|The Cosmic Bull's-Eye: Arp 147|
On the left in the image above, you see an elliptical galaxy that millions of years ago passed right through what used to be a spiral galaxy on the right. All that remains of that spiral, located some 440 million light-years distant, is a massive ring of stars. The collision triggered a tsunami of star formation that raced around the ring. The ring is so bright in X rays that astronomers conclude that many of those newly-formed stars were likely quite massive. Consequently, they lived fast and died young, exploding as luminous supernovae and leaving behind both neutron stars and black holes. What a sight.