Accretion and Ejection around Astrophysical Black Holes

Abstract

Astrophysical black holes should be simple objects with only two parameters: mass and spin. As material accretes onto the black hole this adds two further parameters: accretion rate and, since accretion generally occurs through a preferential plane, the inclination at which we view the system. Inclination becomes particularly important when a fraction of the inflowing material is not accreted but is instead ejected from the system in powerful, highly collimated and sometimes highly relativistic jets. It is these luminous accretion flows and jets that allow accreting black holes to be detected across the entire range of the electromagnetic spectrum from radio up to gamma-ray energies. The emission from the accretion flow and jet should be completely determined by the four fundamental parameters of mass, spin, accretion rate and inclination. Variations in these four parameters should be all that is required to explain the enormous variety of spectra from accreting black holes. In this thesis I present five papers studying emission from black holes of all size-scales and in all accretion regimes, including inclination effects and investigating the possible effect of the most difficult parameter to measure --- black hole spin. Black holes do not exist in isolation. Stellar mass black holes are fed by their companion stars and supermassive black holes by gas from their host galaxies. Not only does the galaxy fuel the growth of the supermassive black hole but equally the outflows that result from black hole accretion affect the growth of the galaxy, heating gas and suppressing star formation. This adds extra importance to understanding black hole accretion and the interplay between accretion and ejection. I find a scenario where low spin black holes are limited to feeding back via winds and moderately relativistic jets, while only the highest spin black holes are capable of producing the most powerful, highly relativistic jets, may be consistent with current observations.