Red Giant Stars CWRU Astronomy Department Home Page Red giants are stars that have exhausted their core hydrogen fuel, and are now in the helium-burning stage of their lives. The burning of helium is known as the triple alpha process .
Red giants are much larger, more massive, and more diffuse than main sequence stars.
They are also much more luminous. They burn helium into carbon, and sometimes oxygen, in their cores, and have hydrogen-burning shells around their cores where helium continues to be produced. Stars that are about solar-sized and larger go through the red giant stage during the course of their lives. Stars that are a lot smaller never get hot enough to burn helium. At this point in a star's life, it starts losing mass.