Questions tagged [black-holes]

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.

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Speed of light problem [duplicate]

This question totally hypothetical and I'm aware we can't travel at speed of light but IF .... If you were to travel at the speed of light according to Einsteins theory of relativity you would gain ...
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Black hole metric of reflected shell of incoming light

At this point in Leonard Susskind's eighth lecture on general relativity, he begins a discussion about finding the metric of a black hole formed by an incoming, spherically symmetric shell of light. ...
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Can we use entangled particles to find out what is going on inside a black hole?

If you throw one entangled particle inside a black hole can we know what is happening with it from looking into another entangled particle outside the black hole?
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Is a black hole just plasma in crystalline form so dense that light cannot enter? [closed]

Is the ring we see around the object the same phenomenon known as triboluminescence? What's the maximum density known matter can exist in limited volume? Wouldn't everything else technically be the ...
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Measured Data Question regarding Galaxies with or without Dark Matter and Supermassive black holes

My understanding is that all Ultra Diffuse Galaxies (UDGs) have no Dark Matter nor do they have Supermassive Black Holes. It is also my understanding that all other galaxies have both Dark Matter and ...
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Partial Transit of an Event Horizon [duplicate]

To all the cosmologists and black hole experts out there: What would happen to a large object (very fast moving asteroid, planetoid, etc.) that was on a trajectory to tangentially intersect an event ...
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Rotation of astrophysical black holes

It's usually stated that "astrophysical black holes are expected to have non-zero angular momentum, due to their formation via collapse of rotating stellar objects". In other words: rotating ...
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Why do we need Quantum Gravity [duplicate]

I know this question has been asked many times but I have not found a satisfying answer to it yet. I understand Gravity as an emergent phenomenon of mass/energy. I understand quantum mechanics as the ...
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Could there be a Planck sized black hole with positive charge in the center of each atom, moving so fast on its way that it has nearly any mass?

Days ago I made a post asking if it would be possible to find a Planck sized black hole in the center of each atom. I was told the Planck mass is much heavier than an atom. Finding a way to have all ...
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What does the no-hair theorem state about the entropy of black holes?

So does the no hair theorem say that all classical black holes will have zero entropy? If yes, why?
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4th order Runge-Kutta Scheme for Reissner-Nordström black hole [closed]

So I have to design a 4th order runge kutta scheme for the following ODES: $\frac{dh}{dv} = \frac{1}{2r}(h - \bar{h}) (g(1-\frac{e^2}{r^2}) - \bar{g})$ $\frac{dr}{dv} = -\frac{1}{2}\bar{g}$ The ODEs ...
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Can a x ray see its own reflection ? / Is opisitional force present between two x-ray transmitters? [closed]

If you downstage a particle exselerater to the point before a black Hole is created ,would an x-ray see its self before the big bang,I which creates the black hole?
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Does the event horizon always stay below you in the frame falling freely with you in a black hole?

Imagine you fall freely into a black hole. You place small test masses inside your frame with a fixed distance between them. What will we see? The only force inside your frame is the tidal force. The ...
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How do infinitely dense singularities evaporate trough hawking radiation?

If we assumed that a black hole with a singularity of infinite density eventually evaporates due to Hawking Radiation, does this affect the singularity itself? If mass is preserved in the singularity ...
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Black $p$-brane solution

Im trying to confirm that the metric (11) in the paper below is a solution to Einstein's equations (6). I tried to use the metric and extract $\lambda=(1-(r_+/r)^{D-3})^{1/2-\gamma/2(D-3)}$ and $R=r(1-...
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What's the spacetime metric in the frame freely falling to and into a black hole?

The normal frame used in black hole physics is the Schwarzschild metric. But how does the metric look like if you fall freely into it from far away? Initially flat and time dependent components? Wil ...
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How can the ratio of a black hole's (or any object's) angular momentum to its mass be less than one?

In the latest Quanta Magazine article, about Kerr black holes, the researchers say their new solution for these objects only works, so far, for Kerr black holes with a ratio of angular-momentum-to-...
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Is there also relativistic length contraction caused by gravitational Lorentz transformation?

When objects move at relativistic speeds, their length as observed from outside gets scaled inversely proportional to the Lorentz factor in direction of the velocity: https://en.wikipedia.org/wiki/...
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Saddle point contributions to the gravitational path integral

In his lectures on black holes and quantum information, Tom Hartman states that the gravitational path integral can be approximated as $$ Z(\beta) \approx \sum_{g_\text{cl}} e^{-I_E[g_\text{cl}, \phi]}...
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Calculating coordinate increase of light ray escaping black hole

Consider a light ray near a black hole described by Eddington-Finkelstein coordinates $(v,r,\theta,\varphi)$. My aim is to calculate the increase of the coordinate $v$ along a radial path from the ...
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Neutron star near black hole mass in a moving frame [duplicate]

Consider a neutron star with a mass close to that necessary to form a black hole. In a moving frame, it has additional kinetic energy, and its energy density should increase. Why is it not possible ...
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How to use the chain rule in the black hole thermodynamics considering $S$, $P$, and $Q$?

To study the first law of thermodynamics in a special case I faced a problem related to the chain rule. Suppose a Smarr formula whith the general form $M=M(S,P,Q)$. Now, considering the entropy $S=S(...
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Schwarzschild Christoffel Symbol Problem

Schwarzchild metric is static, none of its components change over time. Curiously, basis vector $e_r$ does change over time. If we differentiate $e_r$ with respect to time and take the time component ...
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Are there primordial populations of neutron stars and white dwarfs?

There is a well-known prediction that density fluctuations in the first moments of the Big Bang produced primordial black holes. Black holes from stellar collapse have their masses constrained by ...
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About candidates for dark matter [duplicate]

Let me start out by saying that while I read a lot about astrophysics on Wikipedia and in the news and find it very interesting, I never really got into the calculations because I never took a course ...
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Conceptually, why is the entropy of black hole related to Planck length?

I was watching a lecture on the holographic principle, and it presented the equation for the entropy of a black hole as $$S_{BH} = \frac{A}{4l_p^2}$$ My question is why, conceptually, the entropy of a ...
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How can primoridal black holes form with less mass than the Chandrasekhar limit?

So I was looking through some articles about primordial black holes the other day and it said that these black holes can be insanely tiny. Some of the articles state the mass could range from $10^{12}$...
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Does Black Hole requires a material medium to be formed?

Does Black Hole requires Material medium to be formed or it can be formed without any medium (Vacuum)? as anything which can be thrown with the speed of light can form a Black Hole and light can also ...
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Is singularity without black hole possible?

I read things related to the topic I am asking and I found the idea of a "Naked Singularity" but naked singularities can't be created without black hole. I need to know whether it is ...
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Where does the black hole firewall energy come from?

There are a couple threads on the firewall paradox on StackExchange, however I have not been able to find one that explains the physical origin of the firewall in black hole evaporation. There is an ...
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Paradox approaching the speed of light/Planck temperature? [duplicate]

Paradox If we accelerate an object (such as a proton) to closer and closer to the speed of light it will gain relativistic mass until eventually it gains so much (approaching the Planck Temperature) ...
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Gravitational waves strain drop off

For the gravitational waves detected by LIGO back in 14.09.2015, how do we measure how strong the strain from the gravitational waves would be if the collision happened say 1000AU away from Earth? How ...
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Why is the loss of information in a black hole, so disturbing to scientists? [duplicate]

Please keep in mind that I am not a scientist. So please keep you answers in layman’s terms... So my question is based on the “loss of information” after something passes the event horizon of a black ...
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Is it possible to extract energy from black hole and decrease event horizon size faster?

So imagine a black hole that is like 3 times the mass of the sun so that there can be a bigger gravitational gradient. Assume the black hole has no accretion disk, charge, or rotation for simplicity's ...
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Could black holes be the reason for the expanding of the universe?

I would like to start be saying I'm no Physicist. I was wondering if known and mostly unknown black holes could be the reason for the "expanding" of the universe.
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Do strings prevent a black hole singularity? [duplicate]

Spacetime singularities are problematic in quantum gravity. String theory offers a way to construct such a quantum gravity. Do strings offer a solution to this problem in the sense that point-like ...
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Quantum extremal surface and black hole evaporation inquiry

Recently there has been progress made in the black hole information paradox by using the tools of AdS-CFT correspondance. Specifically, the Page curve for an evaporating black hole has been ...
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For someone hovering near a black hole, how would he express the metric?

If someone is hovering above a black hole (not infalling), his metric evaluated at his coordinates $r_*$ is flat (Minkowski), but more generally, for any r, how would the metric be expressed, knowing ...
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Robust prediction of general relativity

What does "the black hole formation is a robust prediction of the general theory of relativity" mean in layman terms?
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Proper Time of Fall in Schwarschild Metric

I've been trying to understand how the proper time of a radial fall into a black hole is finite, but I'm confused because I found many results and they do not seem to be the same. Usually what I see ...
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Does SXS catalog for NR simulations have non-spinning, non-eccentric blackholes?

I am looking for NR waveform for two non-spinning and non-eccentric black hole binary merger for small mass ratio. Somehow, on the SXS catalog website, I don't see any such description. Thanks
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Does a charged particle respond to a charged black hole both gravitationally and electromagnetically?

The Reissner–Nordström metric is given by: $$ds^2= \Bigl( 1-\frac{r_s}{r}+\frac{r_Q^2}{r^2} \Bigr) c^2dt^2- \Bigl( 1-\frac{r_s}{r}+\frac{r_Q^2}{r^2} \Bigr)^{-1}dr^2-r^2d\Omega^2$$ Which is intuitive ...
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About the Kodama vector fields and MS energy in non-spherical symmetry

In an article I saw this statement. For a non-spherical geometry, a Kodama-like vector field is not known yet and its not obvious how our formalism can be extended to these type of geometries. I don’...
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Kerr Black Hole Rendering issues

Alright so, i have been working on a very bootleg 3D render engine for Black Holes in Houdini. And i encountered some results which i am not 100 about. Exibit One; This was the first attempt at an ...
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Energy of two particles moving towards each other at near lightspeed relative to each other [duplicate]

I understand that this question might arise from multiple misconceptions and misunderstanding, I'm not from a physics background. If in a vacuum we had two particles A and B moving towards each other ...
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Why do black holes remain? [closed]

When we think about black holes as not containing matter but being regions of warped spacetime, I can't think why they don't revert to being Euclidian space more quickly. This is because I can see how ...
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Are rotating black holes producing a frame dragging effect inside the event horizon?

Are rotating black holes producing a frame dragging effect inside the event horizon? Is that effect moving space inside the event horizon at speeds far greater than the speed of light?
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Is a black hole a single particle or a bunch of particles that binds together?

We know that in a neutron star all electrons and protons combine together and make neutrons because of the gravitational pulls. We also know that a black hole is much denser than a neutron star, we ...
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Are quasi-normal modes in black hole perturbation theory the same as resonances in Quantum Mechanics?

When we evaluate quasi-normal modes in black hole perturbation theory (also here), by solving the Regge-wheeler potential, is it same as solving the Schrödinger equation for a barrier and finding ...
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Black hole vs Dark energy

This is a follow-up question to this answer. The original question was whether there is a maximum size limit to a black hole in our universe. The answer given was that if the event horizon coincided ...
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