Milky Way reportedly flipped after ancient collision

New simulations by Durham University suggest the Milky Way’s disc could have flipped more than 90 degrees as a result of a major head-on merger with the Gaia Sausage about 10 to 11 billion years ago, potentially explaining why the halo rotates far more slowly than the disc. The findings indicate that galaxies with the slowest-rotating stellar halos are those that experienced both a colossal collision and a subsequent disc flip, reshaping our galaxy’s orientation over hundreds of millions of years. The proposed mechanism links the observed slow halo rotation from Gaia data to a dramatic past upheaval, offering a cohesive narrative for the Milky Way’s early violent history. Researchers arrived at these conclusions by analyzing 25 Milky Way–like galaxies in the Auriga cosmological simulations and comparing them with Gaia’s halo measurements. The results were presented at the Royal Astronomical Society’s National Astronomy Meeting, and are echoed by multiple outlets describing a long-ago, sideways-turn in our galaxy’s orientation. If confirmed, this ‘cosmic gymnastics’ of the Milky Way would add to the picture of a turbulent galactic past driven by major mergers.