General Relativistic Magnetohydrodynamic Simulations of Black Hole   Accretion Disks
  Observations are providing increasingly detailed quantitative information about the accretion flows that power such high energy systems as X-ray binaries and active galactic nuclei. Analytic models of such systems must rely on assumptions such as regular flow geometry and a simple, parameterized stress. Global numerical simulations offer a way to investigate the basic physical dynamics of accretion flows without these assumptions. For black hole accretion studies one solves the equations of general relativistic magnetohydrodynamics. Magnetic fields are of fundamental importance to the structure and evolution of accretion disks because magnetic turbulence is the source of the anomalous stress that drives accretion. We have developed a three-dimensional general relativistic magnetohydrodynamic simulation code to evolve time-dependent accretion systems self-consistently. Recent global simulations of black hole accretion disks suggest that the generic structure of the accretion flow is usefully divided into five regimes: the main disk, the inner disk, the corona, the evacuated funnel, and the funnel wall jet. The properties of each of these regions are summarized. 
J.F. Hawley and J.-P. De Villiers