The fusion of hydrogen, helium, and other
elements in regions of a star's interior outside the stellar
core. As the particular fuel is progressively exhausted, the shell moves
outward until it comes to regions too cool to sustain the reactions. For
example, helium burning might take
place in the core (where the hydrogen has been exhausted) with a shell of
hydrogen burning surrounding it.
Stars may have more than one region of shell burning during their stellar
evolution, each shell with its own nuclear reactions.
|Evolution of a star to the stage where it has both
a hydrogen-burning shell and a helium-burning shell