Since the luminosity rises, the star expands so that the helium fusion ceases, and the hydrogen shell burning restarts.

During helium fusion, stars build up an inert core rich in carbon and oxygen.

The carbon and oxygen from helium fusion would be valuable resources in themselves, he realized.

Carbon-related stars are stars whose spectra indicate production of carbon by helium triple-alpha fusion.

This star is primarily composed of a carbon-oxygen mixture that was generated by helium fusion in the progenitor star.

This eventually leads to ignition of helium fusion (which includes the triple-alpha process) in the core.

In more massive stars, the ignition of helium fusion occurs relatively quietly.

After the flash, helium fusion continues at an exponentially decaying rate for about 40% of the cycle as the helium shell is consumed.

Intermediate-mass stars undergo helium fusion and develop a degenerate carbon-oxygen core.

Eventually the core is compressed enough to start helium fusion, and the star now gradually shrinks in radius and its surface temperature increases.