Rayleigh-Taylor-Unstable Accretion and Variability of Magnetized Stars: Global Three-Dimensional Simulations

TL;DR

This paper uses 3D MHD simulations to study Rayleigh-Taylor instabilities at the disk-magnetosphere boundary, revealing chaotic accretion patterns and their potential impact on stellar variability.

Contribution

It provides the first detailed 3D simulation analysis of Rayleigh-Taylor instability-driven accretion in magnetized stars, highlighting its dependence on system parameters.

Findings

Instability leads to tall, thin plasma tongues near the equator.

Chaotic hot spots and light curves differ from stable accretion.

Instability occurs at small misalignment angles and higher accretion rates.

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 produces 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.