The core of the sun is the region that extends from the center to about 20–25% of the solar radius. It is here, in the core, where energy is produced by hydrogen atoms (H) being converted into nuclei of helium (He). ... The core is the only part of the sun that produces an appreciable amount of heat through fusion.
Rest assured ... When the sun runs low on Hydrogen, it'll go through several complex changes, and it'll end up at much much lower temperature, with much much lower energy output.
