A ringside seat for a slow-motion galactic train wreck

Two galaxies 350 million light years away are in the process of merging, both being distorted by gravitational interactions that are stripping stars and dust away in long tidal tails while triggering concentrated bursts of star formation where clouds of interstellar gas and dust are stirred up. The ongoing cosmic collision gives scientists a ringside seat for a common phenomenon in the universe and one that is expected to play out closer to home as the Milky Way and Andromeda crash together in 4 billion years or so.

Known as Arp 256, the collision seen here represents one of 338 unusual-looking structures in astronomer Halton Harp’s Atlas of Peculiar Galaxies that was catalogued as part of a project to capture different stages of galactic evolution. Many members of the catalogue are dwarf galaxies, but many others are interacting pairs like Messier 51, the famous Whirlpool Galaxy, and the Antennae galaxies. The two members of Arp 256 will continue their slow-motion merger for millions of more years before finally combining to form a single galaxy.

Two galaxies 350 million light years away, caught in the process of colliding by the Hubble Space Telescope. A wide-angle view of the star field in the constellation Cetus, taking with a ground-based telescope, provides context. Image: ESA/Hubble, NASA