The center of the sun is called its core. At the sun's core, atoms are packed very densely at 14 times the density of lead. The temperature of the core exceeds 15 million degrees Kelvin.
The core is the hottest part of the sun. This interior part of the sun houses the nuclear fusion reactions that characterize the sun. In nuclear fusion, two hydrogen nuclei combine to form a helium nucleus. Energy is emitted in the form of gamma rays. A particle called a neutrino is formed, as well. The high temperature of the core of the sun powers this fusion reaction. High temperatures cause hydrogen atoms to move around rapidly and collide with one another.