Thermal Equilibrium Solutions of Black Hole Accretion Flows: Outflows VS Advection

TL;DR

This paper investigates the thermal equilibrium states of black hole accretion flows, highlighting the dominance of outflows over advection in most regions, which aligns with numerical simulations and suggests a common radial structure.

Contribution

It introduces a comparison of outflow and advection cooling rates in accretion flows, emphasizing the significance of outflows beyond the inner region, extending understanding of flow structures.

Findings

Outflows dominate over advection in most of the flow, except near the inner region.

The radial distribution typically features an advection-dominated inner zone and an outflow-dominated outer zone.

Results agree with previous numerical simulations and apply to various accretion regimes.

Abstract

Observations and numerical simulations have shown that outflows generally exist in the accretion process. We revisit the thermal equilibrium solutions of black hole accretion flows by including the role of outflows. Our study focuses on the comparison of the cooling rate of outflows with that of advection. Our results show that, except for the inner region, outflows can dominate over advection in a wide range of the flow, which is in good agreement with previous numerical simulations. We argue that an advection-dominated inner region together with an outflow-dominated outer region should be a general radial distribution for both super-Eddington accretion flows and optically thin flows with low accretion rates.