Schr\"odinger and Klein-Gordon theories of black holes from the quantization of the Oppenheimer and Snyder gravitational collapse

The Schr\"odinger equation of the Schwarzschild black hole (BH) shows that a BH is composed of a particle, the "electron", interacting with a central field, the "nucleus". Via de Broglie's hypothesis, one interprets the "electron" in terms of BH horizon's modes. Quantum gravity effects modify the BH semi-classical structure at the Schwarzschild scale rather than at the Planck scale. The analogy between this BH Schr\"odinger equation and the Schr\"odinger equation of the s states of the hydrogen atom permits us to solve the same equation. Therefore, BHs are well defined quantum gravitational systems obeying Schr\"odinger's theory: the "gravitational hydrogen atoms". By identifying the potential energy in the BH Schr\"odinger equation as being the gravitational energy of a spherically symmetric shell, a different nature of the quantum BH seems to surface. BHs are self-interacting, highly excited, spherically symmetric, massive quantum shells generated by matter condensing on the apparent horizon, concretely realizing the membrane paradigm. The quantum BH descripted as a "gravitational hydrogen atom" is a fictitious mathematical representation of the real, quantum BH, a quantum massive shell having as radius the oscillating gravitational radius. Nontrivial consequences emerge from this result: i) BHs have neither horizons nor singularities; ii) there is neither information loss in BH evaporation, nor BH complementarity, nor firewall paradox. These results are consistent with previous ones by Hawking, Vaz, Mitra and others. Finally, the special relativistic corrections to the BH Schr\"odinger equation give the BH Klein-Gordon equation and the corresponding eigenvalues.