When a star sheds its outer envelope explosively as a nova or supernova, it returns to the interstellar medium elements heavier than hydrogen that it has synthesized in its interior. Future generations of stars formed from this material will therefore start life with a richer supply of heavier elements than the earlier generations of stars. A schematic diagram showing the main sequence and areas occupied by stars at different stages of evolution is Hertzsprung Russell diagram. Absolute magnitude is plotted against color index in this example. The dashed lines link stars of different luminosities with the same spectral types but different color indices.
Temperature conventionally decreasses towards the right.
Eighter magnitude or luminosity relative to the Sun are frequently used for the verticl scale, The resulting graph may also be called a colour magnitude diagram or colour luminosity diagram according to the actual quantities used. As a result of gravitational forces acting against the nuclear structure of the core of a fuel depleted star, tremendous shock waves are generated which cause the outside layers of the star to be blown away from the core. A catastrophic stellar explosion in which so much energy is released that the supernova alone can outshine an entire galaxy of billions stars. In addition to the radiant energy produced, ten times as much energy goes into the kinetic energy of the material blown out by the explosion, and a hundred times as much is curried off by neutrions. This can happen in one of two ways depending on the type of supernova.