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|Noun||1.||spiral nebula - a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center|
extragalactic nebula, galaxy - (astronomy) a collection of star systems; any of the billions of systems each having many stars and nebulae and dust; "`extragalactic nebula' is a former name for `galaxy'"
Andromeda galaxy - a spiral galaxy in the constellation of Andromeda that is visible to the naked eye