What fuel is Betelgeuse burning?

Betelgeuse is a red supergiant star that is primarily burning helium in its core through the process of helium fusion. In its earlier life, it burned hydrogen, but as it evolved, it exhausted its hydrogen supply and transitioned to helium burning. This fusion process generates energy that allows the star to maintain its size and brightness as it approaches the later stages of stellar evolution. Eventually, Betelgeuse will progress to fuse heavier elements until it ultimately undergoes a supernova explosion.