What happens to a star like the Sun?
Protostar gravitationally until core hydrogen ignites
(takes 20 million years).
Burns hydrogen in core (main-sequence phase) for about 11
billion years. (The Sun is now about halfway through this phase.)
When most of core H exhausted, core contracts and heats
up. Energy released expands envelope, and star becomes a ěred giantî
with radius 200 x Rs.
When core temperature reaches 200 million K, three He
atoms begin to fuse into carbon ( ěHe ěflashî). Star contracts and
becomes bluer, and burns He in core for another billion years.
When He fuel is exhausted, star expands and becomes red
again. Outer envelope released as a ěplanetary nebulaî.
Star becomes Carbon/Oxygen core white dwarf of a~0.6 Ms,
and slowly cools.
- Central density 500,000 g/cc. Radius about 1.5 REarth