Hoag's Object: A Strange Ring Galaxy

Explanation: Is this one galaxy or two? This question came to light in 1950 when astronomer Art Hoag chanced upon this unusual extragalactic object . On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag's Object formed remains unknown, although similar objects have now been identified and collectively labeled as a form of ring galaxy . Genesis hypotheses include a galaxy collision billions of years ago and the gravitational effect of a central bar that has since vanished . The above photo taken by the Hubble Space Telescope in July 2001 reveals unprecedented details of Hoag's Object and may yield a better understanding . Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of the Snake ( Serpens ). Coincidentally, visible in the gap (at about one o'clock) is yet another ring galaxy that likely lies far in the distance .