Is It a Black Hole?

We've never seen an event horizon, in the sense that we have nlike, dropped something in it and see it disappear. So if you can think of something else that can do then, you know, maybe it's that other thing instead. But we've also seen gravitational waves right from black holes, or what we think are black holes, crashing into each other. What does that tell us? It tells us there's something very massive with a lot of gravity, and that general relativity mostly works. That could be explained by something else.