Re: Claim CE380: Spiral Galaxies Staying Spiral
- From: "John Bode" <john_bode@xxxxxxxxxxx>
- Date: 20 Sep 2005 15:39:17 -0700
Al wrote:
> <murdock@xxxxxxxxxx> wrote in message
> news:1127102286.110567.104900@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > Al wrote:
> > > <murdock@xxxxxxxxxx> wrote in message
> > > news:1127099233.866464.86460@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Al wrote:
> > > > > "boikat" <boikat@xxxxxxxxxxxxx> wrote in message
> > > > > news:oZmXe.12998$mw5.6141@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > >
> > > >
> > > >He was wrong, or confused. Stuart was right. The galactic arms are
> > > > waves in the medium of the most luminous stars and gas. That should
> > > > have been clear from the original.
>
> Is this really what you meant to say?
> The stars are in a medium that is the stars?
> This is not clear, please say if you made a mistake.
> Al
The stars, gas, and dust of the galaxy form a medium for *density
waves* to propagate. What we see as galactic arms are the crests of
the waves, where the density of stars and gas is higher.
The waves propagate because perturbations in a star's orbit affect the
orbits of its neighbors, which in turn affect the orbits of other stars
(and planets, asteroids, dust, gas, etc.).
I know it's weird to think of stars as a medium for waves because from
our POV they're huge and far apart and it's hard to see how a wave
would propagate among them. At the galactic scale, however, they're
densely packed enough for waves to propagate among them. Think of
sound waves traveling through the air from the POV of an electron, and
it's much the same thing (although the forces involved are quite
different).
.
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