heliumcoreburning
Helium core burning is a stage in the evolution of stars that have exhausted the hydrogen in their core. This process occurs in stars with masses greater than about 0.5 solar masses. When the core temperature and pressure become sufficiently high, helium nuclei begin to fuse into carbon. This is known as the triple-alpha process, where three helium nuclei (alpha particles) combine to form a carbon nucleus.
The helium core burning stage is relatively short compared to the main sequence lifetime of a star.