Cartwheel Galaxy --" When Galaxies Collide"
This image shows a peculiar galaxy what looks like a cart, or wagon, wheel.
It is the result of a rare and spectacular head on collision between this
galaxy and possible one of the other two that you see at the right. The
Cartwheel galaxy was probably shaped like a spiral (like our own Milky
Way) before the collision but, like a stone tossed into a pond, the collision
sent out a ripple of energy that compressed the galaxy's gas in its wake
and distorted its shape. This circular ripple of compressed gas is currently
at the position of the Cratwheel's "rim" and has resulted in a burst of
star formation that causes the rim to shine brightly.