Magnetic Pressure Dominance Stabilizes AGN Disks Against Gravitational Instability

TL;DR

This study demonstrates through MHD simulations that magnetic pressure in strongly magnetized AGN disks can effectively stabilize them against gravitational instability, highlighting a key stabilizing mechanism.

Contribution

The paper provides the first comprehensive simulation evidence that magnetic pressure dominance can stabilize AGN disks against GI, especially in strongly magnetized conditions.

Findings

Strong magnetization stabilizes disks against GI.

Magnetic pressure dominates in stabilized disks.

Weakly magnetized disks remain unstable.

Abstract

Magnetic effects have long been considered a possible factor in stabilizing the outer regions of active galactic nuclei (AGN) accretion disks against gravitational instability (GI). However, the computational demands of testing this hypothesis have prevented comprehensive study of this problem. Here, we present results from a suite of 6 isothermal magnetohydrodynamics (MHD) shearing box simulations, 3 initialized with strong magnetization ($\beta^{\rm{mid}}_{0} = p_{\rm{gas}} / p_{\rm{mag}} = 10^{2.5}$) and 3 initialized with weak magnetization ($\beta^{\rm mid}_{0} = 10^{4}$). For each magnetization, we performed simulations with both strong ($Q_{0} = 1.0$) and weak ($Q_{0} = 10.0$) self-gravity, where $Q_{0} = \frac{c_{\rm{s}}\Omega}{\pi G \Sigma_{0}}$ is the Toomre stability parameter; we also performed pure MHD simulations for comparison. We find that our strongly magnetized disk stabilized against GI after initialization to critical stability against GI, while our corresponding weakly magnetized disk did not. We show that the strongly magnetized, strongly self-gravitating disk became dominated by magnetic pressure, which led to its stabilization.