Causal extraction of black hole rotational energy by various kinds of electromagnetic fields

TL;DR

This paper clarifies the causal mechanism behind black hole rotational energy extraction via electromagnetic fields, emphasizing the role of negative electromagnetic energy in processes like the Blandford-Znajek mechanism.

Contribution

It introduces a formula that provides physical intuition for the causal extraction of black hole energy through electromagnetic processes, including the Blandford-Znajek mechanism.

Findings

Negative electromagnetic energy is crucial for causal energy extraction.

The paper offers a new formula linking electromagnetic energy to black hole spin energy.

Clarifies the causal interpretation of energy extraction mechanisms.

Abstract

Recent general relativistic MHD simulations have suggested that relativistic jets from active galactic nuclei (AGNs) have been powered by rotational energy of central black holes. Some mechanisms of extraction of black hole rotational energy have been proposed, like the Penrose process, Blandford-Znajek mechanism, MHD Penrose process, and superradiance. The Blandford-Znajek mechanism is the most promising mechanism for the engines of the relativistic jets from AGNs. However, an intuitive interpretation of this mechanism with causality is not clarified yet, while the Penrose process has a clear interpretation for the causal energy extraction from the black hole with negative energy. In this paper, we present a formula to build physical intuition so that in the Blandford-Znajek mechanism as well as other electromagnetic processes, negative electromagnetic energy plays an important role to extract the rotational energy of the black holes causally.