Efficient Generation of Jets from Magnetically Arrested Accretion on a Rapidly Spinning Black Hole

TL;DR

This paper uses advanced simulations to demonstrate how rapidly spinning black holes can produce powerful jets by extracting their rotational energy through magnetically arrested accretion, revealing efficiencies exceeding 100%.

Contribution

It presents the first detailed 3D GRMHD simulations showing energy extraction from a spinning black hole via the Penrose-Blandford-Znajek mechanism in a magnetically arrested disc.

Findings

Efficiency of jet production reaches ~30% for moderate spin (a=0.5).

Efficiency exceeds 100% for high spin (a=0.99), indicating energy extraction from the black hole.

Magnetically arrested accretion can explain high-efficiency jets in active galactic nuclei.

Abstract

We describe global, 3D, time-dependent, non-radiative, general-relativistic, magnetohydrodynamic simulations of accreting black holes (BHs). The simulations are designed to transport a large amount of magnetic flux to the center, more than the accreting gas can force into the BH. The excess magnetic flux remains outside the BH, impedes accretion, and leads to a magnetically arrested disc. We find powerful outflows. For a BH with spin parameter a = 0.5, the efficiency with which the accretion system generates outflowing energy in jets and winds is eta ~ 30%. For a = 0.99, we find eta ~ 140%, which means that more energy flows out of the BH than flows in. The only way this can happen is by extracting spin energy from the BH. Thus the a = 0.99 simulation represents an unambiguous demonstration, within an astrophysically plausible scenario, of the extraction of net energy from a spinning BH via the Penrose-Blandford-Znajek mechanism. We suggest that magnetically arrested accretion might explain observations of active galactic nuclei with apparent eta ~ few x 100%.