Rossby Wave Instability in Accretion Discs with Large-Scale Poloidal Magnetic Fields

TL;DR

This paper investigates how large-scale poloidal magnetic fields influence the Rossby wave instability in accretion discs, revealing that magnetic fields can enhance the instability and potentially affect planetesimal formation and wind production.

Contribution

It demonstrates that magnetic fields, especially near equipartition, can significantly enhance the Rossby wave instability in accretion discs, extending understanding of disc dynamics.

Findings

Magnetic fields can increase RWI growth rate by up to 10% in thin discs.

Finite thickness discs with magnetic field gradients show RWI growth rate increase by a factor of ~2.

RWI can operate effectively in discs capable of producing magnetic winds.

Abstract

We study the effect of large-scale magnetic fields on the non-axisymmetric Rossby wave instability (RWI) in accretion discs. The instability develops around a density bump, which is likely present in the transition region between the active zone and dead zone of protoplanetary discs. Previous works suggest that the vortices resulting from the RWI may facilitate planetesimal formation and angular momentum transport. We consider discs threaded by a large-scale poloidal magnetic field, with a radial field component at the disc surface. Such field configurations may lead to the production of magnetic winds or jets. In general, the magnetic field can affect the RWI even when it is sub-thermal (plasma $\beta\sim 10$). For infinitely thin discs, the instability can be enhanced by about 10 percent. For discs with finite thickness, with a radial gradient of the magnetic field strength, the RWI growth rate can increase significantly (by a factor of $\sim 2$) as the field approaches equipartition ($\beta \sim 1$). Our result suggests that the RWI can continue to operate in discs that produce magnetic winds.