Image of the Day: The Cartwheel Galaxy -A Cosmic Mashup


Once a normal spiral galaxy like the Milky Way, the Cartwheel Galaxy about 500 million lightyears from Earth descibed as "one of the most complicated structures" in the universe, underwent a spectacular head-on collision about 200 million years ago with a smaller galaxy as seen in this NASA Hubble Space Telescope true-color image.Moving at high speed, the shock wave from the collision swept up gas and dust, creating a starburst around the galaxy's center portion that went unscathed, which explains the bluish ring around the center, brighter portion. It can be seen that the galaxy is slowly beginning to retake the form of a normal spiral galaxy, with arms spreading out from a central core. There are an exceptionally large number of black holes in the rim of the galaxy as can be seen in the X-ray inset at upper right in the image.

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