White Dwarf Stars

Evolution to white dwarf

All stars with M < 2 Msun will eventually become white dwarfs. Most stars with 2 Msun < M < 10 Msun will probably wind up as white dwarfs. We have some uncertainty as to what happens for high mass stars.

Take a 2 Msun star


1. Red Giant -- He burning in core -- Mass Loss

2. Contracting, heating up -- carbon burning?

3. Planetary nebula -- star ejects more material

4. Runs out of nuclear fuel -- contracts becomes a subdwarf

Lasts ~1012 s ~105 years

5. Stops contracting -- just cools at same radius

What is holding it up?


Electron Degeneracy

Radius gets smaller and smaller -- density gets hgher and higher

What stops it?

Try to put too many electrons in a limited space, each electron needs its own quantum state.

Stops where

Then it just sits there and cools

R ~ 0.01 Rsun ~ 7*108 cm

L ~ 0.01 Lsun = sAT4

Surface gravity is 104 times that of the sun ~ 108 cm s-2

Magnetic fiels: B ~X 1-100 Mgauss

Made of Carbon or heavier elements

Very high conductivity



Sirius B

40 Eri B

Procyon B



DA H lines

DB HeI lines

DO HeII lines

DC continuous

DF CaII lines

DG CaII and FeI lines

C2 bands at l 4670, 5140


Gravitational Redshift

Measure mass dynamically

Measure R from sT4


Therefore the shift = 1 angstrom

First verification of general relativity