Accretion disks around black holes: physical models vs. observations

Abstract

We discuss the problem of the formation of a large‐scale magnetic field in the accretion disks around black holes, taking into account the nonuniform vertical structure of the disk. The high electrical conductivity of the outer layers of the disk prevents the outward diffusion of the magnetic field. This implies a stationary state with a strong magnetic field in the inner parts of the accretion disk close to the black hole. The effects are considered of advection, radial gradients of pressure and radial drift velocity on the structure of accretion disks around black holes. Models with large accretion rate are presented, where there is no continuous local solution. Continuous solutions for advective disks exist for all accretion rates. Despite the importance of advection on it’s structure, the disk remains geometrically thin.