With a diameter of about 170,000 light years, galaxy Messier 101 (M101) is nearly twice the size of our Milky Way. Its orientation allows telescopes to see its spiral structure face-on, inspiring its nickname -- the Pinwheel Galaxy. NASA's Chandra X-ray Observatory has obtained one of the longest exposures ever seen of a spiral galaxy in x-rays. The glowing lights indicate massive stars, black holes and supernova explosions, all wrapped in the hot gas "arms" of the galaxy.