Re: Whence Degeneracy Pressure?

[Greg Clements <clements@CAMPUS.MLC.EDU>]

Chuck Britton wrote:
> I'm still trying to get things settled in my mind.
> Astronomers speak of 'pressure broadening' of spectral lines.
> Low pressure sodium lamps have a MUCH cleaner spectrum than do the
> High Pressure variety.
>
> Isn't this 'pressure broadening' evidence of  the Pauli Condition?

I believe pressure broadening of spectral lines is associated with the
distortion of the electron energy levels due to 1) the collision of
free electrons with atoms and 2) the influence of electric fields of
nearby charged particles and neutral atoms.  The influence of these
interactions is to increase the spread of electron energy values in
the atom.  I don't think this pressure broadening closely relates to
the degeneracy pressure of white dwarfs or neutron stars.

The sharpness of a stellar spectral absorption line is related to the
"surface" pressure of the star.  The giant (large radii) stars have
low surface pressures and sharp spectral lines.

References: "Astrophysics and Stellar Astronomy" by Swihart 1968
pages 106 and 133
    "The Atmospheres of the Sun and Stars" 2nd edition by Aller 1963
pages 310 - 322
    "The Physical Universe, An Introduction to Astronomy" by Shu 1982
pages 163 - 164

Greg Clements
Midland Lutheran College
Fremont, NE