An image of Hoag's Object, a non-typical galaxy of the type known as a ring galaxy, discovered in 1950 by astronomer Art Hoag, who initially thought it to be a planetary nebula. Serendipitously, from the perspective of our solar system what appears to be an even more distant ring galaxy is plainly visible within the gap between this galaxy's central body of mostly yellow stars and the outer ring of blue stars.
A ring galaxy is a galaxy with a ring-like appearance. The ring consists of massive, relatively young blue stars, which are extremely bright. The central region contains relatively little luminous matter. Astronomers believe that ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy. Because most of a galaxy consists of empty space, this "collision" rarely results in any actual collisions between stars. However the gravitational disruptions caused by such an event could cause a wave of star formation to move through the larger galaxy.
Hoag's Object, discovered by Art Hoag in 1950 is an example of such a galaxy.
* Interacting galaxy
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