26 May 2011
Last updated at 12:31
Researchers reporting at the American Astronomical Society have released an atlas of galaxy collisions, gathered from data from the Spitzer and Galex space telescopes. Here, infrared emission from dust in the M51 galaxy pair was pictured (l) by Spitzer, and ultraviolet emission from its new stars was captured (r) by Galex.
As in all the composite images that follow, the two images give a clearer picture of the two galaxies that make up M51. At top is M51B, made largely of older stars, while the spiral M51A has a great many younger stars heating its dust and driving infrared emission.
The atlas is designed to give a better look at galaxy collisions, which happen over millions or billions of years - our own Milky Way will collide with the Andromeda galaxy in about five billion years' time. Here, NGC 470 (l) and NGC 474 (r)approach each other at a distance of about 160,000 light years.
Much closer together are the galaxies NGC 3448 and UGC 6016, separated by about 75,000 light years. The ultraviolet emission seen by Galex shows that a thread of material is beginning to connect the two.
The galaxies NGC 935 and IC 1801 have already begun their galactic smash-up. By observing a range of galaxy collisions, lead researcher Lauranne Lanz of Harvard University's Center for Astrophysics says the atlas "is the first step in reading the story of how galaxies form, grow, and evolve".
The galaxy NGC 520 is actually the result of a merger of two galaxies. The "tidal tails" at lower left and upper right are material that has been stripped from the two galaxies in the process of merging.
The atlas could help astronomers determine the origins of the M101 "Pinwheel galaxy" - which is thought to be the result of a merger of two galaxies, as evidenced by its not-quite-symmetric shape. Blue represents the ultraviolet emission caught by Galex, showing that new star formation is taking place.