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From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.astro
Subject: Re: StarDate: October 12 The Halo of the Milky Way
Message-ID: <50@utastro.UUCP>
Date: Tue, 15-Oct-85 18:35:03 EDT
Article-I.D.: utastro.50
Posted: Tue Oct 15 18:35:03 1985
Date-Received: Thu, 17-Oct-85 20:21:07 EDT
References: <38@utastro.UUCP> <2140@brl-tgr.ARPA>
Organization: U. Texas, Astronomy, Austin, TX
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> 
> Or is this a currently-debated topic in astronomy,
> and things are not as clearly agreed-upon as the impression I got from
> the Disney book leads me to think?
> 
> Will

Bingo.

Actually, the massive halo need only weigh about as much as the visible 
galaxy to stabilize the disk.  Virial theorem measurements of galaxy
masses have led people to propose much larger halo masses.  There is
some controversy over exactly how massive the halo needs to be to
explain these results.  If the halo is very massive then it is not
composed of stars.  This leaves open the possibility that it is
composed of black holes or white dwarfs.  It is not likely to be
dust or monotomic gas. Could be molecular hydrogen but its formation
would be a mystery.  Could be Jupiters (i.e. generic gas giant objects).
Could be Weakly Interacting Massive Particles (acronym is widely used).
-- 
"Superior firepower is an      Ethan Vishniac
 important asset when          {charm,ut-sally,ut-ngp,noao}!utastro!ethan
 entering into                 ethan@astro.UTEXAS.EDU
    negotiations"              Department of Astronomy
                               University of Texas