Burning neon
As a neon-burning process refers to a group of nuclear fusion reactions within heavier star with an initial mass of at least eight solar masses , in which the conversion of the starting material Neon energy is released. This requires high temperatures of at least 1.2 · 10 9 Kelvin and high densities of at least 4 · 10 9 kg / m³.
At such high temperatures, photo disintegration plays an important role. Some of the neon nuclei 20 Ne generated by earlier fusion processes (see carbon burning ) are split into oxygen 16 O and helium 4 He ( α particles ) by high-energy gamma quanta γ :
| 20 Ne + γ | → 16 O + 4 He |
The 4 He can react with another 20 Ne to produce magnesium 24 Mg:
| 20 Ne + 4 He | → 24 Mg + γ |
In an alternative reaction path, a neutron attachment to the 20 Ne takes place, which then reacts with an α-particle and also forms 24 Mg with emission of a neutron n :
| 20 Ne + n | → 21 Ne + γ |
| 21 Ne + 4 He | → 24 Mg + n |
The neutron generated in the second step can be used in a new run of the reaction.
The neon burning starts when the previous carbon burning has used up the carbon in the star's core and an oxygen-neon-magnesium core has been created. The fusion processes come to a standstill, whereupon the radiation pressure in the core is no longer sufficient to counteract its own gravity . It is therefore compressed until the resulting rise in temperature and pressure has finally created the conditions for the neon to burn.
During the neon burn, the core becomes enriched with oxygen and magnesium, and neon is broken down. After a few years (in the Star article there is an exemplary time scale for the duration of the individual burning phases) the star has used up all of its neon, and the core cools down again and is compressed by gravity. The temperature and pressure rise again until the oxygen burns .
See also
credentials
- ↑ Clayton, Donald: Principles of Stellar Evolution and Nucleosynthesis , (1983) bibcode : 1983psen.book ..... C