General Relativistic MHD Jets

TL;DR

This paper reviews the theory and recent numerical simulations of relativistic jets launched by magnetic fields near rotating black holes, highlighting how simulations confirm key mechanisms and reveal dependencies on magnetic field geometry.

Contribution

It provides a comprehensive overview of the Blandford-Znajek mechanism and summarizes recent advances in numerical simulations of black hole jets, including their results and remaining challenges.

Findings

Simulations confirm Blandford-Znajek-like jet launching.

Jet luminosity relates to black hole spin and accretion rate.

Jet properties depend strongly on magnetic field geometry.

Abstract

Magnetic fields connecting the immediate environs of rotating black holes to large distances appear to be the most promising mechanism for launching relativistic jets, an idea first developed by Blandford and Znajek in the mid-1970s. To enable an understanding of this process, we provide a brief introduction to dynamics and electromagnetism in the spacetime near black holes. We then present a brief summary of the classical Blandford-Znajek mechanism and its conceptual foundations. Recently, it has become possible to study these effects in much greater detail using numerical simulation. After discussing which aspects of the problem can be handled well by numerical means and which aspects remain beyond the grasp of such methods, we summarize their results so far. Simulations have confirmed that processes akin to the classical Blandford-Znajek mechanism can launch powerful electromagnetically-dominated jets, and have shown how the jet luminosity can be related to black hole spin and concurrent accretion rate. However, they have also shown that the luminosity and variability of jets can depend strongly on magnetic field geometry. We close with a discussion of several important open questions.