Observational Constrains on the Sgr A$^*$ Black Hole Immersed in a Dark Matter Halo: Shadow and S2 Star Orbit

Abstract: It is widely believed that Sgr A$^*$, located at the center of our Galaxy, is a supermassive black hole. Recent observations of its shadow and long-term monitoring of the S2 star have provided compelling evidence supporting this hypothesis. These observational advancements also offer valuable opportunities to explore the physical properties of the black hole and its surrounding environment. Since a dark matter halo is expected to exist in the Milky Way and around Sgr A$^*$, investigating the behavior of the Galactic Center black hole embedded in such a halo provides a crucial means to simultaneously probe both black hole physics and dark matter properties. In this work, We develop a black hole metric that incorporates a generalized double power law dark matter halo, and analyze the corresponding null and timelike geodesics to investigate how the halo parameters affect the black hole shadow and the motion of the S2 star. Furthermore, by comparing our theoretical predictions with observational data of the shadow and the S2 orbit, we constrained the dark matter halo parameters. The results of this study provide both theoretical and phenomenological insights into the nature of Sgr A$^*$ and the distribution of dark matter in our Galaxy.