Thin accretion disks are stabilized by a strong magnetic field

TL;DR

This study uses 3D simulations to demonstrate that strongly magnetized thin accretion disks around black holes are stable against thermal instability, are thicker than standard models predict, and have similar efficiency despite internal dissipation.

Contribution

It provides the first simulation-based evidence that magnetic pressure stabilizes thin accretion disks, challenging traditional thermal instability assumptions.

Findings

Magnetically dominated disks are thermally stable.

Disks are thicker than standard predictions.

Accretion efficiency matches standard model estimates.

Abstract

By studying three-dimensional, radiative, global simulations of sub-Eddington, geometrically thin black hole accretion flows we show that thin disks which are dominated by magnetic pressure are stable against thermal instability. Such disks are thicker than predicted by the standard model and show significant amount of dissipation inside the marginally stable orbit. Radiation released in this region, however, does not escape to infinity but is advected into the black hole. We find that the resulting accretion efficiency ($5.5\pm0.5\%$ for the simulated $0.8\dot M_{\rm Edd}$ disk) is very close to the predicted by the standard model ($5.7\%$).