The Galactic Center as a laboratory for dark matter and theories of modified gravity

Abstract

[ES]The theory of General Relativity, formulated a little over a century ago by Albert Einstein, implied a paradigm shift in our understanding of gravity and the space we live in, and still today it resists with astounding predictive power to the numerous experimental tests it undergoes. In this context, the Galactic Center of the Milky Way has stood out in recent years as a unique and powerful laboratory at the edge of fundamental physics and astrophysics. Numerous observational pieces of evidence indicate that compact radio source Sagittarius A*, harbored in this region, is a four-million-solar-masses supermassive black hole, as described by General Relativity. As such, high resolution observations of this object and its surroundings not only open a unique new avenue to test the basic predictions of General Relativity but also to falsify it against theories that have been proposed to modify or extend it, to test different paradigms of dark matter and to place constraints on the very fundamental nature of Sagittarius A*. In this thesis, we explore this fascinating possibility. First, we develop a numerical methodology and the appropriate modeling required to produce fully relativistic observables for stars and pulsars in the Galactic Center. We then use current data, mock catalogues for future observations of both known objects and putative ones, and Bayesian inference techniques to derive novel constraints on a variety of different scenarios, including extended dark matter components surrounding Sagittarius A*, black hole mimicker models and modifications to the underlying theory of gravity. Beyond the importance of the constraints derived for these models, which often represent complementary probes to those obtained at different astrophysical or cosmological scales in the literature, our work demonstrates the powerful ability of observations at the Galactic Center to further strengthen the central role of General Relativity and the black hole paradigm and the methodologies we have developed will represent a valuable tool for future research in this field.