Stars are bright, we can see black holes that stars fall into because they interact with the star. Black holes all by themselves (almost) do not emit light and

Stars are bright, we can see black holes that stars fall into because they interact with the star. Black holes all by themselves (almost) do not emit light and we observe them by seeing how they interact with light from further away objects. Jets are more complicated and have some open questions, but the conclusion is unchanged, if you really care then read the book. But if you want to think you know better then you can do that too.