in general relativity. The reason I mention this is because any discussion about less than r=2M (the Schwarzchild radius for the distance from the singularity to the event horizon) is speculative. But we can use solutions based on general realtivity to intelligently speculate about < r=2M (its written this way because M is expressed in geometric units {length}). Those solutions have the mass of the hole centrally located at a infintesimally small space while the rest of the space inside the horizon has a vacuum solution.