  Parikh and Wilczek have shown that Hawking radiation's spectrum cannot be
strictly thermal. Such a non-strictly thermal character implies that the
spectrum is also not strictly continuous and thus generates a natural
correspondence between Hawking radiation and black hole's quasinormal modes.
This issue endorses the idea that, in an underlying unitary quantum gravity
theory, black holes result highly excited states. We use this key point to
re-analyze the spectrum of black hole's quasinormal modes by introducing a
black hole's effective temperature. Our analysis changes the physical
understanding of such a spectrum and enables a re-examination of various
results in the literature which realizes important modifies on quantum physics
of black holes. In particular, the formula of the horizon's area quantization
and the number of quanta of area are modified becoming functions of the quantum
"overtone" number n. Consequently, Bekenstein-Hawking entropy, its sub-leading
corrections and the number of microstates, i.e. quantities which are
fundamental to realize unitary quantum gravity theory, are also modified. They
become functions of the quantum overtone number too. Previous results in the
literature are re-obtained in the very large n limit.
