Magnetocentrifugal launching of jets from discs around Kerr black holes

Strong magnetic fields modify particle motion in the curved space-time of spinning black holes and change the stability conditions of circular orbits. We study conditions for magneto-centrifugal jet launching from accretion discs around black holes, whereby large-scale black hole lines anchored in the disc may fling tenuous coronal gas outwards. For a Schwarzschild black hole, magnetocentrifugal launching requires that the poloidal component of magnetic fields makes an angle less than 60 degrees to the outward direction at the disc surface, similar to the Newtonian case. For prograde rotating discs around Kerr black holes, this angle increases and becomes 90 degrees for footpoints anchored to the disc near the horizon of a critically spinning a = M black hole. Thus, a disc around a critically spinning black hole may centrifugally launch a jet even along the rotation axis.