Transonic black hole accretion disks: A unified model for optically thin and thick disks

We obtain a class of semianalytic global accretion disk solutions around a Newtonian point mass that have a transonic nature. These solutions are automatically optically thin in the inner region and optically thick in the outer region. They approach a self-similar limit very close to the standard Shakura-Sunyaev disk at the outer boundary. These solutions illustrate from first principles the relation of the disk optical depth profile to the global boundary conditions and viscosity alpha.