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Results tagged with black-holes
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user 388464
A black hole is a region of spacetime from which nothing can escape. More formally, the future light cone of any observer within the black hole is completely contained in the black hole, and the black hole region is not within the past light cone of any observer that goes to spatial infinity in an infinite amount of time.
1
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Accepted
Way to get information from inside black hole to outside?
One thought experiment 'paradox' is to hit the end of very long rod with a very large hammer. If the far end moves at the same instant the near end was hit this would be an example of transmitting a s …
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Why does a black hole grow when it consumes matter? Isn't this a contradiction?
An important thing to realise is that the event horizon is not a boundary that light rays can rise up to before being drawn down again. Light rays inside a black hole never travel upwards towards the …
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What is the gravity at the event horizon of a black hole?
The answer in terms of escape velocity $v_e=\sqrt{\frac{2GM}{r}}$ is not correct and this is easy to demonstrate:
If we consider launching a projectile from the surface of the Earth, then if its initi …
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Why is it difficult for 2 black holes to merge?
but I would have still expected the two to rather naturally merge...
Why do you expect them to merge? The simplistic natural expectation for one body orbiting another is that they will continue to d …
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2
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Typically energy of black hole compared to a planet or star of the same mass
As safesphere mentioned, the energy of a black hole with the mass of the Earth has the same energy as the Earth. I think it is also pertinent to add, in the context of the OP, that a black hole does n …
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How to obtain the center of mass energy needed to form a black hole in a particle accelerator?
At CERN routine proton-proton collision energies are about 13Tev. In 2018 they switched to lead ion collisions. These collisions had an collision energy of about 5.36 Tev per nucleon pair and a lead i …
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How do we know that a black hole radius is not significantly contracted for a stationary out...
In this answer, I am ignoring optical effects and illusions of how a body would appear to look from a distance and focussing on actual measurements of length.
Starting with the Schwarzschild metric, a …
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Equation for the curve of a free falling particle in Kruskal diagram
This is not intended to be a formal answer. \i just wanted to post the diagrams I referred to in the comment as I feel they may be useful to the discussion. This first one is from Mathpages;
This sec …
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How can micro black holes exist?
It's very unlikely we will find a primordial blackhole formed at the earliest times of the universe. This is because the background temperature was very high at that time and any blackhole formed will …
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Physical interpretation of the two possible roots for the isotropic Schwarzschild coordinate...
Working with your equation:
$$r' = \dfrac{1}{2}\left(r-\dfrac{R_s}{2}\pm\sqrt{r\left(r-R_s\right)}\right).$$
And substituting the photon orbit radius $(3/2) R_s$ for r we can write:
$$r' = \dfrac{1}{2 …
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What would the collapse of a neutron star into a black hole look like from the center?
A calculation based on the FLWR metric assumes a universe that is basically a uniform distribution of matter and energy throughout the universe and so a uniform average density. The question assumes s …
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Does infinite time dilation increase a photons energy to collapse to a black hole, and does ...
And imagine a photon falling down a similar trajectory next to it, in
a parallel worldline.
The marble and photon cannot follow parallel word lines because no local observer ever measures the speed …
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Does the positive energy particle emitted from Hawking radiation directly equate to the amou...
Even if there was such a thing as particles with negative energy, using them to explain the loss of mass by a black hole by Hawking radiation is flawed, because it is equally likely that a particle wi …
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Orbit description in Schwarzschild metric
The real radius is the Schwarzschild radius, because that is what is measured in reality. The other radius is the Newtonian/Euclidean expectation which is imaginary. The Newtonian radius can be define …
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Will a distant observer really see an object that has fallen close to a black hole freeze in...
One reason the Schwarzschild metric is so well known, is because it was the first exact solution found for a gravitational body in General Relativity and even Einstein did not think an exact solution …
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