General relativistic magnetohydrodynamic simulations of collapsars: Rotating black hole cases

We have performed 2.5-dimensional general relativistic magnetohy-drodynamic (MHD) simulations of collapsars including a rotating black hole. Initially, we assume that the core collapse has failed in this star. A rotating black hole of a few solar masses is inserted by hand into the calculation. The simulation results show the formation of a disklike structure and the generation of a jetlike outflow near the central black hole. The jetlike outflow propagates and accelerated mainly by the magnetic field. The total jet velocity is ∼ 0.3c. When the rotation of the black hole is faster, the magnetic field is twisted strongly owing to the frame-dragging effect. The magnetic energy stored by the twisting magnetic field is directly converted to kinetic energy of the jet rather than propagating as an Alfvén wave. Thus, as the rotation of the black hole becomes faster, the poloidal velocity of the jet becomes faster.