I know that when matter and antimatter collide, they eliminate each other. So it would make sense that none of the stars in our galaxy would be antimatter since it was all part of one big cloud at some point.
But if antimatter and matter behave more or less the same as matter, how much certainty do we have that distant galaxies aren’t composed of antimatter instead of matter?
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Space between galaxies are still populated with a density of 1 million atoms per cubic meter or about 10^-17 Pascals. The mean free path of atoms at that pressure would be around 1 to 10 billion kilometers so even in between galaxies, there would still be atomic interaction and collisions. There is a notable lack of ambient gamma rays from matter anti matter annihilation in that sense.
Space between galaxies are still populated with a density of 1 million atoms per cubic meter or about 10^-17 Pascals. The mean free path of atoms at that pressure would be around 1 to 10 billion kilometers so even in between galaxies, there would still be atomic interaction and collisions. There is a notable lack of ambient gamma rays from matter anti matter annihilation in that sense.
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