A team of Chinese astronomers has discovered that the Milky Way’s dark matter halo stands upright, suggesting that our galaxy’s disk may have flipped in the past few billion years due to cosmic interactions.

Using about 15,000 K-giant stars observed by LAMOST and Gaia, researchers built the first fully data-driven 3D model of the Milky Way’s stellar halo to explore the underlying dark matter distribution. It shows that the dark matter halo is triaxial and nearly oblate, but with its major plane perpendicular to the Galactic disk, a surprising orientation aligned with the plane where our satellite galaxies distribute.

This means the Milky Way’s disk may once have been tilted by gravitational torque during minor mergers, causing a dramatic ‘flip’ in its orientation.In cosmological simulations, only a few galaxies show a similar configuration — and all of them experienced such a disk-flipping event.

‘Our galaxy keeps a memory of its wild past,’ says lead author Dr. Ling Zhu. ‘The flipped disk, vertical halo, and satellite plane are all connected pieces of one cosmic story.’

This discovery ties the long-standing mystery —the satellite plane— with the shape of dark matter halo and disk evolution — offering a new unified view of the Milky Way’s dynamic history.