  We explore the gravitational influence of pressure supported stellar systems
on the internal density distribution of a gaseous environment. We conclude that
compact massive star clusters with masses >= 10^6 M_sun act as cloud
condensation nuclei and are able to accrete gas recurrently from a warm
interstellar medium which may cause further star formation events and account
for multiple stellar populations in the most massive globular and nuclear star
clusters. The same analytical arguments can be used to decide whether an
arbitrary spherical stellar system is able to keep warm or hot interstellar
material or not. These mass thresholds coincide with transition masses between
pressure supported galaxies of different morphological types.
