The gas within galaxies, however, does collide, and an avalanche of star formation commences. Newborn stars heat up surrounding dust clouds, causing them to glow in the infrared, thus being detected by Spitzer. Massive stars born in the merger explode in violent supernovae, leaving behind gas that glows with x-rays to be picked up by Chandra. The galaxies' older stellar tenants still shine on in visible light to be detected by Hubble, completing the galactic picture.
All of these pictures were taken several years apart and recently combined. However, the merger has been ongoing for 100 million years, so not much changes in such a short time span. Indeed, the violence of stellar birth and death in these dancing galaxies seems frozen in time for us to see in all its splendor.
Image Credits: Top – NASA, ESA, SAO, CXC, JPL-Caltech, STScI, J. DePasquale (Harvard-Smithsonian CfA), and B. Whitmore (STScI); Bottom – Ground-based image by Robert Gendler