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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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233 views

How much energy can be radiated as gravitational waves from black hole merger?

In the black hole merger, recently observed by LIGO, about 5% of energy was irradiated in form of gravitational waves. source of data Is there any theoretical limit to how much energy can be ...
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Sources for black hole geodesic orbits

I am looking for good sources that discuss both Kerr and Schwarzschild particle orbits (geodesics). Most sources write down the geodesic equations, constants of motion and the Hamiltonian, but do not ...
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Fluctuating string in AdS black hole

People frequently use fluctuating string in AdS black hole (see 1,2,3 etc) to study dynamics of a "free external quark" in quark-gluon-plasma (QGP) at finite temperature. The background black hole ...
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Falling towards a black hole in a box

I've been studying General Relativity on a friend's notes. There's an exercise I can't quite grasp. An observer is located in a closed, windowless box. The box is falling radially towards a black ...
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Why are orbits $1.5r_{s} < r < 3r_{s}$ unstable around a Schwarzschild black hole?

The "Orbital motion" section of the Wikipedia entry corresponding to Schwarzschild metric reads: A particle orbiting in the Schwarzschild metric can have a stable circular orbit with $r > 3r_s$. ...
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Black Hole and Mach Principle

In the derivation of the spin–orbit interaction, we transform to a frame that is fixed on the electron. I have several questions about this: Will I see any radiation if I orbit around a static charge?...
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Weird Black Hole definition

I'm quite new to the topic of Black Holes, and I can't understand the definition $$B = M-I^-(I^+),$$ where $M$ defines an asymptotically flat spacetime $(M,g_{\alpha\beta})$ (representing an isolated ...
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Energy dissipation from a black hole by neutrinos

Could the high gravitation field of a black hole cause neutrinos to form a Fermi gas or superfluid? Could these neutrinos from the neutrino background of the big bang whose temperature and deBroglie ...
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Gravitational redshift and Energy of a photon

Let us assume that we have a large gravitational field, then the gravitational redshift can be expressed as, $$\frac {v_{\infty}} {v_e} = (1-r_s/R_e)^{1/2}$$ In this equation $v_{\infty}$ represents ...
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Pictures of Different Coordinate Systems in General Relativity

In General Relativity by Woodhouse there are the three following diagrams in Chapter 9 about Black Holes. Despite a (very brief) description of these diagrams in the book itself, I am struggling to ...
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Can mass still be observed in our universe after moving from a black-hole to a white-hole?

This question is based on the recent papers on LQG black-holes by Abhay Ashtekar. Quantum extension of the Kruskal spacetime and Quantum Transfiguration by Kruskal Black Holes When mass moves from ...
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Spacetime geometry of black hole formed by the scattering of two gravitons

In the paper "Breakdown of predictability in gravitational collapse" Stephen Hawking mentions the following on section 5: Consider, for example, the scattering of two gravitons. In this case the ...
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Could you actually see the event horizon of a Black Hole?

For years I thought to myself that surely you'd be able to see the event horizon of a Black Hole when looking at it against the surrounding light. I thought that it would be similar to this: Where ...
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Are there any black hole information loss solutions that do not resort to non-locality?

It seems as though all solutions to the information paradox resort to non local effects. What solutions do we have that preserve locality?
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Can we use entangled black holes to form wormholes?

If any object can be made black hole by crushing it to its Schwarzschild radius, can we do the same process in two different points in the space keeping the quantum states of both the objects ...
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Boundary contributions to the BTZ black hole hamiltonian

I've been trying to understand every step of the (2+1 dimensional) BTZ black hole paper (https://arxiv.org/pdf/hep-th/9204099.pdf ) but I'm stuck in the obtention of the boundary terms in the ...
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Is the Temperature of a Black Hole a Relative Thing?

Because the laws of physics are the same in every reference frame, I assume the relativity of simultaneity [should] in principle apply to the black hole temperature and even evaporation rate. Surely a ...
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How many types of Singularities has string theory successfully resolved?

Except for proposing the fuzzball as a solution for black hole singularity, has string theory successfully explained/dealt with any other form of spacelike or timelike singularities? Kindly explain
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On the Schwarzchild black hole metric:

I've been going through the introduction on Ads/CFT by Horatiu Nastase (https://arxiv.org/abs/0712.0689). In chapter 5, "Black holes and p branes", in Eq. 5.2, it is mentioned the schwarzchild metric ...
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Deriving a path-integral expression for a thermal density matrix with position-dependent temperature

I've been fiddling with deriving a path-integral expression for a thermal partition function with a position-dependent temperature but I'm not sure how to get started on this. Concretely, I'm trying ...
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Black hole internal mathematics

I read the article about mathematicians-disprove-conjecture-made-to-save-black-holes and was wondering: could we compare the universe to Meteorology and geophysics on earth to answer some of questions ...
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What would happen if an object were to pass through the center of a ringularity?

A ringularity is defined by Wiktionary as a black hole with spin, that takes the shape of a ring with zero thickness. I know that the ergosphere imbues a lot of kinetic energy to objects that enter it,...
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Boundary times and bulk time in eternal black hole duality

In AdS/CFT, a particular duality is the correspondence between an eternal black hole in AdS spacetime (a large maximally extended AdS-Schwarzschild black hole) and the thermofield double state, \begin{...
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Nice expressions for geodesics in Penrose diagram for Schwarzschild spacetime?

If $u$ and $v$ are lightlike coordinates for 1+1-dimensional Minkowski space ($ds^2=dudv$), then we can compactify with a coordinate transformation of the form $$U=f(u)$$ $$V=f(v),$$ where $f$ is a ...
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Is it possible to have a state of the universe with no solution to what state it will evolve into in general relativity?

The math shows that it's possible to have a curved 4-dimensional Minkowski space such that there's a continuous bijection from it to $R^4$ and a closed light-like curve and some closed timelike curves ...
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Would naked singularities have a complex irreducible mass?

The formula for the irreducible mass, also known as the Christodoulou and Ruffini equation, is $$M_{\rm irr} = \frac{\sqrt{2 M^2-Q^2+2 M \sqrt{M^2-Q^2-a^2}}}{2}$$ where M is the mass equivalent of ...
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Reduce 10 Killing equations by the dependence of the metric to some coordinates

Each independent components of Killing vector for Schwarzschild that generates isometry are from the translation along $t$ and also from the fact that it is spherically symmetric, i.e \begin{eqnarray}...