Radial accretion flows on static spherically symmetric black holes

TL;DR

This paper studies steady radial matter inflow into static, spherically symmetric black holes, including deformations of Schwarzschild, analyzing flow behavior and deriving unique accretion solutions with specific physical parameters.

Contribution

It generalizes previous models by analyzing accretion on a broad class of static, spherically symmetric spacetimes, including alternative gravity solutions.

Findings

Existence of a unique steady accretion flow for given conditions

Determination of flow parameters like accretion and compression rates

Analysis of flow behavior in various background metrics

Abstract

We analyze the steady radial accretion of matter into a nonrotating black hole. Neglecting the self-gravity of the accreting matter, we consider a rather general class of static, spherically symmetric and asymptotically flat background spacetimes with a regular horizon. In addition to the Schwarzschild metric, this class contains certain deformation of it which could arise in alternative gravity theories or from solutions of the classical Einstein equations in the presence of external matter fields. Modeling the ambient matter surrounding the black hole by a relativistic perfect fluid, we reformulate the accretion problem as a dynamical system, and under rather general assumptions on the fluid equation of state, we determine the local and global qualitative behavior of its phase flow. Based on our analysis and generalizing previous work by Michel, we prove that for any given positive particle density number at infinity, there exists a unique radial, steady-state accretion flow which is regular at the horizon. We determine the physical parameters of the flow, including its accretion and compression rates, and discuss their dependency on the background metric.