Nonaxisymmetric Effects in the Black Hole Accretion Inviscid Hydrodynamics: Formation and Evolution of a Tilted Torus

TL;DR

This study uses 3-D simulations to explore how nonaxisymmetric effects influence the formation and evolution of tilted tori in inviscid black hole accretion flows, revealing precession and complex flow behaviors.

Contribution

It introduces fully three-dimensional simulations of inviscid accretion flows with latitude- and azimuth-dependent angular momentum, highlighting effects like torus precession and the impact of non-rotating equatorial gas.

Findings

Torus precesses even in axisymmetric conditions.

Non-rotating equatorial gas can prevent proper torus formation.

Mass accretion rate remains close to the Bondi rate.

Abstract

We report on the fourth phase of our study of slightly rotating accretion flows onto black holes. The main new element of this study is that we used fully three dimensional (3-D) numerical simulations. We consider hydrodynamics of inviscid accretion flows. We assume a spherically symmetric density distribution at the outer boundary, but brake the flow symmetry by introducing a small, latitude-dependent angular momentum. We also consider cases where angular momentum at large radii is latitude- and azimuth-dependent. For the latitude-dependent angular momentum, 3-D simulations confirm axisymmetric results: the material that has too much angular momentum to be accreted forms a thick torus near the equator. Consequently, accretion proceeds only through the polar funnel, and the mass accretion rate through the funnel is constrained by the size and shape of the torus, not by the outer conditions. In 3-D simulations, we found that the torus precesses, even for axisymmetric conditions at large radii. For the latitude and azimuth-dependent angular momentum, the non-rotating gas near the equator can also significantly affect the evolution of the rotating gas. In particular, it may prevent the formation of a proper torus (i.e. its closing, in the azimuthal direction). In such models, the mass accretion rate is only slightly less than the corresponding Bondi rate.