2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/95315The black hole as the thermodynamical system in equilibrium possesses the periodicity of motion in imaginary time, that allows us to formulate the quasi-classical rule of quantization. The rule yields the equidistant spectrum for the entropy of non-rotating black holes as well as for the appropriately scaled entropy in the case of rotation. We clarify and discuss a role of quasi-normal modes.5 pages, RevTeX4 class; v2, v3: references addedGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext