The gravitomagnetic dynamo in accretion disks of rotating black holes

In previous papers (Khanna & Camenzind 1994, 1995, in the following Paper I, II) we have formulated the axisymmetric kinematic dynamo problem for the innermost region of an accretion disk around a rotating black hole in the context of general relativity. We found that the differentially rotating space around a rotating black hole introduces a general relativistic source term for the poloidal magnetic field (the gravitomagnetic dynamo term), which, together with the differentially rotating disk plasma, can lead to self-excited dynamo action in a resistive accretion disk. This means that Cowling's anti-dynamo theorem does not hold in Kerr spacetime. Here, the equations of the axisymmetric kinematic dynamo problem in the 3+1 split of the Kerr metric are reviewed. New time-dependent simulations of the gravitomagnetic dynamo are presented, showing that the poloidal velocity field of the accretion flow, (v) over right arrow(p), strongly influences the dominant mode of the gravitomagnetic dynamo. With a realistic choice of (v) over right arrow(p) the metastable state of the dipolar magnetosphere built up by the dynamo, can be extended In time by a factor of two.