All Questions
Tagged with black-holes event-horizon
1,182
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Definition of surface gravity via the non-affine geodesic equation
I have found a discrepancy in the way different sources define surface gravity (or derive) via the non-affine geodesic equation satisfied by the a Killing vector $\xi$ on a Killing Horizon (KH), up to ...
- 1,989
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How increase in area of the horizon implies that the horizon in spacelike using Raychaudhuri equation?
In a talk The enigma of black hole horizons, (at 24:37), it is said that
"Raychaudhuri equation implies, if the flux into H is positive, area increases and horizon is spacelike".
How ...
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Will a distant observer really see an object that has fallen close to a black hole freeze in time?
I'm currently taking my first course in general relativity, and I was wondering:
We know from the schwarzschild metric that for a (far away) observer looking at an object falling towards a black hole, ...
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What is the meaning to the switch $dt^2\to-dt^2$ and $dr^2\to-dr^2$ in the Schwarzschild metric?
What is the meaning of the change $dt^2\to-dt^2$ and $dr^2\to-dr^2$ in the Schwarzschild metric, leading to:
$$g=-c^{2}d\tau^{2}=(1-\frac{2GM}{c^{2}r})c^{2}dt^{2}-(1-\frac{2GM}{c^{2}r})^{-1}dr^{2}+r^{...
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Problems with fuzzball black hole creation and low energy physics
The fuzzball proposal intrigues me, but I doubt its ability to match up with semi-classical low energy physics. A variation of my question was asked by the awkwardly titled post:"At the instant ...
- 125
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Does Hawking radiation depend of what's inside a black hole?
Or is it entirely based on the existence of an event horizon?
Does the fact that black holes radiate depend on any properties of its interior?
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Observing an event horizon while approaching one
A thought crossed my mind that I realized was hard to conceptualize so I decided to simplify the question by putting it in terms of event horizons.
If I am an observer approaching black hole "A&...
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Do gyroscopes still work inside event horizon?
Imagine a gyroscope falls into the event horizon of a supermassive black hole, what would happen to the gyroscope? will it remains in the same position before it falls into the event horizon?
- 13k
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Negative $\Lambda$ FLRW spacetimes as infinite black holes?
Consider the Friedmann equation:
$$H^2+\frac{k}{a(t)^2} = \frac{\Lambda}{3}+\frac{8 \pi}{3}\rho$$
and set the parameters for dust in either flat euclidean or open hyperbolic spatial slices with a ...
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Event horizon in stationary spacetime
In the case of non-stationary spacetimes finding the event horizon is no easy task.
The stationary case should somehow be less involved or so it is in some well known cases, such as the Kerr spacetime....
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What are the differences between stationary and nonstationary black holes?
I am a bit confused about what are the properties that hold for black holes in general and which ones only hold for stationary black holes. Let me try to explain what I know and hopefully people can ...
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Why it is the mass instead of the mass distribution used in Schwarzschild metric?
Schwarzschild metric is given by (Carroll, chapter 5)
$$
ds^2=-\left(1-\frac{2GM}{r}\right)\mathrm{d}t^2+\left(1-\frac{2GM}{r}\right)^{-1}\mathrm{d}r^2+r^2d\Omega^2
$$
where $M$ is the total mass of a ...
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Shouldn't all things falling into a black hole meet at the horizon?
Consider two observers starting to fall toward a black hole from rest at different distances from the black hole with their worldlines shown on the Kruskal-Szekeres chart below
On the diagram, it ...
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If I were to drop my phone into a black hole, would I be able to catch it?
Say, for the sake of argument, I am outside the event horizon of a black hole and accidentally drop my phone (or some other object) into the hole. If I were to enter the black hole, would I ever be ...
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Are black holes 4-dimensional balls of spacetime? If so, will they have 3-sphere surfaces?
If black holes are 4-dimensional balls of spacetime, they will have a 3-sphere surface with a 3-dimensional volume. Would this allow infalling matter to remain within this surface?
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