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

Relativistic X-ray emission lines from the inner accretion disks 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 coevolution are presented. The best data and most rigorous results strongly suggest that relativistic X-ray disk lines can drive new explorations of General Relativity and disk physics in the future.