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How does nuclear fusion power the Sun?

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Illustration showing the eight planets of the solar system in order from the Sun-Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune-depicted to scale by size, with labeled diameters in miles and kilometers. The Sun is partially visible on the left for comparison. — Solar system The planets (in comparative size) in order of distance from the Sun.

The Sun is powered by nuclear fusion, a process occurring in its core where extreme pressure and density allow hydrogen nuclei to overcome electrostatic repulsion and fuse into helium.1

The primary mechanism for this energy production is the proton-proton chain, a sequence of thermonuclear reactions where four hydrogen nuclei are combined to form one helium nucleus. During this conversion, approximately 0.7 percent of the original mass is lost, as the mass of four hydrogen atoms is slightly greater than that of a single helium atom. This "missing" mass is converted into energy according to Albert Einstein's formula $E = m c^{2}$ .231

This energy is released as gamma rays, the kinetic energy of product particles, and neutrinos. While neutrinos escape the Sun immediately, the radiant energy travels outward through the solar interior, eventually reaching the surface and providing the light and heat that sustain the solar system.123