shell-source model

The term "shell-source model" in astronomy refers to a model used to describe the interiors of giant and supergiant stars. These stars have evolved past the main sequence and have exhausted the hydrogen in their deep interiors, forming inert cores primarily composed of helium ash. Energy generation in these stars is assumed to occur in a thin shell surrounding this core, where remaining fuel undergoes nuclear fusion.1

This model helps explain the observed luminosities, masses, and radii of giant and supergiant stars. As a star consumes its hydrogen fuel, its core grows, and its outer envelope expands. This process is crucial for understanding stellar evolution, particularly for stars that are more massive than the Sun.12

It's important to distinguish this from the "shell nuclear model" or "shell atomic model," which describe the structure of atomic nuclei and electron energy levels within atoms, respectively.34