All Questions
Tagged with black-holes general-relativity
2,491
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Can black holes exchange Hawking radiation, avoiding complete evaporation?
I was wondering if it would be possible that, as a black hole radiates its mass as Hawking radiation, another black hole could absorb that radiation and then when the second black hole radiates its ...
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Could I peel a black hole or at least sneak a peek beyond the event horizon with compact matter?
If you created an annular ring of compact matter, delicately balancing it and continuously adding matter to the ring in a stable orbit around a dormant black hole, could you peer beyond the ...
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Given gravitational lensing, why would black holes visually appear black?
This image from Wikipedia, also referenced in this question, is an artist's vision of how a black hole should look like:
However, given that a black hole is a gravitational lens strong enough to ...
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Angular velocity of stationary observer
I am studying Kerr metric in Boyer Lindquist coordinates and having trouble in understanding the components of angular velocity of stationary observer with constant r and $\theta$ motion w.r.t ...
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Is it possible to have a stable black hole that does not evaporate?
Black holes would presumably evaporate in the long future via Hawking radiation.
However is this inevitable? Or are there any mechanisms that would compensate the lost mass due to Hawking radiation ...
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Significance of simultaneous transformation of $t$ and $\phi$ in kerr metric
The Kerr metric in Boyer-Lindquist coordinate is invariant under simultaneous transformations $t \rightarrow -t$ and $\phi \rightarrow -\phi$ but not invariant if we apply one transformation only. ...
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Are light rays always bent in any gravitational field, or just in a strong one like a black hole?
This is a follow-up question after this one:
Yes, the curvature is enough to bend lasers. In fact, there is an interesting feature in Schwarzschild spacetime that might answer your question well. ...
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Scattering approach for massless scalar Hawking radiation and Bogoliubov coefficients in Schwarzschild metric
Reflection coefficient from the scattering approach in tortoise coordinates, looks exactly like relationship between modulus squared of Bogoliubov coefficients. However I'm not able to figure out a ...
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Is the curvature so extreme at the event horizon, that you could see curved laser beams?
I have read this:
Because the spacetime curvature at the horizon is so great that there is no light-like world line the extends beyond the horizon.
Why does time stop in black holes?
If the ...
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Is this an actual photo of frame dragging?
Is this new image (below) of polarized light surrounding Sagittarius A, showing actual frame dragging being captured by the magnetic field? The image is from this article If not, how would a photo ...
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Perimeter of Kerr's event horizon
We can compute the "proper circumference" of the Schwarzschild event horizon integrating its line element along its perimeter at a fixed $t$. This would be the minimum length of a rope that ...
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Lagrangian for Kerr-Newman black holes
I am trying to write down the action that is extremized by Kerr-Newman solutions in General Relativity. Specifically, I am interested in parametrizing the Lagrangian by the mass $M$, angular momentum $...
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How to find that there is a conical singularity in the BTZ black hole?
Considering a non-rotating and non-charged 2+1 dimensional black hole, known as the BTZ black hole which obtained by adding a negative cosmological constant $\Lambda=-\frac{1}{l^2},l\ne0$ to the ...
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Reaching a turning point in photon trajectory
Given the geodesic equations for a photon in a Schwarzchild or Kerr metric (provided by a near BH for example), the radial equation has usually two possible signs:
\begin{equation}
\dfrac{dr}{d\tau}= ...
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Are worldlines towards the origin with the Schwarzschild metric finite in time and length?
A recent spacetime video about Kerr's objection to the existence of singularities has made want to clear up something about geodesics towards the origin in the Schwarzschild solution.
It is said that ...
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