Gravitational fields of rotating disks and black holes

The two known exact solutions of Einstein's field equations describing rota ting objects of physical significance - a black hole and a rigidly rotating disk of dust - are discussed using a single mathematical framework related to Jacobi's inversion problem. Both solutions can be represented in such a form that they differ in the choice of a complex parameter and a real solu tion of the axisymmetric Laplace equation only. A recently found family of solutions describing differentially rotating dis ks of dust fits into the same scheme.