Choked accretion onto a Schwarzschild black hole: A hydrodynamical jet-launching mechanism

TL;DR

This paper introduces a new hydrodynamical model for accretion onto Schwarzschild black holes where breaking spherical symmetry causes inflow to choke and redirect excess material into bipolar outflows, potentially explaining jet formation.

Contribution

It presents a novel relativistic accretion mechanism involving symmetry breaking that leads to inflow-outflow configurations, supported by both analytic and numerical models.

Findings

Choked accretion occurs at a threshold rate similar to Bondi-Michel predictions.

The mechanism operates for both relativistic and Newtonian fluids.

Small density asymmetries can induce significant inflow-outflow morphology.

Abstract

We present a novel, relativistic accretion model for accretion onto a Schwarzschild black hole. This consists of a purely hydrodynamical mechanism in which, by breaking spherical symmetry, a radially accreting flow transitions into an inflow-outflow configuration. The spherical symmetry is broken by considering that the accreted material is more concentrated on an equatorial belt, leaving the polar regions relatively under-dense. What we have found is a flux-limited accretion regime in which, for a sufficiently large accretion rate, the incoming material chokes at a gravitational bottleneck and the excess flux is redirected by the density gradient as a bipolar outflow. The threshold value at which the accreting material chokes is of the order of the mass accretion rate found in the spherically symmetric case studied by Bondi and Michel. We describe the choked accretion mechanism first in terms of a general relativistic, analytic toy model based on the assumption of an ultrarelativistic stiff fluid. We then relax this approximation and, by means of numerical simulations, show that this mechanism can operate also for general polytropic fluids. Interestingly, the qualitative inflow-outflow morphology obtained appears as a generic result of the proposed symmetry break, across analytic and numeric results covering both the Newtonian and relativistic regimes. The qualitative change in the resulting steady state flow configuration appears even for a very small equatorial to polar density contrast ($\sim 0.1\,\%$) in the accretion profile. Finally, we discuss the applicability of this model as a jet-launching mechanism in different astrophysical settings.