On Mon, 25 Apr 2011 11:17:14 -0400, Yousuf Khan
wrote:

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

I think "debunk" is the wrong word. The analysis doesn't strongly
argue against the density wave theory (which itself has some direct
observational support), but rather, demonstrates a simulation that is
able to produce arm structure via a different mechansism.

All very interesting and useful. And I think it is far too early to
say with any confidence that either theory is entirely right or wrong,
or that galactic arms aren't the product of multiple causes.