Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site decwrl.UUCP Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!decwrl!dec-rhea!dec-dvinci!fisher 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 UUCP: ... {decvax|allegra|ucbvax}!decwrl!rhea!dvinci!fisher ARPA: fisher%dvinci.dec@decwrl.ARPA