Carbon-burning process

Carbon-burning process is a stage in the evolution of stars. This process involves the fusion of carbon into heavier elements and occurs in high-mass stars that have used up their supply of helium. The carbon-burning phase marks a critical period in the life cycle of a star, leading to the production of elements essential for life as we know it.

Overview

The carbon-burning process begins when the core temperature of a star reaches approximately 600 million Kelvin. At this extreme temperature, carbon nuclei fuse together to form heavier elements such as neon, sodium, magnesium, and oxygen. This process releases a tremendous amount of energy, which contributes to the star's luminosity and supports it against gravitational collapse.

Conditions for Carbon Burning

For the carbon-burning process to commence, a star must have a core temperature of at least 600 million Kelvin and a core density of around 2×10^9 kg/m^3. These conditions are typically found in stars with masses greater than about 8 times that of the Sun. Stars of lower mass do not reach the necessary conditions for carbon burning and end their lives after the helium-burning process, becoming white dwarfs.

Products of Carbon Burning

The primary reactions involved in the carbon-burning process are:

• 12C + 12C → 20Ne + 4He
• 12C + 12C → 23Na + 1H
• 12C + 12C → 24Mg

These reactions produce neon, sodium, and magnesium as the main products, along with the release of alpha particles (helium nuclei) and protons. The exact products and their abundances depend on the specific conditions within the star, including temperature, density, and the presence of other elements.

Significance

The carbon-burning process is a critical step in the nucleosynthesis pathway that leads to the formation of elements heavier than helium. It plays a significant role in the chemical evolution of the universe, contributing to the abundance of elements necessary for the formation of planets and life. Furthermore, the energy released during carbon burning supports the star against gravitational collapse for a time, delaying its eventual death.

Subsequent Evolution

After the carbon-burning phase, stars with sufficient mass can proceed to even higher temperature and density conditions, enabling further fusion processes such as oxygen burning, neon burning, and silicon burning. These processes continue the synthesis of heavier elements up to iron, beyond which nuclear fusion is no longer energetically favorable. The star's core eventually collapses, leading to a supernova explosion or the formation of a black hole or neutron star, depending on the initial mass of the star.

See Also

• Stellar nucleosynthesis
• Helium-burning process
• Supernova
• White dwarf
• Neutron star
• Black hole