**Publication date:** May 1976

**Abstract:**

The motion of particles falling radially from rest at infinity with zero total angular momentum on to a rotating (Kerr) black hole is studied. The shell of such particles, initially spherical, becomes prolate along the axis of symmetry during the fall onto a rotating hole. The shape of the shell from the viewpoint of distant observers is studied by means of the photons moving along the (non-shearing) geodesics of the outgoing principal null congruence. The approach of the particles towards the horizon in terms of the arrival times of these photons to a distant observer, the redshift of the radiation and its intensity show dependence exponentially on the observer’s proper time as in the non-rotating case, however the characteristic e-folding times become infinite as the hole’s angular momentum approaches the extreme value. In the case of an extreme Kerr black hole these exponential laws go over into power laws.

**Authors:**

Bicak, J.; Stuchlik, Z.;