All Questions
Tagged with spacetime black-holes
56
questions with no upvoted or accepted answers
11
votes
1
answer
457
views
Aren't black holes required to exist forever in our frame of reference instead of evaporating?
I know that for an observer far away, nothing ever crosses a black hole horizon (due to time dilation), while in the frame of reference of a falling observer the horizon is nothing special on its way ...
- 3,761
6
votes
0
answers
262
views
Why are there multiple universes in the Reissner-Nordström solution?
I am trying to make sense of the Penrose diagram of a non extremal Reissner-Nordström spacetime, that is, the solution with two horizons. The coordinates are
$$ v'=\text{exp}\left(\frac{r_+-r_-}{2r_+^...
- 873
5
votes
0
answers
761
views
On the embedding of the Schwarzschild metric in six dimensions
At every point of the 4-D space-time, it's metric, being a symmetric 2-tensor, has $\frac{D(D+1)}{2}=10$ independent components. From this we can subtract four degrees of freedom according to the four ...
- 1,349
4
votes
0
answers
84
views
Conformal Diagram for Astrophysical Black Hole
I have a question about the conformal diagram of an ‘astrophysical’ black hole which forms in finite time (but with no evaporation).
Usually I see the conformal diagram presented as something similar ...
- 55
4
votes
0
answers
82
views
Energy of background radiation while falling into a black hole
As you fall into a black hole, the old story is you would be spaghettified - and this question is not about that.
However passing of time would be warped, so you would see the future of the universe ...
- 482
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
3
votes
0
answers
88
views
Intuition for the interior Killing vector fields in Schwarzschild?
The Schwarzschild metric represents a stationary (and static), spherically-symmetric, spacetime. These characteristics are manifested by the four Killing vector fields: one for time translation and ...
- 1,290
3
votes
0
answers
32
views
Question on apparent super efficiency of the magnetic penrose process
Accordingly to this paper $[1]$, the efficiency of the so called Magnetic Penrose Process (MPP) is, for supermassive black holes of mass $M∼10^{10} M_{\odot}$ immersed in a magnetic field having $B∼10^...
- 3,085
3
votes
0
answers
110
views
Question about the energy-momentum tensor and tetrad formalism
Given a metric tensor, you have an Einstein tensor associated with it. If your Einstein tensor is diagonal, you can "match it" with a diagonal energy-momentum tensor. More over, if your ...
- 315
3
votes
0
answers
63
views
Doubt regarding particle dynamics and hydrodynamics in Schwarzschild geometry
The effective potential for particle orbits in the equatorial plane of a Schwarzschild black hole in units $G=M=c=1$ is given by $$V_{\textrm{eff}}=\sqrt{\left(1-\frac{2}{r}\right)\left(1+\frac{l^2}{r^...
- 2,015
3
votes
0
answers
319
views
Is it mathematically possible or topologically allowable for cutouts, or cavities, to exist in a 3-manifold?
A few weeks back, I posted a related question, Could metric expansion create holes, or cavities in the fabric of spacetime?, asking if metric stretching could create cutouts in the spacetime manifold. ...
- 513
2
votes
0
answers
71
views
Has it been observed so far an object moving towards a BH along the trajectory of the polar astrophysical jet?
If we assume that the cause of the astrophysical jet is the magnetism of the BH than an object falling towards the BH in counterdirection of 'polar jet' emitions should not feel any strong deflection ...
- 2,255
2
votes
0
answers
568
views
How to derive the Kerr killing vector?
The Kerr metric have two killing vectors:
$$t^{\mu} \equiv (k_{t})^{\mu} = (1,0,0,0)\hspace{5mm} \mathrm{and}\hspace{5mm} \phi^{\mu} \equiv (k_{\phi})^{\mu} = (0,0,0,1). \tag{1}$$
In general, it is ...
- 3,085
2
votes
1
answer
60
views
A question about changes of the event horizon and the passage of time
If the event horizon of a blackhole doesn't experience the passage of time how can it change in size when it doesn't experience any time to do so?
- 117
2
votes
0
answers
56
views
Exponentially small effects in black hole physics
On page 60 of the following paper1, it is written:
But in gravity, due to exponentially small effects of $O(\exp(−Area/G_N ))$, associated with black-hole physics, even these dressed versions of ...
- 649