Feeding and Feedback in the Nucleus of our Galaxy

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The most up-to-date telescopes and instruments have offered an unprecedented opportunity to study the extreme environment surrounding supermassive black holes (SMBHs) in nearby galactic nuclei. Understanding the physics of these exotic objects, living in the center of most galaxies, is crucial to test General Relativity and to shed light on their impact on galaxy formation and evolution. A particularly good laboratory is our own Galactic Center, where continuous monitoring of the orbits of the young star (S-star) cluster in the inner few light months from the SMBH has allowed a precise derivation of its mass. Still, many uncertainties exist concerning the gas distribution at those distances and its accretion from the Bondi radius up to the black hole event horizon. In a first project, we propose to use the winds of the S-stars as diagnostic tools to infer the properties of the accretion flow (i.e., its density and temperature distributions) at a few thousand Schwarzschild radii from the SMBH (where no current observation can provide a direct estimate). This will be done by means of hydrodynamic simulations, of the type performed by our group to study the gas and dust cloud G2 and by a thorough comparison of the resulting observables with available and future observations throughout the electromagnetic spectrum. Of particular interest is the star S2 which will have its next (very well observed) peri-center passage in early 2018. The second project will consist of a simulation including the whole S-star cluster, to understand how the winds from these stars influence the dynamics and thermodynamics of the various gas phases in the inner few light months. This will tell us whether they have a positive or negative feedback effect on the accretion flow onto the SMBH.