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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Black Hole surface area at Schwarzschild radius is half?

I have been interested in black holes for some time, and am still trying to wrap my head around some of their more obscure properties. Now I know that the Schwarzschild radius is $r= ...
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Any interesting implications of a holographic black hole in a holographic universe?

Bear with me; I don't have a background in physics, nor am I sure I even understand the things I'm talking about. I recently read that math/physics for a holographic black hole could be applied to ...
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Point of no return when falling into evaporating black hole

Captain Foolhardy in his trusty spaceship The Test Particle is in radial free fall towards an evaporating uncharged black hole with no spin in an otherwise empty universe which asymptotes to ...
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Help me calculate the Euclidean action of a gravitating system!

I recently read Gibbons and Hawking's paper Action integrals and partition functions in quantum gravity, Phys. Rev. D 15 (1977) 2752. I am interested in repeating their calculations. It is fairly ...
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41 views

If a super massive black hole captures a very small black hole, would the smaller black hole be immune to spaghettification?

I think to answer this question we would have to fully understand the nature of black holes. It seems to me that the smaller black hole could have a lower density than the larger one. In this case the ...
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What is wrong with this theory? - This is a unique way to visualize the universe [on hold]

Assuming that particles move in two ways: 1st, conformationally changing relative to itself over time regardless of its location in 3d space (i.e. staying in one place but conformationally changing) ...
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36 views

Does the uncertainty principle affect event horizons? [duplicate]

I was thinking about black holes. For a simple black hole the event horizon is given by a distance of 2 times mass (energy) of the black hole. (2m). But according to quantum mechanics, if you try to ...
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Point View and the relativity of everything, also regarding seemingly neutral pen and paper formulas - also, the nonexistence of black holes [on hold]

I am just a programmer with a love for math/physics and ... science fiction, haha! Anyway, to state it right in the beginning: This question is related to the following postulation (of mine, but ...
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53 views

Wave equation on Schwarzschild background

I am trying to follow the solution of the wave equation for a scalar field on Schwarzschild background from http://batteringram.org/science/gr/scalar_wave.pdf. I have a problem on page 2 where they ...
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0answers
33 views

How can a singularity have infinite density? [duplicate]

I've heard many times that black holes have infinite density at their center, but I've also heard astronomers quote mass estimates for black holes. How could the singularity have infinite density if ...
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3answers
66 views

Path of light as it travels between two black holes

What would happen to light passing through a narrow space between the event horizons of two equal-mass black holes? Would it deviate or follow a straight path?
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122 views

Gravitational time dilatation calculation [on hold]

I'm proving an example case from Kip Thorne's book, Science of Interstellar for time dilatation at a Kerr black hole with the following data: \begin{align} a & = 0.998, \\ r & = ...
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Extra dimensions in a black hole [closed]

Could small extra dimensions predicted by string theory exist within a black holes singularity? I believe that these dimensions would not break down in a black hole as opposed to our three dimensional ...
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0answers
64 views

Can tachyons escape the gravitational pull of a black hole?

Anything that crosses the event horizon of a black hole cannot escape the pull since it has crossed the Schwarzschild radius and thus, the escape velocity is greater than the speed of light, and since ...
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3answers
805 views

What is the radius of the event horizon?

I know that the Schwarzschild radius is given by $$r~=~\frac{2GM}{c^{2}}.\tag{1}$$ However, If we had the metric $$ds^2~=~−A(r,t)dt^2+\frac{dr^2}{B(r,t)}+r^2(dθ^2+\sin^2{θ}dϕ^2),\tag{2}$$ where ...
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3answers
136 views

How to derive the Schwarzschild radius? [duplicate]

I know that the Schwarzschild radius is given by $$r=\frac{2GM}{c^{2}}.$$ but I never seen a derivation for this equation. 1- Does anyone know how to derive this equation from general relativity? ...
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69 views

The age of black holes

I have a very small understanding of space-time however I have been watching some interviews and reading articles featuring theoretical physicist Kip Thorne and I have a few questions that I hope can ...
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72 views

Will a black hole cause scattering of a gravity wave?

In my GR textbook, it states that gravity waves can undergo interference but not scattering. I am just starting the chapter on linearised gravity concepts (weak field approximation) and my apologies ...
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4answers
345 views

“Center of a black hole is a time”

$\newcommand{\d}[1]{\mathrm{d} #1}$In one lecture (around 1:33:15) of the series of lectures "Theoretical Minimum" of Prof. Susskind he talks about black holes and the Schwarzschild metric: $$\d ...
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Nonsingularity of the Euclidean black hole metric

How can one show that the nonsingularity of the Euclidean black hole metric is required for thermal equilibrium of the original black hole in Lorentzian signature? It is mentioned in Prof. P. K. ...
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0answers
50 views

question about Blandford-Znajek original paper

I'm trying to follow the original Blandford-Znajek paper (found here), and I can't find how equations 2.1, 2.2 and 2.3 are obtained: 2.1 refers to "the charge density required to ensure that $E \cdot ...
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How can a black hole slow time down without increasing its own speed?

I read that speed of light is the only "speed" or rate of change allowed in universe when you consider 4-dimensional space-time where space and time are orthogonal to each other, which explains why ...
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2answers
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How can light enter a black hole if it cannot get out?

I have known for a very long time that light cannot exit a black hole. I can even understand some of the simpler reasonning about it, such as escape velocity, or space geometry inside the black hole. ...
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342 views

What happens to the total volume of a chunk of space that is being sucked into a black hole?

Does it increased, decrease, or stay the same? Maybe it explodes to infinity... Here is a similar question: Do black holes have infinite areas and volumes? But it's different because it asks how to ...
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2answers
282 views

How can we feel the effects of a Black Hole if all the mass is gone?

This question may help me learn more about the subtleties involved between the notions of gravity, in the Newtonian sense and those of curved spacetime, in the General Relativity sense. I will take ...
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1answer
43 views

Will the rotation of a neutron star prevent it becoming a Black Hole?

This question, to me anyways, is basically a balancing act between 2 possibly opposing effects. Take a neutron star with just too small a mass to overcome it's degeneracy pressure, failing to ...
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Magnetic dipole near black hole

Usually it is said that black holes cannot have electric or magnetic dipole, only electric charge and angular momentum are allowed quantities besides mass So, it would seem that black holes behave as ...
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1answer
66 views

Are moving objects producing stronger gravity fields? [duplicate]

If the strength of gravitational influence exerted by a body is derived from its mass and energy then is it true that a moving object which has some kinetic energy should also produce stronger ...
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28 views

Evaporation of black holes

What is the current scientific consensus about the evaporation of black holes? Is there any experimental evidence that support it? (I distinguish between Hawking radiation and black hole evaporation)
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Are there any planned experiments to intentionally create black holes in the lab for study?

And if they did what kind of machine would be making them? And what would they study?
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Does a body have to compress to its Schwarzschild radius to become a black hole?

When something is compressed to within its Schwarzschild radius, it will compress to a singularity within finite time regardless of what forces are involved. But is there some lesser point at which ...
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1answer
56 views

Difference between anti-matter and matter black holes [duplicate]

Laymen question: Is there any way to determine by observation whether or not a black hole has resulted from the core collapse supernova of a star originally composed of anti-matter versus a star ...
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1answer
66 views

Hawking Temperature of the BTZ Black Hole

The metric of the BTZ Black Hole is given by $$ ds^2 = - N^2 dt^2 + N^{-2} dr^2 +r^2(d\phi + N^\phi dt)^2 $$ with $$ N^2 = -M+ \frac{r^2}{l^2} + \frac{J^2}{4 r^2}, \ \ \ \ \ \ N^\phi = ...
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Charged black holes and AdS/CFT

People generalize the statements of AdS/CFT correspondence by adding black hole (charged black hole) in the gravity theory to provide the dual gauge theory finite temperature (finite density). I have ...
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1answer
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Do all paths leading into a black hole lead directly at the exact center of the singularity? Or could they go very near it and curve back?

I only have a very basic understanding of general relativity, so this might sound stupid. But as I see that gravitational objects orbiting each other, even if one of them is massive, as long as their ...
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92 views

Could the universe's antimatter be hiding in black holes?

As far as we know almost all the mass in the universe is matter, not antimatter. There are three scenarios: The universe started off with more matter than antimatter and the small amount of ...
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Taking selfies while falling, would you be able to notice a horizon before hitting a singularity?

I am generally interested in the role of "pings"(0a) between participants (a.k.a. "signal roundtrips"(0b), as familiar for instance from Synge's "five point curvature detector") in the determination ...
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3answers
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Does it make sense to model the Universe from an outside perspective? [closed]

I was reading some questions and answers about black holes and whether matter can actually pass through the apparent horizon, in particular this one: How can anything ever fall into a black hole as ...
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6answers
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Thought experiment - would you notice if you fell into a black hole?

I've heard many scientists, when giving interviews and the like, state that if one were falling into a black hole massive enough that the tidal forces at the event horizon weren't too extreme, that ...
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Does GR put a theoretical lower limit on the radius of a black hole event horizon?

Within GR theory, without going to the extreme r/0 as a radius, (but approaching that as an asymptotic case), is there any theoretical limit as to how small the event horizon of a rotating and/or ...
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Energy of black hole

If a black hole attracts and engulfs light, then why doesn't the energy of the black hole increase to form a star once again? Black holes form when a star burns off its energy and collapses, so it ...
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Can we assume black hole is just two big stars revolving around each other? [closed]

I am just curious by watching all the black hole theories.I think every phenomenon of the black hole can be explained just by this theory that Black hole is just some bunch of stars(possibly BIG ...
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How fast does a black hole appear to decay from infalling observer's perspective? [duplicate]

Black holes eventually decay by emitting radiation. It can take a long time. But from an outsider's perspective. How long does it take from the perspective of someone falling into it? I understand ...
3
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1answer
81 views

How do black hole jets form? [duplicate]

A black hole, neutron star or any object that has accumulated an accretion disc, sometimes features opposing jets, positioned perpendicular to the accretion disc. I understand that these jets are ...
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1answer
51 views

Does dark matter originate from matter falling into a black hole? [closed]

Is it possible that due to the fact that dark matter is clumped around black holes, that the dark matter used to be matter, fell into a black hole, and simply became dark? Furthermore, if the total ...
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1answer
130 views

What happens when an object passes through the event horizon of a black hole in GR?

I've heard/read many times that in the general relativistic description of a black hole an object would pass through the event horizon unharmed (ignoring tidal forces) while quantum mechanics predicts ...
2
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2answers
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What kind of volume does the event horizon of a Kerr black hole enclose?

I'm sorry if this is a naive question, I'm not too good with General Relativity. I'm aware that a rotating black hole is described by the Kerr Metric, and black holes of this kind have ring ...
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What does white hole look like on a graph paper?

Like a black hole looks like this, what does a white hole looks like? The reason I ask is because I would've imagined that it would look like the exact opposite, i.e. piercing out upwards. But it ...
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Does the holographic principle for black holes mean that information is cloned?

When an object falls into a black hole, does the holographic principle say that the information is copied and stored on the event horizon while the original information falls in?
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131 views

Link between Hawking-Bekenstein Black hole entropy and entanglement entropy

I'm currently doing a project on two sided Ads-Schwarzschild black holes in the context of Ads/CFT. I want to show that the entanglement entropy between the two CFTs corresponds approximately to the ...