Roughly 11,300 years ago, a massive star was at the end of its life, its energy fluctuating as it expelled material from its outer layers. Then it exploded and formed the supernova remnant Cassiopeia A (Cas A). Using the Chandra X-ray telescope, an international team of astronomers discovered that the progenitor star of Cas A had between 15 and 20 solar masses, was likely a red supergiant, and exploded when its core collapsed. “Shortly before the star collapsed, part of an inner layer rich in silicon broke apart and mixed with a neighboring layer containing large amounts of neon [a chemical element capable of emitting a characteristic reddish-orange light],” Kai Matsunaga of Kyoto University, Japan, told Astronomy Today. Neon burns as it is pulled inward and silicon is transported out of the star, indicating that the final burning process rapidly altered the star’s internal structure. The light from Cas A’s explosion reached Earth around the year 1660 (Astrophysical Journal, September 2).
