Study suggests Milky Way may have undergone major disk orientation flip

Astronomers at Durham University have uncovered evidence that the Milky Way may have experienced a dramatic reorientation of its stellar disk during its past. By running high‑resolution supercomputer simulations of Milky‑Way‑like galaxies, the team identified a pattern linking slow rotation in a galaxy’s stellar halo to a significant “disk flip,” in which the disk’s angular momentum vector changes by more than 90 degrees. This finding offers a plausible explanation for long‑standing puzzles about the Milky Way’s warped, tilted disk and the misaligned distribution of its satellite galaxies.

The simulations show that galaxies whose halos rotate slowly are more susceptible to major mergers or accretion events that can torque the disk into a new orientation. In such a scenario, the outer halo retains a memory of the original spin, while the inner disk realigns, producing the observed misalignment. The research also suggests that the Milky Way’s own halo, which rotates only modestly, may have undergone a similar flip in the distant past, reshaping the positions of globular clusters and satellite galaxies.

If the Milky Way did indeed flip its disk, the event would have profound implications for our understanding of galactic evolution. It would help explain the apparent tilt of the Galactic plane relative to the halo and the distribution of stellar streams, and it would provide a new benchmark for testing models of galaxy formation. Future observations, particularly of halo kinematics and satellite orbits, will be crucial in confirming whether such a disk flip occurred and in refining the timeline of the Milky Way’s dynamic history.