Overview
- Researchers from Durham University presented their results on Tuesday at the Royal Astronomical Society meeting that propose the Milky Way’s disk reoriented by over 90 degrees during its early history.
- The team analysed 25 Milky Way–like systems in the Auriga cosmological simulations and found that early galaxies that suffered head-on mergers often undergo slow, large-angle disk flips that leave very slowly rotating stellar haloes.
- They link the proposed flip to the known Gaia–Sausage–Enceladus merger about 10–11 billion years ago, arguing the collision could have torqued the disk inside its dark matter halo and changed stellar orbits.
- An independent study published earlier in 2026 found the Milky Way’s dark matter halo is nearly perpendicular to the stellar disk, a separate line of evidence that supports a past reorientation.
- The claim is currently simulation-driven and provisional, with authors noting flip timescales of roughly 150 million to >1 billion years and calling for specific observational signatures to confirm the scenario and its implications for stars such as the Sun.