QUASI-SPHERICAL LIGHT CONES OF THE KERR GEOMETRY

Quasi-spherical light cones are lightlike hypersurfaces of the Kerr ge ometry that are asymptotic to Minkowski light cones at infinity. We de rive the equations of these surfaces and examine their properties. In particular, we show that they are free of caustics for all positive va lues of the Kerr radial coordinate r. Useful applications include the propagation of high-frequency waves, the definition of Kruskal-like co ordinates for a spinning black hole and the characteristic initial-val ue problem.