How do we know that some galaxies aren’t made of antimatter?

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My limited understanding is that the only interactions we have with other galaxies is through photons, and that photons have no anti-particle (or are their own anti-particle). I’m also under the impression that the vast majority of galaxies are very far apart from each other and moving further away, so we wouldn’t be able to observe matter galaxies interacting with antimatter galaxies. How do we know that some of the galaxies we can see aren’t made of anti-matter? Would it be important if some of them were?

In: Physics

4 Answers

Anonymous 0 Comments

there is a very shallow intergalactic medium. if galaxies or the medium are either matter or antimatter, something would still annihilate faintly. We don’t see that signature, so it is very likely to be the same (anti-)matter.

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