The stars in the spiral arms of M81 (lower part of the image) have formed within the last 100 million years, as have most of the stars in the nearby dwarf galaxy. M81 is similar in size and brightness to our Milky Way. The Galaxy Evolution Explorer telescope (GALEX) reveals that star formation is occurring quite distant from the nucleus of M81. The nucleus, or centre, of M81 shines from the light of 10-billion year old stars near the end of their lives, which produce their energy by burning helium into carbon. Star formation is so violent in galaxy M82 (in the upper part of the image, viewed from its side) that gas and dust is being expelled perpendicular to its disc. Once thought to be an exploding galaxy, the flows are caused by the supernova explosions from the young stars in this galaxy.
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