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From: fisher@dvinci.DEC
Newsgroups: net.astro
Subject: Stardate question:  Shockwave?
Message-ID: <3151@decwrl.UUCP>
Date: Wed, 17-Jul-85 09:46:53 EDT
Article-I.D.: decwrl.3151
Posted: Wed Jul 17 09:46:53 1985
Date-Received: Thu, 18-Jul-85 08:11:37 EDT
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
Lines: 26


The Stardate about the shockwave was very interesting...I had never heard
that theory before, but it raises some questions:

1) What kind of wave is the shockwave?  Matter?  EM?  If matter, it must have
a devil of a job propagating through near vacuum!

2) How does the shockwave move?  Circularly around the galaxy?  If so, why?
(If it is matter, I suppose gravity curves its path, but if not...?)

3) How come non-spiral galaxies don't have shockwaves?

4) The statement that gaps between the spiral arms of the galaxy are caused by
stars "burning out" implies to me that the shockwave's period is on the order
of (distance between arms)/(average star lifetime).  Does this work out to be
a reasonable number (e.g. less than c, but large enough to have propagated
around the galaxy since the universe began)?  I suppose this is an elementary
thing that any respectable astronomer would have worked out before expounding
the theory, but I am curious anyway.

Burns


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