false-colour composite image shows the Cartwheel galaxy as seen by the Galaxy Evolution Explorers far ultraviolet detector (blue); the Hubble Space Telescopes wide field and planetary camera 2 in B-band visible light (green); the Spitzer Space Telescopes infrared array camera at 8 microns (red); and the Chandra X-ray Observatorys advanced CCD imaging spectrometer-S array instrument (purple). Approximately 100 million years ago, a smaller galaxy plunged through the heart of Cartwheel galaxy, creating ripples of brief star formation. In this image, the first ripple appears as an ultraviolet-bright blue outer ring. The blue outer ring is so powerful in the Galaxy Evolution Explorer observations that it indicates the Cartwheel is one of the most powerful UV-emitting galaxies in the nearby universe. The blue colour reveals to astronomers that associations of stars 5 to 20 times as massive as our sun are forming in this region. The clumps of pink along the outer blue ring are regions whe