  Highly condensed gaseous objects with masses larger than 5x10^4 M_sun are
called super-massive stars. In the quasistationary contraction phase, the
hydrostatic equilibrium is determined by radiation pressure and gravitation.
The global structure is that of an n=3 polytrope at the stability limit. Small
relativistic corrections for example can initiate a free fall collapse due to
the 'post Newtonian' instability. Since the outcome of the final collapse -A
super-massive black hole or hypernova- depends sensitively on the structure and
the size of the object, when the instability sets in, it is important to
investigate in more detail the contraction phase of the SMS. If the gaseous
object is embedded in a dense stellar system, the central star cluster, the
interaction and coupling of both components due to dynamical friction changes
the energy balance and evolution of the SMS dramatically. Dynamical friction
between stars and gas, which can be estimated semi-analytically (see Just et
al. 1986), has three different effects on the two-component system. We discuss
in which evolutionary stages and parameter range these interaction processes
are relevant and how they can influence the stability and evolution of the SMS.
