Why most of the galaxies are having two spiral arms only?

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Most galaxies are classified as spiral galaxies, which typically exhibit two prominent spiral arms. The discussion raises the question of why two arms seem to be the norm, with some participants expressing uncertainty about the existence of galaxies with only two arms. There is speculation that certain galaxies, like barred spirals, may appear to have only two arms due to the strength of those arms compared to weaker ones. Visual observations can sometimes create the illusion of fewer arms. Overall, the topic highlights the complexity of galaxy structures and the variations in their arm configurations.
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why most of the galaxies are having two spiral arms only?
 
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jayaramas said:
why most of the galaxies are having two spiral arms only?

Yes, I agree w/ mathman. What gave you the idea that 2 arms was the norm? Can you give a reference?
 


I have never heard of a galaxy with only two arms, although if there was such a thing, that would be interesting to see.
 


kcajrenreb said:
I have never heard of a galaxy with only two arms, although if there was such a thing, that would be interesting to see.

I may be wrong, but I DO seem to remember once (and only once) seeing a pic of a galaxy with only two arms ... or it might be that it only SEEMED to have just two arms because the two were so much stronger than the others ... I can't really recall.
 


Barred spirals may have only two arms, each coming off an end of the bar.
 

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