Quote:
Originally Posted by photon
You've never been there, you don't know for sure. It could be some other phenomenon and it just looks similar to our galaxy.
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One of the cool things about other galaxies is that we may be looking at antimatter galaxies and not even know it as they would be virtually indistinguishable.
The only clue would be a boundary where matter and antimatter are meeting and annihilating each other to produce gamma rays but in the vast expanse and void of the intersteller medium between galaxies, we may not be able to observe this.