How does the proton-proton cycle turn hydrogen into helium in the Sun?

The proton-proton chain is the primary thermonuclear process by which the Sun converts hydrogen into helium, releasing vast amounts of energy in the process. Because atomic nuclei are positively charged and repel one another, this fusion requires the extreme temperatures and pressures found in the solar core to overcome their electrostatic repulsion.123

The cycle proceeds through several key stages:

• Deuterium Formation: Two protons (${}^1$H) collide to form a deuterium nucleus (${}^2$H). This reaction releases a positron and a neutrino.12
• Helium-3 Production: The deuterium nucleus rapidly captures another proton to form a helium-3 nucleus (${}^3$He), emitting a gamma ray in the process.14
• Helium-4 Synthesis: Two helium-3 nuclei eventually collide to form one stable helium-4 nucleus (${}^4$He), releasing two protons back into the core.14

Ultimately, four hydrogen nuclei are consumed to produce one helium nucleus. Approximately 0.7 percent of the original mass is converted into energy according to Einstein's equation, $E=m{c}^2$, which sustains the Sun's luminosity.123