Cosmic Target Practice

When new astronomical images come across my desk, most are often variations on a theme: something I've seen before, perhaps with better resolution or a few new features.  But today I was wowed. Astronomers using both the Chandra X-Ray Observatory and the Hubble Space Telescope created a composite image of a celestial object known as Arp 147, which appears like the mother of all bull's-eyes.  The universe has pretty good aim when shooting at a target. 

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.