Local Stability of Strongly Magnetized Black Hole Tori

TL;DR

This paper studies the local stability of strongly magnetized relativistic tori around Kerr black holes, revealing an inherent non-axisymmetric magnetorotational instability confirmed by numerical and simulation analyses.

Contribution

It provides a combined numerical and analytical investigation into the stability of magnetized black hole tori, highlighting an intrinsic instability regardless of specific background parameters.

Findings

Identifies a universal non-axisymmetric magnetorotational instability in such tori.

Analytical and numerical results are consistent with 3D GRMHD simulations.

Demonstrates the instability's independence from gas-to-magnetic pressure ratio.

Abstract

We investigate the local stability of strongly magnetized relativistic tori orbiting Kerr black holes, for the case of a purely toroidal magnetic field topology. Our approach encompasses both solving the full dispersion relation numerically and solving a simplified analytic treatment. Both approaches indicate that such tori are subject to an unstable non-axisymmetric magnetorotational mode, regardless of such background properties as the gas-to-magnetic pressure ratio and specific angular momentum distribution. We demonstrate that our modal analysis matches well with what is seen in global, three-dimensional, general relativistic magnetohydrodynamic simulations.