On 4/25/11 10:17 AM, Yousuf Khan wrote:
On 24/04/2011 9:19 PM, Sam Wormley wrote:
On 4/21/11 7:45 AM, john wrote:


The arms break up about as frequently as
electrons break up.


Too bad you have never done any self-education about
density waves and spiral arms, John. You might want
to start he http://casa.colorado.edu/~danforth/science/spiral/


Actually, Sam, this study is debunking the density wave theory.

Yousuf Khan

As always, I encourage readers to read the links and the associated
references for a better understanding!

Summary from: http://casa.colorado.edu/~danforth/science/spiral/

"A great deal of work has been done on spiral structure since the early
work of Lindblad. While it seems density waves are a very efficient way
to form arms, there appear to be more than one way to skin a galactic
cat. While some theories such as MHD have been pretty conclusively
discounted, the strengths of those still in the running are
complimentary and may explain different facets of the problem.
Stochastic star formation and chaotic theory seem to explain
smaller-scale structure well while global modes and driven systems are
more coherent over the larger scale. Observations of our own galaxy
suggest that many or all of these systems are at work to one degree or
another".