Approximately 100 million years ago, a smaller galaxy plunged through the heart of the Cartwheel galaxy, creating ripples of brief star formation. As with the Pinwheel galaxy above, this composite image includes data from NASA's Spitzer, Hubble, GALEX and Chandra observatories.
The first ripple appears as a bright blue outer ring around the larger object, radiating ultraviolet light visible to GALEX. The clumps of pink along the outer blue ring are X-ray (observed by Chandra) and ultraviolet radiation.
A combination of visible and infrared light from Hubble and Spitzer, the yellow-orange inner ring and center of the galaxy represent the second ripple, or ring wave, created in the collision. Tints of green are older, less-massive visible-light stars. Although astronomers haven't pinpointed 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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