumptions, to the constraining power with present and future facilities.