solar core

Cut-away illustration of the Sun showing the core region at center. 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/m (150 g/cm) 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 (3.84×10 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.