Helium fusion

Helium fusion is a kind of nuclear fusion that takes place in dense stars. Red dwarf stars are not dense enough to become hot and dense enough to trigger Helium fusion, when they exhaust the Hydrogen used for Hydrogen fusion. A star needs to be forty percent the mass of Sol, our sun, to fuse Helium. Fusing Helium to Carbon releases much less energy than fusing Hydrogen to Helium, so Helium fusing period of a star's life is much briefer than its Hydrogen fusing period.