What happens to the core of a red giant as hydrogen depletes?

As a red giant exhausts its hydrogen fuel in the core, the core becomes increasingly rich in helium. This occurs because, during the main sequence phase of a star's life, hydrogen nuclei fuse to form helium through nuclear fusion. As the hydrogen in the core is consumed, the core contracts under gravity, leading to an increase in pressure and temperature. The rising temperature eventually becomes hot enough to allow the fusion of helium into heavier elements in the later stages of a star’s evolution.

The process significantly enriches the core with helium since hydrogen is no longer available to fuse. This helium-rich core will then undergo further fusion processes in a red giant’s subsequent stages of development, creating even heavier elements. Understanding this mechanism is critical for grasping the life cycles of stars and their eventual fate, as well as the chemical composition of the universe.