An event horizon is a type of boundary such that any information past this boundary is inaccessible to the observer it is defined for. Common examples are the Schwarzschild radius of a black hole (which is defined commonly for all observers outside this radius) and the cosmological even horizon ...

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Can the event horizon save conservation laws for black holes?

How reasonable it it to conclude that, from a remote observer’s frame, matter falling towards a black hole never crosses the event horizon, because ∆ t → 0 as v → c (according to the Lorentz ...
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Doesn't the Schwarzschild metric combined with Hawking radiation imply that nothing ever gets past the event horizon of a black hole?

According to the General Theory of Relativity, the coordinate time distance per spacetime distance traveled by a particle freely falling into a black hole gets closer and closer to $0$ as the particle ...
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How is black hole affected by gravity of nearby bodies?

I run into wikipedia articles about ergosphere of rotating black holes. What if some massive body passes nearby some black hole: is something like ergosphere produced, or is the event horizon ...
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Two spherically symmetric shells of matter collapsing into a black hole

Suppose I have a thin spherically symmetric shell of matter of (rest) mass $M$ that collapses to form a black hole, and later a second thin spherical shell of mass (rest) $M'$, concentric to the ...
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Location of singularity in moving black hole

Say a black hole is travelling at $c/2$, does the shape of the event horizon change? What about the location of the event horizon? If it is travelling at a hypothetical $c$, does the event horizon ...
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Falling into a black hole doesn't reveal the future, but does that mean it's not happening?

In a previous answer it was said that you wouldn't see the universe speed up as you fell into a black hole, which I accept as true. However, is being unable to see or interact with the outside ...
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If spacetime is folded upon itself

Say there are two black holes about a parsec apart. You theoretically fold spacetime upon itself so that the singularities of the black holes are "touching". ...
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Who can see the event/apparent horizon and Hawking effect?

As I understand, the Hawking effect is related with the presence both event and apparent horizon, i.e. if some kind of horizon exist, a loss/gain of information (unformally speaking) exists. My ...
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Why can apparent horizon be computed based on its local geometry?

Why can apparent horizon be computed based on its local geometry? In the paper titled Black Holes, Geometric Flows, and the Penrose Inequality in General Relativity by Hubert L. Bray, has been ...
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Euclidean black hole extrinsic curvature

I have read that the extrinsic curvature at the horizon of a euclidean black hole is zero? Does anybody know how this can be shown?
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The difference between an apparent horizon and event horizon?

I'm currently writing a project on minimal surfaces and general relativity - however I don't understand the difference between the apparent and event horizon? They ultimately both seemed to be defined ...
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Is the Casimir effect also present between two event horizons?

A follow-up to this question: Is the Casimir effect also present between two event horizons?
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Further explanation of the Penrose Conjecture

I'm currently a third year maths undergrad, writing a dissertation on the application of minimal surfaces in space. I have recently come across the Penrose Conjecture that the mass of a spacetime is: ...
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Trapped Surfaces. Any good articles?

I'm currently writing a dissertation on trapped surfaces as minimal surfaces. I have exhausted all of the resources I have, and the internet is pretty limited (in that it is fairly repetitive on just ...
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How can things at the event horizon slow down and appear to stop to a remote observer?

So they say the remote observer will never see anything fallen to the black hole, because any object will slow down as it gets closer to the event horizon and eventually stop to stay there forever. Am ...
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Colliding black holes to an outside observer

We know that a particle approaching an event horizon will appear to an outside observer to slow down and never cross the horizon. What is observed by an outside observer when a singularity ...
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Is it possible to assign a physical radius to a black hole?

The Schwarzschild metric is given by: $$c^2d\tau^2 = \left(1-\frac{r_s}{r}\right)c^2 dt^2-\left(1-\frac{r_s}{r}\right)^{-1}dr^2 - r^2 \left(d\theta^2 + \sin^2 \theta \, d\varphi^2\right).$$ The ...
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Black hole entangled with the cosmological horizon

Maldacena and Susskind recently proposed a interesting and very suggestive duality between entanglement and topological identification: http://arxiv.org/abs/1306.0533 But are such ideas applicable to ...
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What is the status of the area theorem in AdS?

The area theorem, by Hawking (in "Gravitational Radiation from Colliding Black Holes", also found in Wald), states that the area of an event horizon cannot decrease with time. As I understand, there ...
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Radius of apparent event horizon for accelerating observer

This question is related to my last question on the Unruh effect, which can be found here. First, recall the quote from the Wikipedia article on the Unruh effect: An accelerating observer will ...
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Electrodynamic near fields around black holes

For the standard Schwarzschild black hole, the temperature of Hawking radiation is simply related to the Schwarzschild radius as $kT = \hbar c/(4\pi r_S)$, meaning that the typical wavelength of ...
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Topology of a black hole

How many dimensions are theorized for a black hole, in view of the fact that black holes are not observed directly.
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Binary Singularity?

When two black holes collide, if the singularities were very small they would never merge together. they would rotate very fast as something other than a disk. The event horizon would oscillate very ...
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143 views

Is the gravitational acceleration at the event horizon constant?

If the escape velocity at the event horizon of a black hole is equal to the speed of light, does this imply that the gravitational acceleration at the event horizon is also constant? For example, ...
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Is the black hole surface area actually zero?

From quantum mechanics we know that entropy of a part can be smaller than the entropy of the whole. I wonder whether a similar rule works for GR as well. Quantum mechanics predicts that the entropy ...
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What is the difference between cosmological horizon and event horizon?

Do the terms cosmological horizon and event horizon mean the same thing?