These illustrations demonstrate how two galaxies coalesce in a slow dance that lasts about a billion years.
The graphics are taken from a simulation astronomers created to determine how long it takes for galaxies to complete a merger. By understanding the time it takes for two merging systems to become one normal-looking galaxy, astronomers can calculate how many galaxy encounters happen over time. This information yields important clues about how galaxies have changed throughout the universe's history.
Credit: P. Jonsson (Harvard-Smithsonian Center for Astrophysics), G. Novak (Princeton University), and T.J. Cox (Carnegie Observatories, Pasadena, Calif.)