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> Spiral galaxy M81 in Ursa Major
Spiral galaxy M81 in Ursa Major
author: Nasa/ESA/Hubble Heritage Team/Novapix
reference: a-gax30-31009
Image Size 300 DPI: 191 * 128 cm
Though the M81 galaxy is 11.6 million light-years away, this image taken by the Hubble space telescope is so sharp that it can resolve individual stars, along with open star clusters, globular star clusters, and even glowing regions of fluorescent gas. The spiral arms, which wind all the way down into the nucleus, are made up of young, bluish, hot stars formed in the past few million years. They also host a population of stars formed in an episode of star formation that started about 600 million years ago. The greenish regions are dense areas of bright star formation. The ultraviolet light from hot young stars are fluorescing the surrounding clouds of hydrogen gas. A number of sinuous dust lanes also wind all the way into the nucleus of M81. The galaxy's central bulge contains much older, redder stars. It is significantly larger than the Milky Way's bulge. A black hole of 70 million solar masses resides at the center of M81. The black hole is about 15 times the mass of the Milky Way's black hole.
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