Black hole Definition and 999 Threads

By a clock outside the event horizon, things slow down as they approach the event horizon and never quite reach it. From an outside perspective, there shouldn't be anything inside a black hole. Everything should be just outside the event horizon. There shouldn't be a singularity.

According to the General Theory of Relativity, time does not pass on a black hole, which means that processes they don't work either. As the object becomes heavier, the speed of matter falling on it for an observer on Earth will first increase, and then slow down, due to the effect of time...

Hi, I'm trying to derive the equation (14) ##a^r = \frac{a u^r e}{\sqrt{e^2 + g_{tt}}}## from this article No Way Back: Maximizing survival time below the Schwarzschild event horizon and my algebra is really messy, so I'm wondering if I made some mistakes. The authors say: "With the above...

hello,im kinda new to this field,and i have few questions regarding the universe what is dark matter, and how is it related to keeping one galaxy together?like whats its origins and maybe possibly could it be from something else?not necessarily a black hole, maybe another object we havent...

I have this problem: First of all, I would like to have an equation for the proper time. I was using the Eddington-Finkelstein coordinates in the Schwarzschild metric : $$ds^2 = - (1-\frac{2M}{r}) dt^2 + 2dtdr +r^2 d\Omega^2$$ Knowing that the observer falls radially, thus ##d\phi = d\theta =...

Hello everyone!:) This is my first post on here. I'm having trouble understanding what is real for Alice. I looked at different physics websites and there seem to be only a few questions addressing this some of which I don't understand. I thought maybe I'll get some clarity here if I ask my own...

It is often seen in research papers that values of quintessence state parameter $\omega$ is taken between -1 and -1/3. However $\omega=-1$ corresponds to the cosmological constant and -1/3 corresponds to dust phase. Why these two cases are excluded in studying BH extended phase space thermodynamics?

You know how people say that nothing can escape a black hole because gravity is faster than light at the event horizon? Well, I’m going to show that, in fact, you can’t even get to the event horizon. Time is slower near a black hole from an outside perspective, but from inside, time actually...

Hi, I'm wondering if it is possible to calculate the volume of a black hole using the Schwarzschild metric. After computing the volume I get the follow integral: $$V = 4 \pi \int_0^r \frac{1}{\sqrt{ (1- \frac{r_s}{r'})}} r'^2 dr$$ This integral diverges at the upper bound. The only way I...

I need help on an idea I have had for the last couple of months. I am not an astrophysicist so I am here to get some direction on whether this makes sense or not. It is well known that the fabric of space can ben bent by the objects in it. Planets and astreoids can only bend the space-time so...

I am a physics student and I have a question: What happens to light when it passes near a very massive object, like a star or a black hole?

link: "Particle Creation by Black Holes", S. Hawking [FONT=arial]Hello all, I just want to know the meaning of the text followed by equotation 1.2. Especially if the flat or asymptotic flat region could interpreted for Minkowski-Spacetime at an arbitary Point in M or just at the...

I'm bored out of my mind and while watching a PBS spacetime video I had an idea. What if black holes are hosts to universes in between the singularity and the event horizon ? It's 3am so pardon my lack of precision, but chatGPT did formulate my idea pretty well in this conversation : Link to...

Shahar Hod is an Israeli physicist who has specialized in heuristic reasoning about the properties of quantum black holes, one might say in the tradition of Bekenstein and Hawking. By this I mean that, rather than trying to develop a detailed theory of quantum gravity, he has tried to obtain...

I have a question about the evolution of the universe in reverse. I understand that three things happen: 1- The real black holes of the universe in reverse do not accrete, they expel. 2-The universe contracts. 3-The universe reaches the hot and dense state. Is this correct? Points 2 and 3 are...

The other day, a friend and I had a discussion about black holes, namely how the density of a body affects the process of its transformation into a black hole. My friend and I have too little collective knowledge in the field of theoretical physics regarding black holes, so the discussion has...

Suppose an asteroid hits a static black hole almost tangentially, does this cause rotation of the black hole?

If I have any misconceptions or misunderstanding kindly point it out and explain it to me.

How can gravitons escape a black hole? Presumably they must, in order to have an external gravitational effect. I'm sure this is a naive GR-based model of a BH. I guess a BH is a different animal in the QM world?

I have been thinking this for quite a few time. At this point we know that our universe is going through an accelerated expansion phase. I was also doing some work on blackhole thermodynamics, specially P-V criticality, heat capacity, Joule Thomson expansion, heat engine etc. These...

Does light bend around black holes like a satellite "slingshotting" around Jupiter? If so, would there be a need to recalculate the true positions of stars from all the bending of light around black holes on the way to the telescope?

Hi All Considering the relativistic kinematic and mechanical effects of the high gravitational fields of a black hole on an explosive device of X megatons, equipped with a timer to explode in a terrestrial time T after pulling the trigger, would it be possible to send this device directly to a...

One of the nitpicks about Interstellar the film is the tidal wave on Miller's Planet. Miller's Planet is deep in the gravity well of a monster black hole. Lot's to unpack there but the upshot is that there's a tidal wave that sweeps around the planet shaped like a tall, very steep mountain...

I was looking at the proof of zeroth law of thermodynamics from the original paper by Bardeen, Carter, Hawking, which can be found here. Now, we have the Killing vector which is the generator of the horizon, we call it ##l^\mu##, and auxiliary null vector field ##n^\mu##, which we define to be...

I want to show that it is impossible to construct a timelike curve between two points on the event horizon of a black hole. This should be an obvious fact, for example, by considering any particular model of a black hole, one can go to coordinates that extend over the horizon and by observing...

Black holes are expected to evaporate due to Hawking Radiation [1]. As they would lose mass with this process, their radius would also shrink. According to Hawking temperature [2], since it is inversely proportional to the mass of the black hole, as the radius (or the mass) decreases, the black...

Consider a halo made up from massive and stable particles like neutrinos* (let's not consider protons which, although we don't have any experimental evidence showing that they are unstable and decaying, there are some GUTs proposing theoretical mechanisms where they could decay over extremely...

According to a recent paper (https://arxiv.org/abs/2305.18521) (explained here: https://www.ru.nl/en/research/research-news/eventually-everything-will-evaporate-not-only-black-holes) every massive object in the universe will evaporate in a similar way into Black Holes through Hawking radiation...

https://en.wikipedia.org/wiki/Einstein_field_equations If we study when the sun bent the light of the stars behind it, which above terms have the largest influence, and which can be neglected? (I think that the third term can be neglected for such phenomena.) And what changes when we are close...

When objects/galaxies (particles and antiparticles) move across the cosmological event horizon, do they leave behind an “image” on the horizon, such that when we look at the image, we can tell what kinds of objects went through to the other side (ie, we would know information such as the mass...

I have read widely about spacetime but not deeply. I am not good with high mathematics. I am aware of and comfortable with the concept: “matter tells spacetime how to curve, and curved spacetime tells matter how to move.” But not much deeper. This is a thought experiment. Is there an equation...

This question was not my idea. I heard it while watching a YouTube video hosted by a celebrity astrophysicist and a comedian. This astrophysicist answers the physics questions of his Patreon supporters, and one of the supporters asked him about the spaghettification of quarks. I'm paraphrasing...

There is good enough experimental evidence for the existence of a Photon Sphere. Is there clear unequivocal experimental evidence for the existence of an Event Horizon ?

Here is first principles consideration: Since it is a black hole there is an event horizon where timelike worldlines can enter but not exit, this is what defines a black hole instead of a white hole. When evaporation is finished there is no more event horizon, this is what defines the...

If, from an outsider's perspective it takes an infinite amount of time to cross the event horizon, but a finite amount of time for the black hole to evaporate, how does that look like from the perspective of the falling observer. For that matter, how does it look like from the perspective of the...

The level may be higher that Intermediate but I use that in the hope that I'll be able to understand the answer. I moved it here as it didn't really belong in the other thread. Feel free to move it further. I admit I haven't yet read the paper in it's entirety but I hope you'll bear with me. I...

So I just had a question. In a Netflix documentary, they showed these people trying to simulate the conditions of a black hole by having a vortex in a pool of water. they said that light cannot pass through the hole and the physics around is essentially adjacent to the event horizon and what...

I realize that something I thought I understood about a beacon approaching a black hole I am unsure of. My hypothetical - I am at a safe distance from as simple a black hole as it makes sense to discuss. I launch a beacon at it, and I calculate that in one hour of my own proper time the...

https://svs.gsfc.nasa.gov/14576 (NASA's Goddard Space Flight Center/J. Schnittman and B. Powell) Cool!

I'm studying if there is some way to avoid black hole evaporation, even if it requires a very special set up of conditions... Theoretically, extremal black holes (both for rotating Kerr and Reissner-Nordström ones) would avoid evaporation as they would not emit Hawking radiation. Since...

I am a writer completing a science fiction novel involving a four foot diameter black hole (with approx 1.5 times the mass of Saturn) At one point in the story, this small black hole has sling shot past the sun, is headed outward toward the Kuiper belt & Oort Cloud. As it moves, the sun's...

When looking at depictions of black holes, we often get illustrations of a two-dimensional space-time where everything spirals into a "hole". The hole then leads to a singularity usually depicted as a funnel shape. Then there are images of black holes shown as spherical with glowing rings...

Black holes accrete mass around them and it falls gradually up to the even horizon where mass is trapped by the black hole forever. However, the rate of mass falling from the accretion disk to the black hole ranges from being very fast to very long-lived, depending on various conditions...

Homework Statement: I am a writer completing a science fiction novel involving a four foot diameter black hole (with approx 1.5 times the mass of Saturn) In my novel, the black hole is being drawn toward our much more massive sun. I assume the black hole would begin to consume plasma/energy...

Roy Kerr has recently written a preprint (https://arxiv.org/abs/2312.00841) in which he strongly argues against the possible existence of singularities inside Black Holes. I've read that his arguments are really powerful and that he is most likely right. But, does it mean that Kerr has...

from what I understand it is believed that information is preserved but we are still working out how exactly, is this the case?

We know that there is no law of conservation for the entropy. It is quite the contrary: If we have a closed system without exchange of heat the entropy cannot get less. It will reach the max. If we have not a closed system but a stream of entropy only into a system, the entropy will increase...

So, I was thinking, the most massive black holes are expected to evaporates in roughly a googol year. Fine. But I was reading that if protons are stable, every planet and non black hole star remains are basically expected to turn into iron star from quantum tunneling after mind numbing time on...

As I understand things if you're hanging out in your space suit some distance away from a black holes event horizon and your buddy decides to dive on in you will never see him cross the event horizon. You'll see him approach the event horizon but never cross it. It would seem the time needed to...

Of course neither a single Schwarzschild nor a single Kerr black hole, nor a pair of these has an emission spectrum, other than the Hawking one. (Nordström and Newman holes must have it while in binaries, but they are not common). But not having emission spectrum does not rule out having...