Equation of state and transport processes in self-similar spheres - art. no. 024008

We study the effect of transport processes (diffusion and free streaming) o n a collapsing spherically symmetric distribution of matter in a self-simil ar space-time. A very simple-solution shows interesting features when it is matched with the Vaidya exterior solution. In the mixed case (diffusion an d free streaming), we find a barotropic equation of state in the stationary regime. In the diffusion approximation the gravitational potential at the surface is always constant; if we perturb the stationary state, the system is very stable, recovering the barotropic equation of state as time progres ses. In the free-streaming case the self-similar evolution is station ary, but with a nonbarotropic equation of state. [S0556-2821(98)07624-3].