This false-color composite image provided by NASA Thursday April 2, 2009 shows the Cartwheel galaxy as seen by the Galaxy Evolution Explorer's Far Ultraviolet detector (blue); the Hubble Space Telescope's Wide Field and Planetary Camera-2 in B-band visible light (green); the Spitzer Space Telescope's Infrared Array Camera (IRAC) at 8 microns (red); and the Chandra X-ray Observatory's 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 GALEX observations that it indicates the Cartwheel is one of the most powerful UV-emitting galaxies in the nearby universe. Although astronomers have not identified exactly which galaxy collided with the Cartwheel, two of three candidate galaxies can be seen in this image to the bottom left of the ring, one as a neon blob and the other as a green spiral.
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