Strong field Gravity and Black Holes: Images, Quasi-Normal modes, Binaries – StronG

The possibilities of detecting gravitational waves emitted by binaries of compact objects and of "observing" the images of galactic black holes are revolutionizing the physics of space-time. They give a direct access to regions where the gravitational field is extremely strong and they allow the study of phenomena that escaped us until then. They also open the perspective of testing general relativity in a still unexplored regime and of highlighting, for the first time, its limits. The purpose of this project is to study gravity in a strong field regime (at the vicinity of black holes and neutron stars) in order to test the theory in this area. One could expect deviations. For this, it is always very interesting to consider modifications to general relativity in order to predict deviations in the metric, in the quasi-normal modes or in the emission of gravitational waves by binaries... which could be observed.

We will start by considering the largest (physically relevant) class of tensor-scalar theories to date in order to develop, test, and improve our both analytical and numerical methods. The idea will then be to rely on these models to extend these methods so that they apply to all types of modified theories of gravity in order to fully parameterize the space of possibly observable deviations from GR. We will then approach the experimental teams to compare the predictions of these theoretical calculations with the observations. It would be exceptional to observe deviations of the RG, deviations which could guide us towards a new physics. It would also be extremely important to constrain or to eliminate modifications of GR.