Nuclear fusion
In chemistry and physics, Nuclear fusion is the reaction by which two or more nuclei fuse together to form a heavier nucleus, albeit one that is lighter than the sum of the constituent nuclei. The missing mass is converted to energy as per the famous <math>E=\frac{m}{c^2}</math> formula.
The fusion of nuclei lighter than iron, which has the highest binding energy alongside nickel, releases more energy than was used to start the process, while fusion of post-iron elements requires more energy than is released.
Fusion occurs naturally in stars, where the process is started by gravitational contraction and the resulting heating. Once a threshold is reached in mass (roughly Template:Convert), a proton-proton reaction starts, due to the core reaching temperatures in excess of ten million Kelvins, and quickly becomes self-sustaining due to gravitational confinement.
Nuclear fusion was first observed by Mark Oliphant in 1932, building on experiments in nuclear transmutation by Ernest Rutherford. Currently, nuclear fusion is under research as an alternative energy source, with leading experiments in Europe.