The Rapid Formation of the Metal-poor Milky Way

Using isochrone ages for main sequence turn off and subgiant stars observed in the H3 survey we measured the end of star formation in accreted dwarf galaxies that built up the metal poor populations of the Milky Way. With these star formation truncation times we inferred a rapid assembly of the Galactic halo that culminated with the GSE merger 10 Gyr ago, marking the last majorly disruptive merger in the Milky Way's history.