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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Will the Big Rip tear black holes apart?
There seems to be an obvious contradiction between the predictions of the physics of black holes and the Big Rip, a predicted event about 16.7 Gyr in the future where local groups, galaxies, solar ...
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random matrix ensembles from BMN model
My friends working on Thermalization of Black Holes explained solutions to their matrix-valued differential equations (from numerical implementation of the Berenstein-Maldacena-Nastase matrix model) ...
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214 views
How much of a star falls into a black hole?
http://blogs.discovermagazine.com/badastronomy/2011/04/05/astronomers-may-have-witnessed-a-star-torn-apart-by-a-black-hole/
A lot of the star in the disc, a lot of the star in the jets, precisely how ...
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89 views
Hawking radiation for closely orbiting black holes
Suppose we have two black holes of radius $R_b$ orbiting at a distance $R_r$. I believe semi-classical approximations describe correctly the case where $R_r$ is much larger than the average black body ...
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Do spacelike junctions in the Thin-Shell Formalism imply energy nonconservation and counterintuitive wormholes?
The Thin Shell Formalism (MTW 1973 p.551ff) is used to properly paste together different vacuum solutions to the Einstein equations. At the junction of the two solutions is a hypersurface of matter – ...
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376 views
what happens to information when black holes merge
When a small black hole mergers with the larger black hole, Would an observer trapped in the smaller black hole be able to detect any difference? Does the observer still exists in the smaller black ...
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323 views
Charged Black holes - What is the Interest in those?
Here in this forum (and elsewhre) I read about "charged" black holes.
What is the background for this questions? Is this more a question of
theroretical interest?
In "practice" :=) black holes ...
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What is the “Event Horizon” of a black hole [duplicate]
Can someone please explain what the event horizon of a black hole is? I mean is it the actual surface of the black hole or is it the point of no return where light can no longer escape?
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Entering a black hole, jumping into another universe---with questions
I'm quite familiar with SR, but I have very limited understanding in GR, singularities, and black holes. My friend, which is well-read and is interested in general physics, said that we can "jump" ...
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333 views
Black holes in a head-on collision
Assume two uncharged non-rotating black holes traveling straight at each other with no outside forces acting on the system. What is thought to happen to the kinetic energy of these two masses when ...
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224 views
Do black holes have infinite areas and volumes?
How to calculate the area / volume of a black hole?
Is there a corresponding mathmetical function such as rotating 1/x around the x-axis or likewise to find the volume?
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67 views
How will a super massive black hole effect our galaxy?
I've recently learned that the general consensus is that several (if not, most) galaxies have super massive black holes in their center, in particular the Milky Way. This, at least to me, makes ...
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169 views
Why do the stars in the galaxy core move so fast?
There are a bunch of stars orbiting the black hole in the center of our galaxy.
These stars move at huge speed. Why do we see this? Why do the black hole not impose any noticeable time dilation on ...
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414 views
Can we have a black hole without a singularity?
Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, ...
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193 views
Fighting a black hole: Could a strong spherical shell inside an event horizon resist falling in to the singularity?
As a thought experiment imagine an incredibly strong spherical shell with a diameter a bit smaller than the event horizon of a particular large black hole. The shell is split into two hemispheres, ...
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771 views
Black hole analog experiment?
This question is directed mostly at people giving lectures on black holes, but input by other physicists or students is very much appreciated.
Do you know a good (home)-experiment with a black hole ...
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284 views
What is exactly the density of a black hole and how can it be calculated?
How do scientists calculate that density? What data do they have to calculate that?
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257 views
Information loss in a black hole
How does the Holographic Principle help to establish the fact that all the information is not lost in a black hole?
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338 views
The Uncertainty Principle and Black Holes
What are the consequences of applying the uncertainty principle to black holes?
Does the uncertainty principle need to be modified in the context of a black hole and if so what are the implications ...
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763 views
If there was a black hole on earth, what would it look like?
If an answer does exist, I'd love to hear it. I'm trying to incorporate a doomed earth story in something I'm writing, and the end of the world I'm going for is a black hole.
Let's say the black hole ...
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4answers
607 views
Gravity on supermassive black hole's event horizon
M = black hole mass
Gravitation is about 1/r^2
Schwarzschild radius r is ~ to M
Greater BH -> weaker gravitation on its horizon.
Lets take black hole so enormous that the gravitation on its ...
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2answers
81 views
Have scientists been able to find an example of a possible White Hole?
We went to a planetarium last night last night and watched "Black Holes" narrated by Liam Neeson. If I recall correctly, he said that scientists believe that they have identified a number of Black ...
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514 views
Why is spacetime near a quantum black hole approximately AdS?
In this link, one of the answers contains the statement
If you examine the space-time near a finite area quantum black hole,
you will see an approximate AdS space.
Presumably "approximate" ...
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418 views
Can colliding gravitational waves create a black hole?
Whether gravitational waves are real or just a coordinate freedom was argued in the early days of GR. Eventually the conclusion was that they were real. And if they are 'real' then I'm curious if...
...
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3answers
119 views
Is it possible to have a singularity with zero mass?
A singularity, by the definition I know, is a point in space with infinite of a property such as density.
Density is Mass/Volume.
Since the volume of a singularity is 0, then the density will thus ...
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Do neutrinos of any flavor get trapped in black holes?
This question has been bothering me a bit. I know that neutrinos have super small mass and they interact via the weak force. Since they have a non-zero mass, they should be affected by black holes and ...
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403 views
What happens to light that falls into a black hole?
When light enters a black hole, what happens to it?
I imagine the photons will either fall into the singularity, or the light will orbit just inside the event horizon indefinately.
(Some background ...
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164 views
Why are geons unstable? Are there other problems with geons?
I read in various places geons are "generally considered unstable." Why? How solid is this reasoning?
Is the reason geons are not studied much anymore because we can't make more progress without ...
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122 views
Decoherence inside black holes
I have a question about decoherence. Assume there is a macroscopic black hole floating around and you have some macroscopic object with you with a huge number of internal degrees of freedom. ...
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104 views
following up dark matter accretion in supermassive black holes
A while ago, there was some conspicuous evidence that supermassive black holes didn't seem to be eating dark matter at the expected rate of 70%-30%, in fact, only 10% of the black hole mass increase ...
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174 views
Is a black hole's surface area invariant for distant intertial observers?
Let's imagine I'm very far from any massive objects, so my local space-time is Minkowskian. Off in the distance is a black hole, far enough away that it doesn't noticeably curve space-time near me, ...
5
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2answers
568 views
Is it mathematically possible for a black hole to be connected to a white hole or a worm hole?
I know that there's no evidence at this point for "white holes" however would it even be mathematically possible for a black hole to be connected to a white hole (total opposite so everything would be ...
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167 views
Information Loss in annihilation
The concept of information loss is usually discussed with respect to a black hole. My understanding is that whatever matter you put into the black hole, it has only 3 "hairs" and so one doesn't know, ...
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Solid objects inside the event horizon - can they remain “solid”?
So, once something is inside a black hole's event horizon, it can only move towards the center. This is fine for a point-object. But 3D solid objects rely on molecular forces to stay in one piece. ...
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Do new universes form on the other side of black holes?
I have four questions about black holes and universe formations.
Do new universes form on the other side of black holes?
Was our own universe formed by this process?
Was our big bang a black hole ...
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76 views
Is there a black hole interior in black hole complementarity?
According to black hole complementarity, for an external observer, the interior of the black hole is replaced with a stretched horizon at a Planck distance above where the horizon ought to be. Is this ...
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155 views
Thought Experiments on black holes, (im)possible perpetual motion and minimum mass for photographic plates
Consider a black hole in vacuum at Temperature T. The setup that I am interested is a one that collects thermal photons from a black hole by enclosing in a spherical photographic plate and then ...
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209 views
From the perspective of an observer inside a black hole's horizon, where does the energy for Hawking radiation come from?
Would energy be seen to "flow" to the outside of the black hole? Through what mechanism?
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Hayden-Preskill informational mirrors and decryption
I do have a question about an assumption made in the very interesting Hayden-Preskill paper of black holes as informational mirrors. Alice throws her top secret quantum diary which is $k$ qubits long ...
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0answers
80 views
Do semiclassical GR and charge quantisation imply magnetic monopoles?
Assuming charge quantisation and semiclassical gravity, would the absence of magnetically charged black holes lead to a violation of locality, or some other inconsistency? If so, how?
(I am not ...
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paper about black branes and implications to 4d black holes
This paper makes a case for piezoelectric response (electric dipole moment under mechanical oscillations) of black branes. This paper does not make an implication of their results for 4D black holes ...
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Maximal kinetic energy due to gravitational attraction
Two related questions:
Small object of mass $m$ is falling into the supermassive black hole of mass $M$. What is the maximal kinetic energy can be acquired by the small object, from the point of ...
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Geometric entropy vs entanglement entropy (dependent on curvature coupling parameter)
I have a quick question. In hep-th/9506066, Larsen and Wilczek calculated the geometric entropy (which I believe is just another name for entanglement entropy) for a non-minimally coupled scalar field ...
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8answers
615 views
Flat space limit of the Schwarzschild metric and Hawking temperature
The Schwarzschild metric reduces to the Minkowski metric in the limit of vanishing $M$, but the Hawking temperature which is proportional to $1/M$ diverges in the same limit. This would imply that ...
4
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2answers
426 views
Can black holes be created on a miniature scale?
A black hole is so powerful to suck everything into itself. So is it possible that mini black holes can be created? If not then we could have actively disproved the rumors spread during LHC ...
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337 views
Can a black hole be formed by radiation?
I'm trying to find out if black holes could be created by focusing enough light into a small enough volume.
So far I have found (any or all may be incorrect):
Maxwell's equations are linear, ...
4
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3answers
57 views
What would a rotating black-hole look like to a “geo-stationary” observer orbiting the black hole
A rotating black hole is believed to contain a ring singularity rather than a point.
However, if an astronaut is orbiting the black hole at exactly the same angular velocity as the blackhole (in ...
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2answers
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What is the escape velocity of a Black Hole?
The escape velocity of Earth is $v=\sqrt{\frac {GM}{R}}$, where $M$ is the mass of the Earth and $R$ it's radius (approximating it as a sphere), and is much less than light speed $c$.
What is the ...
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1answer
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What kind of systems of black holes satisfy the laws of black hole thermodynamics?
I've come across black holes thermodynamics multiple times recently (both at this site and elsewhere) and some things started bugging me.
For one thing, first law bothers me a little. It is a ...
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Which gets you first when you are falling into a black hole, the black hole singularity or the cosmic background radiation?
If you look up while you are falling into a black hole you see the universe blue shifted, that is, you see the universe moving quickly forward in time compared to your local time. Since this effect ...
