Speaker
Description
How old is the Universe? What happened to the Milky Way at the very beginning of its formation? To answer these questions, we analyze a sample of 28 extremely metal-poor field stars in the solar vicinity. We determine their ages and kinematical properties, and combine these together with their chemical composition to study their origin. The mean age of the sample is 13.8 ± 0.5 Gyr, suggesting that many of these stars formed at the very beginning of Milky Way assembly. Moreover, the detailed analysis of their orbital parameters reveals that the oldest of these stars are most probably associated with the pristine bulge of the Milky Way. Other metal-poor stars in the sample belong to Gaia-Enceladus-Sausage and Thamnos accreted events and the Milky Way in-situ population. Based on our findings, the first component to form in the Milky Way was the bulge through rapid collapse; the other components have grown later on, with a significant contribution of accreted structures.