THE GRAVITOMAGNETIC DYNAMO EFFECT IN ACCRETION DISKS OF ROTATING BLACK-HOLES

We present a previously unknown dynamo effect that arises from the cou pling of the gravitomagnetic held of a Kerr black hole with electromag netic fields. The axisymmetric dynamo equations are derived in the 3 1 split of Kerr spacetime. They are formally identical to their equiv alents in flat space, augmented by a general relativistic source term for the poloidal magnetic field provided by the gravitomagnetic held. There is no need for any particular small-scale plasma motions. The ef fect does, however, require finite conductivity and is enhanced by ana omalous or turbulent magnetic diffusivity. The results of our time-dep endent numerical simulations of the mean field dynamo in a turbulent a ccretion disk prove that the gravitomagnetic dynamo has growing modes in the vicinity of a rotating black hole.