Only hydrogen, helium, and traces of lithium nuclei were formed in the primordial nucleosynthesis, that ended some 20 minutes after the Big Bang. Lithium and beryllium were later formed in substantial amounts from spallation of carbon, nitrogen and oxygen atoms hit by cosmic rays in the interstellar medium, but heavier elements mainly came from burning in stellar interiors or explosive nucleosynthesis in supernovae.
Hence, when the first stars formed 300-500 million years after the Big Bang they were made out of pristine gas, unpolluted by metals. The study of the extremely metal-poor stars, born when very few supernovae had yet enriched the primordial interstellar medium, is unique to our Local Group. Only there, thanks to its proximity, can we analyze individual stars in sufficient numbers and at high spectroscopic resolution to guide our understanding of the physics of star formation, supernovae feedback, and the early build-up of galaxies.
We are committed to large observational programs which look for the imprint of the first stars in the Universe, in the halo of our Galaxy and in its satellites.