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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The Strength Of A Black Hole

Does the gravitational strength of a black hole at its singularity change the more it pulls things into it?
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Why is matter drawn into a black hole condensed into a single point within the singularity? [duplicate]

Possible Duplicate: Why is matter drawn into a black hole not condensed into a single point within the singularity? When we speak of black holes and their associated singularity, why is ...
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307 views

Entropy of a black hole can be zero?

Black holes are one of highest density objects in the universe. Because of this high density(m/v) more matter is highly compressed in a very small volume( i am guessing that molecules cant freely move ...
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Classical black holes?

How big should the black hole be so we can consider it to be classical? When they claim that we can not probe shorter distances than the Planck length, can it be true? The argument says that, ...
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Could gravity hold electron charge together?

Could the gravitational force be what holds the charge of the electron together? It seems to be the only obvious possibility; what other ideas have been proposed besides side-stepping the issue and ...
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Charges and Topology

I must apologize, I was a little bit excited when I began understanding some of this, I can not say I can compete with professionals, and words are still difficult concepts. In (1) S.H. et al. it is ...
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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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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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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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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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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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Spinning micro blackholes power conversion

In the context of energy extraction of spinning black holes, there are two known mechanisms: the Penrose process and the Blandford-Znajek process. The former relies on fragmentation of accreting flow, ...
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Uncertainty principle within a neutron star or black hole

Take the time-energy uncertainty relation, $\Delta$$E$$\Delta$$T$$\ge$$\hbar/2$. My question is based on my confusion about the effect this relation may have within the interior of a highly ...
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Is there a numerical calculation for black hole - neutron star merges?

I think it might be even a more frequent event as the black hole merges. It would be similar to the black hole merges in the gravitational wave spectrum, but it could have a very clear neutrino and ...
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How does a rotating black hole look like? How would it be to descend into one?

This image from Wikipedia shows how a black hole would look like: A black circle that acts as a gravitational lens for light rays coming from behind. How would a rotating black hole look like? How ...
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Two spherically symmetric shells of matter collapsing into a black hole

Suppose I have a thin spherically symmetric shell of matter of (rest) mass $M$ that collapses to form a black hole, and later a second thin spherical shell of mass (rest) $M'$, concentric to the ...
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34 views

How can a black hole have a charge? [duplicate]

Under current particle theory, the four fundamental forces use a force-carrying particle. The particle for electromagnetism is the photon. By definition a black hole is a mass from which light can ...
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How does blackholes become supermassive? [duplicate]

I am not an expert in this field. I have seen documentaries on the Universe and have a basic idea of how black holes come to existence. When black holes form from supernovae they have a initial mass ...
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Colliding black holes to an outside observer

We know that a particle approaching an event horizon will appear to an outside observer to slow down and never cross the horizon. What is observed by an outside observer when a singularity ...
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Relation between black hole mass and size applied to observable universe [duplicate]

If I apply the relations given in http://xaonon.dyndns.org/hawking/hrcalc.js and http://www0.arch.cuhk.edu.hk/~hall/ag/sw/SpinCalc/SpinCalc.htm to the values for the mass of the observable universe ...
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Can you communicate future information through the event horizon?

According to Hawking on "Particle Creation by Black Holes", there exists a relationship between the entropy outside of an event horizon, flux within the event horizon, and the area of that same event ...
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Phenomena in the intersection of general relativity and quantum mechanics

I am looking for physical phenomena that have aspects involving both general relativity and quantum mechanics. The only example I know is Hawking radiation. While black holes are objects that cannot ...
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29 views

Accretion disks on neutron star binaries

Why does hydrogen gas from accretion disks not constantly get sucked onto/into a neutron star or into a black hole? I understand that some gets sucked into the black hole and some may come down and ...
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50 views

Ricci tensor of Metric black holes with nils and solv geometries of Horizon

The metric of black holes with nils and solv geometries of the horizon is generically represented by $$\mathrm{d}s^2=-r^{2z}\mathrm{d}t^2+\frac{\mathrm{d}r^2}{r^2}+\sum_{I=1}^3 r^{2q_I}(w^I)^2$$ How ...
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Black Hole singularity in Loop Quantum Gravity

How is the singularity of a Black Hole treated in Loop Quantum gravity ? Does it go away ? And if it does, what's after the event horizon ?
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Quantum Gravity Singularity Question?

I am not a expert in QG (Quantum Gravity) or GR (General Relativity) for that matter so please forgive if I make any small mistakes, its just a curious question but I know that a singularity is a ...
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Location of singularity in moving black hole

Say a black hole is travelling at $c/2$, does the shape of the event horizon change? What about the location of the event horizon? If it is travelling at a hypothetical $c$, does the event horizon ...
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Black Hole Entropy Calculation

I was watching "Leonard Susskind on The World As Hologram" ( youtube ). At one point he describes the way Bekenstein calculates the entropy of a black hole. Paraphrasing: Take a minimally sized black ...
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How close would you have to be to the merger of two black holes, for the effects of gravitational waves to be detected without instruments?

Assume two black holes in the most common size range, spiraling into each other until they merge. The event releases significant amounts of energy via gravitational waves, which warp the space-time. ...
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124 views

Interstellar Movie: Black hole shown in the movie [duplicate]

In the interstellar movie, the black hole shown has a ring of light orbiting around it. From what I know, (correct me if I'm wrong) that light is unable to escape the gravity of the blackhole and ...
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Boyer–Lindquist coordinates

In the Kerr solution to the vacuum Einstein Equation written in Boyer–Lindquist coordinates. Because it is not spherical polar coordinates, $r$ ranges from 0 to infinity does not cover all the space, ...
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Pumping charged particles (of same charge) into a blackhole

Would would happen if you started pumping charged particles of same charge into a black hole? Let's assume that you have an infinite number of those charged particles. What will happen to the event ...
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24 views

Evaporation of a black hole [duplicate]

What happens to the singularity within a black hole when a black hole evaporates? If there is a point in space which is both infinitely dense and small, do they simply evaporate as well?
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Introductions to no-hair theorem(s)

I wanted to ask if anyone can provide a reference that is an introduction on the no-hair theorem(s) (conjecture(s)). Review papers on the topic would be gratefully accepted as well. I have already ...
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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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Gravitational singularity

Is it possible that the gravitational singularity actually turns out to be a genuine singularity once we have a true theory of quantum gravity in place. There is a lot of talk about singularity but ...
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Would a supermassive black hole accretion disk really vaporize solid objects?

Both the movie Interstellar and Greg Egan's Incandescence involve worlds deep inside accretion disks of large holes, kept at a comfortable temperature. Is this (remotely) realistic? Although ...
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Is it possible to assign a physical radius to a black hole?

The Schwarzschild metric is given by: $$c^2d\tau^2 = \left(1-\frac{r_s}{r}\right)c^2 dt^2-\left(1-\frac{r_s}{r}\right)^{-1}dr^2 - r^2 \left(d\theta^2 + \sin^2 \theta \, d\varphi^2\right).$$ The ...
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Manifold for Schwarzschild and Bertotti-Robinson

In short: what is the manifold in discussion for Schwarzschild metric $$ ds^2 = -(1-\frac {2M}r)dt^2 + \frac1{1-\frac{2M}r} dr^2 + r^2 (d\theta^2 + \sin^2 \theta d\phi^2)$$ and Bertotti-Robinson ...
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External source of virtual particles near a black hole?

I've just read the following quote from the Wikipedia page on Hawking Radiation... In order to preserve total energy, the particle that fell into the black hole must have had a negative energy ...
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What exactly is black hole complementarity and why is it necessary for solving black hole information paradox?

What exactly is black hole complementarity and why is it necessary for solving black hole information paradox? The first question is about the story of vacuum fluctuation causing Hawking radiations. ...
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Can a quark irreversibly pass though an event horizon?

This is an attempt to transform a question I asked about a year ago into a binary yes-or-no question: Since a quark has electrical charge, can it irreversibly pass though an event horizon? The ...
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Calculate the mass of a Schwarzchild black hole with Komar integral [closed]

In Wald's GR, Komar integral is Eq. (11.2.9): $$M=-\frac{1}{8\pi}\int_S\epsilon_{abcd}\nabla^c\xi^d$$ $S$ can be chosen as a 2-sphere, the boundary of a spacelike hypersurface $\Sigma$ such that the ...
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Gravity's effects on photons moving away from source

As a photon has no mass and must always have velocity c, if I were to shine a laser straight up (so Earth's gravity would be pulling straight back on it), what would the effect be on the photon? It ...
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59 views

Problem about Schwarzschild Radius [closed]

I'm a high school student in korea. Could you help me solve this problem? I should express theta as schwarzschild Radius (=Rs) and b when v_0 → c(=3x10^8m/s) help me......
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44 views

Hawking Radiation: Couldn't virtual particles make black holes more massive? [duplicate]

From what I understand about Hawking radiation, a virtual particle comes into existence very near the event horizon of a black hole. This causes one part of the particle to fall into the black hole, ...
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177 views

Maxwell's equation for non inertial observer

Applying Maxwell's equation we can prove that light will move at the speed of light for every inertial frame, is it true as well for non-inertial frames? How light moves slowly near a black hole??
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Can one model a spiral galaxy with a similar manifold to one for a whirlpool?

My question is more of a phenomenological question than literal, since the forces involved are very different. When one looks at the distortions (or wrinkles or whatever you wish to call them) in the ...
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The Effect of Tortoise Coordinates

Referring particularly to http://arxiv.org/abs/hep-th/9909056 in regard to the wave equation for Schwarzschild-AdS black holes (p.4), I'm trying to understand tortoise coordinates. So starting ...
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Why exactly is it that light cannot escape a black hole? [duplicate]

I understand that the gravity has to have a pull greater than the speed of light, but I thought that when gravity pulls light it doesn't accelerate it only blue-shifts it. So then why does gravity ...