Strongly magnetized accretion with low angular momentum produces a weak jet

TL;DR

This study uses general relativistic magnetohydrodynamic simulations to show that low angular momentum accretion onto supermassive black holes suppresses jet formation, while angular momentum can enable powerful jets, highlighting the role of turbulence and feedback.

Contribution

It demonstrates that magnetic turbulence from black hole feedback suppresses jets in low angular momentum accretion, challenging the assumption that magnetic flux always leads to strong jets.

Findings

Low angular momentum accretion suppresses jet formation due to turbulence.

Angular momentum in inflowing gas enables powerful jets by suppressing turbulence.

States with low angular momentum may resemble conditions near Sgr A*.

Abstract

We study the spherical accretion of magnetized plasma with low angular momentum onto a supermassive black hole, utilizing global general relativistic magnetohydrodynamic simulations. Black hole-driven feedback in the form of magnetic eruptions and jets triggers magnetized turbulence in the surrounding medium. We find that when the Bondi radius exceeds a certain value relative to the black hole's gravitational radius, this turbulence restricts the subsequent inflow of magnetic flux, strongly suppressing the strength of the jet. Consequently, magnetically arrested disks and powerful jets are not a generic outcome of the accretion of magnetized plasma, even if there is an abundance of magnetic flux available in the system. However, if there is significant angular momentum in the inflowing gas, the eruption-driven turbulence is suppressed (sheared out), allowing for the presence of a powerful jet. Both the initially rotating and nonrotating flows go through periods of low and high gas angular momentum, showing that the angular momentum content of the inflowing gas is not just a feature of the ambient medium, but is strongly modified by the eruption and jet-driven black hole feedback. In the lower-angular-momentum states, our results predict that there should be dynamically strong magnetic fields on horizon scales, but no powerful jet; this state may be consistent with Sgr A* in the Galactic center.