Synthesis of carbon in a burning star. Two alpha particles react to form beryllium-8. Beryllium-8 and an alpha particle react to form carbon-12, proceeding via the Hoyle state. This state in carbon-12 is a “resonance” in the beryllium-8 plus alpha-particle system. Once the resonant state is formed, it tends to decay by breaking up into beryllium-8 and an alpha particle. However, approximately four out of ten thousand decays bring the excited carbon-12 nucleus to its stable ground state.