Magnetic fields in the accretion disks for various inner boundary conditions

TL;DR

This paper models magnetic fields in accretion disks using galactic dynamo approaches, emphasizing the impact of boundary conditions on magnetic field strength and ensuring fields remain below equipartition levels.

Contribution

It introduces a dynamo-based model for accretion disk magnetic fields considering various boundary conditions, linking galactic dynamo methods to accretion disk physics.

Findings

Magnetic field strength depends critically on boundary conditions.

Zero and fixed magnetic boundary conditions prevent fields exceeding equipartition.

The model aligns magnetic field estimates with physical constraints of accretion disks.

Abstract

The magnetic fields of accretion disks play an important role in studying their evolution. We may assume that its generation is connected to the dynamo mechanism, which is similar with that in the galactic disks. Here, we propose a model of the magnetic field of the accretion disk that uses the same approaches that have been used for galaxies. It is necessary to obtain the field, which is expected to be less than the equipartition value, and without destroying the disk. To do so, it is necessary to formulate the basic properties of the ionized medium and to estimate the parameters governing the dynamo. We used the no-z approximation that has been developed for thin disks. We also take different boundary conditions that can change the value of the field significantly. We show that the magnetic field strictly depends on the boundary conditions. Taking zero conditions and the fixed magnetic field condition on the inner boundary, which are connected to the physical properties of the accretion disk, we can avoid solutions that are greater than the equipartition field.