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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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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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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Can a particle of finite size escape from a black hole if it is overlapped with event horizon but not totally in it?

As we know, particles have finite size, if a particle, a part is inside the event horizon and the remain part is outside the event horizon, is it still considered as "unable to escape from black holes"...
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How does some of the black hole (BH) mass escape the event horizon (EH) of either BH, or the merged EH of two merged BHs?

BH mass is a conserved quantity and cannot escape the horizon of a BH. Yet in mergers some percent (in GW150914 it was about 5 percent, or 3 solar masses) of the binary's mass escaped either before (...
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Practical time travel: time dilation above the event horizon

Imagine there is a huge black hole with very small gravity gradient so that one doesn't get killed by spaghettification after even nearing the event horizon. Now imagine a very curious creature ...
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What would the Sagittarius A black hole look like if we were in a spaceship just outside its event horizon?

Let's pretend that our spaceship is shielded well enough that being in the presence of the black hole won't kill us with radiation. I have read that the black hole is as large as the space between the ...
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Do black hole merger simulations include regions inside event horizons?

Inspired by this question, I would like to ask the following specific point. In numerical simulations of general relativity that involve black holes, like the ones used to understand the black-hole ...
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How to explain two possible problems with dark matter

Can someone please answer how dark matter theory resolves/eliminates these two possible problems Dark matter, per my understanding, due to gravity, keeps moving, and due to its non-interactive ...
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Does Birkhoff's theorem hold inside the event horizon?

Can Birkhoff's theorem be used to say that the blackhole exterior and interior sections of Kruskal-Szekeres's solution (or coordinate transformations of it like Gullstrand–Painlevé coordinates, etc.) ...
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Can gravitational waves act as information carriers between observers in- and outside a black hole?

Is it possible to utilize gravitational waves as a delivery system for information between two observers straddling the event horizon of a black hole? And why ?
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What is the structure of an event horizon for colliding black holes?

I would suspect that two black holes within close vicinity of one another would warp each other's event horizons such that the Schwarzchild's radius would no longer apply. Do the event horizons ...
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Flirting with a large black hole event horizon

I read with large black holes the tidal forces at the event horizon aren't particularly great, so you may not feel anything particularly special when you cross them. I also understand that if one is ...
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Hawking radiation for an observer at infinity

As an external observer at infinity, I observe a star collapsing. But because the surface of the star will be infinitely redshifted, I will never see the formation of the black hole. For me, there ...
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Conditions at black hole's event horizon

This question had, at least partially, been discussed here before, but I feel that the record has not been set straight. There seem to be lack of agreement regarding conditions (like gravitational ...
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Hawking radiation: why do only negative mass particles fall into black holes? [closed]

So I have read other questions asked about this topic, but they focus more on positive or negative energies of the virtual particles, and I want to ask specifically about the negative mass issue. ...
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Considering Hawking radiation, can an object ever actually cross event horizon of a black hole? [duplicate]

The Schwarzschild solution of Einstein's field equations clearly shows that a far away observer sees time slow down for an in-falling object. Relative to him, it takes an infinite amount of time for ...
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What is really going on in the ergosphere of a Kerr black hole?

Considering the Kerr metric with $GM>a$, we can compute 2 event horizons: $r_\pm=GM\pm \sqrt{G^2M^2-a^2}$ These event horizons are null surfaces, and trajectories are timelike between $r_+$ and $...
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Black Hole Matter to Subatomic Exchange

When matter enters a black hole with a singularity the particles smaller than photons released come from within the black hole or do subatomic particles shed from matter just before matter passes the ...
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When is the event horizon a Killing horizon?

I know the definition of both (event horizon is closure of causal past of future null infinity whilst Killing horizon is a null surface where some Killing vector becomes null e.g. the surface where it ...
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Apparent Horizon vs. Event Horizon

I understand that an apparent horizon is the boundary of trapped codimension-2 surfaces in the spacetime (surfaces from which both ingoing and outgoing light rays must be converging). Meanwhile, an ...
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Can a solid object inside the black hole event horizon avoid the singularity? [duplicate]

I will ask this as a simple lay man. Let's consider an astronomical black hole that was creating by in falling matter on a neutron star. As neutron star get heavier it gets smaller and a Schwarzschild ...
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When a neutron star accumulates enough mass, does a black hole start at its center?

With less dense bodies, such as the earth and the sun, the center has less gravity/density (since there's an equal amount of mass surrounding the center, pulling out on it from all directions). Does ...
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A two-dimensional event horizon?

Today, I came across an article which says that the Universe began with the collapse of a 4-dimensional [spatial] Universe. Well, I don't know if there's any way to confirm these like it is with all ...
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Does the maximally-extended Schwarzschild horizon see the entire past of the parallel universe?

I've seen similar discussions for the inner horizons of Kerr and Reissner-Nordstöm metrics, but I've never seen mention for the simple maximally extended Schwarzschild geometry: As an infalling ...
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How does light behave within a black hole's event horizon?

If the event horizon of a black hole is the distance from the center from within which light cannot escape, imagine a person with a flashlight falls into the black hole. He points his flashlight in a ...
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Where is the event horizon in a black hole?

At the beginning I thought that the event horizon coincides with the surfaces, but then making a new name when you could just call it surface would seem a bit pointless. Then where is the event ...
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If nothing ever falls into a black hole, why is there a puzzle about information?

From an outside perspective, nothing can ever pass the event horizon. It just scooches asymptotically close to the event horizon. So (from our perspective on earth), when a black hole reduces in mass,...
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Is a black hole's mass uniformly distributed?

If you were to fly around a black hole, would the gravitational pull be uniform and centered on the singularity, regardless of your relative location? If yes, how can this be consistent with models ...
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Particles inside black hole does not hit singularity

We say that if any particles from outside fall into the black hole, they eventually hit singularity. Then why not particles already inside the black hole are at singularity? Or are they? If yes, then ...
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Schwarzschild equation physical meaning

When you pass an event horizon of a black hole according to the Schwarzschild equation time and space swap the physical meaning. So you can no longer move away from a black hole, in similar way as you ...
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What is the temperature of the event horizon?

In a discussion with my son about absolute zero, we arrived at the conclusion that the event horizon might be the place to look, as it "absorbs?" all energy, including light. Found this in the ...
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Event-horizon black hole

A object which passes the event horizon need a finite proper time for this. But a infinite far observer wouldn't see that the object passes the event horizon. But if the observer doesn't see this, ...
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Acceleration in AdS

I've been reading some notes ("Anti-de Sitter space" by Bengtsson) on anti-de Sitter space. It is shown in equation 152 that timelike observers at fixed radial distance from the origin experience a ...
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Are black holes naked singularities for an observer within the event horizon?

A naked singularity means that you can see an infinitely dense thing. Black holes don't count because it sucks up all the light, so you won't see or otherwise detect it. But wait, if you are within ...
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Higher dimensional trapped surface and its condition?

In higher D-dimensional spacetime, a marginally trapped surface is a closed spacelike (D-2)-surface whose outer null normals have zero convergence. It is very like a marginally trapped surface in the ...
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Why does a black hole grow when it consumes matter? Isn't this a contradiction?

I've been thinking about this for a while but can't get my head around it. A black hole's mass is such that its gravity can overcome light. Its event horizon, as I see it, is the boundary up to which ...
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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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Event horizon temperature

If the acceleration of a particle at the event horizon is "infinite", then its Unruh radiation must be infinite. Yet the Hawking radiation of a black hole is finite.. how comes the difference?
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Black hole surrounding an object?

When a particle crosses the event horizon of a black hole, at one short moment in time would it appear for that particle as if it was surrounded by a black hole? Regardless of which direction you ...
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Information encoded on the surface of a black hole

If an object that enters a black hole has its information content frozen at the event horizon, in what sense is it frozen? The usual analogy is of a hologram encoded in 2d which can be decoded into a ...
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What happens within the convergence of two event horizons? [closed]

What would happen if someone stood between two equally massive black holes, so that every particle of their body was contained in the region of both event horizons? Would they be: a) Totally ...
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Do particles in a black hole stay in constant orbit?

Would particles behave the same way as a satellite orbiting earth, only far more compact and rapid correlating to the gravitational force of the black hole?
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If nothing can escape a black hole, where does Hawking radiation come from? [duplicate]

Hawking radiation is a form of electromagnetic wave travelling at the speed of light. Hawking radiation is radiated from a black hole. If nothing can escape the gravitational pull of a black hole, how ...
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Is the event horizon also the boundary region of the mass contained by a black hole?

I was recently playing around with classic Newtonian mechanics and calculated that the Earth would have to be compressed to a spherical region of $8.8 \ mm$ (Its Schwarzchild radius) to turn its ...
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If black holes almost or barely collide

Consider black holes approaching each other at some relative velocity and varying impact parameters. For impact parameters above some value they will sail past each other. For impact parameters below ...
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If spacetime is folded upon itself [closed]

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". So the picture link I left above shows ...
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Problem imagining how does a black hole merger look like from far away

Suppose we have two black holes moving on a path of direct frontal collision. Is it correct that from far away, due to time dilation, we can never "detect" that the two black holes merging or ...