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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Is there a matching material interior for the Kerr solution of Einstein's equations?

Is there a matching material interior for the Kerr solution of Einstein's equations? I can only find informal and conflicting information about this. Some time ago, I've heard that it was expected to ...
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How bright was the AGN eruption at the center of the Milky Way ~2 Ma ago?

The black hole at the center of the Milky Way is believed to have erupted as an active galactic nucleus approximately 2 million years ago, at which time it would have been visible to early humans. How ...
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How many bits are encoded on the surface of the smallest black hole?

Here's my guess ($157\, \textrm{bits}$) and how I got there. Please feel free to disregard completely and give your own answer. My understanding (please correct any wrong assumptions as there may be ...
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459 views

Euclidean derivation of the black hole temperature; conical singularities

I am studying the derivation of the black hole temperature by means of the Euclidean approach, i.e. by Wick rotating, compactifying the Euclidean time and identifying the period with the inverse ...
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33 views

How much extra distance to a CERN event horizon? [duplicate]

How much extra distance would a scientist have to travel to get to the event horizon of a mini black hole if they ever make one?
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153 views

How much extra distance to an event horizon?

How much extra distance would I have to travel through space to get from Earth to a stellar mass event horizon? (compared to the same point in space without a black hole)
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216 views

Bekenstein entropy black hole v.s Hawking entropy black hole

Historically, Bekenstein estimated the entropy associated with a black hole in 1973, obtaining: $$ S_B = \frac{\ln(2)k_Bc^3}{8\pi\hbar G}A. $$ He already acknowledges in his article that his estimates ...
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What's the timescale until the Medium Crunch?

The future of the universe seems to be: clusters of galaxies drift apart due to space expansion until they all pass out of each other's cosmic event horizon. Gravitationally bound clusters overcome ...
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226 views

Watching something fall into a black hole from far away

I am observing (theoretically) an object falling into a black hole from a safe distance away. My understanding is that from far away it appears as if the body will asymptotically approach the event ...
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153 views

Photon “stuck” on the event horizon of a black hole

According to what I've read on special relativity, $c$ is the speed limit for every object in the universe, and according to Einstein, an object's speed through the three spatial dimensions plus its ...
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Euclidean black hole extrinsic curvature

I have read that the extrinsic curvature at the horizon of a euclidean black hole is zero? Does anybody know how this can be shown?
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Does someone falling into a black hole see the end of the universe?

This question was prompted by Can matter really fall through an event horizon?. Notoriously, if you calculate the Schwarzschild coordinate time for anything, matter or light, to reach the event ...
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Could dark energy make a large black hole less black?

Theoretically, if a black hole grew to a huge scale such that the effect of dark energy was large, could the black hole become 'normal' space again (i.e. no horizon or singularity)? What I'm trying ...
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363 views

Black-hole firewall and holographic principle [closed]

Can the firewall be viewed as the holographic boundary? Naively a hologram 3d image can not cross the hologram 2d surface that produces that image. According to the metaphor the boundary - 2d field ...
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Specific questions on Bekenstein's article on the generalized second law of BH-thermodynamics

I am reading Bekenstein's article from June 1974, Physical Review D, vol. 9, no. 12, "Generalized second law of thermodynamics in black-hole physics". On the second page he starts his discussion by ...
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2answers
143 views

Dipping a Dyson Ring below the event horizon

The basic assumption about inescapability beyond the Event Horizon is that the necessary escape speed (orbital speed) would exceed speed of light, therefore no object can achieve it. Now, would it be ...
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58 views

Surface gravity for a rotating charged black hole

I have that the surface gravity (at the outer event horizon) for a Kerr-Newman black hole is $$ K_+ = \frac{r_+-r_-}{2(r_+^2+(J/M)^2)} = ...
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201 views

Does a black hole have an interior or does the spacetime manifold itself end at the event horizon? [closed]

There have been a number of intriguing ideas over the years hinting at the possibility that a black hole might not have an inside, that it might consist of nothing but a surface and an external ...
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730 views

Why the center of our galaxy doesn't absorb us?

Depending on the theories, the center of our galaxy is a super massive black hole, this is easy to accept as a truth, but what I couldn't simply devour is how the solar system is orbiting around it ...
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Photons hitting the Black Hole Singularity

I was watching one of Dr. Susskind's Lectures on String theory and he was talking about black hole singularities (see the 40 minute mark of this lecture ...
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Are Stephen Crothers' claims legitimate? [closed]

I came up last night with a talk given by Stephen J. Crothers in which he claims that black holes and the Big Bang have no basis in general relativity. But is he really true? How legitimate are his ...
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101 views

How does Hawking radiation grow as a black hole evaporates?

The temperature of Hawking radiation is inversely proportional to the mass of a black hole, $T_{\rm H}\propto M_{\rm BH}^{-1}$, and so as the black hole shrinks the temperature of the radiation should ...
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60 views

How is black hole affected by gravity of nearby bodies?

I run into wikipedia articles about ergosphere of rotating black holes. What if some massive body passes nearby some black hole: is something like ergosphere produced, or is the event horizon ...
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127 views

Schwarzschild solution in arbitrary dimensions

Is there any generalized Schwarzschild solution for an arbitrary number of dimensions? Is it necessary to calculate each individually, or is there a relationship between them?
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Can the vacuum be filled with virtual micro-black holes?

Since the vacuum is thought to be virtual particles, is it possible that there might be virtual micro-black holes with virtual horizons and virtual hawking radiation which form and evaporate at a rate ...
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The surface area to volume ratio of a sphere and the Bekenstein bound

I am trying to relate the surface-area-to-volume-ratio of a sphere to the Bekenstein bound. Since the surface-area-to-volume-ratio decreases with increasing volume, one would surmise that, per unit of ...
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Trapping Light in a shell

I was curious about this. Is it theoretically (mathematically) possible to create a shell such that when a photon 'hits' the shell, the spacetime at the shell surface is such that the photon travels ...
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What's the relation between the Euler $\psi$ function, the digamma function, and the hypergeometric function?

Can somebody help me out with the intermediate details of eqn. (2.5) in this paper? Generalized gravitational entropy. Aitor Lewkowycz and Juan Maldacena. arXiv:1304.4926. Is the Euler $\psi$ ...
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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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1answer
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Deriving the Schwarzschild solution

I am CS student and i want to create graphical simulation of black hole, so I need to use The Schwarzschild solution to calculate possible coordinates of given body every second. First try in 2D ...
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106 views

Does gravity limit the number of bosons that can occupy the same single-particle state?

QFT says that an unlimited number of bosons can occupy the same "state" (what I mean by that is that the whole system's wavefunction is composed of a product of many identical wavefunctions). ...
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Can matter really fall through an event horizon?

This question is closely related to Event horizons without singularities from about a year ago (May 2012), which John Rennie answered nicely and persuasively. My variant of the question is this: ...
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In black hole complementarity, does Bob literally observe Alice's death?

I'm interested in the picture of black hole complementarity where an observer (Bob) far away from the black hole watches another observer (Alice) fall in, and develops a very different picture of ...
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100 views

Whose reference frame to use for $d \theta$ near a black hole?

Using the Schwarzchild metric for a body circularly orbiting a nonspinning black hole (i.e. $dr=0$), the relation between $d\tau$, the time between two light pulses sent out infinitesimally close ...
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Does cosmic censorship rule out stable toroidal black holes? How?

I'm having a hard time understanding what the arguments against stable toroidal black holes are saying. For many of these, I can't figure out if they're talking about: A non-rotating toroidal event ...
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246 views

Surface gravity of Kerr black hole

I'm going through Kerr metric, and following the 'Relativist's toolkit' derivation of the surface gravity, I've come to a part that I don't understand. Firstly, the metric is given by ...
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2answers
152 views

Does the black hole only increase?

I don't understand this: The more mass a Black Hole has, the more gravity it create! The more gravity it has, the more mass it can get! With this lines, someday, all the universe will be a black ...
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Asymmetric Schwarzschild solution - unequal mass on each side

Look at any Kruskal–Szekeres coordinate plot of the Schwarzschild solution. It shows the same mass everywhere. Yet the two sides cannot talk to each other, in that no information, particles, etc can ...
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Equilibrium for a rope hanging in a Schwarzschild spacetime

Update: Trimok and MBN helped me solve most of my confusion. However, there is still an extra term $-(2/r)T$ in the final result. Brown doesn't write this term, and it seems physically wrong. Update ...
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Hypervelocity black holes

Is it possible for a black hole to be ejected from a galaxy after an encounter with the central supermassive black hole? What would be the impact of the passage of the hyperV-BH through the galaxy? ...
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What would a person *unmoving* look like on a Minkowski diagram?

If you were to draw a person on a Minkowski diagram, that was unmoving (though time was still passing) what would that look like? (As a light cone and ignore the observer.) Also what would it look ...
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101 views

Can micro black holes form in the Sun?

Wikipedia writes to say ...
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Spaans, “On Quantum Contributions to Black Hole Growth”

This paper was posted to arxiv a couple of weeks ago: http://arxiv.org/abs/1309.1067 From the abstract: The effects of Wheeler's quantum foam on black hole growth are explored from an ...
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Which way do black hole jets spin?

The centers of black holes and quasars often have jets coming out the two poles of an accretion disk, say north and south. Is it known if the two jets spin in the same direction or opposite ...
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206 views

Holographic principle “inside-out view”

From the perspective inside a black hole: Is information about everything outside a black hole - the rest of the cosmos - represented on the inside of the (event) horizon too? NB. I realize it is the ...
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The speed of light through space and its effects on black holes

I was curious about a couple of things that don't quite make sense to me: (and probably won't when I get the technical answer, but I'll ask it anywise.) When light travels through space, is its ...
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79 views

Energy of a black hole : a quizz question

Consider a standard eternal Schwarzschild black hole of mass $M$. One wants to speak about the energy $E$ of a black hole, so let 's present this as a quizz. 1) This is a non-sense to speak about ...
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105 views

Visual representations of black holes

Some black holes emit jets that are rapidly circling the poles of what appears to be a sphere at the center of the black hole, cf. Fig. 1. Is there really a sphere here and how far (relative to the ...
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Are electrons just incompletely evaporated black holes?

Imagine a black hole that is fast-approaching its final exponential throws of Hawking evaporation. Presumably, at all points in this end process there there will remain a region that identifiably ...
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If you flew into a black hole

Would you outlive everyone? I'm coming from the point of view that time would be experienced more slowly (although not from your point of view) the denser the gravity gets.