Ancient Galactic Collision Shaped the Milky Way’s Spin
Astronomers link an 11-billion-year-old major merger, Gaia–Sausage–Enceladus, to the Milky Way’s evolving disk, showing the collision triggered early starbursts and helped establish the current rotation; simulations with Auriga and observations of star clusters connect these violent events to disk rebuilding and lasting structural imprints.