Type II Supernovae
Please Note: The above picture is exagerated as to the sizes of the layers and is only a reference graphic, which I created Myself.
Here is a legend for the graphic.
Here is a more presice explination of the process: (a simpler one is found in the report and is easier to understand, for me)
Stars energy is basically fusion reactions. The only thing keeping the gravity of this star from forcing a collapse in on itself is the intense radiation pressure provided by the fusion reactions. In the early stages it fuses its hydrogen into helium, a heavier element. This is the basic 10 million years of a star's life. After this the Hydrogen at the core of the star is exausted and the fusion continues in shell around the helium core. The core contracts under gravity until its temperature is high enough to form the helium into carbon and oxygen. This continues for around 1 million years. Next same thing happens to the carbon core as it is fused into neon, sodium, and magnisium. This new stage lasts around 10,000 years. Again, with a denser core the gravitational pull increases and contracts the core more until the temperatures rise to form heavier elements as the neon is converted to oxygen and magnisium. This lasts around 12 years. The next stage is even shorter, only 4 years, as it is turned to silicone and sulpher. The last stage will now only take a week. The immense gravity and heat turns the silicon to iron. This is the last straw, no more energy can be obtained from the iron core. The result is that the gravity increases and the radiation pressure is lowered, since the core is no longer fusing and radiating pressure. Once the core of iron reaches 1.4 solar masses (1.4 times as large as our sun.), the radiation is overtaken by gravity and the star collapses in on itself. Gravity now condenses the core more. This time the result is that the center endothermically decays into neutrons. The core collapses from half the Earth's diameter to about 100 kilometres in a few tenths of a second and in about one second becomes a 10 kilometer diameter neutron star. The outside collapses onto the inside and a huge amount of potential energy is released, but the blast has not happened yet. The shock wave travels through the star and produces fusion reactions and even heavier elements, such as cobalt and nickle. The shock wave with all the energy hits the surface at 15000 km/s, the temperature rises to 200,000 degrees. THIS is the bang. We get a supernova a galaxy about once every 50 years or close to that.