Repeat the climb on the HR diagram
When the core of the Sun is completely fused to Carbon, the same
process of a shrinking core, shell burning, and expanding envelope
occurs just like that following hydrogen exhaustion. The star climbs
back up the HR diagram to become a red supergiant.
Carbon core:
- radius is comparable to the Earth (6,000 km)
- composed of carbon (ash from helium burning)
- temperature is about 300 million Kelvins
- density is 1010 kg/m3
Hydrogen Envelope:
- radius is comparable to Earth's orbit (100,000,000 km)
- composed of hydrogen and helium, some carbon
- temperature is very cool (3,000 K)
- density is very low (about 10-4 kg/m3)
Helium shell burning around this core is so violent that it blows
off the outer layer of the star.
- the core becomes a white dwarf
- the ejected envelope becomes a planetary nebula
