Cartwheel galaxy. Composite image of the Cartwheel Galaxy and its companions photographed by the Hubble Space Telescope (HST) in blue and infrared light. The 150, 000 light year diameter ring of the galaxy is the result of a collision with another galaxy, possibly the irregular companion at right. The Cartwheel, about 500 million light years from Earth, is thought to have originated as a flat spiral galaxy, especially as new spiral arms and dust lanes may be seen. The ring was formed by an expanding shockwave from the collision, sweeping up gas and dust and forming hot new stars and supernovae.