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Astr111 Photography Projects, Fall 2004

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M 82, Vicky Charles

M 82

M82 is a very nice example of a “disk” irregular galaxy. Disk galaxies often have beautiful patterns in the form of spiral arms or luminous bars. Encounters with neighbors cause numerous changes in the gravitational field within the disk, which tends to compress the gas in some regions. If the density of the gas in these regions exceeds a certain critical value, star formation can take place, resulting in the formation of red diffuse emission nebulae and blue clusters of hot young stars, which slowly change their color to the yellow when they come to age, and their hottest stars have disappeared. When interacting heavily with nearby galaxies, colliding, for example, normal disk galaxies can take on a very irregular shape.

This picture of M82 has a very irregular shape, but is still the home to many stars. The fact that the center is a great deal brighter than the edges shows that the majority of the stars are found in the middle of the galaxy, and the fact that the light in the middle can not be clearly sectioned off into separate stars tells us that the galaxy is quite far away from us. As is common with galaxies, M82 has a great deal of dust surrounding it. M82 is actually located very close to its neighbor galaxy, M81, and it has been discovered to orbit M81. The close proximity of these galaxies might have been the reason for the dark lane of dust now found in the middle of M82. A collision could have occurred long ago and left M82 with the unusual shape it has today.