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From: nather@utastro.UUCP (Ed Nather)
Newsgroups: net.astro.expert
Subject: Re: What Color Are Neutron Stars
Message-ID: <32@utastro.UUCP>
Date: Wed, 3-Apr-85 17:10:16 EST
Article-I.D.: utastro.32
Posted: Wed Apr  3 17:10:16 1985
Date-Received: Sat, 6-Apr-85 02:32:25 EST
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Organization: U. Texas, Astronomy, Austin, TX
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> <>
> 	While contemplating the universe, a question came to mine.

Did it have a return address? :-)

> What color are cold neutron stars?
> They don't have the usual electrons 
> to absorb/reradiate electromagnetic energy.
>
> Karl Dahlke    ihnp4!ihnet!eklhad

They do have on the outside, which is not "pure neutronium" by any
means, but is a thin "ocean" of neutron-rich atoms near the iron
peak in the curve of binding energy.  As such they can radiate into
space just like a white dwarf star, only more slowly, because their
surface area is so much smaller.  Since even the oldest possible 
white dwarf has not had time to cool off in our young Universe, I'm
sure the oldest neutron star is in the same boat, only hotter.
They have neutrino cooling to help, but that only really works at 
very high temperatures.  I expect the coolest would still appear to 
be white to our earth-bound eyeballs, maybe blue-white, but I 
haven't calculated anything.

-- 
Ed Nather
Astronony Dept, U of Texas @ Austin
{allegra,ihnp4}!{noao,ut-sally}!utastro!nather