Milky Way’s ancient 90-degree flip reshaped its halo
New Gaia measurements and computer simulations show the Milky Way’s halo rotates more slowly than its disk, likely because the galaxy underwent ancient head-on mergers and a dramatic disk flip that reoriented the disk by about 90 degrees. This misalignment slows halo rotation and could have shifted the solar system’s orbit, though the exact mechanism remains under investigation.