15 May 2023
Our Galactic Center: a laboratory to study fundamental physics and astrophysics in the strong field regime
Our Galactic Center Sagittarius A* harbors an extremely massive (4x 10^6 solar mass) and compact body that is currently identified as a supermassive black hole. This region of our Galaxy has been the subject of numerous astrometric and spectroscopic observations at various wavelengths for the last few decades. Recently, our Galactic Center has also become a laboratory to test the theory of general relativity. Indeed, observations of stars orbiting in a relativistic regime the central black hole have allowed to measure the gravitational redshift induced by the black hole, as well as the relativistic precession of the periastron. Moreover, the Event Horizon Telescope measurements have allowed to realize the first image of this black hole and also to test the theory of gravitation. Finally, the future LISA space mission will measure gravitational waves emitted by stars orbiting close to the black hole horizon, offering a unique opportunity to test relativity and to explore the distribution (and the orbital properties) of stars around this black hole.
Within SYRTE, we are involved in the development of tests of general relativity around this black hole: regarding the redshift measurement, the derivation of constraints on alternative theories of gravitation and also with searches for variations of the fine structure constant (a signature of a violation of Einstein’s equivalence principle). We are also involved in astrophysical studies, in particular concerning triple systems: search for a hypothetical companion (intermediate mass black hole) to the central black hole, modeling of gravitational waves emitted by binary systems orbiting this black hole, etc.
Our involvement is theoretical: we propose new ideas for measurements and analysis. We are also involved in the fine relativistic modeling of observations in the electromagnetic spectrum as well as for gravitational waves. Finally, we participate in the planning of the observations to optimize the telescope time and also in the statistical analysis of the data.