Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes

TL;DR

Relativistic X-ray lines from black hole accretion disks serve as powerful probes of strong gravity, revealing black hole spin, relativistic effects, and variability, with implications for understanding black hole evolution and testing General Relativity.

Contribution

This review highlights recent observational and theoretical advances in using relativistic X-ray lines to study black hole spin and strong gravitational effects.

Findings

Detection of relativistic lines in stellar-mass black holes

Evidence of black hole spin from X-ray lines

Line flux variability on orbital timescales

Abstract

Relativistic X-ray emission lines from the inner accretion disk around black holes are reviewed. Recent observations with the Chandra X-ray Observatory, X-ray Multi-Mirror Mission-Newton, and Suzaku are revealing these lines to be good probes of strong gravitational effects. A number of important observational and theoretical developments are highlighted, including evidence of black hole spin and effects such as gravitational light bending, the detection of relativistic lines in stellar-mass black holes, and evidence of orbital-timescale line flux variability. In addition, the robustness of the relativistic disk lines against absorption, scattering, and continuum effects is discussed. Finally, prospects for improved measures of black hole spin and understanding the spin history of supermassive black holes in the context of black hole-galaxy co-evolution are presented. The best data and most rigorous results strongly suggest that relativistic X-ray disk lines can drive future explorations of General Relativity and disk physics.