A star's evolution after the red giant phase depends on its mass For stars from 1 to 2 solar masses, the hydrogen burning shell eats its way outward leaving behind more helium ash The core becomes more massive and contracts Contraction heats the core, it becomes more dense. The density of the core increases to where the electrons and helium nuclei become degenerate Electron and Neutron degeneracy are stellarapplications of the Pauli Exclusion Principle. The core begins to act more like a liquid than a gas, it becomes incompressible, further contraction stops.