All Questions
Tagged with black-holes causality
107
questions
2
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1
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98
views
How much time does it take for the gravitons generated by a black hole singularity to travel before exerting gravity forces on other celestial bodies?
It is known to all that the travelling speed of gravitons (the propagation speed of gravitational field) is not instant. So for black holes, the gravitons (the gravitational field) generated by the ...
1
vote
1
answer
117
views
(1+1)d collapsing null-shell?
I am trying to understand the following Penrose diagram (from https://arxiv.org/abs/1507.03489)
According to the authors, it is depicting the formation of a (1+1)d black hole from a collapsing null ...
- 329
3
votes
1
answer
279
views
Can we identify a given metric as a black hole solution?
Given a metric $g_{\mu \nu}(x)$, can we identify whether it corresponds to a black hole? To be more precise, can we perform some calculations or define certain parameters of the metric which can help ...
- 93
1
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0
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88
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What specifically prevents the geodesics in Kerr BH from continuing beyond the second world line located inside the inner event horizon?
In a Kerr black hole, the inner event horizon is also called the Cauchy horizon. According to the answer to the question linked here, why are inner horizons Cauchy horizons, the Cauchy horizon only ...
3
votes
1
answer
808
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Why are inner horizons Cauchy horizons?
I know that RN black hole has two horizons, one outer one and one inner one. The outer one is the event horizon.
As far as I know, a Cauchy horizon is the boundary of the domain of dependence of a ...
- 339
0
votes
2
answers
120
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What prevents two particles that made a black hole to unmake it?
Assume you have two high energy particles approaching each other and forming a black hole even before colliding (but before a singularity is formed, which I am not sure that is possible). If the laws ...
user338734
5
votes
2
answers
351
views
How do we determine whether a surface is an event horizon? Exactly what to calculate to do this?
Event horizons play an important role in relativistic astrophysics, especially for black holes, but also for other spacetimes. It is fundamental to be able to determine whether a given surface is an ...
3
votes
1
answer
73
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Black hole metric of reflected shell of incoming light
At this point in Leonard Susskind's eighth lecture on general relativity, he begins a discussion about finding the metric of a black hole formed by an incoming, spherically symmetric shell of light. ...
- 737
15
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2
answers
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If the escape velocity at the event horizon is the speed of light does it mean that slower bodies won't move away at all?
If we say that the escape velocity from a planet is say 10 km/s we think that a slower body will move away from that planet but will be eventually forced to fall back on the planet. In simple words we ...
- 2,255
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106
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How is the singularity of Schwarzschild space-like if a one can take a time like path to it?
It is known that when one crosses the event horizon of a Schwarzschild black hole, one cannot return and is destined to hit the $r=0$ horizon. My understanding is that this can be seen from the ...
-4
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1
answer
245
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Self-coupling of gravity and gravitation escaping a black hole - contradiction?
The field equations are non-linear, that can be interpreted as gravity is coupling with itself, see for example here:
Non-linearity and self-coupling of gravity
I'm trying to understand what that ...
- 255
3
votes
1
answer
356
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Neutrinos and black holes
As a new user I could not comment on Do neutrinos of any flavor get trapped in black holes?
My question is that the Ice Cube facility has mapped Neutrinos coming from black holes, as stated in ...
0
votes
1
answer
219
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Physical properties of an event horizon
This question may seem a little naïve, but I need help with the basics of black hole physics. I'm having difficulty understanding the topology of the event horizon. Apologies for any errors in ...
- 1
8
votes
3
answers
1k
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Is there any *global* timelike Killing vector in Schwarzschild geometry?
I have been dealing with the following issue related to the Schwarzschild geometry recently. When expressed as:
$$
ds^{2}=-\left(1-\frac{2GM}{r}\right)dt^{2}+\frac{1}{1-\frac{2GM}{r}}dr^{2}+d\Omega_{2}...
- 503
0
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7
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392
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If light and gravity travels at the same speed then why light cant escape the gravitational pull of black holes?
Speed of gravity is infinite?
If fastest thing is light then how universe is spreading faster than the speed of light?
