heliumcore

The helium core is the central region of a star where helium is the dominant element. It forms after the hydrogen in the core is exhausted, leaving a helium-rich core that contracts and heats as the star evolves.

In stars with relatively low to intermediate mass, the contracting helium core becomes electron-degenerate and reaches ignition conditions abruptly in a helium flash. In more massive stars, helium ignites non-degenerately at lower density, and the core begins sustained helium fusion without a flash.

Once helium fusion begins, the star enters the helium-core burning phase, primarily via the triple-alpha process, which converts helium into carbon (with some oxygen). This phase lasts longer in more massive stars and shorter in lighter ones, shaping the subsequent evolution of the star.

Helium-core burning shifts the star’s position on the Hertzsprung-Russell diagram to the horizontal branch or red clump for many low- and intermediate-mass stars. After helium is exhausted in the core, the star ascends the asymptotic giant branch, eventually ending life as a white dwarf composed mainly of carbon and oxygen.

The study of helium cores is central to understanding stellar evolution, nucleosynthesis, and the late stages of low-to-intermediate-mass stars, as well as the chemical enrichment of galaxies through advanced evolutionary phases.