nucleosynthesis: Transformation of Hydrogen to Helium

The first step is the fusion of four hydrogen nuclei to make one helium nucleus. This “hydrogen-burning” phase supplies energy to stars on the main sequence of the Hertzsprung-Russell diagram. There are two chains of reactions by which the conversion of hydrogen to helium is effected: the proton-proton cycle and the carbon-nitrogen-oxygen cycle (sometimes referred to simply as the carbon cycle). They were both first studied and proposed as sources of stellar energy by H. Bethe and independently by C. von Weiszäcker. The proton-proton cycle operates in less massive and luminous stars like the sun, while the carbon-nitrogen-oxygen cycle (which speeds up dramatically at higher temperatures) dominates in more massive and luminous stars.

Sections in this article:

• Introduction
• Creation of the Heavier Elements
• The Carbon-Nitrogen-Oxygen Cycle
• The Proton-Proton Cycle
• Transformation of Hydrogen to Helium
• Bibliography

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