All Questions
26
questions
1
vote
0
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49
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About the geometric optics approximation in Hawking radiation
I have read Hawking's famous paper Particle creation by Black Holes (Ref. 1) and I have some doubts about the geometric optics approximation and its implications in the argument being made. The ...
- 1,989
1
vote
1
answer
62
views
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
1
vote
0
answers
32
views
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 ...
- 293
3
votes
3
answers
364
views
Falling angle of a photon near the event horizon
I have been doing simulations using Mathematica of light and matter paths (plotted in the $r, \phi$ Schwarzschild coordinates) around a black hole, in the Schwarzschild metric. This was in order to ...
- 31
1
vote
2
answers
192
views
Explanation about black holes
As a newbie I was reading the book "The Theory of Everything", and came about these two paragraphs which I just don't understand:
I had already discussed with Roger Penrose the idea of ...
- 41
4
votes
2
answers
1k
views
Is Schwarzschild black hole solution geodesically complete?
I try to answer the question whether spacetime of Schwarzschild vacuum solution is geodesically complete by analyzing its null geodesics. The infinitesimal length element is $$ds^2=(1-\frac{r_s}{r})~c^...
- 1,948
1
vote
1
answer
121
views
Relativity and kinetic energy of a mass falling into a black hole
If a mass is accelerated by the application of a force, the mass/kinetic energy of the object approaches infinity as it approaches the speed of light.
Now let's consider the same mass falling toward a ...
1
vote
3
answers
153
views
Can I really see what is on the opposite side of a black hole?
This question is only about objects outside the event horizon. Both the observer and the object are just outside the event horizon.
I have read this question:
An observer can see the back side of the ...
- 29k
0
votes
1
answer
43
views
Calculating coordinate increase of light ray escaping black hole
Consider a light ray near a black hole described by Eddington-Finkelstein coordinates $(v,r,\theta,\varphi)$. My aim is to calculate the increase of the coordinate $v$ along a radial path from the ...
- 743
5
votes
2
answers
123
views
Do test particles initially comoving with a black hole accelerate away from it?
This question feels ridiculous, but I really am confused. If you Google Image search "schwarzchild light cones" it shows how, relative to the frame comoving with the singularity, the speed ...
- 2,475
19
votes
3
answers
2k
views
How close does a photon have to get to a black hole to do a full loop?
How close does a photon have to get to a black hole to do ONE full loop? By full loop I mean it curves once around the black hole, and then it ends up on the same trajectory as it was one before it ...
- 2,908
0
votes
0
answers
65
views
Schwarzschild black hole and two particles
I'm looking to solve a problem using general relativity theory to "get a taste" of it. I've little knowledge of the the theory so just want to "taste" it before diving deep into ...
- 101
1
vote
2
answers
247
views
Trajectory of a photon beyond the event horizon
So this random question popped up in my mind. As we know the photons get deflected if they pass in the vicinity of a black hole. At the event horizon(right before it), they form the photon sphere. The ...
- 139
2
votes
2
answers
371
views
Is the Schwarzschild horizon lightlike?
It is often said that the event horizon of a Schwarzschild black hole is lightlike. Is this correct and, if so, what exactly does this mean?
Intuitively, this may mean that any two points on the ...
- 12.7k
4
votes
4
answers
659
views
Entering a black hole, does the incident angle matter at all?
Inside the black hole (as you enter the EH), all objects (massive or massless) must move towards the singularity. The singularity becomes a moment in future.
In the context of general relativity, ...
- 29k