Bright Spiral Galaxy M81 in Ultraviolet from Galex

Explanation: Where are the hot stars in M81, one of the closest major spiral galaxies? To help find out, astronomers took a deep image in ultraviolet light of the sprawling spiral with the Earth-orbiting Galex telescope . Hot stars emit more ultraviolet than cool stars, and are frequently associated with young open clusters of stars and energetic star forming regions . Magnificent spiral galaxy M81, slightly smaller in size to our own Milky Way Galaxy , shows off its young stars in its winding spiral arms in the above image . Less than 100 million years old, the young stars are blue in the above false-color Galex image and seen to be well separated from the older yellowish stars of the galactic core. Visible above M81 is a satellite galaxy dubbed Holmberg IX . Studying the unexpectedly bright ultraviolet glow of this small irregular galaxy may help astronomers understand how the many satellites of our own Milky Way Galaxy developed. M81 , visible through a small telescope, spans about 70,000 light years and lies about 12 million light years away toward the constellation of the Great Bear ( Ursa Major ).