Contribution to the angular momentum transport paradigm for accretion disks

TL;DR

This paper investigates the magnetic and velocity structure of thin accretion disks around stars, analyzing how magnetic backreaction influences radial infall and contributes to angular momentum transport.

Contribution

It develops a detailed model of the magnetic and velocity fields in accretion disks, highlighting the role of small-scale magnetic oscillations and currents in angular momentum transfer.

Findings

Small-scale magnetic oscillations induce significant toroidal currents.

Backreaction effects can oppose accretion but remain negligible with weak magnetic fields.

The model supports the importance of magnetic fields in disk dynamics.

Abstract

We analyze the stationary configuration of a thin axisymmetric stellar accretion disk, neglecting non-linear terms in the plasma poloidal velocity components. We set up the Grad-Shafranov equation for the system, including the plasma differential rotation (according to the so-called co-rotation theorem). Then, we study the small scale backreaction of the disk to the central body magnetic field and we calculate the resulting radial infalling velocity. We show that the small scale radial oscillation of the perturbed magnetic surface is associated to the emergence of relevant toroidal current densities, able to balance the Ohm law even in the presence of quasi-ideal values of the plasma resistivity. The contribution to the infalling velocity of the averaged backreaction contrasts accretion, but it remains negligible as far as the induced magnetic field is small compared to that of the central body.