Supernova remnant Cassiopeia A, composite image. This is the remains of a star that exploded 325 years ago. Infrared data (red) from the Spitzer Space Telescope show warm dust in the outer shell with a temperature of about 25 degrees Celsius. Visible data (yellow) from the Hubble Space Telescope show the filamentary structure of hot gases with a temperature of about 10,000 degrees Celsius and X-ray data (blue and green) from the Chandra X-ray Observatory show extremely hot gases with a temperature of about 10 million degrees Celsius that were created when material ejected from the supernova smashed into surrounding gas and dust.