Three-Dimensional MHD Simulations of Accretion Disks and Jet Formation

Abstract

By using a parallelized three-dimensional magnetohydrodynamic (MHD) code based on an explicit finite differencing scheme, we carried out 3D MHD simulations of accretion disks. In weakly magnetized disks, magnetic fields are amplified due to the growth of the magneto-rotational (or Balbus & Hawley) instability. The field amplification saturates when N = Pga Pmag ~ 10 — 30. In strongly magnetized disks, the buoyancy instability coupled with differential rotation further amplifies magnetic fields. We also carried out global three-dimensional simulations of a torus threaded by large-scale vertical magnetic fields. We confirmed that a bipolar jet is formed and that the magnetic braking drives the avalanche-like accretion near the surface of the torus. Due to the growth of non-axisymmetric instabilities, helical structures appear both in the disk and in the jet.