Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies .
However , a low metallicity does not prove that a star formed in this ancient era , as metal-poor stars form over a range of redshift in different environments .
Theoretical models of Milky Way formation have shown that at constant metallicity , the oldest stars are those closest to the center of the Galaxy on the most tightly-bound orbits .
For that reason , the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe .
We report the dynamics and detailed chemical abundances of three stars in the bulge with \mathrm { [ Fe / H ] } \lesssim - 2.7 , two of which are the most metal-poor stars in the bulge in the literature .
We find that with the exception of scandium , all three stars follow the abundance trends identified previously for metal-poor halo stars .
These three stars have the lowest [ Sc ii/Fe ] abundances yet seen in \alpha -enhanced giant stars in the Galaxy .
Moreover , all three stars are outliers in the otherwise tight [ Sc ii/Fe ] – [ Ti ii/Fe ] relation observed among metal-poor halo stars .
Theoretical models predict that there is a 30 % chance that at least one of these stars formed at z \gtrsim 15 , while there is a 70 % chance that at least one formed at 10 \lesssim z \lesssim 15 .
These observations imply that by z \sim 10 , the progenitor galaxies of the Milky Way had both reached \mathrm { [ Fe / H ] } \sim - 3.0 and established the abundance pattern observed in extremely metal-poor stars .