Black hole Definition and 999 Threads

[post moved to relativity forum: https://www.physicsforums.com/threads/black-hole-evaporation-mechanism.1059236/]

Or is Hawking radiation something? Can't be both, however if you choose one theory over another, why do you do so. Those of you who are younger will not remember a World without the information paradox, but when I was younger it did not exist in any way because nothing escaped the event...

I find it interesting that the more massive the black hole, the weaker the fall acceleration at the distance of the Schwarzschild radius - that's why you wouldn't necessarily notice anything special in the event horizon.

These are the points in the book: What is "naturally used"? Does it hold only as the observer crosses the event horizon? How can they "use" them?

Thought experiment: What will happen if you place a mirror behind the event horizon and turn on the light in its direction?

First of all, I wish everyone a Happy New Year. I am interested in your expertise on a special constellation, which I will first briefly describe. If you observe an object that is approaching the event horizon of a black hole, it is said that at some point the distant observer will have the...

Below is the description from the book. I thought that hyperbolas in the right quadrant are time-like and hyperbolas in the upper quadrant are space-like. If it were so, the surface ##r=0## would be space-like, but the book says otherwise. -- ?

At a descriptive level, negative energy quanta enter a black hole during Hawking radiation. But when one tries to understand it mathematically, it seems that negative "energies" appear in two very different senses, which seem to be totally unrelated to each other. At one level one has Bogoliubov...

The title is a direct quote of this video by Dr. Becky Smethurst, an astrophysicist specializing in black hole research. This is a mistake, right? Supermassive black holes, for example, don't have tiny radii, compared to stellar mass BHs. Then there's the equation she presents seconds later...

Looking at Kruskal diagrams, it seems to me we should not be able to see evidence of black holes. Assuming our frame is a hyperbola of roughly constant ##r## in such a diagram, as the black hole's constituent mass comes together time slows (from our POV) to the extent that it never crosses the...

Dear all, recently I was brushing up my knowledge of black holes with (among others) Zee's "Einstein gravity in a Nutshell" and encountered the analytical continuation of the Schwarzschild black hole in the famous Kruskal-Szekeres coordinates (Zee: chapter VII.2). The corresponding diagram can...

Hi I have two black holes 1 Sun mass each, when they merge a significant percentage of the mass is lost and is radiated away, so the combined black hole remnant is only, say, 1.8M. What is a behavior of the test body on an orbit far away from that binary? I assume that after some time...

Here's my reasoning. The event horizon is the point where the escape velocity becomes greater than the speed of light. This results in the event horizon spacetime boundary having infinite time dilation. So, that must mean that inside the boundary of the event horizon, time dilation must...

As the summary says: a light black hole has stronger surface gravity and tidal forces just outside the horizon than a supermassive black hole. So if you want to hoover just outside the horizon of a black hole and care about your well-being it better be supermassive. I understand this perfectly...

As Hawking radiation does away with black holes in the eons of time it takes to evaporate, what is the limiting mass at the final stages of the black hole evaporation? Is it Planck mass? or some fractional mass of the initial BH?

*********Disclaimer******** Hi, I want to ask this community about some black hole shinanigans. I've spent some time searching for this topic here because I don't want to be the guy who spams a forum with a question already answered a hundred times over. Since none of the threads I found...

I was wondering if someone could answer my question. I know I may be dumb but I don't really understand why our universe has a limited capacity for mass. If I remember correctly black holes occur when concentration of mass causes a hole in spacetime. I don't really understand I guess how space...

When you are calculating the gravitational force between two masses and one of them is a black hole, do you still use the distance to the center of mass as you would in Newtonian gravity to find the force? Or is the distance measured only to the event horizon? Is the inverse square law modified...

Long time had this question about how fast a planet, dwarf or not or even a rogue asteroid can move relative to the core of the Galaxy, where, if my understanding is correct it has to be a supermassive black hole. Knowing satellites revolves around a planet and this system circles around a star...

I very often see in movies and works of fiction that scientists explain that with a black hole you can travel in time and how the characters use black holes to travel in time, more precisely to the past Do scientists really believe that time travel through black holes is likely? If so, why?

Not directly from the core, but a trajectory that goes to the event horizon, and gets corrected to a perfect, perpendicular bisector path by the gravity of the core, when it reaches the event horizon. Would they escape the event horizon, since they have to always move at c? On this trajectory...

Studying and tinkering with some solutions, I've come to some realizations and questions regarding the regularization of coordinate singularities, so I'd like to see if my conclusions are good, and I guess I have some questions as well. There are two questions/conclusions, but since they...

The Bekenstein Bound places a upper limit on the amount of entropy that a given volume of space may contain. This limit was described by Jacob Bekenstein who tied it quite closely to the Black Hole Event Horizon. Put simply, black holes hold the maximum entropy allowed for their volume. If you...

Just preordered a “Black Hole” version of the watch. It tries to mimic what it would look like to travel through a wormhole, in celebration of Einstein’s theory of relativity.

Black holes are everywhere in astrophysics. There are numerous discussion about how black holes look like, what happens to gas falling into black holes, how light bends around black holes, whether there is loss of information when mass or energy falls in, etc. There is thought to be a black hole...

There seems evidence for a runaway supermassive black hole. https://phys.org/news/2023-04-strange-streak-young-stars-evidence.html

Suppose two electrons are entangled with opposite spins. Electron #1 passes through the event horizon of a black hole, together with Laboratory Assistant #1. Suppose the assistant measures electron #1's spin after they pass through the event horizon (according to #1's [proper] time) and measures...

From NASA: https://www.nasa.gov/feature/goddard/2023/hubble-sees-possible-runaway-black-hole-creating-a-trail-of-stars "We think we're seeing a wake behind the black hole where the gas cools and is able to form stars. So, we're looking at star formation trailing the black hole," said Pieter...

https://iopscience.iop.org/article/10.3847/2041-8213/acc32d From the abstract, "We present a new reconstruction of the Event Horizon Telescope (EHT) image of the M87 black hole from the 2017 data set. We use PRIMO, a novel dictionary-learning-based algorithm that uses high-fidelity simulations...

I'm posting this in "Quantum Physics" although it is just as much "General Relativity". A paper entitled "Quantum gravitational corrections to particle creation by black holes" was published in Science Direct earlier this month. It appears to provide an event horizon mechanism for holding...

https://www.france24.com/en/live-news/20230329-astronomers-discover-one-of-biggest-black-holes-ever-recorded https://universe.nasa.gov/black-holes/types/ - didn't find this very helpful ESA Euclid mission overview - https://www.esa.int/Science_Exploration/Space_Science/Euclid_overview (to be...

We know the Big Bang Theory states that our universe was started from a hot-dense point. But should't it became black hole and every matter and radiation pulled to singularity? We would not be her if that is the case.

[FONT=arial]Observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy [FONT=arial] Comments?

In the paper https://arxiv.org/abs/1210.4699. How to solve this equation? I've tried it, it's not same as in this paper. Even zero order still not the same. This is what I try to do at zero order. input $$E=E_0\left(r_0\right)$$ $$H=H_0\left(r_0\right)$$ $$b=b\left(r_0\right)$$...

I am having a debate with someone who appears knowledgeable about black holes from the language he is using but we have a disagreement about if matter can enter a black hole. He is trying to tell me the gravitational gradient near the event horizon is such that spaghetification occurs as you...

I've been seeing popularizations recently that talk as though it's widely accepted that astrophysical black holes contain CTCs. Example: https://www.abc.net.au/news/2023-01-04/are-black-holes-time-machines-yes-but-there-s-a-catch/101822002 Is this accurate? Eternal black hole solutions contain...

About a month or two ago I started doing simulations of light physics around black holes and yesterday I got a fast Christoffel symbols function for the Schwarzschild metric in cartesian coordinates, but now the photon ring appears flipped. I feel as though it is wrong. But as I am still pretty...

I found related questions being debated on the web so i'm not sure wether the question is closed. The following simple reasoning seems to imply that indeed the contracting universe is able to destroy its blackholes but what's wrong with it ?: The black hole solution is usually computed outside...

What does and observer inside of a collapsing shell observe? Lets say we have a shell of matter collapsing to a black hole. What would observers near the center see? How would the rest of the universe appear when, The shell is approaching the Schwarzschild radius? After the shell passes the...

One of the leading theories of physics is that forces are mediated by virtual particles. Well, it seems as though these virtual particles can escape a black hole. Why is that?

Suppose you have two small masses spiraling into a black hole in similar trajectories. Does the mass of these small masses make any difference to the rate of inspiraling? What if one is a thousand times more massive than the other...

The paper is The Volume Inside a Black Hole (0801.1734) Looking at the abstract, I have a question already. It is stated: Because the light rays are orthogonal to the spatial 2-dimensional surface at one instant of time, the surface of the black hole is the same for all observers (i.e. the...

There are a number of videos of simulations of this. They all end with complete blackness. This seems wrong to me because light is concentrated by the black hole. There should be more light closer to the center. On second thought I guess it is OK. While the observer would encounter more...

Was just wondering if there is anything fundamentally preventing a system of planets being in permanent orbit around a black hole, without ever spiralling in. Assuming that the black hole doesn't absorb any significant amount of additional mass. Of course I know it wouldn't provide any energy to...

I apologise for my very limited understanding of quantum physics: my background is in General Relativity. A wave function is said to represent the probability of a particle being at some point in space/time, and I take that to mean that the probability of a quantum event is a density on...

Not sure how to mark the level, I know what the math in the Einstein field equations represents (stress energy tensor, Riemann curvature etc), but have no facility in doing anything with that math. so take 2 black holes, with say 100 solar masses. A is not spinning, B is spinning at...

So the theory is the center of a "black hole" is nothing more than a planetoid of incredibly dense material, and the black hole is just this planet's atmosphere for lack of a better description. Thoughts?

I have tried inserting in the above formula 2m for r, but I get a huge answer. The correct answer is ##1.28*10^9 N/kg## for person A and ##1.28*10^-3 N/kg## for person B. I also suspect that the formula for the Lorentz factor (##1/\sqrt{1-2GM/r*c^2}##) has some relevancy here, but I cannot...

About a year ago, I heard Leonard Susskind discussing how entangled black holes could create spacetime. As I was listening to Prof. Susskind describe the mechanisms for creating entangled black holes, and how these black holes might create their own spacetime, it occurred to me that if we were...

I'm wondering about some aspects about black holes (BH) and singularities, but since all my questions have to do mostly with quantum mechanics, I placed this thread in here. OK, let's assume there IS a singularity in the middle of a BH. A) Pauli exclusion principle (PEP) says no two fermions...