MRI: a possible mechanism for funnel flows?

TL;DR

This paper explores how diamagnetic effects influence the magnetorotational instability (MRI) and its potential role in guiding plasma from accretion disks to funnel flows in classical T Tauri stars, using advanced magnetohydrodynamic modeling.

Contribution

It introduces a novel model incorporating diamagnetic effects into MRI, revealing a non-propagating mode that can lift plasma along magnetic field lines, and highlights the significance of magnetic and velocity gradients in MRI activation.

Findings

Diamagnetic effects modify MRI to produce a non-propagating mode.

Magnetic and velocity gradients enhance MRI's power.

Diamagnetic effects are crucial in triggering MRI at the disk-magnetosphere boundary.

Abstract

The magnetorotational instability (MRI) has been suggested to have an important role on the dynamics of accretion disks. We investigate MRI as an alternative way for guiding the plasma from the disk to the funnel flow at the disk-magnetosphere boundary of classical T Tauri stars (CTTSs) by considering the diamagnetic effects. We solve the magnetohydrodynamic equations by including the effect of both the magnetic field gradient and the perpendicular (to the field) velocity gradient produced by the magnetization current at the disk-magnetosphere boundary for the first time. Diamagnetic current modified MRI produces a non-propagating mode which may lift the plasma from the disk towards the vertical magnetic field lines. Our model also shows that the diamagnetic effects play an important role in triggering the MRI. The instability becomes more powerful with the inclusion of the gradient in the magnetic field and the perpendicular velocity.