New answers tagged black-holes
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Necessity of Singularity in General Relativity
According to Thorne and Susskind, the fact that a black hole's mass is distributed as a 2-dimensional surface (the event horizon), and not a volume, indicates that the black hole has no interior.
You ...
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Necessity of Singularity in General Relativity
To solve the GR equations at singularity you need to divide by zero. You can't divide by zero. This means that GR doesn't make predictions about what happens there. There is no solution to equations ...
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Necessity of Singularity in General Relativity
Well the famous singularity theorems show (very very roughly speaking) that in the theory of classical GR, collapse beyond horizon implies a singularity. Classical GR is not the true theory of physics,...
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Necessity of Singularity in General Relativity
What is it that preludes the predicted field, even at $r<r_{Schwarzschild}$, from simply terminating at the surface of a collapsar of dense matter, and taking some other form inside it?
This is ...
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Why singularity in a black hole, and not just "very dense"?
Is it not possible that, like snowflakes, no 2 black holes are exactly identical and each black hole should be treated as a unique set of parameters.
Black hole A uses 30% of these rules 30% of those ...
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Hawking Temperature of the BTZ Black Hole
Another option for finding the Hawking temperature of the BTZ black hole is by the formalism of the surface gravity $\kappa$ which connected to the Hawking temperature via:
$$T_H=\frac{\kappa}{2\pi}$$
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Can black holes fully merge, according to a distant observer?
Black hole forms once there is sufficient mass in a volume of space. Once you get close enough to a black hole according to distant observer, it's event horizon will expand and swallow you before you ...
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Can you calculate the radius of a hypothetical singular surface inside a black hole from observing changes to its linear momentum?
No, because as an observer outside the event horizon, you will never be able to see an object cross the event horizon. (See This post)
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Is the size of a black hole singularity smaller than a fundamental particle?
We know that black hole is infinitely densed.
More exactly: The theory of general relativity predicts
that the center of a black hole is infinitely dense.
This theory predicts very well everything ...
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Is the size of a black hole singularity smaller than a fundamental particle?
While @paulina's answer: we don't know is correct, because quantum gravity is not understood, I'll answer for a classical Schwarzschild blackhole as described by Kip Thorne.
The size is zero, however ...
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Is the size of a black hole singularity smaller than a fundamental particle?
The very short answer to this is: We have no idea.
General relativity predicts that the singularity of a Schwarzschild black hole (which I assume is what you mean by "actual black hole") is ...
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Does black hole formation contradict the Pauli exclusion principle?
In actuality, there is no such thing as this so called singularity...
It's a convenient mathematical invention to represent something of which we understand very little.
Although quantum physics can ...
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Memory effects from black hole migration in the early universe
I can look at the black hole after some time when it has moved away a little bit. Now the region of space that was previously inaccessible to me is accessible.
I think your misconception is thinking ...
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David Tong, notes on General Relativity, pg. 25
I was puzzled enough to look at what the notes actually say. You have the quote right though.
I think he starts from
$$
\sqrt{a+x}= {\sqrt a}\sqrt{1+ \frac x a}\\
\approx \sqrt{a}\left(1+ \frac 12 \...
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Why does angular momentum shorten the Schwarzschild Radius of a black hole?
Black holes aside, adding the freedom of rotation within the 3 standard volumetric dimensions essentially increases dimensionality. Rotation is a place to store momentum and energy without ...
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How to derive the surface gravity in terms of redshift factor in static spacetime?
Unfortunately, I do not know how to continue this approach, but I can suggest a different way.
One can start by considering the expression
$$\sqrt{\nabla_\mu V \nabla^\mu V}$$
By plugging in the ...
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Are we certain of the mass we calculate for supermassive black holes?
It's a question of magnitudes. The density of dark matter required to explain the rotation curves of a galaxy is far too low to make a significant contribution to the mass pulling on stars and gas ...
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How to Understand Negative Energy in the Ergoregion?
I suppose you are in the context of a rotating black hole, which is described by the Kerr metric, which in Boyer–Lindquist coordinates is ($c = 1$)
\begin{equation*}
ds^{2} = - \left( 1 - \frac{GMr}{\...
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Why does rotation make black holes smaller?
@Yukterez: the area $A=16\pi\mathcal{M}^2$ comes from the expression $A=\int \sqrt{|\gamma|} d\theta d\phi$ (being $\gamma_{\mu\nu}$ the induced metric on the event horizon), which describes exactly ...
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Imagining Graham's number in your head collapses your head to a black hole
A simple answer which slightly expands on the other (excellent) answers here, coming at it from an information-theory perspective:
The Kolmogorov complexity of Graham's number is significantly smaller ...
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Photonic black holes
For the sake of argument, let us simplistically take the photon energy $E=hf$, and see what kind of black hole we get.
The Schwarzschild radius of a given parcel of energy $E$, which has an equivalent ...
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Photonic black holes
"According to electromagnetic theory, the rest mass of photon in free space is zero and also photon has non-zero rest mass, as well as wavelength-dependent. The very recent experiment revealed ...
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Photonic black holes
A photon in a box has mass and pressure. Put it in an impossibly small box and it'll theoretically make a black hole.
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Imagining Graham's number in your head collapses your head to a black hole
Bekenstein Bound
The Numberphile mathematicians were clearly describing an explicit representation of the bits in Graham's number, rather than any symbolic one (obviously, just writing "G" ...
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Imagining Graham's number in your head collapses your head to a black hole
Without watching the video and going with your headline, my first guess would have been to use some black hole thermodynamics. If we trust a well known internet black hole calculator, then a 1.6e-35m ...
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Imagining Graham's number in your head collapses your head to a black hole
Simply put, what's stated in the video is misleading to an extent that it's fair to say it's wrong.
Ignoring problems of how you define the word 'imagining' (this is physics stack exchange, after all),...
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Schwarzschild Radius of the Universe
The answer by probably_someone is technically incorrect. He is confusing the Schwarzschild radius with an event horizon. They are not the same thing.
the conditions that the author assumed in the ...
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Different Bekenstein bound equations – what’s the difference?
They seem to differ only on the choice of units. The second version uses units with $k = 1$ and the last equation uses units with $k = \hbar = c = 1$. These sorts of unit systems are very common in ...
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WKB Approximation of the Quasinormal Mode Spectrum of the Poschl-Teller (PT) Potential
Okay so this question was really bugging me so I spent the afternoon learning how to do the approximation.
The general Poschl-Teller Potential is $V(x) = \frac{V_o}{\cosh^2(\alpha \cdot (x-x_0))} $
I ...
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Physical meaning of Boyer-Lindquist coordinate
For me, the BL coordinates allow to plot the particle location $ (x,y,z) $ around a Kerr black hole in a Cartesian frame of a static observer:
$$ x=\sqrt{r^2+a^2}\sin\theta\cos\phi $$
$$ y=\sqrt{r^2+a^...
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Is the information or energy in a black hole converted to another form of energy during decay of Hawking radiation?
If a large amount of non-rotating thermal energy collapses into itself, the result is a non-rotating black hole, whose energy is thermal energy.
If one unit of thermal energy is conducted away from ...
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Extreme Mass Ratio Inspirals and GWs cycles
There is no well established taxonomy of dividing the inspiral into "late" and "early" parts. When people do talk about the "late inspiral" they mean "that part of ...
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WKB Approximation of the Quasinormal Mode Spectrum of the Poschl-Teller (PT) Potential
Schrödinger operators with reflectionless Pöschl-Teller potentials arise in the study of SUSY chains of one-dimensional non-linear field theories labeled by $N$. The two first members of the family ...
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Binary black hole merging condition
The critical impact parameter $b_{\rm crit}(v)$ depends on the highly non-linear general relativistic interaction of the two black holes. The only way we currently have to address this question is ...
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Black Hole Formation -- How Can an Event Horizon be Observed to Grow?
It's the total mass that counts and we can indirectly observe a black hole growing through changes in the behaviour of objects surrounding it, those affected by its gravity and rotation. Naturally, ...
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How come the magnetic field disappears when a neutron star becomes a black hole, while the rotation remains?
Árpád Szendrei asked: "How come the magnetic field disappears when a neutron star becomes a black hole?"
If a net electric charge remains, the star would collapse to a Kerr Newman black ...
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When you are in a gravitational field, do object far away get physically closer to you as you get closer to the mass?
This is to answer the latest version of the question, as phrased in the comments:
I should have clarified in the question [...] The only thing that truly matters is clock ticks counted by each ...
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Is the information or energy in a black hole converted to another form of energy during decay of Hawking radiation?
The reason that information is lost according to the information loss paradox is that Hawking radiation is completely thermal radiation, meaning that it is uncorrelated and carries no information ...
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