NASA's Spitzer Space Telescope reveals differences in the distribution of young and old stars in Arp 65, a pair of interacting galaxies in Andromeda. Cool, old stars are bright at 3.6 microns (blue), so the smooth grand-design spiral patterns of the galaxies' old stellar disks show clearly at this wavelength. The galaxies take on a clumpier appearance in an image taken at 8 microns (red), revealing clusters of young stars.
NASA / JPL / Caltech / M.L. Giroux, et al.