Relativistic Dyson Rings and Their Black Hole Limit

In this Letter, we investigate uniformly rotating, homogeneous, and axisymmetric relativistic fluid bodies with a toroidal shape. The corresponding field equations are solved by means of a multidomain spectral method, which yields highly accurate numerical solutions. For a prescribed, sufficiently large ratio of inner to outer coordinate radius, the toroids exhibit a continuous transition to the extreme Kerr black hole. Otherwise, the most relativistic configuration rotates at the mass-shedding limit. For a given mass density, there seems to be no bound to the gravitational mass as one approaches the black hole limit and a radius ratio of unity.