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
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.