Perturbations of self-similar Bondi accretion

Abstract

The question of stability of steady spherical accretion has been studied for many years and, recently, the concept of spatial instability has been introduced. Here we study perturbations of steady spherical accretion flows (Bondi solutions), restricting ourselves to the case of self-similar flow, as a case amenable to analytic treatment and with physical interest. We further restrict ourselves to its acoustic perturbations. The radial perturbation equation can be solved in terms of Bessel functions. We study the formulation of adequate boundary conditions and decide for no matter-flux-perturbation conditions (at the Bondi radius and at r=0). We also consider the problem of initial conditions and time evolution, in particular, of radial perturbations. No spatial instability at r=0 is found. The time evolution is such that perturbations eventually become ergodic-like and show no trace of instability or of acquiring any remarkable pattern.