Universality of the Blandford-Znajek emission in stationary and axisymmetric spacetimes

TL;DR

This paper investigates the universality of the Blandford-Znajek mechanism across various black-hole spacetimes, revealing invariance at leading order and potential for probing strong-field properties in rapidly rotating black holes.

Contribution

It demonstrates that the lowest-order Blandford-Znajek power is universal across different black-hole spacetimes and explores how higher-order effects can distinguish black-hole properties.

Findings

Lowest-order BZ power is invariant across spacetimes.

Higher-order BZ luminosities vary with black-hole spacetime.

Rapidly rotating black holes can reveal strong-field spacetime features.

Abstract

The Blandford-Znajek (BZ) mechanism is widely recognised as the most compelling process to extract rotational energy from an accreting black hole and power the emission of relativistic jets. We explore the universality of this process for generic black-hole spacetimes within the Konoplya-Rezzolla-Zhidenko formalism and find that the lowest-order contribution to the BZ power is invariant across different black-hole spacetimes. We also show that at the next-leading-order, different black-hole spacetimes will lead to different BZ luminosities. As a result, while slowly rotating black holes cannot be distinguished via measurements of their jet power, rapidly rotating ones have the potential of providing information on the strong-field properties of the spacetime when independent measurements of the BZ luminosity and of the black-hole angular velocity are available.