Magnetospheric Accretion and Ejection of Matter in Resistive Magnetohydrodynamic Simulations

TL;DR

This study uses resistive magnetohydrodynamic simulations to demonstrate the formation of micro-ejections from a resistive magnetosphere around young stellar objects, highlighting the roles of magnetic reconnection and physical resistivity.

Contribution

First to show that quasi-stationary micro-ejections can be launched purely due to resistive effects and magnetic reconnection in magnetospheric accretion models.

Findings

Micro-ejections are produced by pressure and magnetic forces.

Mass flux of micro-ejections increases with magnetic field strength.

Micro-ejection flux is unaffected by disk to corona density ratio.

Abstract

The ejection of matter in the close vicinity of a young stellar object is investigated, treating the accretion disk as a gravitationally bound reservoir of matter. By solving the resistive MHD equations in 2D axisymmetry using our version of the Zeus-3D code with newly implemented resistivity, we study the effect of magnetic diffusivity in the magnetospheric accretion-ejection mechanism. Physical resistivity was included in the whole computational domain so that reconnection is enabled by the physical as well as the numerical resistivity. We show, for the first time, that quasi-stationary fast ejecta of matter, which we call {\em micro-ejections}, of small mass and angular momentum fluxes, can be launched from a purely resistive magnetosphere. They are produced by a combination of pressure gradient and magnetic forces, in presence of ongoing magnetic reconnection along the boundary layer between the star and the disk, where a current sheet is formed. Mass flux of micro-ejection increases with increasing magnetic field strength and stellar rotation rate, and is not dependent on the disk to corona density ratio and amount of resistivity.