Single versus the Repetitive Penrose Process in a Kerr Black Hole.

Extracting the rotational energy from a Kerr black hole (BH) is one of the crucial topics in relativistic astrophysics. Here, we give special attention to the Penrose ballistic process based on the fission of a massive particle μ_{0} into two particles μ_{1} and μ_{2}, occurring in the ergosphere of a Kerr BH. Bardeen et al. indicated that for the process to occur, some additional "hydrodynamical forces or superstrong radiation reactions" were needed. Wald and Chandrasekhar further expanded this idea. This animosity convinced Piran and collaborators to move from a simple three-body system characterizing the original Penrose process to a many-body system. This many-body approach was further largely expanded by others, some questionable in their validity. Here, we return to the simplest original Penrose process and show that the solution of the equations of motion, imposing the turning point condition on their trajectories, leads to the rotational energy extraction from the BH expected by Penrose. The efficiency of energy extraction by a single process is quantified for three different single decay processes occurring, respectively, at r=1.2M, r=1.5M, and r=1.9M. An interesting repetitive model has been proposed by Misner et al. [Gravitation (W. H. Freeman, San Francisco, 1973)]. Indeed, it would appear that a repetitive sequence of 246 decays of the above injection process at r=1.2M and the corresponding ones at r=1.5M and r=1.9M could extract 100% of the rotational energy of the BH, so violating energy conservation. The accompanying article, accounting for the existence of the BH irreducible mass, introduces a nonlinear approach that avoids violating energy conservation and leads to a new energy extraction process.