A giant wave in the Milky Way may have been created by another galaxy

The Milky Way appears to have a vast ripple spreading out across at least a quarter of its disc. If confirmed, the structure might be a relic from a brush with another galaxy, but not all astronomers are convinced that it actually exists.

While illustrations normally show our galaxy as a flat disc with a bulge in the middle, its structure is much more complicated. Astronomers have mapped undulating clouds of stars and gas that create waves across small sections of the Milky Way. They have also found that…