**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.;