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

摘要

Geometrically thick tori with constant specific angular momentum have beenwidely used in the last decades to construct numerical models of accretionflows onto black holes. Such discs are prone to a global non-axisymmetrichydrodynamic instability, known as Papaloizou-Pringle instability (PPI), whichcan redistribute angular momentum and also lead to an emission of gravitationalwaves. It is, however, not clear yet how the development of the PPI is affectedby the presence of a magnetic field and by the concurrent development of themagnetorotational instability (MRI). We present a numerical analysis usingthree-dimensional GRMHD simulations of the interplay between the PPI and theMRI considering, for the first time, an analytical magnetized equilibriumsolution as initial condition. In the purely hydrodynamic case, the PPI selectsas expected the large-scale $m=1$ azimuthal mode as the fastest growing andnon-linearly dominant mode. However, when the torus is threaded by a weaktoroidal magnetic field, the development of the MRI leads to the suppression oflarge-scale modes and redistributes power across smaller scales. If the systemstarts with a significantly excited $m=1$ mode, the PPI can be dominant in atransient phase, before being ultimately quenched by the MRI. Such dynamics maywell be important in compact star mergers and tidal disruption events.