why most of the galaxies are having two spiral arms only?
The general description seems to imply many arms.
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.
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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