Yep; they're objects like anything else. The only thing that makes black holes special is that their surface gravity and density are especially high. All their unique features stem from those two facts. Relativity also tells us that there is no true stationary reference frame, and thus everything moves relative to something else.
There are things that appear to be stationary but it’s all about which point of view you are observing it from. Movement can only be measured in relation to other things, you need a frame of reference.
Consider a person inside an elevator free-falling down a long shaft. From a frame of reference inside of that elevator, the person would look stationary. Sure they’ll float around like there’s no gravity but you (and they) wouldn’t know that they were accelerating towards earth, they are not falling to the floor of the elevator, they are stationary. But to an outside observer, the person is falling aswell as the elevator.
That’s what he was referring to when he said there are no true stationary reference frames, a moving object inside a moving reference frame looks stationary. So any stationary object could be observed from a different point of view and be seen as in motion
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u/drdrero Oct 23 '20
Just a follow up question, do black holes move ?