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 Information Paradox: Why Isn't the Position of A Black Hole Count as Part of Its “Information”?

It's often said that a black hole only has three properties: its mass its electric charge, and its angular momentum Why isn't it's position and velocity relative to other objects part of this ...
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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 ...
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67 views

Why are black holes called singularities? [duplicate]

I have researched black holes but I can't seem to find the answer. Any help would be appreciated.
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51 views

Do objects' velocities slow down going into black holes? Would they appear to?

I always hear that time slows down as you enter a black hole, and when I hear this, I always mentally imagine all of a person's motions, including their net velocity relative to the black hole, ...
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Can a particle tunnel from inside a black hole?

Event horizon isn’t special from GTR standpoint, and at least in AdS/CFT correspondence gravity can be “removed” from consideration entirely. So can a particle whose wave function is completely inside ...
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Relation between dark matter and supermassive black holes located in the center of galaxies

This research (see link), conducted on 3000 elliptical galaxies (which are typically galaxy merger results), reports finding "distinct relationship between the mass of the dark matter halo and the ...
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Black holes have conservative potentials. Why don't things “swing” in and out?

Black holes attract objects via gravity, which is a conservative force. Thinking from conservation of energy, It seems like for an object moving toward them, they should be able to "swing" into and ...
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How can a black hole be a cause of a Big Bang? [closed]

Is it possible that Big Bang occurred as a result of the black hole formation - that is the matter compressed so densely that it "exploded" within the boundaries of its horizon and became a what we ...
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123 views

Black-holes, space time and their bending [closed]

I have been watching some videos related to how space-time is bent because of the mass (just "visually", not mathematically), and then I watched some videos about black holes. My own conclusions ...
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38 views

Clocks at rest in Kruskal coordinates

The proper time in Kruskal coordinates is given by $$d\tau^2=\frac{4}{e^rr}(dT^2-dX^2)$$ (where r is measured in units of Schwarzschild radii). Since at $T=+/-\infty$, $dT^2-dX^2$ goes to zero for an ...
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Do black holes violate the first law of thermodynamics?

When a black hole absorbs matter is it destroying that mass, thereby destroying energy, therefore violating the first law of thermodynamics?
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Is it theoretically possible to prevent or deter a star from becoming a black hole?

Suppose NASA decides too many black holes are being produced in a year, so it decides to do something about that. Given our current scientific knowledge, is there theoretically any way NASA could ...
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77 views

How small would an electron have to be in order to become a black hole?

According to quantum mechanics electrons don't behave like everyday objects. Would this prevent the formation of a black hole? If so why? Also, assuming they behave like everyday objects, at what ...
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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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288 views

Are black holes in a binary system with white holes, and are they both wormholes? [closed]

What is a black hole? The general explanation is that a black hole is small region in space with such strong gravitational effects that nothing can escape and even light is trapped inside of the event ...
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138 views

Why can black hole evaporate if objects need infinity time to reach event horizon (as seen by a distant observer)?

I am new to black hole, but have a question about it: Object needs infinity time to reach event horizons (as seen by a distant observer). Particle-antiparticles separates, one of them drops into ...
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47 views

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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182 views

The black hole paradox

I recently read in the news that Stephen Hawking claims to have solved the Black Hole Information paradox. I researched a bit about the paradox and the research that Stephen Hawking did to solve it. ...
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273 views

Certain doubts regarding the movie 'Interstellar' [closed]

In the movie, or rather a scientific fiction, Interstellar, we saw in the last part, that the actor falls into the black hole, travels in time, which is a dimension inside the black hole, and then, ...
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84 views

Black Holes and Einstein Field Equations

I recently watched a video where Michio Kaku argues that there must be something fundamentally wrong with the theory of General Relativity because it gives time t=0 as a solution at the centre of a ...
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Trying to give a (non-rotating) black hole an electric dipole

Suppose there is a Schwarzschild black hole. You add positrons to the north "pole" and electrons to the south "pole". From an external observer, objects that you add end up "stuck" to the horizon. ...
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86 views

Does spaghettification really happen with conditions found close to a black hole?

This website tries to explain why the term spaghettification doesn't actually occur when something gets close to a black hole. The argument of the author is that the equations we use to predict the ...
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1answer
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Could the Big Bang have simply been two black holes hitting each other at 99% of the speed of light? [closed]

Given two equally massive black holes moving at 99% of light speed, it seems there would clearly be enough energy for most (99%?) of the mass of both to be ejected and / or radiated well beyond the ...
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Can something (again) ever fall through the event horizon?

Since I am more confused by the answers given in this site to the many variants and duplicates of this question, with some arguing that from the point of view of the falling observer, it happens in ...
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37 views

Does a wormhole on the event horizon keep working?

Recently the discovery of how to build a magnetic wormhole has been all over the news. These wormholes tunnel magnetic fields instantly from one point to another point. (Although the current model is ...
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Do matter that falls in a black hole go to the future and the end of the universe?

Black holes are black because everything that enters don't exists anymore. When you pass the event horizon, the time stops for you, all the future of the universe has passed for you and the universe ...
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What is the meaning of t=infinity at the black hole horizon?

Looking at the Kruskal diagram for black holes, it seems to me that at the horizon, all free falling objects cross the horizon at the same coordinate radius and time. Does this not mean that all ...
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Can I say that the two-body problem is also a vacuum solution for the special case of two orbiting black holes?

A two body system is one where two bodies orbit each other. In the case of two orbiting black holes, since an individual black hole is described by a vacuum solution, can I say that the two-body ...
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1answer
54 views

How can black holes be observed to grow? [duplicate]

If, from the reference frame of an observer at rest outside a black hole, it takes an infinite amount of time for an object to be observed to fall into a black hole, how can black holes ever be ...
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79 views

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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110 views

Could black holes interact with dark matter at distances far greater than matter?

I watched this Nova episode on super massive black holes and learned that the speed at which the outer stars in a galaxy orbit correspond to the size of the black hole at the galaxy's center. They ...
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Is there any situation in which a primordial black hole-sized black hole form AFTER the “Big Bang?”

I have seen that primordial black holes may have formed at the start of the universe due to the density of matter. So, is there any way in which our current Universe could spawn a non-stellar mass ...
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Before we realized that supermassive black holes were at the center of large galaxies, how did the models explain galaxies?

So, I was watching this show on Netflix about supermassive black holes. I didn't realize that astronomers were surprised to find these black holes at the center of galaxies, because I cannot imagine ...
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Black Hole horizons and the Equivalence Principle?

In the reference frame of a freefalling observer, does crossing the event horizon not cause a contradiction between two classical principles that supposedly apply at the event horizon: the equivalence ...
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Can photons be converted to dark matter in black holes? [duplicate]

I'm a pharmacy student so if it's not a good theory let's just not laugh at me :) I was wondering if it is possible that when the light enters a black hole and gets trapped in its gravity, its energy ...
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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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Is Hawking radiation valid for a microscopic black hole?

A black hole evaporates by Hawking radiation. The computation of the evaporation time uses some approximations. Question: Is the evaporation time valid for a microscopic black hole? In particular, ...
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What the lifetime of a massless black hole of photons?

Let a bundle of photons very concentrated in a very small area so that the space-time is curved as a black hole, and the photons can't escape: this is what I call a massless black hole of photons. ...
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1answer
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If a black hole is just warped spacetime, then where is the electric charge?

I've heard Kip Thorne repeatedly state that matter is destroyed when a black hole is created, that all you are left with is distorted spacetime. "The idea that black holes are made from very ...
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time span in a black hole vs earth [closed]

This is a thought experiment: I am an immortal and I live for 1 billion years on earth. My identical twin brother spends the same amount of time in/on a black hole. To him, did he spend exactly 1 ...
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40 views

Blackholes / density [duplicate]

If a star explodes to form a black hole how does the gravitational field become infinite from one state to the next? ie: it seems additional mass has been added or is this simply a function of ...
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Black Hole - Between event horizon and singularity

Dear Physics Board Users What is between the singularity and the event horizon? If the gravitation gets bigger and bigger coming nearer to a black hole, is then the gravition inside even bigger that ...
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If a spaceship accelerates enough can it overcome spaghettification?

If a spaceship accelerates at the right amount would that counteract the spaghettification caused by falling into a black hole?
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75 views

Do black holes have a puff pastry point?

If a person falls into a certain sized black hole they accelerate very fast, which increases the g forces on them. These g forces flatten the person out into a pancake. As the person falls further ...
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Stand on a black hole

Is there an theoretical possibility that an black hole rotates so fast that the acceleration pushing you out of the black hole is nearly equal to the gravity?
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Why do physicists believe the “no-hair conjecture” to be true? [duplicate]

The no-hair conjecture states that a black hole is completely characterized by its mass, electric charge, and angular momentum. Most physicists take it as given. My question is, why? It implies the ...
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1answer
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Question about Black Holes

I'm not a physicist so I'm sorry if this question is stupid from your point of view, but I believe it's not. Let us make this thought experiment: Take a black hole and put near it (but at a safety ...
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Black hole physics beyond the perturbation theory

Motivated by this question: Perturbation of a Schwarzschild Black Hole How would one deal with the situation where black hole experiences not only small perturbations but major changes to the metric? ...
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Probing beyond the black hole event horizon

Black holes are interpreted to have a "break down" of general relativity at their point of singularity. The region near the singularity is expected to be described by some theory of quantum gravity. ...
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Could you view yourself in high gravity situations?

I'm trying to understand what effects gravity can have on light. First of all, I don't understand how gravity can even affect it, since it doesn't have mass, right? That is probably a separate ...