Figure 11-8 RIVUXG A Supernova Remnant This composite image shows Cassiopeia A, the remnant of a supernova that occurred about 3000 parsecs (10,000 ly) from Earth. In the roughly 300 years since the supernova explosion, a shock wave has expanded about 3 parsecs (10 ly) outward in all directions from the explosion site. The shock wave has warmed interstellar dust to a temperature of about 300 K (Spitzer Space Telescope infrared image in red) and has heated interstellar gases to temperatures that range from 104 K (Hubble Space Telescope visible-light image in yellow) to 107 K (Chandra X-ray Observatory X-ray image in green and blue).