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 omega=omega(R)+i omega(I). We show that this behavior is the same as that of damped harmonic oscillators whose real frequencies are (omega(2)(R)+omega(2)(I))(1/2), rather than simply omega(R). Since, for highly excited modes, omega(I)>omega(R), 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 Delta A=8 pi l(Pl)(2), in contrast with the original result Delta A=4log(3)l(Pl)(2).