The smallest observed spiral galaxies I can find are NGC 2976 and NGC 4605, both with a diameter of 20 kly, but I don't have anything like an exhaustive source to search. I've also found a mention that the Small Magellanic Cloud (7 kly diameter) might have had more spiral structure before it was distorted by the Milky Way.

From looking at these galaxies, spiral structure seems to be less clear the smaller the galaxy is, which makes me think there might not be a clear lower limit. Still, I'm curious how small a galaxy with recognizable spiral structure could be, either based on observations or theory.

  • $\begingroup$ NGC 6503 is only ~15 klyr across… $\endgroup$ – pela Mar 10 at 9:57
  • $\begingroup$ memeguy.com/photos/images/… $\endgroup$ – userLTK Mar 10 at 12:11
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    $\begingroup$ en.wikipedia.org/wiki/Dwarf_spiral_galaxy 5kly, think this is what you were looking for. $\endgroup$ – Dkcash413 Apr 11 at 22:35
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    $\begingroup$ Dkcash413 - The size mentioned in that article is 5 kpc, not 5 "kly". $\endgroup$ – Peter Erwin Apr 12 at 9:56
  • $\begingroup$ How are those "diameters" defined? Galaxies do not have sharp edges (in their stellar or gas distributions), so it's impossible to answer your question unless you can provide a specific metric (exponential scale length? half-light radius?). $\endgroup$ – Peter Erwin Apr 13 at 15:29

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