Accretion of supersonic winds onto black holes in 3D: stability of the shock cone

TL;DR

This study uses 3D numerical simulations to analyze the stability of shock cones formed by supersonic winds accreting onto rotating black holes, confirming stability in regimes previously thought unstable.

Contribution

First 3D simulations confirming shock cone stability and testing flip-flop instability under various conditions around rotating black holes.

Findings

Shock cones remained stable in all tested scenarios.

No flip-flop instability was observed despite conditions favoring it.

Numerical errors and velocity perturbations did not trigger instability.

Abstract

Using numerical simulations we present the accretion of supersonic winds onto a rotating black hole in three dimensions. We study five representative directions of the wind with respect to the axis of rotation of the black hole and focus on the evolution and stability of the high density shock cone that is formed during the process. We explore both, the regime in which the shock cone is expected to be stable in order to confirm previous results obtained with two dimensional simulations, and the regime in which the shock cone is expected to show a flip-flop type of instability. The methods used to attempt triggering the instability were first the accumulation of numerical errors and second the explicit application of a perturbation on the velocity field after the shock-cone was formed. The result is negative, that is, we did not find the flip-flop instability within the parameter space we explored, which includes cases that are expected to be unstable.