>>3469231>how does this prove black holes exist
Basically, because it shows up exactly in the way that the theories behind black holes predict.
So it doesn’t technically “prove” it, just provides overwhelming evidence for the theory’s correctness.
Like, given previous evidence of webbed footprints, missing breadcrumbs, discarded feathers, and quacking noises, scientists hypothesize the existence of a Duck. Then they manage to get a video of an animal with feathers and webbed feet making quacking noises and eating breadcrumbs. Yeah, it’s true that it might be a cat in a costume with some sort of voice changing device, but... it walks like a duck and it talks like a duck, so it’s likely a duck.