Study: Milky Way Flipped 90° After Ancient Galaxy Crash
The Spin
Narrative A
The Milky Way's disc almost certainly flipped more than 90 degrees after a massive head-on collision with the Gaia-Sausage-Enceladus galaxy 10 to 11 billion years ago. Supercomputer simulations of 25 Milky Way-like galaxies show that slow stellar halo rotation is a direct fingerprint of that kind of catastrophic merger and disc reorientation. The Sun itself may have once traveled a completely different path through space. The galaxy's apparent stability today masks a violently transformed past.
Narrative B
Rather than simply rewriting the Milky Way's history, this study could reshape how astronomers investigate galaxy formation. If confirmed, the slow motion of ancient halo stars may preserve a record of the Milky Way's lost orientation, allowing scientists to reconstruct past mergers, trace the evolution of dark matter, and better understand how spiral galaxies — and our own solar system's cosmic environment — came to be.