A Structure Model for Black Holes: Atomic-like Structure, Quantization   and the Minimum Schwarzschild Radius
  A structure model for black holes is proposed by mean field approximation of gravity. The model, which consists of a charged singularity at the center and quantum fluctuation of fields around the singularity, is similar to the atomic structure. The model naturally quantizes the black hole. Especially we find the minimum black hole, whose structure is similar to the hydrogen atom and whose Schwarzschild radius becomes about 1.1287 of the Planck length. 
Yukinori Nagatani (Okayama Inst. Quantum Phys.)