New facets of the Penrose process: Black hole bomb with massive particles and particle decay near a naked singularity

Abstract:
We consider the decay of a particle with some energy E_0 > 0 inside the ergosphere of a black hole. After the first decay, one of the particles with the energy E_1 < 0 falls toward the black hole, while the second particle with E_2 > E_0 moves in the outward direction. The second particle bounces back from a reflecting shell and the process repeats itself.

For radial motion of charged particles in the Reissner-Nordström black hole spacetime, the result depends strongly on the concrete scenario that one might consider. In particular, an indefinitely large growth of energy inside the shell is possible, such that it gives rise to a black hole bomb. We also consider a similar multiple process with neutral particles in the background of a rotating axially symmetric stationary dirty black hole.

We demonstrate that if particle decay occurs in a turning point, the black hole bomb in this case is impossible. For a generic point inside the ergoregion, there is a condition for the black hole bomb to exist. This condition relates the ratio of masses before and after decay and the velocity of the fragments in the center of mass frame. We also analyze a complementary case when the metric represents a naked singularity and show that in this case a super-Penrose process is possible.