| On 22 September, 2004, a supernova was discovered in the spiral galaxy NGC 6946 in the constellation of Cygnus, near the border with Cepheus. A supernova is a star exploding in a huge catastrophic event that causes such a bright eruption that it can be seen from galaxies distant from the one where it occurred. This is a type II supernova, which means it is caused by the core of an old star collapsing after it has burned all its nuclear fuel. The core collapse releases a huge amount of gravitational energy, which produces a shock wave that passes out of the star, causing nuclear reactions as it goes. The shock wave produces an initial bright burst, then the elements cobalt and nickel, produced by the nuclear reactions mentioned, will decay producing yet more light for several weeks. |
