1. The burnt-out cores of low mass, post-main sequence stars
White Dwarf Stars
The burnt-out cores of low mass, post-main sequence stars

2. As cores contract, the density goes to “astronomical” levels, matter acts in funny ways
Gas in this room, the “perfect gas law” PV=nRT. Pressure depends on both density and temperature
Extremely dense, “degenerate” gas PV=Kn. Pressure depends only on density
Demo

3. The structure of a star: a balance between gravity and gas pressure
Self gravity
Gas pressure
Technical term: hydrostatic equilibrium

4. Equations give radius of white dwarf as a function of its mass
What one might expect for how R depends on M

5. What the solution really is for a white dwarf star

6. Main features to note about white dwarf solution
Note the size: objects with masses like the sun, but radii like the Earth
The size becomes smaller with increasing mass
There is an upper limit (the Chandrasekhar mass) to the mass of a white dwarf

7. Point to emphasize: white dwarfs are real!

8. Many white dwarfs have been cataloged
Note in particular 40 Eridani B, which is in
The sky now, and can be seen with small
telescopes

9. More information on 40 Eridani B
All Star Line Up.webarchive

10. What happens to massive stars?
Cores are chemically differentiated
And too massive to be held up
By electron degeneracy force…
The cores collapse

11. Core collapse of a massive star has two consequences
Massive explosion (1044 Joules)
Production of a neutron star

12. Formation of a neutron star from stellar core
As core collapses, matter becomes compressed
Electrons and protons forced together e+p > n + nu (neutronization)
Core of the becomes a neutron fluid
Neutronization produces a burst of neutrinos
Neutron fluid in core becomes degenerate and rigid

13. The physics of a self-gravitating neutron blob (neutron star)
Radius versus mass relation for neutron star
Notice size of neutron star
Masses extend above Chandrasekhar limit

14. Theoretical prediction of the existence of a neutron star
The remnant after the explosion of a massive star
An object having the mass of the Sun (or more) but in an object with the diameter of Iowa City!
An equivalent to the Chandrasekhar mass (largest possible mass of a neutron star)
Do they exist?