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From: wmartin@brl-tgr.ARPA (Will Martin )
Newsgroups: net.astro
Subject: Re: StarDate: October 12 The Halo of the Milky Way
Message-ID: <2140@brl-tgr.ARPA>
Date: Tue, 15-Oct-85 11:43:40 EDT
Article-I.D.: brl-tgr.2140
Posted: Tue Oct 15 11:43:40 1985
Date-Received: Thu, 17-Oct-85 07:44:12 EDT
References: <38@utastro.UUCP>
Reply-To: wmartin@brl-bmd.UUCP
Organization: USAMC ALMSA, St. Louis, MO
Lines: 37

In article <38@utastro.UUCP> dipper@utastro.UUCP (Debbie Byrd) writes:
[Extracts:]
>
>The Milky Way also has a halo -- a thin scattering of stars around the
>flat disk of the galaxy.  The halo of the Milky Way contains the
>galaxy's oldest stars -- some traveling alone -- some in round, compact
>globular star clusters.  Unlike the disk of the galaxy, the halo lacks
                                                                  ^^^^^
>the gas and dust that are the raw materials for new stars.
>
>The stars that now make up the halo of the galaxy still lie in that
>more or less round volume of space surrounding the flat disk of the
>galaxy.  Meanwhile, the rest of the galaxy continued to contract -- to
>collapse finally into a rotating disk.  Today, most of the galaxy --
                                                ^^^^
>including our sun -- lies within this rotating disk.  But the halo of
>stars remains outside the disk -- a skeleton left behind from the early
>evolution of the galaxy.

I added the "^^^" pointers above. I am in the midst of reading Michael
Disney's THE HIDDEN UNIVERSE, in which the emphasis is on the "missing
mass" problem, and, according to this book, our galaxy, and every other
large galaxy, is surrounded by a quite massive halo of invisible
material -- I think the figure given is that this invisible matter has
to be from 10-20 times the mass of the visible material of the galaxy --
which is necessary to explain the form and stability of the various
galaxies and clusters.

So this would disagree with the points above, wherin the "halo" is not
made up of gas and dust, and also where "most" of the galaxy is defined
as the inside (visible) matter.

So, which is right? 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