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Re: Hot chocolate and galaxies

Subject: Re: Hot chocolate and galaxies
From: Joseph Lazio
Date: 05 Mar 2006 13:58:34 -0500
Newsgroups: sci.astro
>>>>> "k" == khatcat  <khatcat@xxxxxxxxxxx> writes:

k> This morning, I was stirring my hot chocolate when I noticed that
k> the froth on the top of my hot chocolate looked a lot like a spiral
k> galaxy.  It had a central bulge (containing the bigger bubbles) and
k> occasionally sprouted spiral arms.  Are the same forces /
k> principles at work in galaxy formation as stirred hot chocolate?

Generally, no.  A system of stars, like a galaxy, is governed by
a long-range force (gravity) and is collionless (i.e., stars rarely
collide in a galaxy).  In contrast, a beverage is an example of
collional physics, in which the particles are constanly colliding.

Having said that, one can obtain quite similar patterns.  For
instance, in a recent review article, Sandage (<URL:
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ARA%26A..43..581S
>) describes how to stir coffee and add cream to it in a way to mimic
various galaxy patterns.

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