Gravitational waves observations have changed the way we study the cosmos and broaden our knowledge about one of the most energetic and cataclysmic processes in the Universe: compact binary coalescence. The aftermath of this collision is a nal black hole in a highly perturbed state. Equilibrium is reached through the radiation of the excess energy under the form of gravitational waves. This stage is known as ringdown and encodes information about the structure of the vibrating black hole. In this talk, I will discuss how the analysis of gravitational-wave ringdown signals, detected by the LIGO-Virgo network, has allowed to test funda- mental laws of physics, such as the no-hair theorem and the black hole area law.
Cosimo Nigro, César Jesús-Valls, Jan Ollé