When small nuclei combine to form a larger nucleus, the process is called nuclear

The process you are describing is called nuclear fusion. Nuclear fusion occurs when two or more lighter atomic nuclei collide at extremely high speeds and combine to form a heavier nucleus. This process is fundamental to the energy production in stars, including our Sun. During fusion, some of the mass from the fusing nuclei is converted into energy, as described by Einstein’s equation $E=mc^2$.

In stars, hydrogen nuclei fuse to form helium, resulting in the release of a tremendous amount of energy in the form of light and heat. This energy is what makes stars shine and is also the powering force behind stellar phenomena.

The conditions required for nuclear fusion are extremely high temperatures and pressures, typically found in the core of stars. The process is distinct from nuclear fission, which involves the splitting of a heavy nucleus into smaller nuclei. Fusion has the potential to provide a clean and virtually limitless source of energy for future power generation, but achieving the necessary conditions for sustained fusion on Earth has proven to be a significant scientific and engineering challenge.