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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Are there any known non-zero mass objects travelling at almost $c$ observed in the universe so far?

Have we ever observed a body or particle with non zero mass traveling at almost $c$? I'm asking this because according to relativity as an object approaches light speed it's mass approaches infinity, ...
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Acceleration 4-vector in Schwarzschild metric [on hold]

I am working on A note of a paradoxical property of the Schwarzschild solution by Abramowicz M. A. and Lasota J-P It is a note on surprising cases in the context of the standard Schwarzschild ...
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If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?

I'm a big fan of the podcast Astronomy Cast and a while back I was listening to a Q&A episode they did. A listener sent in a question that I found fascinating and have been wondering about ever ...
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Black hole singularity from collapsing light vs dust

Consider two black holes, one formed from a spherical cloud of electromagnetic radiation, and one formed from a non-interacting dust solution. The stress energy tensor is traceless for ...
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How were the solar masses and distance of the GW150914 merger event calculated from the signal?

The GW150914 signal was observed, giving us the frequency and amplitude of the event. Because LIGO has two detectors a rough source location could be derived. But how do these three factors allow for ...
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What was the frequency of the gravitational wave recently detected, and why?

In one early Internet post there was a graphic that appeared to show the gravitational wave (pulse) at about 30 cps. And another video it was stated that the gravitational wave would be as high as ...
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Redshift of merging black holes

How did they found that the gravitational waves where emitted at redshift $z=0.09$? I understand the measurement of redshift for an electromagnetic wave where we have measured in a lab various ...
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Can we see the famous black hole pair or its effect on other stars in any other means but LIGO?

If the source of LIGO's detection is a pair of black holes, can we see them using a traditional electromagnetic/neutrino/some other kind of telescope? Or can we see their effect on other stars in ...
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How do gravitational waves and black holes interact?

Following the first detection of gravitational waves yesterday (11 Feb. 2016) by LIGO, I have a couple of questions about how gravitational waves and black holes interact. Assume that there is a ...
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Why doesn't the light get out?

You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now I wave my magic gedanken ...
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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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Does the size of a black hole change depending on its charge or spin?

I was talking to this friend of mine who said that the size of a black hole could vary depending on its "charge" and spin. He said the size of a black hole would reduce if it had a spin or charge. The ...
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Why can an electric field escape from a black hole?

I know this is a duplicate question but the other answers didn't explain clearly my problem. The talkes about no hair theory for explaining the communication and information problem of matter inside ...
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So Black Holes Actually Merge! In 1/5th of a Second - How?

I've read a lot of conflicting answers in these forums. However, today saw the awesome announcement of gravitational waves. Two black holes merged: ...
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How much light is necessary to form a black hole [duplicate]

I suppose that enough light in a small enough volume could create a black hole. What is the good quantity that can tell when light can or cannot make a black hole? Energy density? But there must be ...
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Can black holes with the same mass evaporate with different speeds?

I am curious about the following observations: (1) For a normal Schwarzschild black hole, it evaporates according to $dm/dt=-1/m^2$; (2) We have eternal black holes which do not evaporate (though ...
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Question about the Blandford–Znajek process

I've been trying to understand the Blandford–Znajek process which explains how Gamma Ray Bursts form, but it's still not clear to me how it works. In this article, several theories about the formation ...
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Scattering in Black Holes

Let's take your favorite Black Hole and consider the scattering problem for a scalar field around it. Suppose that the Klein-Gordon equation can be separated in the radial and the angular part. Which ...
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Looking out from a collapsing star

From the perspective of the surface of a collapsing star, if you were riding it in as it formed a black hole, what would you observe looking out into the rest of the universe? As you approached the ...
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Merger of old black holes

On the eve of a possible announcement on the production of gravitational waves via a black hole merger, I think this question is quite aptly timed. I have a few questions regarding the evolution of ...
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Is there a limit to the size of black hole?

I have read answer by @John Rennie in regards to the size and density of black hole. In the last sentence he states that super supermassive black hole ...
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If black holes warp space-time infinitely, does that mean space-time goes on infinitely in all directions?

My thoughts are if a black hole warps space-time infinitely then does that mean space-time goes on in all directions infinitely? Maybe (probably) my understanding of space-time is not great, if ...
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Information Preservation and Weather Forecasting for Black Holes

Referencing Stephen Hawking's recent paper Information Preservation and Weather Forecasting for Black Holes and this question. I understand concept of holding the information on the apparent horizon ...
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Why is it difficult for 2 black holes to merge?

Apparently as part of the merger of galaxies, sometimes the central supermassive black holes of colliding galaxies get really close, however once they come to a distance of about <1 parsec, it ...
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Black Hole Collision [duplicate]

What would happen if two equally massive black holes directly collided at 5% the speed of light. I'm not talking about slowly orbiting each other for thousand of years. I mean one instant catastrophic ...
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Why can't we see black holes?

Is it all because they are so black? But even our tech is not able to see black holes. We can only tell where black holes are, when they are eating stars. Or it's because they consume light ?
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Cold Solid Matter at the End of a Black Hole's Acceleration Disk?

Is it possible that black holes magnetic field are rapidly cooling matter using a type of magneto caloric effect and cold fusion creating new matter only possible with a black hole's gravity? A type ...
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Black hole starship: Would micro black-hole Hawking radiation emit anti-matter?

My understanding of Hawking radiation is that virtual particle pairs of matter and anti-matter are created from vacuum energy and one of those virtual particles may escape while the other enters the ...
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Big Bang Quarks Travelling at Light Speed [closed]

When I think of an explosion it lasts a fraction of second. When the entire mass of the universe explodes how much time passes before the perfect sphere slows from traveling at/near the speed of light ...
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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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is the potential energy of a black hole infinity

It appears like black holes posses an escape velocity greater than the velocity of light. It takes an atom infinity energy to travel at speed of light.Do black holes posses that energy to retain ...
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Isn't gravity non-local and non-causal?

The way I think of this is that, I can ask physical questions about a space-time which are impossible to answer unless one knows the full space-time, and hence I am inclined to believe that gravity is ...
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How long can a particle survive inside of the horizon of a black hole?

By examining the causal structure of a Schwarzschild black hole, one can see that a particle in region II is unable to escape to $r=\infty$. Such diagrams do not show, however, how long a particle ...
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Shapes in a black hole

A question around an answer of Timaeus What happens to a particle in the exact center of a Kerr black hole?-answer Outside both is a normal type region of spacetime. In between the two the $r$ ...
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What happens to a particle in the exact center of a Kerr black hole?

Kerr black holes (and Kerr-Newman black holes), instead of the "point" singularity theorized in spherically symmetric black holes, instead have a "ring" singularity, spread along the equatorial plane ...
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Will the CO–0.40–0.22 black hole companion of Sagittarius A merge with it?

According to "Signature of an Intermediate-Mass Black Hole in the Central Molecular Zone of Our Galaxy" by Oka, Mizuno, Miura and Takekawa, there is a second black hole, with a mass of ~ $10^5$ Sun , ...
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Space-time and gravitational fields

I am reading a book by Carlo Rovelli, Seven Brief Lessons On Physics, and would like to check if I have understood something. Apologies if my question is badly phrased, feel free to edit where ...
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Two black holes prepared from different initial states

I have asked a similar question, I would like to reformulate it in more details. Here is a thought experiment: Assuming we can create black holes by squeezing photons, we can then prepare two ...
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A problem with ADM mass in the derivation of 1st law of black hole thermodynamics

The definition of ADM mass is $M=\frac{1}{16\pi}\lim_{r\rightarrow\infty}\int(\frac{\partial h_{\mu\nu}}{\partial x^\mu}-\frac{\partial h_{\mu\mu}}{\partial x^\nu})N^\nu dA$ according to Wald. ...
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How has the world remained in balance?

In the center of our galaxy, there is a Supermassive black hole. We were told in early astronomy units of school that black holes are giant vacuums that will absorb/consume the area around it. My ...
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Is a larger black hole a faster or a slower processor?

For a remote observer, a black hole with mass $M$ has a temperature $T=1/M$. Now I am confused with the problem: A larger black hole can achieve a task faster or slower if it's regarded as a kind ...
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Is there a doppler effect on the images of stars around rotating black holes?

I'm an illustrator working on a project involving rotating black holes like those discussed in "Gravitational Lensing by Spinning Black Holes in Astrophysics, and in the Movie Interstellar" by James, ...
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Evaporating black hole Penrose diagram

The context for this is the diagram from From where (in space-time) does Hawking radiation originate? - the more I think of it, the less it makes any sense ) This particular question is about ...
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Does time symmetry still holds when a particle drops into a black hole?

When a particle drops into Earth, it hits the ground and rebounds, if time reverse, it is equivalent to another particle moves with same speed but opposite direction. But at the case that a particle ...
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Worldlines in Schwarzschild geometry

I have an observer and a photon on a hypersurface $ \theta=\pi/2$ . My observer has $e, l$ constants of motion (energy and angular momentum divided by mass) and photon has $e',l'$. What conditions ...
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Has a stellar blackhole more mass than previously?

What is the coefficient of mass gained/lost by a star in its first phase transitioning into a blackhole. Does the blackhole have more or less mass than the star it was made from? Thank you Regards
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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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What are the virtual particles generated during the Hawking radiation?

What are the virtual particle pairs generated during the Hawking radiation? If a photon is emitted by Hawking radiation, what is its negative energy partner which fell into the black hole? Does it ...
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Black hole evaporation, mass or bit?

Usually when we talk about black hole evaporation, mass or energy is taken as the target and the evaporation time is computed based on mass loss in a given time period. Is there any work to analysis ...
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A ball in the gravity potential field of a black hole — seems a paradox

As illustrated in the following diagram (A, B, C, D are 4 specified space points, and C is close to a black hole), a small ball at distance of a black hole is stationary (suppose now it's mass is m0) ...