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

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Discussion Overview

The discussion revolves around the observation that many galaxies appear to have two spiral arms. Participants explore the reasons behind this phenomenon, question its validity, and reference various types of galaxies, including barred spirals. The scope includes conceptual understanding and observational astronomy.

Discussion Character

  • Debate/contested, Conceptual clarification

Main Points Raised

  • One participant questions the assumption that most galaxies have only two spiral arms, suggesting that many arms are implied in general descriptions of spiral galaxies.
  • Another participant expresses uncertainty about the existence of galaxies with only two arms and asks for references to support the claim.
  • Some participants share personal recollections of seeing images of galaxies that might appear to have only two prominent arms, though they acknowledge uncertainty about the details.
  • A participant mentions that barred spiral galaxies may have two arms that extend from the ends of the bar structure.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether most galaxies have two spiral arms, with multiple competing views and uncertainties expressed throughout the discussion.

Contextual Notes

There are limitations in the discussion regarding the definitions of spiral arms and the observational criteria used to classify galaxies, which remain unresolved.

jayaramas
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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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