Realizability of stationary spherically symmetric transonic accretion
  The spherically symmetric stationary transonic (Bondi) flow is considered a classic example of an accretion flow. This flow, however, is along a separatrix, which is usually not physically realizable. We demonstrate, using a pedagogical example, that it is the dynamics which selects the transonic flow. 
Arnab K. Ray, J. K. Bhattacharjee