Solar core

The solar core is the hot, dense region at the center of the Sun where energy is generated by nuclear fusion. It is considered to extend from the Sun's center to about 0.2 of the solar radius (139,000 km; 86,000 mi). It is the hottest part of the Sun and of the Solar System. It has a density of 150,000 kg/m3 (150 g/cm3) at the center, and a temperature of 15,000,000 K (27,000,000 °F; 15,000,000 °C). The core is made of hot, dense plasma (ions and electrons), at a pressure estimated at 26.5 million gigapascals (3.84×1012 psi) at the center. Due to fusion, the composition of the solar plasma drops from about 70% hydrogen by mass at the outer core, to 34% hydrogen at the center. The core contains 34% of the Sun's mass, but only 3% of the Sun's volume, and it generates 99% of the fusion power of the Sun. There are two distinct reactions in which four hydrogen nuclei may eventually result in one helium nucleus: the proton–proton chain reaction – which is responsible for most of the Sun's released energy – and the CNO cycle.