Chapter 17  Stellar Evolution

What is this?

A star spends most of its life as a main sequence star

Hydrogen fusion 4H -> He

Remember lifetime proportional to 1/M^2.5

Life is determined by the mass (and initial chemistry)

Low Mass < 2 M_Sun

Intermediate Mass 2-8 M_Sun

High mass >8 M_Sun

Low mass stars have radiative cores and convective upper layers (like the Sun)

Red giants and supergiants

Why does it change?

         Hydrogen shell burning

Evolutionary track

Helium Flash

Helium burning

Evolutionary track H-R diagram of an old cluster

         Mass loss  and thermal pulses

End of the Sun

Planetary Nebulae   - The quiet way to die

         A large beautiful variety 1 2 3 4 5

Summary Luminosity Radius

Intermediate

No He flash just 3He -> C burning

        Then PN and wd

What is this?

High Mass

H fusion is different (but with the same result)

         High mass can burn C

                 Heavier elements in the core

Evolution H-R Diagram

The trouble with iron – no energy profit

         But the core does it anyway!

         Star explodes and recycles heavier elements

Supernovae

Crab 1054 Cas A SN1987A

Where does the energy go?

Light

         Ejection velocity

         Construction of new elements

         The neutron star or black hole  magnetic field, spin, heat

neutrinos

For stars >100 M_Sun pair-instability supernova

         Over 130 M_Sun blows star entirely apart

If white dwarfs are < 1.4 M_Sun but started out as large as 8M_Sun    and

Neutron stars are < 3 M_Sun  but started out >8M_Sun

What happened?

Just when you thought you had it all figured out…..

The binary star Algol = 3.7M_Sun main sequence dwarf and a .8M_Sun subgiant

When one star in a binary evolves to fill its Roche surface it transfers mass to the other.

Sometimes theycome in contact.