# The large-scale magnetic field of a thin accretion disk with outflows

## TL;DR

This paper presents a self-consistent model of magnetic fields and outflows in thin accretion disks, showing how external magnetic fields are advected inward and drive powerful outflows that significantly influence disk structure and could explain observed AGN outflows.

## Contribution

The study develops a global disk-outflow model demonstrating efficient inward advection of external magnetic fields and their role in launching high-velocity outflows in thin accretion disks.

## Key findings

- Magnetic field strength in the inner disk can be several orders higher than the external field.
- Outflows can reach velocities of 0.2-0.3 times the speed of light.
- Mass loss in outflows can be 10-70% of the accretion rate.

## Abstract

The large-scale magnetic field threading an accretion disk plays an important role in launching jets/outflows. The field may probably be advected inwards by the plasma in the accretion disk from the ambient environment (interstellar medium or a companion star). It has been suggested that the external field can be efficiently dragged inwards in a thin disk with magnetic outflows. We construct a self-consistent global disk-outflow model, in which the large-scale field is formed by the advection of the external field in the disk. The outflows are accelerated by this field co-rotating with the disk, which carry away most angular momentum of the disk and make its structure significantly different from the conventional viscous disk structure. We find that the magnetic field strength in the inner region of the disk can be several orders of magnitude higher than the external field strength for a geometrically thin disk with $H/R \sim 0.1$, if the ratio of the gas to magnetic pressure $\beta_{\rm out} \sim 10^2 $ at the outer edge of the disk. The outflow velocity shows layer-like structure, i.e., it decreases with radius where it is launched. The outflow can be accelerated up to $ \sim 0.2-0.3$c from the inner region of the disk, and the mass loss rate in the outflows is $ \sim 10 - 70\%$ of the mass accretion rate at the outer radius of the disk, which may account for the fast outflows observed in some active galactic nuclei (AGNs).