Abstract The launching of astrophysical jets provides the most compelling observational evidence for direct extraction of black hole (BH) spin energy via the Blandford–Znajek (BZ) mechanism. While it is known that spinning Kerr BHs within general relativity (GR) follow the BZ jet power relation, the nature of BH energy extraction in general theories of gravity has not been adequately addressed. This study performs the first comprehensive investigation of the BZ jet power relation by utilizing a generalized BH spacetime geometry that describes parametric deviations from the Kerr metric of GR yet recovers the Kerr metric in the limit where all deviation parameters vanish. Through performing and analyzing an extensive suite of three-dimensional covariant magnetohydrodynamics simulations of magnetized gas accretion onto these generalized BH spacetimes, we find that the BZ jet power relation still holds, in some instances yielding jet powers far in excess of what can be produced by even extremal Kerr BHs. It is shown that independent variation of the frame-dragging rate of the BH can enhance or suppress the effects of BH spin, and by extension, of frame-dragging. This variation greatly enhances or suppresses the observed jet power and underlying photon ring image asymmetry, introducing a previously unexplored yet important degeneracy in BH parameter inference. Finally, we show that sufficiently accurate measurements of the jet power, accretion rate, and photon ring properties from supermassive BHs can potentially break this degeneracy, highlighting the need of independent investigations of BH frame dragging from observations.
Chatterjee et al. (Wed,) studied this question.