Массивті жұлдыздардағы кремнийдің жанасуы

Very brief sequence of nuclear fusion reactions that occur in massive stars
In astrophysics, silicon burning is a very brief sequence of nuclear fusion reactions that occur in massive stars with a minimum of about 8–11 solar masses. Silicon burning is the final stage of fusion for massive stars that have run out of the fuels that power them for their long lives in the main sequence on the Hertzsprung–Russell diagram. It follows the previous stages of hydrogen, helium, carbon, neon and oxygen burning processes. Silicon burning begins when gravitational contraction raises the star's core temperature to 2.7–3.5 billion kelvins (GK). The exact temperature depends on mass. When a star has completed the silicon burning phase, no further fusion is possible. The star catastrophically collapses and may explode in what is known as a Type II supernova.

After a star completes the oxygen burning process, its core is composed primarily of silicon and sulfur. If it has sufficiently high mass, it further contracts until its core reaches temperatures in the range of 2.7–3.5 GK (230–300 keV). At these temperatures, silicon and other elements can photodisintegrate, emitting a proton or an alpha particle. which creates new elements by the alpha process, adding one of these freed alpha particles However, since no additional heat energy can be generated via new fusion reactions, the final unopposed contraction rapidly accelerates into a collapse lasting only a few seconds. that quickly cools down into a neutron star if the mass of the star is below Between and , fallback of the material will make the neutron core collapse further into a black hole. The outer layers of the star are blown off in an explosion known as a Type II supernova that lasts days to months. The supernova explosion releases a large burst of neutrons, which may synthesize in about one second roughly half of the supply of elements in the universe that are heavier than iron, via a rapid neutron capture sequence known as the r process (where the "r" stands for "rapid" neutron capture).

This graph shows the binding energy per nucleon of various nuclides. The binding energy is the difference between the energy of free protons and neutrons and the energy of the nuclide. If the product or products of a reaction have higher binding energy per nucleon than the reactant or reactants, then the reaction is exothermic (releases energy) and can go forward, though this is valid only for reactions that do not change the number of protons or neutrons (no weak force reactions). As can be seen, light nuclides such as deuterium or helium release large amounts of energy (a big increase in binding energy) when combined to form heavier elements—the process of fusion. Conversely, heavy elements such as uranium release energy when broken into lighter elements—the process of nuclear fission. In stars, rapid nucleosynthesis proceeds by adding helium nuclei (alpha particles) to heavier nuclei. As mentioned above, this process ends around atomic mass 56. Decay of nickel 56 explains the large amount of iron 56 seen in metallic meteorites and the cores of rocky planets.