Highly condensed gaseous objects with masses larger than 5 \cdot 10 ^ { 4 } M _ { \odot } are called super-massive stars .
They are thought to be possible precursors of super-massive black holes in the centres of galaxies .
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 \etal [ ] ) , has three different effects on the two-component system : 1 ) The gas is heated by decelerating the stars .
This may stall the contraction process for a while until the stars in the ’ loss cone ’ , these which cross the SMS , lost their kinetic energy ( for the total heating rate see Amaro-Seoane & Spurzem [ ] ) .
2 ) This cooling of the loss cone stars lead to a mass segregation in the stellar component resulting in a much more condensed central stellar core .
3 ) The inhomogeneities due to the gravitational wakes in the gas changes the effective absorption coefficient of the gas .
This affects the condition for hydrostatic equilibrium and may give essential deviations from the n = 3 
polytrope .
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 .