Accretion onto a black hole in a string cloud background

TL;DR

This paper analyzes how a string cloud background affects black hole accretion, deriving analytic solutions for accretion rate, flow parameters, and temperature profiles, showing increased accretion with higher string cloud parameter.

Contribution

It provides the first analytic solutions for spherically symmetric accretion onto a black hole in a string cloud background, including explicit dependence on the string cloud parameter.

Findings

Accretion rate increases with the string cloud parameter α.

Derived explicit formulas for accretion rate and critical radius.

Temperature profiles and gas compression ratios are obtained.

Abstract

We examine the accretion process onto the black hole with a string cloud background, where the horizon of the black hole has an enlarged radius $r_H=2 M/(1-\alpha)$, due to the string cloud parameter $\alpha\; (0 \leq \alpha < 1)$. The problem of stationary, spherically symmetric accretion of a polytropic fluid is analysed to obtain an analytic solution for such a perturbation. Generalised expressions for the accretion rate $\dot{M}$, critical radius $r_s$, and other flow parameters are found. The accretion rate $\dot{M}$ is an explicit function of the black hole mass $M$, as well as the gas boundary conditions and the string cloud parameter $\alpha$. We also find the gas compression ratios and temperature profiles below the accretion radius and at the event horizon. It is shown that the mass accretion rate, for both the relativistic and the non-relativistic fluid by a black hole in the string cloud model, increases with increase in $\alpha$.