Three-Dimensional Simulations of Magnetized Thin Accretion Disks around Black Holes: Stress in the Plunging Region

TL;DR

This study uses 3D general relativistic magnetohydrodynamic simulations to analyze stress and angular momentum transfer in thin accretion disks around non-spinning black holes, finding minimal magnetic coupling at the ISCO.

Contribution

It provides the first detailed 3D GRMHD simulation results showing that magnetic stress at the ISCO is negligible for thin disks, supporting classical accretion disk models.

Findings

Angular momentum profile deviates less than 2% from standard models.

Magnetic torque at ISCO is about 2% of inward angular momentum flux.

Magnetic coupling across ISCO is insignificant for thin disks.

Abstract

We describe three-dimensional general relativistic magnetohydrodynamic simulations of a geometrically thin accretion disk around a non-spinning black hole. The disk has a thickness $h/r\sim0.05-0.1$ over the radial range $(2-20)GM/c^2$. In steady state, the specific angular momentum profile of the inflowing magnetized gas deviates by less than 2% from that of the standard thin disk model of Novikov & Thorne (1973). Also, the magnetic torque at the radius of the innermost stable circular orbit (ISCO) is only $\sim2%$ of the inward flux of angular momentum at this radius. Both results indicate that magnetic coupling across the ISCO is relatively unimportant for geometrically thin disks.