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Abstract

In this thesis, the accretion and ejection processes from a black hole accretion system is investigated by means of resistive general relativistic magnetohydrodynamic simulations. As a supplement to the results from prior research with non-relativistic simulations, my results confirm that the winds and outflows originated from thin accretion disks can also be observed in general relativistic simulations. In the first part, the execution of the implementation of resistivity, namely magnetic diffusivity, into the existing non-resistive general relativistic magnetohydrodynamic code HARM is illustrated. The test simulations of the new code {\HAR} include the comparison with analytical solution of the diffusion equation and a classic shock tube test. {\HAR} shows reliable performances in these tests. In the second part, {\HAR} is applied to investigate the evolution of magnetized tori. The results show that the existence of resistivity leads to inefficient accretions of matter from tori onto black holes by weakening the magnetorotational instability inside the tori. An indication for a critical magnetic diffusivity in this simulation setup is found beyond which no magnetorotational instability develops in the linear regime. In the third part, as the main purpose of this PhD project, {\HAR} is used to perform simulations of magnetically diffusive thin accretion disks that are threaded by a large-scale poloidal magnetic field around non-rotating and rotating black holes. These long-term simulations last 3000 code time units, which are about 195 rotation periods at the disk inner boundary, correspondingly. Their computational domains extend from black hole horizon to 80 Schwarzschild radii. Outflows driven from the accretion disk are clearly seen. These outflows have the typical radial velocity of 0.1 speed of light. In my analyses, I argue that these outflows are driven by the magnetic pressure gradient from the toroidal magnetic field generated by the rotation of the disk. The small ratios of the poloidal field strengths to the toroidal field strengths suggest the interpretation of the outflows as ``tower jet," rather than centrifugally driven winds (Blandford-Payne effect). Furthermore, I find direct evidence of the growths of magnetorotational instabilities inside the accretion disks, which are suppressed by the increasing levels of magnetic diffusivity. This suppression leads to inefficient accretion and ejection processes of the accretion system. Finally, the influences of rotating black holes on the accretion systems are explored. The results show an suppression effect on the black hole spin on the accretion and ejection processes in the system. The tangled field lines within the ergosphere induced by the black hole rotation produce magnetic pressure that pushes against the accreting matter from the disk. In the simulations with large spin parameters, energy extraction from the black hole (Blandford-Znajek effect) is observed, which is, nevertheless, $\sim 10^{2}$ times smaller than the energy production from the disk outflow.