Galactic traffic jams

Back in January 2006 I wrote a post about density waves in galaxies. It is tempting to think about the spiral arms seen in Grand Design spirals such as M51 as structures of matter that stay fixed with respect to the stars, gas and dust in the galaxy i.e. if your star isin a spiral arm it will always be in the spiral arm. Real life isn't so neat and tidy though. It turns out that matter (the stars, gas and dust) can migrate in bulk around the spiral arm structure that we observe. The spiral arm is actually a density wave. The nearest everyday analogy I can think of is as a traffic jam. The cars on a motorway may be moving forwards through a traffic jam, but the jam itself can be stationary or, more likely, moving backwards.

On my previous post I linked to an animation of a traffic jam density wave. Now, via fyc on Twitter, the University of Nagoya have provided a video which shows a circular traffic jam. This research was done to study traffic management but just so happens to give a better demonstration for spiral arm density waves too.

Posted in astro blog by Stuart on Wednesday 05th Mar 2008 (12:09 GMT) | Permalink
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