Can the BZ mechanism power steady jets?

TL;DR

This paper questions the effectiveness of the Blandford-Znajek mechanism in powering jets, highlighting how black hole charge neutralizes the electric fields needed, and suggests accretion disc energy as the primary jet source.

Contribution

It introduces the impact of black hole charge on the BZ mechanism and argues that accretion disc energy likely powers jets across various astrophysical objects.

Findings

Black hole charge neutralizes electric fields in the BZ mechanism.

Jets are more likely powered by accretion disc energy than black hole spin.

The BZ mechanism may not be the primary jet driver in many systems.

Abstract

We consider the Blandford-Znajek (BZ) mechanism for extracting black hole spin energy to drive astrophysical jets. Analyses of the BZ mechanism generally take no account of any electric charge on the black hole. But, as noted by Wald and others, if the medium surrounding the black hole is an ionized plasma with mobile charges, then a spinning hole quickly acquires an electric charge. The effect of this charge is to nullify the electric field structures which drive the BZ mechanism. Since jets are now observed in a wide variety of classes of accreting objects, most of which do not contain a central black hole, it seems likely that the jet driving mechanism in all astrophysical objects uses energy directly from the accretion disc, rather than black hole spin.