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From: cooper@pbsvax.DEC (Topher Cooper HLO2-3/M08 DTN225-5819)
Newsgroups: net.physics
Subject: Re: Color of Neutron Stars.
Message-ID: <1523@decwrl.UUCP>
Date: Fri, 5-Apr-85 15:02:34 EST
Article-I.D.: decwrl.1523
Posted: Fri Apr  5 15:02:34 1985
Date-Received: Sun, 7-Apr-85 03:32:13 EST
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I read a monograph, surveying what was then known about the
structure and behavior of neutron stars, about 13 years ago.
Sorry I don't have a citation, but it was one of a major
series of monographs in physics.  Most of it was way beyond
me, but it was nicely written with the consequences of the
calculations and formula described in comprehensible English.
If you can find it I recommend it, though it is undoubtedly
out of date.

One of the interesting results was, that for a stable neutron
star, the pressure at the surface was insufficient to cause
degeneracy of the matter (i.e., the surface would be fairly
ordinary atomic matter).

It was speculated that that matter would be mostly or wholly
iron (the trough in the curve of binding energy).  It would
be expected that the "typical" neutron star would have a
very intense magnetic field, a result of compression of the
"ancestral" stars ordinary magnetic field.  This field would
be expected to be intense enough to cause the iron from the
surface to form into "hairs" similar to the lines of iron
filings formed with a bar magnet.

I also seem to remember that there was a shallow (a meter or
two) atmosphere, but I'm afraid I don't remember what it was
composed of.  As best I remember it, this atmosphere resembled
a good vacuum.

Neglecting the atmosphere, then, the color would be that of
iron at the temperature of the neutron star, red-shifted
appropriately for the intensity of the gravitational field
and the distance from which the star's surface is being
observed.  From close up the hair would have the effect
of providing some visual texture.

In the absence of a companion star dumping matter onto its
surface, a stabilized neutron star has no source
of energy.  It would therefore eventually cool to the 3K
background level.  However, my guess is that it would take
a LONG time to cool to anything like this level.  I would
guess a very high initial temperature (it started life as
a star with a run-away nuclear reaction, then was compressed
extrodinarily), and it has a low (to say the least) surface area
relative to its mass.  At any given time in history, you would
therefore expect to find a wide range of temperatures for
neutron stars.  Take your pick.

		Topher Cooper

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