Silicon-burning process

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. Silicon burning proceeds by photodisintegration rearrangement, which creates new elements by the alpha process, adding one of these freed alpha particles (the equivalent of a helium nucleus) per capture step in the following sequence (photoejection of alphas not shown): {| border="0" |- style="height:2em;" | ||+ || ||→ || |- style="height:2em;" | ||+ || ||→ || |- style="height:2em;" | ||+ || ||→ || |- style="height:2em;" | ||+ || ||→ || |- style="height:2em;" | ||+ || ||→ || |- style="height:2em;" | ||+ || ||→ || |- style="height:2em;" | ||+ || ||→ || |} Although the chain could theoretically continue, steps after nickel-56 are much less exothermic and the temperature is so high that photodisintegration prevents further progress. The silicon-burning sequence lasts about one day before being struck by the shock wave that was launched by the core collapse.