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More on four arms vs. two

Submitted by Kevin Jardine on 26 August, 2010 - 09:55

This NASA image of Messier 106 provides a good example of the difficulties involved in determining the number of arms in a spiral galaxy.

Messier 106 has two arms which are invisible at optical wavelengths but very visible at radio and x-ray frequencies.

I gave the Messier 106 example in a blog post last year but the image I linked to today tells the story a bit more clearly.

Thanks to Universe Today for drawing my attention to this image.