Black hole Definition and 999 Threads

Now, it's been said that the majority of the entropy in the universe resides within the cumulative entropy of black holes inside the universe. How do they know that? Now, I'm not so interested in how they determine the black hole's entropy, I know there's a relatively simple formula for that...

I'm no expert in this stuff, and perhaps I don't understand these diagrams, but having said that, I don't understand why the typical Penrose diagrams I see of black holes look the way that they do. They all have a 45 degree (light speed) angle for the event horizon of the black hole, and they...

A 4 ft diameter black hole (1.5 to 2 times the mass of Saturn) is headed toward Earth. Will Earth be able to defend itself using missiles with nuclear bombs? How to calculate such a problem?

I’m sure that when a star is in the process of becoming a black hole, there must therefore be one inside it at some point during the process (correct me if I’m wrong on that). But if so, how long does that take? Could there exist a supergiant star that has a black hole inside it for a long...

Hey to all,... It is now generally believed that information is preserved in black-hole evaporation. This means that the predictions of quantum mechanics are correct whereas Hawking's original argument that relied on general relativity must be corrected. However, views differ as to how...

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one of the claimed successes of string theory is its ability to derive the correct Hawking-Bekenstein equations to calculate the quantum entropy of a black hole without any free paramenters, specifically Extremal black hole entropy using supersymmetry and maximal charge. I was wondering if...

First of all, I want to note that geometry is being discussed, which in fact is the General Theory of Relativity. And in any geometry, there are infinitely thin, weightless, etc. lines, rulers, and so on. In the future I will remind you about this. The system of units is meters. There is a...

In a hypothetical deep space experiment in the distant future with appropriate safety precautions in place, how much force/power/energy would be required to create an artificial 1000kg black hole? I haven’t the faintest clue & this isn’t for homework. Where would I even begin looking for an answer?

If an observer never falls into a black hole, something it observes that does fall in takes an infinite time to reach the event horizon. If an observer falls into a black hole along with an object, it will not lose information on the falling object, but will lose that from the outside of the...

https://www.bbc.com/news/science-environment-60708711 Scientists claim hairy black holes explain Hawking paradox https://arxiv.org/abs/2112.05171 Quantum Hair and Black Hole Information Xavier Calmet, Stephen D.H. Hsu It has been shown that the quantum state of the graviton field outside a...

If you're in a relativistic starship, approaching the speed of light, then if you get too close to it, do you end up becoming a black hole? Relativistic length decreases as you get closer to light speed. Relativistic mass increases as you do the same. Will your relativistic mass and relativistic...

Well, not right away. It's about 10 000yrs in the future. From: THE ASTROPHYSICAL JOURNAL LETTERS The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate Popular version...

In textbooks, Bekenstein-Hawking entropy of a black hole is given as the area of the horizon divided by 4 times the Planck length squared. But the corresponding basis of the logarithm and exponantial is not written out explicitly. Rather, one oftenly can see drawings where such elementary area...

The Kerr solution describes the gravitational field of a rotating black hole. Oftenly, the hole is said to be „spinning“, what appears as misleading to me. My questions: 1.) Is it correct to say that angular momentum in this way is treated like orbital angular momentum, not like spin? 2.) Can...

Hi everyone, I was in physics class and the professor asked if the inertia of matter changes in a black hole and I would like to know if anyone has the answer to this question.

To keep things "simple", the black hole is 1E30 kilograms. The statite (stationary satellite, blue) hovers above the hole at a fixed location (twice the Schwarzschild radius from the singularity) by tremendous acceleration. The statite drops a probe (green) that begins to fall toward the hole at...

If all the matter was condensed to a single point at the beginning of the universe, then why didn't it all collapse into a black hole? I have heard speculation that the laws of physics change with time, is this the reason why there was no black hole at the beginning or is the reason more...

Recently I have seen a number of General Relativity visualisations that show spacetime flowing towards any mass, similar to water flowing into a sink hole. ScienceClic's video is an example. That model is also used in the "waterfall model" to explain the event horizon of a black hole, as the...

I know black holes are stars that fuse together elements until they reach iron which doesn't radiate energy to counterbalance the gravity, but do any stars fuse elements heavier than iron that would once again give off energy prior to it imploding? By the way, why doesn't iron creation create...

This is a bit hypothetical obviously as I doubt the conditions for this scenario would ever occur in the real universe. Imagine a black hole, about 10 solar masses. It is, amazingly, sitting in an area of space that is a perfect vacuum. Just by chance, a rogue antimatter star of exactly the...

Hello everyone, I have a hard time to conceptualize the case of a moving black hole. We know from SR that time slows down for moving objects; but time dilation at the event horizon is already equal (tends) to zero. It seems that it can create some sort of conflict for the black hole movement...

https://phys.org/news/2021-11-lack-massive-black-holes-telescope.html I wonder how this affects the 'known', or rather, 'observed', mass in the galaxy and universe.

Hey everyone, if I were to view a shining person rotating near a black hole at near the speed of light there would be 2 kinds of redshifts: gravitational redshift and relativistic doppler effect redshift. Right? But, say at some point, the person is traveling towards me, then the doppler effect...

I'm not sure how to approach this question. So I start off with the fact the path taken is space-like, $$ds^2>0$$ Input the Schwarzschild metric, $$−(1−\frac{2GM}{r})dt^2+(1−\frac{2GM}{r})^{−1}dr^2>0$$ Where I assume the mass doesn't move in angular direction. How should I continue?

I am under the impression that an outside observer would see things redshifted as the person they are observing approaches the event horizon. So, it seems reasonable that someone from inside the black hole would see incoming light blueshifted. Is this inaccurate? Why or why not? If it is...

Let's say you have an absolutely giant black hole, so big that items inside of it leisurely approach the singularity, reaching it in about a million years (or whatever time it takes for a black hole to form from matter accumulation). Could matter slowly accumulating somehow form its own black...

Disclaimer: I'm not a scientist, please excuse my ignorance if the following seems stupid. Since time slows down as an object gets nearer to the EH, would an outside observer, living and observing for an almost infinite amount of time ever see an object/particle cross the event horizon...

If: Gravity propagates via "particles" of gravity, and The particles of gravity are massless and so move at the speed of light then how can the gravity particles escape from a black hole? Aren't they as trapped as the photons? It seems as if black holes should present no gravitational field...

The experiment I am thinking about is a spaceship that approaches the horizon of a supermassive black hole by firing its engines in the opposite direction of its motion. I have the following questions: 1. When the ship is in a stable orbit, just above the horizon, how would an observer far away...

Dear all, For a new book I'm writing I'm investigating some common misconceptions in physics. And of course, that means confronting myself with my own confusion. One thing I've never got clear in my head, and which I find hard to answer using google and my textbooks on GR, is the following: how...

Since my understanding of these geometries is wrong, I'll do this in numbered steps - the easier to correct my logic. I think the big problem I have is with the time dimension. There seems to be a presumption that the time vector will drive a falling object into a central singularity. But how...

Could dark matter consist of black holes formed shortly after the big bang? They would form the perfect development seed. If they all have Sun-like masses then they are not detectable from here (they are just 3 kilometers wide!). They have virtually no collisions with stars and could form a...

What is the definition of volume inside a black hole? we know the grr element of Schwarzschild metric is negative inside event horizon, so how to define a volume inside event horizon? if there is no definition of volume, is there the definition of density?

Assume a Schwarzschild black hole. Near the event horizon other than Hawking radiation the behavior of matter and energy are fairly accuratly described by general relativity. How close can one get to the center (the singularity based on GR) before one must switch to a quantum gravity theory...

From "standard" formula we have that the gravity acceleration a = GM/r^2 and that the Schwarzschild radius rs = 2 GM / c^2 Is it possible to compute the gravity acceleration at Schwarzschild radius putting r = rs? In this case we will have a = c^4 / (4GM) This mean that a very very...

First, I was not sure whether this should go into the Relativity or the Quantum Physics rubric, but since the central question is about entanglement, I opted for the Quantum. I do not have the necessary sophistication to follow string theory arguments, and even most explanations in...

As closer the observer will be to the event horizon, the more the time dilatation will be. As we know, if the observer O1 has a clock, another observer O2 very far from the black hole will se the O1 clock "slowing" down as O1 approach the event horizon. The limit is that the O1 clock "stops" at...

It's one of those staples of sci-fi. Unless you're going for a hard sci-fi that uses rotation or linear acceleration to achieve simulated gravity, your starship will likely use "gravity plating". As we all know, gravity plating is just a plot device, usually for shows with more limited budgets...

Ok, I know, it's science fiction, you can make anything work if you really want it to. I'm planning out a sci-fi story which I wanted to try and keep as grounded as possible in believable scientific concepts. For context, the basic premise is: humanity detects a wormhole on the outer edge of the...

Hi All I'm sure this question has been covered previously , but when searching I do not find a definitive answers. I recently watch some talks given by Kip Thorne that had me thinking about black holes and their densities. So my deduction is as follows . Using General relativity, and...

This is the problem statement: We can start by writing ## (\star d \star d \xi)_a = - \nabla^b (d\xi)_{ab} = - \nabla^b \nabla_a \xi_b + \nabla^b \nabla_b \xi_a = 2\nabla^b \nabla_b \xi_a ##. Then with ##\nabla_a \nabla_b \xi_c = R_{cbad} \xi^d = -R_{bcad} \xi^d## we can contract over...

Electrostatic repulsion of two electrons is about 4.17*10^42 stronger than their gravitational attraction, and is mediated by massless carriers. Black holes preserve charge, and charging a BH with even a moderate electric (negative) charge will result in BH repulsing electrons instead of...

Black holes suck things in and the current explanation is that they bend spacetime. I have my own hypothesis though. If electrons shoot out photons when they switch positions in the atom that would mean that at the very least electronshave photons in them. Atoms always try to have the right...

If a Black Hole is spinning (perhaps they all do) I have heard it distorts the 'fabric' of Space-time in the vicinity. What is the 'friction' component which allows the distortion?

[Mentor Note -- Specialized question moved to the general technical forums] Homework Statement:: To show that ##J = Ma## for the charged Kerr metric [Wald Ch. 11 Pr. 6] Relevant Equations:: \begin{align*} \mathrm{d}s^2 = &- \left( \frac{\Delta - a^2 \sin^2{\theta}}{\Sigma}\right) \mathrm{d}t^2...

Theoretically could an observer in a black hole perceive hawking radiation escaping the black hole as a black hole within the black hole? Also if so maybe that black hole could produce a radiation similar to or related to hawking radiation (Making a strange entangled system for conservation of...

I've been stuck starting anywhere with this. I need to finish this class for graduation and i'd like a safety net of a passing grade with this.

If a string of blinking Christmas lights extends from the center of a black hole out to a large radius r. What do I see, if I am perpendicular to the line of lights, at radius r? Experiment specifics 3 solar mass, non-charged, non spinning black hole. Observer is 1,000 Au from the center of...

I know that for the infalling observer the horizon is a fake singularity that can be removed via the Eddington-Finkelstein co-ordinates but wouldn't the classic Swartsheild co-ordinates still apply for the outside observer? So, while for the infaller it takes a finite time, the outside...