All Questions
Tagged with black-holes general-relativity
2,491
questions
11
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11
answers
4k
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What would one use a theory of quantum gravity for?
I am generally wondering how useful new more ambitious theories would be considering that even with standard non-relativistic electrostatic QM one usually has to employ unsatisfyingly crude ...
- 1,202
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votes
1
answer
116
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Time required to reach Black Hole's Event Horizon from outsider perspective?
Let's imagine a pair of particles that is entangled. One (call it $P_1$) is released and then falls to a black hole from a distant $x_0$, (for example $x_0=5r_s$) and velocity $v_0(=1/2c)$, while the ...
3
votes
1
answer
150
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Do black holes evaporate prior to crossing their event horizon? [duplicate]
Bob falls into a black hole, watched by Alice who is far away.
Alice sees Bob asymptotically approach the event horizon while his clock asymptotically approaches 12:00 noon as his image redshifts (...
- 161
1
vote
2
answers
78
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Probability of a primordial black hole absorbing background radiation?
I'm thinking of the early universe when there was a lot of energetic radiation around. A primordial black hole (PBH) that would be about to evaporate completely about now, would have an initial mass ...
- 6,112
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1
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Regularization of black hole singularities
Hi I have a question: when dealing with the gravitational Lorentz factor from schwarzchild solution to EFE, used in defining gravitaional time dilation and one encounters singularities at $r=0$ or $r=...
5
votes
2
answers
151
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Is the Schwarzschild singularity a limit of the Kerr singularity?
In a Schwarzschild black hole, the singularity is spacelike. In a Kerr black hole, it is timelike.
Is there any continuous transformation between those solutions? Can the Schwarzschild solution be ...
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0
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50
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0
votes
0
answers
91
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What are regular event horizons?
I am studying uniqueness theorems of Black Holes and I often see the word "regular event horizon" instead only event horizon. Many textbooks and literature do not define this term. Please ...
- 59
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0
answers
81
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(Sufficiently) Rigorous argument for Planck scale and formation of black holes
I used to hear the arguments about how if we go down to Planck scale (see, e.g., this lecture notes that I am reading but by no means the only place I saw this) then "you would need energies of ...
2
votes
1
answer
163
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Why domain of Kerr black hole includes negative values for $r$ coordinate?
I understand the domain of $t$ is all real numbers but mathematically, how to prove the domain of $r$ coordinate is also all real numbers except $r=0$ when $\theta = \pi/2$. I know that we get two ...
- 59
0
votes
2
answers
135
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Does someone falling into a spinning black hole see the end of the universe?
It is well known that if you fall into the Schwarzschild black hole you cannot see the entirety of the outside spacetime since there are photons which cannot catch up with you before you reach the ...
- 572
1
vote
1
answer
106
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Is it possible that the mass of a black hole is located at the event horizon?
Due to gravitational time dilation, an object falling into a black hole appears to slow down as it approaches the horizon, never actually reaching it. If it were to somehow enter the event horizon, ...
0
votes
1
answer
90
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Length near the black hole
One meter rod at long distance is thrown to the Schwarzschild black hole. How its length near the black hole seems to distant observer?
- 626
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1
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Black holes, singularities and topology in relativity
General relativity is defined on a base manifold which, viewed as a topological space, is simply connected (which means there's no holes). However, we know that inside a black hole there's a ...
- 309
2
votes
3
answers
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Orbit description in Schwarzschild metric
Suppose to have a restricted 2-body system (BH + star with $M_{BH}\gg M_{\mathrm{star}}$) and you want to describe the orbit of the star relative to the BH, i.e. in the Schwarzschild metric.
Usually, ...
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