All Questions
677
questions
2
votes
4
answers
186
views
Necessity of Singularity in General Relativity
The Schwarzschild solution is the standard example used to describe a black hole, its important points being the event horizon and the central singularity. But this solution is derived by assuming an ...
- 9,500
0
votes
0
answers
79
views
End points of event horizon
I am reading The Nature of Space and Time by S. W. Hawking. In the last paragraph on page 16 he said that:
event horizon may have past end points but don't have any future end points
I understand ...
- 59
0
votes
1
answer
76
views
Black Hole Formation -- How Can an Event Horizon be Observed to Grow? [duplicate]
This is a question about black hole formation. To be clear, I’m not suggesting that black holes don’t form. It’s that I’m having trouble with the accepted explanation so there’s a flaw in my logic ...
- 21
3
votes
1
answer
79
views
How to Understand Negative Energy in the Ergoregion?
I am trying to understand the Penrose process and having trouble explaining negative energy in the ergoregion.
How I interpret it is:
Energy is the dot product between the four momentum of the object ...
- 63
4
votes
0
answers
59
views
Can wormhole inside a black hole become an escape?
I did not major in Physics so not sure if this is a proper question; but according to some Google search there do exist papers discussing wormhole inside black hole like this, which I am not able to ...
- 141
0
votes
2
answers
58
views
When it comes to getting closer to the Schwarzschild radius, how is discrete a limit?
From Keeton (2014) in Principles of Astrophysics: Using Gravity and Stellar Physics to Explore the Cosmos, Gravitational time dilation near a large, slowly rotating, nearly spherical body, such as the ...
-1
votes
1
answer
57
views
Why does the timelike killing vector become spacelike inside the ergoregion?
Why does the timelike killing vector become spacelike inside the ergoregion?
Some textbooks make this claim and move on to explain negative energy, but I could not find any proof for this claim. I can'...
- 63
0
votes
2
answers
105
views
Realistic black holes
If I understand the answers provided in this Link Why singularity in a black hole, and not just "very dense"?
Then the singularity at $r=0$ may just be a mathematical artifact, and may not ...
4
votes
3
answers
672
views
What is the proof that the Schwarzschild metric is not static inside the horizon?
In Lecture Notes on General Relativity, Sean M. Carroll shows that the Schwarzschild metric is not only stationary but also static (Chapter 7, page 169, Eq. 7.20 and following interpretation). On the ...
- 1,948
0
votes
1
answer
103
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Birkhoff's theorem and Schwarzschild vacuum solution [duplicate]
Birkhoff's theorem states that any spherically symmetric solution of the vacuum field equations must be static and asymptotically flat, but the well-known Schwarzschild solution satisfies these ...
- 1,948
0
votes
1
answer
103
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Interior Solution for Black Hole in Particular
This paper seems to suggest that the interior metric for a black hole in particular (a.k.a not a different kind of spherically symmetric non-rotating body) is just the exterior Schwarzschild metric ...
- 323
4
votes
1
answer
169
views
How are objects inside a black hole affected by the gravity of objects outside the black hole?
There are many Q&As about whether something inside a black hole can escape the event horizon if another massive object gets close enough to pull it out. I realize the answer (I think universally ...
- 450
2
votes
0
answers
68
views
Is there a formula relating the rate/speed a black hole event horizon will grow, to the density of the medium surrounding it?
I am thinking about the average density of the space around the black hole, not the density immediately adjacent to the event horizon which might be different. It will probably be best to model the ...
- 131
0
votes
2
answers
112
views
Event horizon is a null surface - what about the angular coordinates?
From the Schwarzschild metric $$ds^2=(1-2m/r)dt^2-(1-2m/r)^{-1}dr^2-r^2(dθ^2+\sin^2θ dϕ^2)$$ on the surface $r=2m$ (setting $dr=0$) we have $$ds^2=-r^2(dθ^2+\sin^2θ dϕ^2).$$
This looks spacelike ($...
- 366
0
votes
2
answers
179
views
How do we know that a black hole radius is not significantly contracted for a stationary outside observer?
It is my understanding that just as special relativity contracts length with velocity general relativity contracts length with gravity. Would this mean the radius of a BH is smaller than it would ...
- 1,348