Ancient Galactic Merger Impacted Star Formation in the Milky Way

Abstract

S ome 8 to 11 billion years ago, researchers believe the Milky Way absorbed a small dwarf galaxy, known as Gaia-Sausage-Enceladus, after the two collided. This absorption changed the structure of our Galaxy as well as its chemical makeup. The remnants of the dwarf galaxy also shaped the Milky Way’s outer halo and its centrally located “inner thick disk.” Now Ioana Ciucă of the Australian National University and her colleagues have analyzed data from nearly 70,000 stars to understand the role the merger played in subsequent stellar evolution within the inner thick disk [1]. The team finds that the stars that formed directly after the merger