Hugo Candan :
Team : ASTRE
Supervisor : Philippe Grandclément
In recent years, several observations have shed new light on the nature of the compact objects in our Universe. One can mention the study of the environment of supermassive black holes by the instruments Gravity and the Event Horizon Telescope and also the observations of the gravitational waves emitted during the merger of two compact objects. If the current observations are consistent with the compact objects being black holes in General Relativity, there is hope, as they become more precise and numerous, that deviations from this paradigm could be unveiled. Such deviations could come from the fact that General Relativity is not the final theory describing gravity. Good candidates for alternative theories of gravity are scalar-tensor theories. It is rather interesting to study predictions of such theories about blackholes. To this day, very few rotating blackhole solutions have been found. But in nature, black holes always have a non-zero spin. The aim of the thesis is to investigate rotating black hole solutions in scalar-tensor theories. If such solutions are to be found, emphasis will be put on the study of quasi-normal modes, and the extraction of possible interesting observables.
