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DrLich
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During the neon-burning process in stars, why do two Neon-20 atoms fuse into Oxygen-16 and Magnesium-24 instead of forming Calcium-40?
Thank you very much!Bandersnatch said:The 2Ne20->O16+Mg24+energy reaction is the nett result. It's actually two reactions.
First, neon is photodisintegrated into oxygen and an alpha particle:
Ne20+gamma->O16+He4
Normally the reverse reaction would occur, keeping the neon stock steady. But with sufficient temperature, alpha capture by another neon nucleus is preferred:
Ne20+He4->Mg24+gamma
So you need two neon nuclei, one to donate the alpha particle, the other to subsequently absorb it. It's not that the two neons collide, and two other nuclei pop out.
See e.g. here:
https://iopscience.iop.org/article/10.1088/0004-637X/797/2/83
The neon-burning process is a stage in the evolution of massive stars, occurring after the helium-burning phase. During this process, neon (Ne) is fused into heavier elements, primarily magnesium (Mg) and silicon (Si), through nuclear reactions at extremely high temperatures (around 1.2 billion Kelvin). This phase typically occurs in stars with masses greater than approximately 8 solar masses, leading to the formation of a core composed of heavier elements.
Neon burning occurs after the helium-burning phase and before the final stages of stellar evolution, which include carbon and oxygen burning. It typically takes place in the core of a star when the core temperature and pressure are sufficient to initiate the fusion of neon into heavier elements. This stage is part of the red supergiant phase for massive stars.
For neon burning to occur, specific conditions must be met, including extremely high temperatures (around 1.2 billion Kelvin) and sufficient pressure within the stellar core. These conditions are achieved when a star has exhausted its helium fuel and contracts under gravity, leading to increased core temperatures that enable the fusion of neon into heavier elements.
During the neon-burning process, neon is primarily converted into magnesium (Mg) and silicon (Si). The reactions can also produce smaller amounts of other elements, such as phosphorus (P) and sulfur (S), depending on the specific fusion pathways and conditions present in the star's core.
After the neon-burning process, the star continues to evolve, leading to further stages of nuclear fusion, including carbon and oxygen burning. Eventually, the core becomes composed of iron and other heavy elements, at which point fusion reactions become endothermic, leading to the star's collapse and potentially resulting in a supernova explosion. The remnants may form neutron stars or black holes, depending on the initial mass of the star.