Energy extraction from a rotating black hole via magnetic reconnection: parameters in reconnection models

TL;DR

This paper extends models of energy extraction from rotating black holes via magnetic reconnection by treating key parameters as free variables, analyzing their effects, and proposing a weighted covering factor to better represent real astrophysical scenarios.

Contribution

It introduces a more flexible theoretical model with free parameters and a new weighted covering factor to better match real astrophysical conditions.

Findings

Energy extraction depends on geometric index and guide field fraction.

The weighted covering factor provides a comprehensive measure of energy extraction capability.

Reconnection parameters significantly influence the efficiency of energy extraction.

Abstract

Works on the energy extraction from a rotating black hole via magnetic reconnection attract more attentions in recent years. Discussions on this topic, however, are often based on many simplifications, such as assuming a circularly flowing bulk plasma and a fixed orientation angle. A significant gap remains between theoretical models and the magnetic reconnection occurring in real astrophysical scenarios. In our previous work, we investigated the influence of orientation angle on energy extraction and figured out the differences between the plunging and circularly flowing bulk plasma. We introduced the concept of covering factor to quantify the capability of an accretion system in extracting energy via magnetic reconnection from a rotating black hole. In this work, as an improvement, we extend our discussions by treating the parameters in reconnection models as free parameters, bringing the theoretical model closer to the situations in real astrophysical systems. We employ two reconnection models, in which the geometric index and the guide field fraction are respectively induced. We separately present the dependences of energy extraction on the geometric index and the guide field fraction. More importantly, we propose to define the averaged covering factor weighted by reconnection rate to quantify the overall capability of an accretion system in extracting energy via magnetic reconnection from a rotating black hole, under the assumption that the magnetic reconnection process occurs stochastically and randomly within the ergosphere.