Maximal efficiency of the collisional Penrose process with a spinning particle. II. Collision with a particle on the innermost stable circular orbit

We analyze the collisional Penrose process between a particle on the innermost stable circular orbit (ISCO) orbit around an extreme Kerr black hole and a particle impinging from infinity. We consider both cases with non-spinning and spinning particles. We evaluate the maximal efficiency, η_max=(extracted energy)/(input energy), for the elastic collision of two massive particles and for the photoemission process, in which the ISCO particle will escape to infinity after a collision with a massless impinging particle. For non-spinning particles, the maximum efficiency is η_max\approx 2.562 for the elastic collision and η_max\approx 7 for the photoemission process. For spinning particles we obtain the maximal efficiency η_max\approx 8.442 for the elastic collision and η_max\approx 12.54 for the photoemission process.