Self-consistent Multidimensional Penrose Process Driven by Magnetic Reconnection

Abstract

Astronomical observations and numerical simulations are providing increasing evidence that resistive effects in plasmas around black holes (BHs) play an important role in determining the phenomenology observed from these objects. In this spirit, we present a general approach to the study of a Penrose process driven by plasmoids that are produced at reconnection sites along current sheets. Our formalism is meant to determine the physical conditions that make a plasmoid-driven Penrose process energetically viable, and can be applied to scenarios that are dominated by matter or magnetic field, that is, in magnetohydrodynamical or force-free descriptions. By exploring reconnection from an axisymmetric but curved surface, our approach can be considered genuinely multidimensional and allows us to explore conditions that are beyond the ones explored so far and that have been restricted to the equatorial plane. Furthermore, it provides a direct contact with numerical simulations of accretion onto BHs, which exhibit an intense reconnection activity outside the equatorial plane. Finally, to describe the kinematics of the plasma self-consistently, we use the well-known configuration of an equilibrium torus with a purely toroidal magnetic field. For such a torus, we discuss the existence of an “ergobelt,” i.e., a nontrivial surface penetrating the ergosphere and acting as a natural site for the occurrence of reconnection, and from where we estimate the energetics of a plasmoid-driven Penrose process.