The Chandra X-Ray Observatory spent 150 hours examining supernova remnant G21.5-0.9, revealing a beautiful ghostly shell. The shell is created by the shockwave of particles ejected by the supernova explosion as they slam into material that was sloughed off earlier by the star. This shockwave heats the surrounding material to millions of degrees causing it to blaze in the X-ray spectrum visible to Chandra. The star that produced this explosion was probably 10 times larger than the Sun.