From protogalaxy through thick and thin: Why did the Milky Way evolve in three kinematic phases?

Olti Myrtaj, James S. Bullock, Michael Boylan-Kolchin +9

APOGEE and Gaia data suggest the Milky Way's kinematic structure evolved through three distinct phases: a disordered protogalaxy, which ``spun up'' into a thick stellar disk, and t…