# Tagged Questions

A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

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### Speed of stuff falling into a black hole, beyond the event horizon [duplicate]

We know the escape velocity from the event horizon (EH) $= c$. Anything that crosses the EH is destined to reach the singularity. Whether the escape velocity (beyond the EH) can be calculated, or not, ...
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### Does anything exist between singularity and the event horizon of a black hole

It is said that anything that falls into the event horizon, quickly reaches the singularity. That would imply - there should be nothing between event horizon, and the singularity. Is that true? If not,...
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### Electromagnetic four-potential for Kerr-Newman solution

Any textbook or paper on the Kerr-Newman metric I found contains the solution for the electromagnetic tensor $F^{\mu}_{\phantom{\mu} \nu}$. Can you provide a (reliable) reference for the solution ...
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### What are black holes made of, and if one “eats” enough, will it cease being a black hole?

I kind of already know the answer to the second part (which must be 'yes'), but I'd still like to know what black holes essentially are. Are they made out of a special material to have density as high ...
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### Black Holes and the Multiverse [closed]

Are there any peer-reviewed theories which explore the idea that black holes in our universe may spawn other universes - or that our universe came from a black-hole-like event in another universe? ...
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### Event horizon, and Hawking radiation [duplicate]

When the escape velocity from EH is c, then how can Hawking radiation escapes it? Does it travel faster than c? Or, it escape from outside the EH? If so, how a BH can evaporate beyond EH?
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### Interior material and spacetime of a black hole described from outside

This question is mostly about general relativity. Answers regarding the quantum physics behind it are also appreciated, but first I would prefer solutions from a relativistic viewpoint. If you ...
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### LIGO detection: What do we know about the black hole system?

I would to know how much we can infer from the LIGO detection on the black hole system. I understand that at least the following can be verified: Spins Inclination Initial masses Final masses ...
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### Kerr Metric from rotated Schwarzschild?

Say we have got a system in GR that is described by the Schwazschild metric. Then we perform a coordinate transform that gives the metric in a rotating system. Why is the transformed metric not the ...
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### Singularity - exactly what is it?

In quantum mechanics and gravity theories one always meets the word "singularity" in connection with talks about black holes and the big bang, etc. Now in mathematics a singularity is well defined – ...
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### Aren't black holes required to exist forever in our frame of reference?

I know that for an observer far away, nothing ever crosses a black hole horizon (due to time dilation), while in the frame of reference of a falling observer the horizon is nothing special on its way ...
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### What is an extremal horizon?

In the contest of holography and thermodynamics, what is an extremal horizon? I am going through a paper by Hartnoll, Santos - Disordered Horizons: Holography of randomly disordered fixed points. They ...
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### Possibility of white holes in universe

Is there any possibility of white holes (where nothing can enter but just comes out) as like black holes?
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### If our universe is a “baby universe” [closed]

There are several theories that claim that our universe is simply a black hole in a "parent" universe: Stephen Hawking wrote a book called Black Holes and Baby Universes. Here he talks about black ...
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### The inside of of a black hole

I am looking for a confirmation (or correction) of my thinking about the nature of the black holes. As I am not a physicist and only a physics enthusiast, my understanding is probably very simplified ...
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### Binary black hole merger viewed from inside the event horizon

How did the metric evolve inside the event horizons of the black holes whose merger caused the GW150914 signal? In principle the Schwarzchild metric of a non-rotating black hole is known inside the ...