Physical Interpretation of the Spectrum of Black Hole Quasinormal Modes

When a classical black hole is perturbed, its relaxation is governed by a set of quasinormal modes with complex frequencies =ₑ+i₈. We show that this behavior is the same as that of damped harmonic oscillators whose real frequencies are (ₑ^2+₈^2) ^1/2, rather than simply ₑ. Since, for highly excited modes, ₈ₑ, this observation changes drastically the physical understanding of the black hole spectrum and forces a reexamination of various results in the literature. In particular, adapting a derivation by Hod, we find that the area of the horizon of a Schwarzschild black hole is quantized in units =8l₏₋^2, in contrast with the original result =4log (3) l₏₋^2.