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Re: Physicists Howl at Dark Matter

Subject: Re: Physicists Howl at Dark Matter
From: Steve Willner
Date: 12 Sep 2006 14:44:27 -0400
Newsgroups: sci.astro, sci.skeptic
[sci.math, sci.physics.relativity snipped]

In article <[email protected]>,
 Lester Zick <[email protected]> writes:
> The flatness of orbital velocities throughout
> Andromeda is best explained by a disk of uniform density inverse
> square gravitationally attractive matter much as the galaxy appears to
> be in purely visual terms. 

In "visual terms," the surface brightness of the M31 disk decreases
exponentially with a scale length of about 5 kpc.  (I'm not surprised
a radio interview failed to make that clear.)

As others have noted, the same pattern of a flat rotation curve but
decreasing mass (for an assumed constant mass-to-light ratio) is
observed in a great many galaxies; it is nothing peculiar to M31.

Steve Willner            Phone 617-495-7123     [email protected]
Cambridge, MA 02138 USA                 
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