End stage evolution of the Sun

(1) As the core collapses, it heats the surrounding H to burn furiously in a shell around the core

(2) Energy from H burning shell and gravitational energy released by shrinking core causes the Sun to expand into a Red Giant

(3) As the He core continues to collapses, it rises to tremendous temperatures and pressures

(4) The free electrons are forced so close together that they form a degenerate gas that resist further compression

(5) Degenerate helium core

(6) H burning shell dumps He in the core, causing it to shrink and heat up

(7) When core reaches 100,000,000 K helium fusion ignites

(8) Helium core fusing to form carbon

(9) Core cannot cool by expansion, so the core heats up until ignites a Helium Flash (runaway He fusion reaction

(10) He fusion continues in the core

(11) As the core temperature decreases, the energy output drops, the star shrinks and the surface heats up Yellow Giant

(12) He core now fusing into Carbon + H Shell burning

(13) 2nd Red Giant Phase (Sun swells up even larger than before)

When Helium exhausted in core, Carbon core contraction (until it forms a carbon degenerate core) + He Shell burning + H Shell burning

(14) Planetary Nebula - shell of gas and dust expelled from a low mass red giant