What is the exact meaning of vicinity of Blackhole or a disk? Is this the same as inside the horizon for black holes? If so, why people don't say inside of BH, simply. What is the difference?

I use this phrase actually! and it may seem obvious but not to me, please somebody make it clear. I searched but I couldn't find an exact answer.

Edited: Until which radius from Blackhole I can use this word meaningfully? It's not clear to me its astronomical dimension. "near" is not enough to me. If it could be inside a horizon and also outside of it, it makes a huge difference from point of view of the observer at infinity, as you know, how I can call them by the same name and sometimes I mean one sometimes the other one.

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    $\begingroup$ The phrase "in the vicinity of a black hole" just means near a black hole, and normally outside the event horizon, but that can depend on the context. What sort of disk are you talking about? $\endgroup$ – PM 2Ring Jan 4 '19 at 15:17
  • $\begingroup$ @ PM 2Ring, thank you for your answer. If I take it as outside the horizon until where? ISCO? "near" is kind of vague to me. also, about the disk, I mean for accretion disks, because in some texts always see this pharse "in the visinity of disk". $\endgroup$ – Schok Jan 4 '19 at 15:21
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    $\begingroup$ Please add that information to your question. And explain what ISCO means. Yes, "vicinity" is a bit vague, so it should only be used when a vague description of location is sufficient. If you have trouble with a particular passage from a text, then you can quote it in your question and of course give a reference to the text it comes from). That will make it easier to give a more definite answer, once we can see the context. $\endgroup$ – PM 2Ring Jan 4 '19 at 15:32
  • $\begingroup$ @Pm 2Ring: ISCO means the last stable orbit of photon near a BH. always we hear this word, in papers, in class, in seminars. I want to know where I can use it meaningfully. $\endgroup$ – Schok Jan 4 '19 at 15:40
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    $\begingroup$ Someone has flagged this question for closure as "unclear", but it seems clear enough to me: the OP wants to know if "vicinity" has an exact astronomical dimension. It's not a good question but it's a valid one. I'm voting to leave it open. $\endgroup$ – Chappo Hasn't Forgotten Monica Jan 5 '19 at 1:24

From the Oxford English Dictionary:

"vicinity" just means "the area near to or surrounding a place"

so "in the vicinity of a black hole" just means "near to a black hole."

Other dictionaries say "immediately next to" so in response to your comment about vagueness, treat vicinity as the immediate neighbourhood of the black hole. You will not find an exact meaning - it is used as it is in English. There is no specific distance measurement. You don't have a distance from radius which would stop being in the vicinity.

  • $\begingroup$ thank you for your answer, but I'm searching the exact meaning in black hole text, not as a normal word in English. "near", means exactly until where from a BH I can use this word? $\endgroup$ – Schok Jan 4 '19 at 15:25
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    $\begingroup$ You will not find an exact meaning - it is used as it is in English. There is no specific distance measurement. $\endgroup$ – Rory Alsop Jan 4 '19 at 15:32

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