1. Degeneracy Pressure - again

Why important:

Helium flash (electron degeneracy)

White Dwarfs ('' )

Neutron stars (neutron degeneracy)

Why: exclusion principle

no two of the same particles can be in the same state and same place at the same time

Why insensitive to temperature:

- Number of states increases with energy of particle

- Temperature (T): measure of average particle speed

(see Chap. 5, p.112, fig. 5.8)

- Kinetic energy speed²

T is related to energy

E = kT

(k is another "magic" constant)

(a figure goes here, to be shown in class)






Definition:

Fermi Energy = top energy state of degenerate electrons

Degeneracy is lifted when E (= kT) is roughly equal to the Fermi Energy

2. Fundamental Particle Zoo

- 3 families of leptons

- 3 families of quarks

Never a ``naked'' quark!

Families are a function of mass

Recall:

mass energy

(E=mc²)

Consequences for degeneracy:

Eventually ``Fermi energy'' exceeds energy difference between mass of two particles

Easier for new particles to be created

3. Death of a low mass star

Mass < 1-3 M

After Helium core burning on Horizontal Branch ...

- inert carbon core

- volume of grape = 1 ton, i.e. dense

- intense shell burning:

HeC

HHe

- blows of outer layers

- formation of nebula

planetary nebula

+

``naked'' hot core

white dwarf

Why white? ------ hot

Why dwarf? ------ small

recall: E R² T⁴

4. Planetary nebula

- rich in carbon

enrich the ISM with dust

Why do they look like rings?

- actually shells

- projection effect

- longest path-length at edge

Fate:

nebula slowly disperses and mixes with ISM

ISM = interstellar medium

5. Fate of White Dwarf

Inert carbon core supported by electron degeneracy pressure

.............. forever!

cools and fades ................

``down and out on the HR diagram''

- predict many in solar neighborhood (<10pc)

can't see 'em!

recall: distance-limited vs. brightness-limited samples!

What's a 'clinker' ?

(a) both radiate emission lines

(b) both are made of hot gas

(c) both have carbon

(d) both have stars inside them

(e) both are usually shaped like single evacuated shells

(a) it would never reach the Horizontal Branch

(b) core-bounce wouldn't occur

(c) there would be no Helium Flash

(d) shell-burning wouldn't occur

(e) in fact, it would never become a giant