See also my article on Wormholes.
Roy Kerr, in 1963, found another solution to Einstein’s equations. Kerr’s idea is that any collapsing star should rotate. Rotating stars would accelerate as they begin to collapse. Kerr’s idea was that a rotating massive star, when it collapses, does not form a point. However, it forms a ring. The distinction lies in whether you approach the ring from the side or from the top or bottom. If one were shot to the ring’s side, you would be crushed at infinite spacetime curvature. However, if one approached this Kerr ring singularity from the top or bottom, you would experience strong gravity, however, not infinite. This means that one could, in principle, survive gravitational field at black hole’s center and tunnel right through to the mirror universe. The Kerr black hole could be a gateway to another universe!
Roy Kerr
An example of the structure of the rotating black hole and it's ring-like singularity.