Wednesday, July 22, 2026

The Milky Way Flipped its Disk Billions of Years Ago

The Milky Way in the sky over the ESO's La Silla Observatory in Chile's Atacama Desert. The Milky Way's thick disk is full of older stars and rotates more slowly than its thin disk, which is full of younger stars. New research says a cosmic flip is responsible for this puzzling arrangement. Image Credit: ESO/B. Tafreshi (twanight.org)

The Milky Way has two disks, the thin disk where most of the stars dwell, and the thick disk, populated by much older stars. The ESA's Gaia mission showed us that the thick disk rotates more slowly than the thin disk. The culprit, according to powerful simulations, was a disk flip in the MW's past, driven by a merger.



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