In astrophysics, fluid solutions are often employed as "'stellar models "'. ( It might help to think of a perfect gas as a special case of a perfect fluid . ) In cosmology, fluid solutions are often used as cosmological models.
22.
There is no difficulty whatsoever in obtaining models of " static " spherically symmetric stellar models, in which a perfect fluid interior is matched across a spherical surface, the surface of the star, to a vacuum exterior which is in fact a region of the Schwarzschild vacuum.
