The Effects of Gas Angular Momentum on the Formation of Magnetically Arrested Disks and the Launching of Powerful Jets

TL;DR

This study uses 3D relativistic magnetohydrodynamic simulations to explore how gas angular momentum influences the formation of magnetically arrested disks and the launching of powerful jets from black holes.

Contribution

It demonstrates that a minimum specific angular momentum is required for stable MAD formation and jet launching, and reveals jet behaviors in low-angular-momentum accretion flows.

Findings

High-efficiency jets (>100%) can be launched from sufficiently rotating flows.

Episodic jets with ~10% efficiency can occur even with low angular momentum.

Low-angular-momentum flows exhibit unique behaviors like different rotation directions and persistent outflows.

Abstract

In this letter, we investigate Bondi-like accretion flows with zero or low specific angular momentum by performing 3D general relativistic magnetohydrodynamic simulations. In order to check if relativistic jets can be launched magnetically from such flows, we insert a large-scale poloidal magnetic field into the accretion flow and consider a rapidly spinning black hole. We demonstrate that under such conditions the accretion flow needs to initially have specific angular momentum above a certain threshold to eventually reach and robustly sustain the magnetically arrested disk state. If the flow can reach such a state, it can launch very powerful jets at $\gtrsim 100\%$ energy efficiency. Interestingly, we also find that even when the accretion flow has initial specific angular momentum below the threshold, it can still launch episodic jets with an average energy efficiency of $\sim 10\%$. However, the accretion flow has nontypical behaviors such as having different rotation directions at different inclinations and exhibiting persistent outflows along the midplane even in the inner disk region. Our results give plausible explanations as to why jets can be produced from various astrophysical systems that likely lack large gas specific angular momenta, such as Sgr A*, wind-fed X-ray binaries, tidal disruption events, and long-duration gamma-ray bursts.