Fact Sheet
Cosmic Bauble
It looks like a brightly colored Christmas ornament, but this is really the expanding remains of an exploded star known as Cassiopeia A. This supernova remnant is about 10 light-years in diameter. It formed when a supergiant star exploded about 400 years ago (as seen from Earth). Its outer layers, which are shown in red and green in this X-ray image from the orbiting Chandra X-Ray Telescope, are expanding at almost one-tenth of lightspeed. The outer blue layer is a shockwave produced as material from the exploding star plows into surrounding gas. Cassiopeia A is an important object in the effort to understand how massive stars explode. [NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.]
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