Global Simulations of Differentially Rotating Magnetized Disks : Formation of Low-Beta Filaments and Structured Corona

Abstract

We present the results of three-dimensional global magnetohydrodynamic (MHD) simulations of the Parker-shearing instability in a differentially rotating torus initially threaded by toroidal magnetic fields. An equilibrium model of magnetized torus is adopted as an initial condition. When $β_0 = P_{\rm gas}/P_{\rm mag} \sim 1$ at the initial state, magnetic flux buoyantly escapes from the disk and creates loop-like structures similar to those in the solar corona. Inside the torus, growth of non-axisymmetric magneto-rotational (or Balbus & Hawley) instability generates magnetic turbulence. Magnetic field lines are tangled in small scale but in large scale they show low azimuthal wave number spiral structure. After several rotation period, the system oscillates around a state with $β\sim 5$. We found that magnetic pressure dominated ($β< 1$) filaments are created in the torus. The volume filling factor of the region where $β\leq 0.3$ is 2-10%. Magnetic energy release in such low-$β$ regions may lead to violent flaring activities in accretion disks and in galactic gas disks.