Physics of accretion and outflows around black holes

Accretion around and onto black holes is a ubiquitous phenomenon in the field of astrophysics. Here we carry out numerical studies of the physics of accretion around black holes in three separate venues, specifically, angular momentum transport within black hole and cataclysmic variable disks, radiation powered by black hole accretion in the context of Gamma Ray Bursts (GRBs), and the formation of structure and stars around Sagittarius A*. We examine the effects of external hydrodynamic turbulence and cooling on the transport properties of the Magnetorotational Rotational Instability (MRI) and conclude that the MRI remains a robust method by which to redistribute angular momentum in ionized accretion disks, even when external turbulence produces velocity fluctuation an order of magnitude stronger than those generated by the MRI. We also find that cooling isothermal disks tends to reduce the efficiency of the MRI. We next calculate the detailed spectrum of Jitter Radiation produced by electrons in Weibel magnetic fields possibly present in GRB afterglows. We conclude that detailed observations may allow for some disambiguation between Synchrotron and Jitter radiation in GRB afterglows but that it fails to solve the current observational issues. Finally we perform a series of hydrodynamic and magnetohydrodynamic simulations of Bondi-Hoyle-Lyttleton (BHL) accretion of gravitationally bound and unbound material onto a super massive black hole. Unfortunately, boundary conditions appear to fail after the cloud has left the simulation domain making analysis of the results troublesome. However, we do find that the amount of accreted material is a small portion of the original cloud in the unbound case. The magnetized run failed to achieve circularization making any conclusions speculative at best. We conclude that the behavior in the unbound case may possibly explain the inefficient star formation rate in the galactic center if it is due to BHL accretion of turbulent magnetized, giant molecular clouds interacting with Sagittarius A*.