Papaloizou-Pringle instability suppression by the magnetorotational instability in relativistic accretion discs

TL;DR

This study uses 3D GRMHD simulations to investigate how magnetic fields and the magnetorotational instability suppress the Papaloizou-Pringle instability in relativistic accretion disks, revealing a complex interplay affecting disk dynamics.

Contribution

First numerical analysis of the interaction between PPI and MRI in magnetized relativistic accretion disks using an analytical equilibrium initial condition.

Findings

MRI suppresses large-scale PPI modes and redistributes power to smaller scales.

PPI can temporarily dominate if initially strongly excited but is ultimately quenched by MRI.

Magnetic fields influence the development and suppression of non-axisymmetric instabilities.

Abstract

Geometrically thick tori with constant specific angular momentum have been widely used in the last decades to construct numerical models of accretion flows onto black holes. Such discs are prone to a global non-axisymmetric hydrodynamic instability, known as Papaloizou-Pringle instability (PPI), which can redistribute angular momentum and also lead to an emission of gravitational waves. It is, however, not clear yet how the development of the PPI is affected by the presence of a magnetic field and by the concurrent development of the magnetorotational instability (MRI). We present a numerical analysis using three-dimensional GRMHD simulations of the interplay between the PPI and the MRI considering, for the first time, an analytical magnetized equilibrium solution as initial condition. In the purely hydrodynamic case, the PPI selects as expected the large-scale $m=1$ azimuthal mode as the fastest growing and non-linearly dominant mode. However, when the torus is threaded by a weak toroidal magnetic field, the development of the MRI leads to the suppression of large-scale modes and redistributes power across smaller scales. If the system starts with a significantly excited $m=1$ mode, the PPI can be dominant in a transient phase, before being ultimately quenched by the MRI. Such dynamics may well be important in compact star mergers and tidal disruption events.