# Questions tagged [black-holes]

A black hole is a volume from which matter cannot 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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### Physical reality of inner event horizon and inner ergosurface in a rotating black hole in D. Wiltshire et al. “The Kerr spacetime”

In chapter 1/The Kerr spacetime-a brief introduction by Matt Visser of D. Wiltshire, M. Visser, S.M. Scott "The Kerr spacetime - Rotating black holes in general relativity" the author presents a ...
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### Tensor product of universe Hilbert space and black hole Hilbert space equals?

I'm a newbie struggling to parse concepts important in black hole, holographic principle and related issues. My query comes from Thomas Thiemann’s Modern Canonical Quantum Gen. Relativity, which ...
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### Redshift z=40 and gravitational waves

Why z=40 is the critical value of the redshift (more or less) to decide find out primordial gravitational waves around it? I have read that is related to the following issue: black hole mergers ...
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### Celestial Body Approaching Speed of Light, “Observed” as a Black Ellipsoid?

I have an interesting question, one which I think may not work haha, but please bear with me. Let's work with our sun, with mass of about $2 \times10^{30}$ kg. According to the following formula, ...
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### Dimensional reduction from even to odd dimensions and Chern-Simons terms

I'll be taking some Lagrangians from this paper to try and keep personal typos out of the discussion I have been looking at the dimensional reduction of Einstein-Maxwell-Dilaton theories and I am ...
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### Positive frequency modes and lightlike coordinates

My question is about defining positive frequency modes of radiation in a generic (static) spacetime. I mean, take a black hole and Eddington-Finkelstein null coordinates; $u$ and $v$ are Killing ...
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### Does large angular momentum cause swirly bridges when two black holes merge?

Attached is an image that shows the bridge formed between two adjacent black holes. It shows three example mergers. Two non-rotating black holes are shown in the first example merger. In the case of ...
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### Is Poplawski's “Cosmology with torsion” a “variable speed of light” cosmology?

In his 2010 paper "Cosmology with torsion", Poplawski mentions that, in the hypothesized formation of a new temporally-local universe within a black hole, its "expansion is not visible for observers ...
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### Does Black hole tears and compresses the nucleus of atoms?

Part 1 Stephen Hawking describes the flight of a fictional astronaut who, passing within a black hole's event horizon, is "stretched like spaghetti" by the gravitational gradient (difference in ...
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### black hole potential well

Let d be the distance (in some coordinate system) from a particle to the event horizon of a black hole. For a particle starting at distance d>0 above the event horizon to rise away to a very large (...
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### How to find tetrads corresponding to a given metric?

In General Relativity, sometimes doing calculations with a set of orthonormal tetrads $h^{a}_{\mu}$ where $h^{a}_{\mu}$$h^{b}_{\nu}$$\eta_{ab}=g_{\mu\nu}$ for some metric $g_{\mu\nu}$ is easier ...
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### Are the quasinormal modes scalar quantities?

I am studying the so-called quasinormal modes (QNMs) in the context of the AdS/CFT correspondence and I got stuck. For instance, if I choose a weird patch of coordinates for the, say, AdS5-...
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### what is the metric of N-sheeted $AdS_3$?

Suppose the AdS$_3$ metric is given by $$ds^2 =d\rho^2+cosh^2\rho d\psi^2 +sinh^2 \rho d\phi^2$$ what is the n-sheeted space of it? Can the n-sheeted BTZ be constructed from it by identifications ...
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### How can the energy of a spinning black hole be converted into magnetic field?

I've read about the Blandford-Znajek process, and what I understood is that the black hole is treated as if it were a conducting sphere spinning rapidly with an accretion disk around it, and the ...
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### Lense-Thirring Precession of short GRBs

Stone et al. 2014 have proposed that the jet resulting from the merger of a black hole (BH) and neutron star (NS) may precess due to Lense Thirring torques A large rotating mass e.g. the Earth, can ...
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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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### Rigorous Proof of General Relativity's Non-renormalizability?

The answer to this question and the comments on it implies that general relativity has not been rigorously shown to be non-renormalizable for all loop diagrams -- only shown for two loops. However, ...
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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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### Nonsingularity of the Euclidean black hole metric

How can one show that the nonsingularity of the Euclidean black hole metric is required for thermal equilibrium of the original black hole in Lorentzian signature? It is mentioned in Prof. P. K. ...
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### 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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### Is there a map which shows all the black holes in our galaxy?

I am looking for a map which shows all black holes in the Milky Way. See this exoplanet map for what I mean. If it is not existing (yet). Is there at least an online catalogue which summarizes for ...
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### What are the equations of motion that model near light speed orbits of a massive body about incredibly massive bodies?

In Kip Thorne's recently published book, The Science of Interstellar, he describes, by means of an illustration, the complex nature of a spacecraft orbiting a massive black hole with velocities ~ 0....
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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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### Electric and magnetic field in a black hole

I have many questions about this topic: Does the electric field of a charged black hole look like this? I mean how can it have an electric field if nothing can escape from a black hole, and what is ...
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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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### Statistics of Black Holes

I am hoping to collect information about the sampling distribution of black hole sizes, densities, and their relative spatial distribution within galaxies and other formations. By sampling ...