The life cycle of the Sun H-R Diagram When temp reaches 350x106K the – electrons become non-degenerate, the RED GIANT BRANCH – As core contracts, core temp core expands and cools, stable HE core reaches 108K He burning ignited in the core via with H shell burning. triple alpha process. Red Giant has dense core containing most of its mass at ~ 50 x106K, core is so dense electrons become degenerate electron gas (no ASYMPTOTIC GIANT BRANCH - longer obey perfect gas law and pressure does not Triple-Alpha process converts helium increase with temperature) . High thermal core to carbon. He exhausted in core, conductivity of degenerate electron gas allows but He burning continues in burning to spread quickly through the core. The surrounding layer. C core contracts, increase in temperature does not cause an increase burning outer layer, causing the in pressure, and so the heat energy increases the envelope to expand 2nd Red Giant rate of the triple alpha process generating more Phase. (AGB Star) energy, further increasing the temperature – HELIUM FLASH PLANETARY NEBULA - The SUBGIANT BRANCH -MST, H-burning electrons in the core become stops in core, but continues in a shell degenerate again. Triple-alpha around the core. Core contracts, process is very sensitive to temp heating layer of burning hydrogen, changes. He burning shell causes the heating surrounding envelope star to become unstable. The star radius of star increases, luminosity pulsates (thermal pulses) and ejects increases, temperature decreases. outer layers via its super wind. Since core is degenerate it cannot PMS STAR- contracts while contract and never reaches accreting matter onto its core, temperature for C burning temperature rises, eventually heats WHITE DWARF BLACK DWARF up to 107K, thermonuclear reactions begin. When star no long contracts Triple-Alpha Process to provide energy, is in thermal equilibrium and obtains energy from H burning Zero-Age Main Sequence Star .