Event horizons under the effect of the Penrose process

Abstract

We investigate how test particles absorbed by a black hole affect the properties of the event horizon. We consider particles that arrive from infinity with positive energy and cross the horizon. We also study the absorption of particles with negative energy, which are generated inside the ergosphere as the result of the decay of other particles, following the dynamics of the Penrose process. We show that, in general, the absorption process leads to an increase in the horizon radius and, consequently, of any physical quantity that is proportional to the horizon radius, such as the irreducible mass or the entropy.