Heliumverbrennung

Heliumverbrennung, also known as the triple-alpha process, is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into one carbon-12 nucleus. This process is crucial for the production of carbon in stars and is a key step in stellar nucleosynthesis.

The triple-alpha process begins when two helium-4 nuclei fuse to form an unstable beryllium-8 nucleus. This beryllium-8 nucleus has a very short half-life and typically decays back into two helium-4 nuclei. However, if a third helium-4 nucleus collides with the beryllium-8 nucleus before it decays, they can fuse to form a stable carbon-12 nucleus. This reaction releases a significant amount of energy.

The triple-alpha process requires extremely high temperatures and densities, typically found in the cores of stars that have exhausted their hydrogen fuel. These conditions are usually reached in red giant stars, which have expanded and cooled on their surface but have very hot and dense cores. The energy generated by helium fusion contributes to the outward pressure that supports the star against gravitational collapse.

The abundance of carbon in the universe is a direct result of the triple-alpha process. Carbon is a fundamental element for life as we know it, and its production in stars makes it available for the formation of planets and organic molecules. Without helium burning, the universe would be significantly different, lacking the building blocks for complex chemistry and potentially life. This process is a prime example of how stellar evolution shapes the chemical composition of the cosmos.