USATODAY.com – What a shock! Galaxies caught colliding
A cosmic pileup
Stephen’s Quintet is a cluster of five galaxies located about 300 million light-years away in the constellation Pegasus. For decades, astronomers using optical telescopes have known that galaxies in the cluster had experienced encounters in the past and that some were colliding even now.
But it wasn’t until they used Spitzer’s Infrared Spectrograph on the galaxy cluster that they could make out the details of what was happening.
They discovered that one of the galaxies, called NGC7318b, is currently falling toward three of the others at a very high speed and generating a giant shock wave, or “bow shock,” in front of it. A bow shock is akin to the ripple raised by a boat’s bow as it moves through the water.