Solar core

The core of the Sun is considered to extend from the center to about 0.2 solar radius. It is the hottest part of the Solar System. It has a density of up to 150,000 kg/m³ (150 times the density of water on Earth) and a temperature of close to 15,000,000 kelvins (by contrast, the surface of the Sun is close to 6,000 kelvins). Energy is produced by exothermic thermonuclear reactions (nuclear fusion) that mainly convert hydrogen into helium. The core is the only location in the Sun that produces an appreciable amount of heat via fusion: the rest of the star is heated by energy that is transferred outward from the core. All of the energy produced by fusion in the core must travel through many successive layers to the solar photosphere before it escapes into space as sunlight or kinetic energy of particles.
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