Abstract
This third lecture is dedicated to the properties of supermassive black holes. How is the mass of a black hole calculated? Direct measurement, using the kinematics of the gas and stars that revolve around it, requires high spatial resolution, and only concerns nearby galaxies studied with the Hubble Space Telescope. A proportional relationship between the mass of the black hole and the mass of the bulge of the host galaxy has been demonstrated. For very distant galaxies, temporal and spectral resolution can replace spatial resolution, but the black hole must be active, i.e. an AGN. If the AGN continuum varies in time, then we can study how the variation propagates to the BLR region with broad lines, then to the narrow lines (NLR). This is known as reverberation mapping. In some cases, very powerful H2O masers can also be used to map and track temporal variations in matter very close to the black hole, in a Keplerian orbit.
Reverberation mapping has revealed a relationship between BLR luminosity and size, which is then used in conjunction with measured BLR kinematics. The physics of the accretion disk is complex, with highly turbulent gas. A characteristic magneto-rotational instability (MRI) has been demonstrated. We have also observed nuclei that accrete a lot of matter but do not radiate. It would appear that anadvection-dominated accretion flow(ADAF) regime exists in a large number of nearby galaxies, including the Milky Way, which radiates at only 10-9 times the Eddington luminosity. In this regime, all the energy dissipated by viscosity is not radiated, but drawn directly into the black hole. This regime occurs at low accretion rates. There is no longer a thin disk, but a thick torus. In this regime, a corona is formed, and hard X-rays are emitted by reverse Compton emission on relativistic electrons.
