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. During this phase, the star's outer layers expand significantly, and the star becomes cooler and redder, evolving into a red giant. For stars with masses similar to or slightly larger than the Sun, this stage is followed by helium shell burning around a carbon-oxygen core. More massive stars may undergo further fusion stages, but helium burning is a crucial step in their life cycle. The energy released from helium fusion supports the star against gravitational collapse. The products of helium burning, primarily carbon and oxygen, can be enriched in the star's atmosphere and eventually expelled into the interstellar medium through stellar winds or supernova explosions.