Spherically-symmetric Accretion onto a Black Hole at the Center of a Young Stellar Cluster

TL;DR

This paper develops a self-consistent model of spherically symmetric accretion flows onto a black hole at the center of a young stellar cluster, revealing how the flow regime depends on cluster parameters and identifying a critical luminosity that separates different accretion behaviors.

Contribution

It introduces a bimodal stationary solution for accretion flows influenced by young stellar clusters and a central black hole, highlighting the role of a critical luminosity in flow regimes.

Findings

Hydrodynamic flow depends on cluster parameters and a critical luminosity.

Below the threshold, flow separates into accretion and wind zones.

Above the threshold, catastrophic cooling inhibits stationary solutions.

Abstract

We present a self-consistent, bimodal stationary solution for spherically symmetric flows driven by young massive stellar clusters with a central supermassive black hole. We demonstrate that the hydrodynamic regime of the flow depends on the location of the cluster in the 3D (star cluster mechanical luminosity - BH mass - star cluster radius) parameter space. We show that a threshold mechanical luminosity (L_crit) separates clusters which evolve in the BH dominated regime frome those whose internal structure is strongly affected by the radiative cooling. In the first case(below the threshold energy) gravity of the BH separates the flow into two distinct zones: the inner accretion zone and the outer zone where the star cluster wind is formed. In the second case (above the critical luminosity), catastrophic cooling sets in inside the cluster. In this case the injected plasma becomes thermally unstable that inhibits a complete stationary solution. We compared the calculated accretion rates and the BH luminosities with those predicted by the classic Bondi accretion theory and found that Bondi's theory is in good agreement with our results in the case of low mass clusters. However, it substantially underestimates the accretion rates and BH luminosities if the star cluster mechanical luminosity, L_sc, approaches the threshold value (L_sc > 0.1 L_crit).