Quarks to Cosmos Lecture Sheet 11

Stellar Evolution (Sun)

What balances hydrostatic equilibrium on the main sequence?

Gravity vs fusion pressure.

What element accumulates in the Sun's core during the main sequence?

Helium.

Does a solar-mass star stay the same during the main sequence?

No; it brightens and expands.

What happens as the Sun leaves the main sequence?

Core contracts, outer layers expand → red giant.

Appearance in red giant phase?

Bigger, cooler, redder, more luminous.

What is the helium flash?

Sudden He fusion in a degenerate core.

Why doesn’t the core expand during the helium flash?

Electron degeneracy pressure.

Triple-alpha process?

3 He → C.

What builds up during He burning?

Carbon and oxygen.

End of AGB phase produces?

Planetary nebula + white dwarf.

What stabilizes a white dwarf?

Electron degeneracy pressure.

What process heavy stars undergo that Sun will not?

Fusion to iron and core collapse (>8 solar masses).