Seminarium Teorii Względności i Grawitacji

The Newman-Janis algorithm originally allowed for the derivation of the Kerr-Newman black hole and a rederivation of the Kerr Black hole. Its generalizations can be used to mathematically generate rotating solutions from nonrotating spherically symmetric solutions within general relativity. However, the properties of the energy-momentum tensor in the rotating case may not correspond with what one might expect based on the spherical case. This talk presents information about the properties of the energy-momentum tensors for the popular Gurses-Gursey generalization of the algorithm for Kerr-Schild systems, and for the more general Drake-Szekeres generalization. In particular, we find a specific equation of state which is preserved when passing to the rotating system with the Gurses-Gursey generalization, and show that the Drake-Szekeres method can result in energy-momentum tensors with unusual properties such as complex eigenvalues.