Overview
- The simulation analysis led by Kirill Batrakov, presented Tuesday at the Royal Astronomical Society meeting, shows Milky Way–like galaxies can undergo gradual disk reorientations exceeding 90 degrees that produce very slowly rotating stellar haloes.
- The team links the proposed flip to a head‑on collision with the Gaia‑Sausage–Enceladus dwarf galaxy about 10–11 billion years ago, which in the models provides the gravitational torque needed to tilt the disk over hundreds of millions to a billion years.
- The work was motivated by ESA Gaia data that show the Milky Way's stellar halo orbits far more slowly than expected for the Galaxy's mass, a kinematic puzzle the flip scenario can naturally reproduce in the simulations.
- An independent 2026 study from a Chinese Academy of Sciences team finds the Galaxy's dark‑matter halo is nearly perpendicular to the stellar disk, a geometric result that offers circumstantial support for gradual reorientation but does not prove a real flip occurred.
- Researchers stress the hypothesis is provisional and say targeted observational tests beyond halo rotation — for example specific stellar‑stream signatures or relic orbital patterns — are needed to confirm whether the Milky Way actually experienced a disk flip.