Pseudospectrum and binary black hole merger transients

Abstract The merger phase of binary black hole coalescences is a transient between an initial oscillating regime (inspiral) and late exponentially damped (ringdown). In spite the non-linear character Einstein equations, dynamics presents surprisingly simple behaviour consistent with effective linearity. On other hand, energy loss through event horizon by scattering to infinity renders system non-conservative. Hence, infinitesimal generator (effective) linear non-selfadjoint operator. Qualitative features transients in driven (in general, non-normal) operators are captured pseudospectrum time generator. We propose as unifying framework thread together phases coalescences, from inspiral-merger transition up quasinormal mode ringdown.