Supernova Remnant of Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion 325 years ago. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died.
Cassiopeia A is a supernova remnant. It is the strongest radio source in the sky outside the solar system and was one of the first radio sources to be discovered, in 1947. The cloud of material ejected in the explosion is about 10 light years across and is expanding at the rate of 4,000-6,000 km/s. It has a temperature of about 50 million degrees Fahrenheit.
Remnants of supernova Cassiopeia A illuminate the heavens like Fourth of July fireworks. The colorful streamers float across the sky in this photo exposed by NASA's Hubble Space Telescope in 2000 and 2002. Cassiopeia A is the youngest known supernova remnant in our Milky Way Galaxy and resides 10,000 light-years away in the constellation Cassiopeia.
The Danish astronomer Tycho Brahe was noted for his careful observations of the night sky from his observatory on the island of Hven. In 1572 he noted the appearance of a new star, also in the constellation Cassiopeia. Later called SN 1572, this supernova was associated with a remnant during the 1960s.