| Some gamma-ray bursts (GRBs), some X-ray binaries, and all active galactic nuclei (AGN) are likely powered by accretion onto a rotating black hole. I model the global, time-dependent accretion flow around a black hole using the nonradiative viscous hydrodynamic (VHD), Newtonian magnetohydrodynamic (MHD), and general relativistic MHD (GRMHD) equations of motion, which are integrated numerically. I wrote the VHD and nonrelativistic MHD numerical codes, and I coauthored the GRMHD code. I found that GRMHD numerical models of thick disks around a rotating black hole show that an evacuated, nearly force-free magnetosphere develops as predicted by Blandford and Znajek (1977). The BZ solution for the energy extracted is remarkably accurate in this region for a slowly rotating black hole and qualitatively accurate for all rotating black holes. GRMHD numerical models of rapidly rotating black holes show a mildly relativistic, collimated Poynting jet around the polar axis. Currently, no self-consistent MHD model of the accretion flow around a black hole shows a jet with Lorentz factors greater than 3. Additional physics is likely required to obtain Lorentz factors of 100 as some GRB models predict, and to obtain up to Lorentz factors of 10 as observed in some microquasars and AGN. |
