Astroquizzical: Why do galaxies have two spiral arms? (Synopsis)

When you close your eyes and picture a galaxy, what pops into your mind? For most people, it's a beautiful, spiral shape, where a bright central region fans out with arms that wind around and around, over and over, littered with brilliant, glittering stars. And in almost all the pictures you see, there are two main arms making this up, with perhaps additional "spurs" shooting off of the primary arms.

Image Credit: NASA/JPL-Caltech/ESO/R. Hurt. Image Credit: NASA/JPL-Caltech/ESO/R. Hurt.

But is this really representative of what galaxies look like? Or is it just that these are the images of galaxies that stand out most for us?

Moreover, how do the galaxies that are this way come to be this way, and will they stay this way forever?

Image Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University) Image Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University).

Jillian Scudder has the (fantastic) answers for you on this edition of Astroquizzical!

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1) I thought the rationale behind dark matter halo theory was that the inner and outer portions of a rotating galaxy have the same red shift, or velocity relative to the observer.

2) There was a well written paper out in the last two years that explained the spiral shape and wave-like harmonics by using a rotating lawn/water sprinkler analogy. The shape is more or less an emergent property- wish I could remember the reference off the top of my head.

Fibonacci pattern

By Ragtag Media (not verified) on 28 Jul 2015 #permalink

I hate this :C tooo hard :CCC

By sdasdasdasdsad… (not verified) on 28 Jul 2015 #permalink