Nuclear fusion
= Nuclear fusion
{title2=$Q=(m_{\rm initial}-m_{\rm final})c^2$}
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.