Polytropic spherical accretion flows on Schwarzschild black holes.

We study the Michel flow on a spherically symmetric black hole background for a polytropic equation of state. Based on standard tools from the theory of dynamical systems, we prove that for a polytropic index γ lying between 1 < γ ≤ 5/3 there exists a unique accretion flow for a given particle density number at infinity. This number can be matched to the density of the interstellar medium. [ABSTRACT FROM AUTHOR]