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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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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68 views

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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1answer
57 views

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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77 views

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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69 views

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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139 views

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 ...
5
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180 views

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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90 views

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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41 views

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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89 views

Effective potential for Kerr incorrect?

I am self-learning GR. Background I have been following Christopher Hirata's lecture notes on Kerr geodesics. In Equation 38, the effective potential $V(r)$ is given by: $V(r)=(1-\epsilon)^2r^4-2Mr^...
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136 views

Does time and time dilation exist in a black hole?

Since being near stronger gravitational fields causes time dilation, can this be generalized to the region beyond the event horizon? i.e , is it meaningful to say that someone outside the black hole ...
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228 views

Can we detect gravitational waves generated from inside the event horizon of a black hole? [duplicate]

General relativity prevents light from escaping a black hole, but does it also apply to gravitational waves?
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45 views

Is there a parametrization for the shape of space?

I was thinking about how the space is curved. And how do we know that the shape of space arround a singularity is something like that: So I was trying to make a similar parametrization of this kind ...
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81 views

Why do black holes need a quantum mechanical description?

I read about black holes, about the Schwarzschild metric, Einstein field equations and their solution in the vacuum for a spherical body. I understood black holes are object whose gravity is enormous,...
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1answer
126 views

About the LIGO result and Abhas Mitra [closed]

Well I read this article https://en.wikipedia.org/wiki/Abhas_Mitra and he has claimed that "The so-called massive Black Hole Candidates (BHCs) must be quasi-black holes rather than exact black holes" ...
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79 views

Is it possible to travel faster than the speed of light under extreme warping of spacetime?

The event horizon of a black-hole is defined as the point at which light itself cannot escape, supposedly due to a black-hole's immense gravity and effect on spacetime. However, would this not require ...
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120 views

Why doesn't the cosmological constant cause black holes to form?

The cosmological constant acts as matter with positive energy but negative pressure. Then a region $R$ should have energy $E\sim \Lambda r^3$. On the other hand, we know that the energy for a black ...
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Blackhole and light [duplicate]

I was talking with my friend about blackholes and I asked him "Why blackhole 'sucks' the photons?" He had no deeper understanding so he answered that "I dont know, may the light is affected, because ...
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54 views

the significance of fifth dimension blackholes [closed]

is there a significance of fifth dimension black holes in theoretical and experimental physics? the concept of the fifth dimension is really hard to wrap my head around and i do not see how these ...
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85 views

How much energy can be radiated as gravitational waves from black hole merger?

In the black hole merger, recently observed by LIGO, about 5% of energy was irradiated in form of gravitational waves. source of data Is there any theoretical limit to how much energy can be ...
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99 views

$AdS_5$ Schwarzschild Black hole Temperature

This question is an extension of my previous Phys.SE question, but now in $AdS$ spacetime. I am attempting to derive the Temperature of the Schwarzschild solution in this space, which is given by: $$-...
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42 views

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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2answers
117 views

Can we make any implications about the internal structure of black holes from the 'chirp' that LIGO observed?

Are there any implications about a black hole's internal structure we can make based on the chirp issued? For example that a black hole does in fact contain or does not contain a singularity rather ...
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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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59 views

Vibrating black holes

From http://ligo.org/science/Publication-S5S6RD/index.php "Every star in the universe vibrates or oscillates in some manner. Turbulence on the surface of the Sun causes well-known solar oscillations ...
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Can a micro black hole hover above a regular black hole?

So let's say you have a black hole $A$, that is small enough for its gravity to be very small, but has strong hawking radiation, and larger black hole, $B$, with very small hawking radiation, but ...
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29 views

How is a black hole formed? [duplicate]

As far as I know, whenever we talk about a black hole, we refer to a static or stationary solution to Einstein field equations. I know the formation of a black hole can be discussed by the numerical ...
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Could the September 2015 LIGO gravity wave “detection” from “merging black holes” be fake? [closed]

The following Physical Review D article gives reasonable bounds for gravitational wave detection for Supernova core collapse. These bounds cannot be overwhelmingly different from the bounds on GW ...
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Derivation for the temperature of Reissner-Nordström (charged) black hole

A lot of the text for this is from "How does one correctly interpret the behavior of the heat capacity of a charged black hole?" but this concerns a different question. The Reissner-Nordström black ...
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115 views

How can a five-dimensional black hole 'break' general relativity? [closed]

By the laws of general relativity and the existence of black holes, what makes our universe to be just 4 dimensional but not 5 or more because a 5-d black hole can violate theory of relativity? ...
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111 views

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 ...
2
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1answer
88 views

How they can estimate when the black holes collided in the recent LIGO discovery? [duplicate]

How they can estimate when the black holes collided in the recent LIGO discovery? If LIGO can detect ripples in the gravitational waves, how they can figure out how old those waves are? Surely ...
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Are we sure that there are at most x different types of black holes?

If I'm not mistaken, there are a limited different types of black holes. Depending on were I look, the black holes are categorizes according to size, or categorized according to surroundings and ...
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Can light escape a black hole? [duplicate]

I heard that a black hole is not black because it's escape velocity is greater than or equals to the speed of light. But instead it is black because the light that gets emitted from a black hole gets ...
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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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What is the speed of gravity in a Schwarzschild metric?

The question "How does gravity escape a black hole?" has been asked, but the responses are not fully satisfying. Frederic Brunner gives a startling intuitive answer: "Gravitational attraction ... is ...
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Choice of the coordinate system in a spherically symmetric solution

For a static spherically symmetric solution, the metric can be written as $$ds^2=-A(r)^2 dt^2+\frac{dr^2}{B(r)^2}+C(r)^2d\Omega^2$$ In some cases, we can write $C(r)=R$ and interpret then $C$ (or $R$)...
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Will a collapsing black hole be ensured to be in eternal equilibrium at some point?

I'm just even if at all hobbyist in this matter. I learned that stars will collapse at some point and go supernova or turn into black holes if not able to keep equilibrium. But what happens in the ...
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On geometry of light's path in the Universe

Is it possible for us to see our own galaxy from different perspective, as path of light emitted from our galaxy is curved by any possible ways and travelled back to our eyes even if it take much time?...
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What's the difference between these two operations? [closed]

Assuming we have a black hole with mass $M$, we have two different operations on it: (1) Let the black hole to radiate for a while (before Page time) and collect all the radiation and collapse the ...
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Do Supermassive Black holes ever stop growing?

Do the Supermassive Black holes at the centre of large galaxies ever stop growing? In other words, do they eventually consume their entire 'host' galaxy?. is it a case of: the more they suck in > the ...
4
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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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37 views

Collapsing the early radiation of a black hole into another black hole [duplicate]

Can we collect and collapse the early radiation of a black hole into another black hole? I am confused since: For a black hole with mass $m$ and entropy(DOF) $A=m^2$, assuming 10% of mass is ...
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40 views

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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54 views

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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1answer
75 views

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 ...
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Does the mass lost by merging black holes depend on how they merged?

We've all heard the news about the detection by gravitational waves of two black holes, one 29 solar masses and the other 36 solar masses, spiraling into each other to create a single black hole of 62 ...
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Do the LIGO observations constitute proof of a black hole merger, and what happened to the black holes?

Information says that the gravitational waves, recently detected by LIGO, correspond (according to Einstein theory equations) to the effect of two black holes merging (with the masses of both black ...
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Does flat-land really exist?

In a paper "Out of the White Hole: A Holographic Origin for the Big Bang." The authors talk about the possibility that our 4D(3+1) universe could of emerged from a 5D(4+1) Schwarzschild black hole. ...