Amplification of Magnetic Fields in an Accretion Disk with a Starburst Torus

Abstract

Abstract It is widely believed that a black hole is surrounded by an accretion disk. Such an accretion disk should have magnetic fields whose evolution is important to understand the disk dynamics, since the viscosity in the disk must originate from magnetic turbulence. In the case of the accretion disk of AGN (active galactic nuclei) with a circum-disk star-burst region, we point out that the so-called $ \alpha $-dynamo effect via radiation drag due to an exterior radiation field around the disk works well. This is possible since the drag time-scale is longer than the dynamical time-scale. Importantly, we find that the starburst AGN satisfies this criterion. Thus, the magnetic field of the accretion disk of the starburst AGN is amplified by the dynamo effect owing to the radiation drag. This results in enhancing the mass-accretion rate to the massive black-hole of AGN within the star-burst region.