Magnetically Driven Accretion in the Kerr Metric. III. Unbound Outflows

We have carried out fully relativistic numerical simulations of accretion disks in the Kerr metric. In this paper we focus on the unbound outflows that emerge self-consistently from the accretion flow. These outflows are found in the axial funnel region and consist of two components: a hot, fast, tenuous outflow in the axial funnel proper and a colder, slower, denser jet along the funnel wall. The funnel-wall jet is excluded from the axial funnel by elevated angular momentum and is also pressure-confined by a magnetized corona. Inside the funnel, a large-scale poloidal magnetic field spontaneously arises from the coupled dynamics of accretion and outflow, although there was no large-scale field in the initial state. Black hole rotation is not required to produce these unbound outflows, but their strength is enhanced by black hole spin. When the black hole spins rapidly, the energy ejected can be tens of percent of the accreted rest mass. At low spin, kinetic energy and enthalpy of the matter dominate the outflow energetics; at high spin, the balance shifts to Poynting flux. We compare the outflows observed in our simulations with those seen in other simulations.