What process occurs in the sun's core where hydrogen atoms combine to form helium?

The process in the sun's core where hydrogen atoms combine to form helium is known as nuclear fusion. In this process, extreme temperatures and pressures within the sun enable hydrogen nuclei (protons) to overcome their natural repulsion (due to positive charge) and collide with enough energy to fuse together, creating helium nuclei. This reaction releases a tremendous amount of energy in the form of light and heat, which is crucial for sustaining the sun's energy output and, by extension, life on Earth.

In contrast to nuclear fusion, fission reaction involves the splitting of heavy atomic nuclei into smaller ones and is generally associated with nuclear power technology on Earth, not solar processes. Thermal radiation involves the emission of energy from an object based on its temperature and does not account for the nuclear transformations in the sun's core. Lastly, photosynthesis is a biological process by which plants convert light energy into chemical energy, fundamentally different from the nuclear processes occurring in the sun. Thus, nuclear fusion is the key mechanism that powers the sun and enables the energy that reaches the Earth.