Modes of Accretion in X-ray Sources
  Three classical modes of accretion are briefly discussed: wind-fed, spherical, and disk. The three modes are illustrated with the mass transfer onto black holes in high-mass X-ray binaries. Then a new regime of mini-disk accretion is described and it is argued that observed wind-fed X-ray sources are likely to accrete in this regime. Switching from one accretion mode to another can cause the observed spectral state transitio ns. 
Andrei M. Beloborodov (CITA)