What type of nuclear reaction naturally occurs on the Sun?

Nuclear fusion is the process that occurs naturally on the Sun, which is essential for its energy production. This reaction involves the merging of light atomic nuclei to form a heavier nucleus, releasing a substantial amount of energy in the process. In the core of the Sun, hydrogen nuclei fuse to create helium through a series of reactions known as the proton-proton chain reaction. These fusion processes generate the immense heat and light that the Sun emits, ultimately providing energy for life on Earth.

The conditions within the Sun—extremely high temperatures and pressures—facilitate this fusion process, allowing it to occur continuously and sustain the Sun's long lifespan. The energy produced through fusion is also what balances the gravitational forces pulling inward, maintaining the Sun's structure.

In contrast, nuclear fission, which involves the splitting of heavier atomic nuclei into lighter ones, does not occur naturally in the Sun. Radioactive decay refers to the process by which unstable atomic nuclei lose energy by emitting radiation, which is not the dominant reaction in the Sun's core. Thermal radiation is a process of energy transfer via electromagnetic waves but is not a type of nuclear reaction occurring within the Sun.