[Richard Beck]

Richard Beck asked the Naked Scientists:
   
Hi Ben,

We are positioned somewhere in between a pair of arms in our galaxy.  Is it the case that we always have been and always will remain in between these arms or do stars move together and then move apart  to give the appearance of a static arms but just as traffic clumps at busy times on a motorway are these arms actually waves.  If the star density is high on an arm, do the stars move together and crash into each other and if not, why not?  What is the average spacing between the stars in the average galactic arm?

Many thanks

Richard Beck

What do you think?