Transcript: The core of an evolving star like a red giant contracts until the temperature reaches roughly two hundred million Kelvin. At this point a new energy source is available from the fusion of helium nuclei by the triple alpha process. This is a two stage reaction. In the first stage two helium four nuclei combine to form a beryllium 8 nucleus with a photon, and in the second stage a beryllium 8 nucleus combines with a helium 4 nucleus to form a carbon 12 nucleus with a photon released. Beryllium is unstable, and so the decay of beryllium before it can combine with another helium nucleus reduces the efficiency but does not quench the process. In low mass stars the energy released can rapidly heat the core and cause what’s called a helium flash. This can consume the helium fuel in only a few seconds although the effects are seen at the outer cool envelope of the star hundreds or thousands of years later and can last thousands of years. The Sun faces a helium flash roughly three hundred million years after it leaves the main sequence.