Bob the Super Hamste writes: "The BBC is reporting that the mystery of a 2000 year old supernova has been solved. The supernova RCW 86 was observed in 185AD by Chinese astronomers and was visible for eight months. Recently sicentists have wondered how the supernova grew so big. By combining data from the Chandra X-ray telescope and the XMM-Newton Observatory with recent images from the US space agency Nasa's Spitzer and Wide-field Infrared Survey (Wise) telescopes scientists scientists have figured out that the supernova expanded into a relatively empty bubble of space. These empty bubbles of space are typically associated with a core collapse supernova but the core remnant is high in iron which instead is associated with a type 1A super nova. The findings are published in the Astrophysical Journal."