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What is the origin of spiral structure in galaxies?

In Astronomy & Space
   

    


This is a very interesting question and it's something that extragalactic astronomers have thought about quite a lot. Spiral arms are seen in about two thirds of the brightest 1500 galaxies (as seen from Earth) and we ourselves live in a spiral galaxy, so it must be something very generic that causes it.


It turns out that if you assume that the arms are material (i.e. made up of stars that always remain in the arm and are just denser than the stars outside the arm) then very quickly the arms would wind up as the galaxy rotates (well quickly compared to the age of the universe!). So the process which make spiral arms must maintain them too (or they would disappear).
412 days ago
  
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