The Cartwheel Galaxy

The striking ring-like shape of the Cartwheel Galaxy, ESO 350-40, is a direct result of a smaller galaxy—possibly one of two objects to the right of the ring—that careened through its core. The collision sent a ripple of energy into space, plowing into the gas and dust in front of it and pushing the galaxy’s circumference outward at roughly 200,000 miles per hour. This cosmic-sized tsunami left in its wake a firestorm of new star creation. The bright blue knots that trace the galaxy’s expanding outer edge are captured by Hubble as immense clusters of newborn stars. The Cartwheel Galaxy was presumably a normal spiral galaxy like our Milky Way before the collision. A spiral structure is beginning to re-emerge, as seen in the faint arms or spokes between the outer ring and the bulls-eye-shaped galactic nucleus. At approximately 150,000 light-years across, the outer ring is so large that our entire Milky Way Galaxy would fit inside it.