Anna Frebel

 "What the most metal-poor stars tell us about the early Universe"

 The chemical evolution of the Galaxy and the early Universe is a key
 topic in modern astrophysics. Since the most metal-poor Galactic stars
 are the local equivalent of the high-redshift Universe, they can be
 employed to reconstruct the onset of the chemical and dynamical
 formation processes of the Galaxy, the origin and evolution of the
 elements, and associated nucleosynthesis processes. They also provide
 constraints on the nature of the first stars and SNe, the initial mass
 function, and early star formation processes. The discovery of two
 astrophysically very important metal-poor objects recently lead to a
 significant advance regarding these topics. One object is the most
 iron-poor star yet found (with [Fe/H]=-5.4). The other star displays
 the strongest known overabundances of heavy neutron-capture elements,
 such as uranium, and nucleo-chronometry yields a stellar age of ~13
 Gyr.  Metal-poor stars, once also identified in dwarf galaxies, are
 vital probes also for near-field cosmology. Their chemical signatures
 now suggest that systems like these were building blocks of the Milky
 Way's low-metallicity halo. This opens a new window to study galaxy
 formation through stellar chemistry.