The role of Biermann battery mechanism in appearance of magnetic fields in accretion discs

At present, there is little doubt that accretion discs surrounding compact astrophysical objects such as black holes, white dwarfs and neutron stars may have magnetic field structures. Thus, they explain the transfer of angular momentum between different parts of the disc and some other processes. There are various ways to explain the occurrence of these magnetic fields. In this paper we study the possibility of generation of magnetic fields due to the Biermann battery mechanism. It is associated with radial flows of protons and electrons. Due to their different masses, they interact differently with the rotating medium, producing circular currents that generate magnetic fields. Previously, a similar process was studied for galactic discs and it was shown that the battery mechanism can generate initial magnetic fields in such objects. Here we discuss the action of the Biermann battery for accretion disks. This requires solving an integral equation of the second kind, which arises if we take into account the self-interaction of the magnetic field. It is shown that corresponding fields are quite significant and can play an important role in the evolution of magnetic fields in discs.