Non-modal effects in black hole perturbation theory

05.03.2025 11:30 – 12:30

The dynamics of linear perturbations of black hole spacetimes are often discussed in terms of quasinormal modes. However, quasinormal modes are eigenfunctions of a non-normal operator, for which the spectral theorem does not apply. I will show that, as a consequence, there are non-modal effects which can lead to large-amplitude growth of linear perturbations in finite time, despite all quasinormal modes decaying exponentially. In the example I will present, the physical mechanism is a transient form of superradiance, which is qualitatively similar to the transition to turbulence in Navier-Stokes shear flows.

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Bâtiment: Ecole de Physique

EP234

entrée libre