Collisionless Accretion of Finite-Angular-Momentum Plasma onto a Spinning Black Hole

TL;DR

This study presents the first fully kinetic simulations of collisionless plasma accretion onto a spinning black hole with finite angular momentum, revealing behaviors similar to magnetically arrested disks and insights into jet formation.

Contribution

It introduces a novel kinetic simulation approach for accretion flows with finite angular momentum, bridging the gap between fluid models and collisionless plasma physics.

Findings

Kinetic simulations reproduce MAD-like magnetic flux saturation.

Pressure anisotropy is regulated by kinetic instabilities.

No efficient matter penetration into the jet funnel observed.

Abstract

In low-luminosity active galactic nuclei like M87* and Sgr A*, the accretion disk around the central supermassive black hole is tenuous and collisionless. As a result, the usual ideal magnetohydrodynamics (MHD) approximation may not be applicable. In this Letter, we report on the first fully kinetic simulations of the accretion process where the plasma initially has finite angular momentum. The simulated accretion flow behaves remarkably similarly to the magnetically arrested disk (MAD) regime of ideal MHD, reproducing episodes of magnetic flux saturation and eruption typical of MADs. The resemblance to fluid models owes largely to kinetic instabilities, which regulate pressure anisotropy in the disk, allowing fluid terms to dominate the angular momentum transfer. In addition, by handling vacuum regions effectively, our kinetic approach probes the matter supply to the jet funnel. We observe no efficient penetration of the accreting material into this region, which suggests that a pair discharge may be required to sustain the Blandford-Znajek process.