Astronomers have pondered for years why our galaxy, the Milky Way, is warped. Data from ESA’s star-mapping satellite Gaia suggest the distortion might be caused by an ongoing collision with another, smaller, galaxy, which sends ripples through the galactic disc like a rock thrown into water.
Source:
https://phys.org/news/2020-03-milky-warp-galactic-collision-gaia.html