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Astronomers have devised a game to help uncover the basis of galactic pile-ups. The game, part of the ongoing web-based project Galaxy Zoo, shows players images of colliding galaxies and asks them to match those to simulations. By selecting the closest matching simulation, players can help astronomers to work out how the real galaxies actually merged. The astronomers say that humans are much better than computers at spotting the patterns and similarities.

The developers described the game as a "cosmic fruit machine". It shows players one real galaxy image and, on command, eight randomly selected simulations pop into the "slots" surrounding that image. The aim is for players to choose the simulations that look most similar to the real galaxy and take those through to the next round to examine them further. The simulated images show the different aspects of galaxy formation, so as people play, they will generate data that will help astronomers' understanding of these collisions.

The strength of the game is that it takes results from many people, said Dr Chris Lintott from Oxford University, one of the members of the Galaxy Zoo team. These galactic mergers could be the key to why the Universe contains a mixture of different galaxies - some with trailing spiral arms, others more like compact balls of stars.