The Milky Way could contain thousands of stars from another galaxy

The Milky Way might contain thousands of stars that were expelled from Andromeda, our closest galactic neighbour – and may even have brought planets with them.

Some stars in the Milky Way are moving so fast that they can escape our galaxy’s gravitational pull, which raises the question of whether similarly speedy stars could exist in, and potentially leave, other galaxies as well.

Now, Lukas Gülzow at the Karlsruhe Institute of Technology in Germany and his colleagues have calculated that the Milky Way …