  Solutions of the stationary axisymmetric Einstein equations describing the
interior of circularly rotating dust are investigated in order to study their
potential applicability as galaxy models. It is shown that such interior
solutions cannot be used as global metrics without becoming unphysical in
certain regions of space. Although definite results concerning the
non-existence of a continuation into a vacuum can only be derived for interior
solutions describing rigidly rotating dust, the present analysis exhibits that
the case of non-rigidly rotating dust would in general also be inadequate as a
physically reasonable galaxy model.
