Accretion to Magnetized Stars through the Rayleigh-Taylor Instability: Global Three-Dimensional Simulations

TL;DR

This paper uses 3D MHD simulations to study Rayleigh-Taylor instabilities at the boundary of accretion disks and magnetized stars, revealing complex plasma tongue structures and chaotic hot spots that impact observable phenomena.

Contribution

It provides the first detailed 3D simulation analysis of Rayleigh-Taylor instability effects on accretion processes at the disk-magnetosphere boundary.

Findings

Rayleigh-Taylor instability causes plasma tongues near the equator.

Hot spots during instability are more chaotic than in stable accretion.

Instability is linked to higher accretion rates and small misalignment angles.

Abstract

We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It manifests itself in the form of tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and number of the tongues changes with time on the inner-disk dynamical timescale. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator. The instability appears for relatively small misalignment angles, $\Theta\lesssim30^\circ$, between the star's rotation and magnetic axes, and is associated with higher accretion rates. The hot spots and light curves during accretion through instability are generally much more chaotic than during stable accretion. The unstable state of accretion has possible implications for quasi-periodic oscillations and intermittent pulsations from accreting systems, as well as planet migration.