Astronomers have long puzzled over the Milky Way's two distinct disk structures: a thin, fast-rotating spiral disk and a thick, slowly rotating stellar halo. Using the Auriga simulations, a team led by Kirill Batrakov of Durham University modeled 25 Milky Way-like galaxies over billions of years to understand this discrepancy. The simulations showed that galaxies with a slowly rotating outer halo shared three key traits: early formation, a major merger like the Gaia-Sausage-Enceladus collision, and a disk-flip event.