Stefan's Quintet

Stephan's Quintet in the constellation Pegasus is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered.
The group was discovered by Édouard Stephan in 1877 at Marseilles Observatory.
The group is the most studied of all the compact galaxy groups.The brightest member of the visual grouping is NGC 7320 that is shown to have extensive H II regions, identified as red blobs, where active star formation is occurring.