Rossby Vortices in Thin Magnetized Accretion Discs

TL;DR

This paper investigates how magnetic fields influence Rossby wave instability in thin accretion disks, revealing suppression effects at certain plasma beta values and magnetic field configurations that could be observable.

Contribution

It demonstrates the impact of toroidal magnetic fields on RWI growth rates and vortex evolution in magnetized accretion disks using MHD simulations.

Findings

Magnetic fields suppress RWI growth at plasma beta between 10 and 1000.

Vortices twist and expel magnetic fields, creating observable polarized dust emission signatures.

Magnetic effects are negligible at high plasma beta (>1000).

Abstract

We study the Rossby wave instability (RWI) in a thin accretion disc threaded by an initially toroidal magnetic field using the magnetohydrodynamics (MHD) code PLUTO. We find that for plasma $10^1 < \beta < 10^3$ , the growth rate and late-time density are suppressed, whereas for plasma $\beta > 10^3$, the magnetic field has negligible effect. The initially toroidal field is twisted inside the vortex and expelled at late times. This creates a radially directed field outside the vortex region, which can be understood via a simple kinematic model of a magnetic field in a rotating fluid and may be observable via polarised dust emission.