Nearby galaxies: Messier 81 & Messier 82
Messier 81 & 82: full field of view of the instrument -1 square degree

Various resolution downloads:
[Scaled 1/8th: 2350x2350 pixels - JPEG - 311Kb] 
[Scaled 1/16th: 1175x1175 pixels - JPEG - 100Kb] 
[Scaled 1/32th: 588x588 pixels - JPEG - 30Kb] 

Scientific description:
Galaxies are huge condensations of stars, gas, and dust that are embedded within a sphere of mysterious dark matter. All the components are bound together by their mutual gravitational attraction. A massive galaxy like our home galaxy, the Milky Way, is made up of more than 100 billion stars. Large galaxies seem to like company; they're always associated with others, either in relatively small groups with a few tens of members, or in larger clusters made of hundreds, even thousands thousands of galaxies. 

This sociability has a consequence: at sometime most large galaxies will experience a close encounter with one or more of their neighbours. As the two galaxies fall towards each other under the pull of gravity, tidal forces will distort, even disrupt the common lenticular shape of one or both of the interacting pair. As a result of these forces a huge quantity of material is stripped off the galaxies and flung into intergalactic space. In addition, these interactions often lead to an intense burst of star formation that seems to be triggered as the gas and dust, disturbed by the strong pull of a companion galaxy, is compressed in unusual flows. 

Here, Messier 81 (bottom) and Messier 82 (top), two magnificent galaxies in the Northern sky, located about 12 million light years away from us, have experienced such event recently. The extremely perturbed appearance of the smaller galaxy is the "smoking gun" that a close encounter has happened. The much larger Messier 81 also shows some clear signs of disturbance. A significant part of one of her spiral arms is stripped away, nearly completely. Astronomers now believe that such stripped material may reassemble into dwarf galaxies of a few hundreds of thousands of stars. 

Technical description:
MegaPrime / MegaCam (central 36 CCDs - 18Kx18K pixels)
Field of view: 60'x60' (1 square degree)
Filter used: g' (level of intensities)
Exposure times: 25 minutes total
Observed at the CFHT in January 2003

Credit line: "Canada-France-Hawaii Telescope / 2003"

Copyright © 2003 Canada-France-Hawaii Telescope Corporation


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