Fusion combines nuclear reactants into heavier compound nuclei or products. A net decrease in rest mass releases energy; heavier fusion reactions can instead require energy. Stellar nuclear fusion uses exothermic networks to power stars, and quantum tunnelling through the Coulomb barrier permits many charged-particle reactions at stellar temperatures.
Repulsion between positively charged nuclei creates this electrostatic energy barrier outside the short-range nuclear interaction. Quantum tunnelling allows reaction at thermal energies below its classical height and contributes the penetration factor in the Gamow peak.
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Nuclear fusion is a process in which two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy in the process. This is the same reaction that powers the sun and other stars. In fusion, the strong nuclear force overcomes the electrostatic repulsion between the positively charged protons when the nuclei are brought close enough together, allowing them to merge.