Supernova Nucleosynthesis - Supernova

Supernova

A supernova is a massive explosion of a star that occurs under two principal scenarios. The first is that a white dwarf star undergoes a nuclear based explosion after it reaches its Chandrasekhar limit after absorbing mass from a neighboring star (usually a red giant). The second, and more common, cause is when a massive star, usually a red giant, reaches Nickel-56 in its nuclear fusion (or burning) processes. This isotope undergoes radioactive decay into Iron-56, which has one of the highest binding energies of all of the isotopes, and is the last element that produces a net release of energy by nuclear fusion, exothermically. All nuclear fusion reactions that produce heavier elements cause the star to lose energy or are said to be endothermic reactions. The pressure that supports the star's outer layers drops sharply. As the outer envelope is no longer sufficiently supported by the radiation pressure, the star's gravity pulls its outer layers rapidly inward. The star collapses very quickly, and strikes the incompressible core causing a shockwave that progresses outward through the unfused material of the outer shell. The pressures and densities in the shockwave are sufficient to induce fusion in that material and the star explodes.