Supernova nucleosynthesis

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Nucleosynthesis

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Supernova nucleosynthesis refers to the production of new chemical elements inside supernovae. It occurs primarily due to a neutron capture process known as the r process. However, there are other processes thought to be responsible for some of the element generation, notably a proton capture process known as the rp process and a photodisintegration process known as the gamma (or p) process

1 Supernovae
2 Elements fused
3 The R-Process
4 See also
5 External links

[edit] Supernovae

Main Article: Supernova.

A supernova is a massive explosion of a star that occurs under two possible scenarios. The first is that a white dwarf star undergoes a nuclear based explosion after it reaches its Chandrasekhar limit from 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 iron in its nuclear fusion (or burning) processes. Iron has one of the highest binding energies of all of the elements and is the last element that can be produced by nuclear fusion, exothermically. All nuclear fusion reactions from here on are endothermic and so the star loses energy. The star's gravity then pulls its outer layers rapidly inward. The star collapses very quickly, and then explodes.

[edit] Elements fused

Composite image of Kepler's supernova from pictures by the Spitzer Space Telescope, Hubble Space Telescope, and Chandra X-ray Observatory.

Due to the large amounts of energy released in a supernova explosion much higher temperatures are reached than stellar temperatures. Higher temperatures allow for an environment where elements up to the atomic mass of 254 are formed, californium being the heaviest known of, though it is seen only as a synthetic element on Earth. In nuclear fusion processes in stellar nucleosynthesis, the maximum weight for an element fused is that of iron, with an atomic mass of 55.845. Fusion of elements as heavy as iron is quite rare and occurs only in the largest of stars. A neutron capture process known as the s process which also occurs during stellar nucleosynthesis can create elements up to bismuth with an atomic mass of approximately 209. However, the s process occurs slowly so most of the elements heavier than oxygen that make life possible were created in supernovas.

[edit] The R-Process

During supernova nucleosynthesis, the r process (r for rapid) is the primary reason for supernova's fusion ability. The process is a neutron capture process which occurs in high neutron density with high temperature conditions. In the r process nuclei are bombarded with a large neutron flux to form highly unstable neutron rich nuclei which very rapidly undergo beta decay to form more stable nuclei with higher atomic number and the same atomic weight. The neutron flux is abnormally high at about 10²² neutrons per square centimeter per second.