Stars which are many times the sun's mass spend a long time in the giant stage, and in the giant stage the surface of the star is not subject to very much gravitational attraction, and so the star is able to eject a lot of... of matter. Even the sun does that at the moment. It's known as the Solar Wind and that ejects particles which, in the case of the sun, we see in the Northern Light. But in... if you have a big giant, then this wind is much stronger and it has been found by Pachinsky - an astrophysicist at Norwood, Princeton - who... that stars up to about eight times the solar mass lose so much matter by blowing out wind that they collapse finally into... into a white dwarf. Now, if however you go beyond that, then not all the mass is blown out. You go through all the stages that I mentioned, finally producing nickel 56, and once you have produced nickel 56, then there is no further way of producing nuclear energy near the center of the star. So the only force then acting is gravity, and the center of the star then collapses catastrophically into a neutron star, and that is such a strong collapse that it is able to expel all the rest of the star, and you see that then as a supernova. These supernovas were discovered scientifically by Zwicky and Baadere in the 1930s and they... there are two types of supernovas. One is this type, and that's the only type I want to talk about. The other type starts from white dwarfs coming to the limit of their stability before they collapse by gravitation. The white dwarf type is called Type One, and the end of evolution of... of a big star is called Type Two.