From: ted@rosencrantz.stcloudstate.edu
Subject: Re: galaxies distribution
Date: Fri, 11 Aug 2000 04:56:54 GMT
Newsgroups: sci.physics.research
Summary: [missing]

In article <8movqe$7md$1@bw107zhb.bluewin.ch>,
I.Vecchi <vecchi@weirdtech.com> wrote:

>Do the deviations of  the galaxies' speed
>from the overall expansion fit into a Maxwell-like distribution? In other
>words, once one subtracts the universes's expansion, does the velocity
>distribution of galaxies  behave like that of the molecules of a rarefied
>gas?

No.  The effective "temperature," or to be more specific the rms
peculiar velocity of the galaxies, varies a lot from place to place,
so there's not a single Maxwell-Boltzmann distribution that accurately
characterizes the distribution of speeds.  For instance, galaxies in
rich galaxy clusters have higher peculiar velocities than galaxies
that are "in the field" (not part of a cluster).  There's a very good
reason for this: when a galaxy cluster forms, the galaxies fall into a
potential well, so they "heat up."

(The reason for the scare quotes above is to emphasize that I'm not
talking about the temperature within the galaxies; I'm talking about
the kinetic energy of each galaxy as a whole.  I'm sure most people
reading this understand that; I just wanted to make 100% sure it was
clear.)

There's no reason you should expect the peculiar velocities
of galaxies to have come into thermal equilibrium with each other:
they're so far apart, and the interactions between them are so
weak, that they can't equilibrate.

-Ted