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Galactical archeologyΒΆ

The study of the history of galaxies has begun; in particular, the study of their shape. Not all galaxies have a ‘perfect’ symmetric shape. The massive ones do, such as ours, the Milky Way, and our closest neighbor, Andromeda. But many ‘smaller’ galaxies exist that do not respect such symmetry. And recent very sensitive images of space have started to reveal the history of these forgotten ones.

For instance, the Triangulum galaxy is a small galaxy (about 2 billion stars only) that has a large portion of her stars disperse into its outer reaches. Its closeness to Andromeda suggests that Andromeda could be the cause of such ‘abnormal’ shape. Using observations and numerical simulations, McConnachie et al. (Nature, 3 September 2009) provide strong evidences that 2.5 billion year ago, the Triangulum galaxy passed so close to Andromeda that it triggered an outward dispersement of her stars. A small scare in Andromeda at the exact location estimated by the models confirms the story.

As Gnedin concludes his summary of McConnachie et al.’s article:

“Alas, the beauty of cosmic cathedrals is only perfect to the near-sighted; look deeper, and under the veil of perfection you’ll find the messy traces of their violent past. Every galaxy is an irregular one, if one only looks deep enough.”