All Questions
Tagged with black-holes causality
107
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Light-like normal vectors
Can someone please show me how to mathematically establish that the normal vector to the event horizon of a Kerr Black Hole is light-like?
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Rotating Black Holes
All stars rotate. And the more they contract the faster the rotation, so is there such a thing as a non-rotating black hole? And as gravity is less at the equator of a rotating star, assuming that ...
- 1,710
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How can time go in different directions in the Universe?
This is not a duplicate, I am not asking about any kind of time dilation caused by a BH. My question is about the direction of time (and if it is possible to have different directions for time, other ...
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What is the formal difference between the light cone and a black hole?
A black hole can be loosely defined as a spatial closed surface from which nothing, not even light, can leave.
The light cone of special relativity is in some sense similar to a black hole because by ...
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How does the Penrose diagram for a spinning black hole differ in realistic scenarios (formed by stellar collapse)?
The Penrose diagram for a non-spinning Schwarzschild black hole is
Notably, there is a second universe "on the other side" of the black hole. However, actual black holes form by stellar collapse, and ...
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Time direction in the BH parallel exterior region
In the III region of the maximally extended Schwarzschild solution, described in the Kruskal coordinates , Sch. time runs in the reversed direction as compared to the I - event horizon III-II of the ...
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Could you escape a black hole - using a black hole? [duplicate]
I'm pretty sure the answer to the question in title is "No". But why?
Below is a naive Newtonian simulation I made. You can see that in the animation, both black hole's horizons seem to "recede" for ...
- 3,107
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Is the Taub-NUT solution stationary?
The Wikipedia article about the Taub-NUT spacetime says that it was a first attempt in finding the Kerr solution. Since the Kerr spacetime is a stationary solution, meaning that it admits an ...
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How come no information can travel faster than light when we can measure a black hole's mass? [duplicate]
So I learned about the Schwartzchild radius, which is the radius of an object's event horizon. But how we define an event horizon is that it's a region of space where the gravitational acceleration ...
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Is there a general definition of a causal horizon?
In the Schwarzschild spacetime with metric in standard Schwarzschild coordinates
$$ds^2=\rho(r)dt^2-\rho(r)^{-1}dr^2-r^2d\Omega^2,\quad \rho(r)=1-\dfrac{2GM}{r},$$
we have a coordinate singularity ...
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Definition of trapped surface
The definition of a trapped surface in Sean Carroll's "Spacetime and Geometry" is as follows.
"A compact spacelike, two dimensional submanifold with the property that outgoing future directed light ...
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Is space becoming time-like inside an event horizon a consequence of our coordinate system?
Is the fact that "space behaves like time" inside an event horizon a consequences of our particular coordinate system? Or is it a universal fact?
I am asking based on the statement in this video How ...
- 3,423
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Penrose spacetime diagram for the Schwarzchild solution
Consider the metric corresponding to the Schwarzchild solution. It represents a Non-rotating Black hole. When we want to understand the causal structure of the spacetime we find the null geodesic ...
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Event horizon of a black hole
Except from the mathematical derivation, is there a physical reason of why do we call the event horizon of a black hole a null surface? Is the concept of event horizon being a null surface any how ...
- 1,222
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How high can a light-beam (or apple) travel when pointed (thrown) out from the event horizon? [duplicate]
I am a bit confused at the idea that information cannot be sent out from behind the event horizon of a black-hole. Consider the following figure: (source This link)
An apple thrown up from the ...
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