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Metal-poor stars in the Milky Way are local relics of the epoch of the firststars and the first galaxies. However, a low metallicity does not prove that astar formed in this ancient era, as metal-poor stars form over a range ofredshift in different environments. Theoretical models of Milky Way formationhave shown that at constant metallicity, the oldest stars are those closest tothe center of the Galaxy on the most tightly-bound orbits. For that reason, themost metal-poor stars in the bulge of the Milky Way provide excellent tracersof the chemistry of the high-redshift universe. We report the dynamics anddetailed chemical abundances of three stars in the bulge with [Fe/H]$\lesssim-2.7$, two of which are the most metal-poor stars in the bulge in theliterature. We find that with the exception of scandium, all three stars followthe abundance trends identified previously for metal-poor halo stars. Thesethree stars have the lowest [Sc II/Fe] abundances yet seen in $\alpha$-enhancedgiant stars in the Galaxy. Moreover, all three stars are outliers in theotherwise tight [Sc II/Fe]-[Ti II/Fe] relation observed among metal-poor halostars. Theoretical models predict that there is a 30% chance that at least oneof these stars formed at $z\gtrsim15$, while there is a 70% chance that atleast one formed at $10 \lesssim z \lesssim 15$. These observations imply thatby $z\sim10$, the progenitor galaxies of the Milky Way had both reached [Fe/H]$\sim-3.0$ and established the abundance pattern observed in extremelymetal-poor stars.

Chemistry of the Most Metal-poor Stars in the Bulge and the z > 10 Universe