Energy extraction via magnetic reconnection in magnetized black holes

TL;DR

This paper investigates the energy extraction process from magnetized black holes via magnetic reconnection, considering the magnetic field's backreaction on spacetime, and identifies optimal conditions for efficient energy extraction.

Contribution

It extends the Comisso-Asenjo mechanism by incorporating magnetic backreaction using the Kerr-Melvin metric, revealing the impact of magnetic field strength on energy extraction efficiency.

Findings

Stronger magnetic fields can enhance plasma magnetization but may hinder energy extraction due to backreaction.

An optimal moderate magnetic field maximizes energy extraction efficiency.

Excessively strong magnetic fields prevent circular orbits, limiting energy extraction.

Abstract

The Comisso-Asenjo mechanism is a novel mechanism proposed recently to extract energy from black holes through magnetic reconnection of the surrounding charged plasma, in which the magnetic field plays a crucial role. In this work, we revisit this process by taking into account the backreaction of the magnetic field on the black hole's geometry. We employ the Kerr-Melvin metric to describe the local near-horizon geometry of the magnetized black hole. By analyzing the circular orbits in the equatorial plane, energy extraction conditions, power and efficiency of the energy extraction, we found that while a stronger magnetic field can enhance plasma magnetization and aid energy extraction, its backreaction on the spacetime may hinder the process, with a larger magnetic field posing a greater obstacle. Balancing these effects, an optimal moderate magnetic field strength is found to be most conducive to energy extraction. Moreover, there is a maximum limit to the magnetic field strength associated with the black hole's spin, beyond which circular orbits in the equatorial plane are prohibited, thereby impeding energy extraction in the current scenario.