Carbon-burning process

The carbon burning is a nuclear fusion reaction by which energy is produced in massive stars with an initial mass of at least four solar masses. It occurs after the fusion of lighter elements has come to a standstill. The misleading term carbon burning is historical and has nothing to do with a chemical burn.

The carbon burning sets high temperatures of over 6,108 degrees Kelvin and densities of about 2108 kg / m³ advance. Energy expenditure is proportional to the 27th power of the temperature. Consequently causes an increase of the temperature by 5%, an increase to 373 % in the release of energy.

First type of fusion

The first possibility of a merger is that it combines carbon 12C with helium 4He.

Second type of fusion

Another possibility is the fusion of two carbon nuclei 12C. In a series of reactions one or two other cores are produced:

For the two as endothermic reactions marked energy must be expended, that is, they provide the star no energy. The second reaction, n arise in the magnesium 23mg and a neutron, is one of the few fusion processes in the course of stellar evolution, where at all neutrons are released.

Expiration

The carbon burning starts when the helium burning is extinguished. During the helium burning star helium ( He) are transformed into carbon and oxygen until no longer enough helium is present to maintain the fusion. The inactive, mainly consisting of carbon and oxygen core crashes then by the gravitational force into itself, resulting in a temperature and density increase causes until finally the ignition temperature is reached for the carbon burning. By radiation pressure generated then the core is stabilized, and its further compression is stopped. The increase in temperature in the interior of the star in a shell around the core area again the helium burning insert, a so-called shell burning. The strong increase in the release of energy by nuclear fusion causes a swelling of the star to the red giant star.

During carbon burning, the core area is enriched with the reaction products of oxygen, magnesium ( Mg) and neon (Ne ), until after a few thousand years, the carbon is depleted and the fusion reaction comes to a standstill. Thereafter, the core cools down again and there was another together. In the article there is a star exemplary time scale for the duration of each firing stages. The contraction causes a rise in temperature until the Neonbrennen can use. Around the core of the star, in turn, the shell is then burning of carbon, further outside of helium and hydrogen (see hydrogen burning ) a.

After completion of the star Neonbrennens masses become unstable with between four and eight solar mass, since they do not have sufficient mass to obtain the core by means of a further compression of the rise of the temperature to the required temperature of the oxygen firing. Thus, there is the core of the outward radiation pressure due to the absence of the fusion reaction. Then collapse the core accelerated due to its own mass. According to the Pauli principle must be no two electrons in the same state. Thus, electrons have to move to higher energy levels. This causes a degeneration pressure that eventually counteracts the collapse. But unlike stars with a mass up to three solar masses here is this degeneracy pressure is not sufficient to bring the contraction to a complete standstill. As a result, there is an inverse beta decay of the protons, which originate from all protons in the nucleus neutrons. Here, the degeneracy pressure decreases abruptly and the nuclear transformations accelerate. All this happens in a few seconds throughout the nucleus and leads to an enormous release of energy, and has as a result of a so-called supernova. As a remnant finally remains only a about 10 km in diameter comprehensive neutron star.

Stars with masses larger than eight solar masses go to the Neonbrennen and finally merge all the lighter elements up to iron. The individual combustion phases go always faster over each other.

Hydrogen burning helium burning · · · carbon burning Neonbrennen · · oxygen burning silicon burning

  • Astrophysical process
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