Black hole Definition and 999 Threads

Hello everyone! Im a newcomer, a teenager who has countless doubts with respect to relativity, quantum theory etc. But these two questions bother me the most: 1) Hawking radiation states that when the separation of a particle (eg. a photon) into charged particles happens in the event horizon...

According to Cosmic Sensorship Conjecture, naked singularities are prohibited in General Relativity. To my knowledge, naked singularity means light from the singularity can escape to infinity. In Reissner-Nordström metric, references say naked singularity appears only if ##GM^2<P^2+Q^2##...

so, i love physics, and the more i look the more it seems our understanding of things are wrong. no planet #9, but now a mysterious planet-nine, dark energy, etc etc. so my question probably lies in theory, but getting close to applied physics. planet-nine, from what i have seen, the...

"Before the big bang, scientists believe, the entire vastness of the observable universe, including all of its matter and radiation, was compressed into a hot, dense mass just a few millimeters across." Isn't this describing what the singularity of a black hole is? Black holes spin extremely...

The question is probably naive, but please don't block this thread before I get an answer... As far as I know, mass doesn't exist by itself, it is rather an "attribute" of matter or, let's say it is attached to particles...no particle = no matter = no mass. Now, inside a black hole...

It seemed to have been asked before, but I am still a bit confused. How is the velocity dispersion formed? Doesn't the evidence of dark matter tells us that the orbital speed is uniform in a galaxy? Is there a direction of dispersion? (e. g velocity gets larger to the core) And why does...

I know this is (probably) not going to work.. But I can't figure out why not :-) So here is the theoretical situation... Lets say we have 2 black holes that, somehow, we can perfectly control (velocity, position, rotation etc. etc.). Now, one of my probes accidentally falls into one of the...

I assume that, via scattering processes, the speed of light slows from that in a vacuum close to the centre of a black hole to zero at the event horizon. How is the gradient in its speed defined throughout this volume? Is an analogy with a sound wave reaching an interface appropriate?

I know that a black hole it's a singularity, but its event horizon gets bigger the more mass/energy you throw in. I thought that like dark matter interacts gravitationally with regular matter , it would interact with black holes, eventually falling , increasing the mass of the black hole and...

Earth will not fall into sun because it has inertia, keeping it in orbit. Even if it suddenly loses some inertia, it falls to a lower orbit and won't fall into the sun, as its inertia increase again due to conservation of angular momentum. So, if a thing fall near a black hole, shouldn't it make...

Since gravity is stronger the closer you get to center mass, is it possible some neutron stars have a black hole inside?

Its thought that nothing can escape a black hole (correct me if I'm wrong) but what happens when a larger black hole eats a smaller one? Could there be a instance in time where matter was torn out of the smaller black hole, past its event horizon and into the bigger one? Thanks!

What happens to the information about the objects falling into the black hole? Are their states somehow contained in the Hawking Radiation, and if so, how? Or is the information scrambled as it passes the EH?

What are black holes made of?

So let's say an astronaut was being sucked into a black hole and was able to escape spaghettification and all the death a black hole brings. Since black holes bend space-time itself, the astronaut would experience a differen't time zone than an outside observer (time is relative). The astronaut...

I’ve heard that the black holes that merged together and were the source that triggered gravity wave detector, have lost three solar masses. I understand to a very limited degree the basic notion of energy conversion like is the case in nuclear fusion/fission, annihilation, chemical energy...

I have a doubt about black holes. (I'm sorrying for my poor English.): 1 - Does an observer outside a black hole see forever (i.e. his lifetime) a object stationary when it reaches the event horizon? 2 - Or photons emitted by the object have its wavelength so red-shifted that the observer...

I know that string theory is not the flavor of the month, but the fuzzball idea circumvents the singularity which i think is a possible step forwards, is there any other theory that replaces the black hole singularity? https://en.wikipedia.org/wiki/Fuzzball_(string_theory)

As the tittle says, what is the mass of a black hole made of? Would it be made of the neutrons (and protons, electrons) that formed the earlier star? If no, what happens to those particles? Where do they go to after the black hole is formed?

I have to do a project on wormholes as solutions to the EFE, but I'm only and undergrad and have not yet taken any GR classes. I found a paper by Michael Morris and Kip Thorne with a derivation of a simple wormhole (many assumptions), but because of my lack of experience I can't tell what the...

In Hawking's "Black hole explosions?" 1974 letter to Nature, he states: My question is: wouldn't it be a terrible idea to generate a black hole of any size in a particle accelerator? http://www.nature.com/nature/journal/v248/n5443/abs/248030a0.html

If we were to take a microwave picture of a region of space said to have a black hole, would we be able to spot the black hole? Would we see a cold spot surrounded by a more hotter background?

So I have been watching COSMOS of late and in the 4th (I think) episode it states the possibility that other universes exist inside of black holes. I am aware of the immense strength of a black hole's gravitational pull so my question is this: Is there a material strong enough to resist it and...

I was reading about the pressure which is created when fermions are close of each other like in an electron gas, and I started thinking about what causes a black hole to form. Firstly, what happens when two fermions are forced to occupy the same place (and state)? By the exclusion principle I...

Hello to all. I've been trying to plot some graphs on Mathematica but I have faced some troubles so far. I am working on this paper by Lattimer on binary systems: https://arxiv.org/abs/astro-ph/0002203 I am trying to reproduce Figure 11 but something seems to go wrong. Here's what I have...

I have a story where an extremely advanced species has figured out how to produce and control kugelblitzes to a high enough degree that they can calculate the distance to an enemy and produce and fire one to explode at the target. Would there be any possible defense against such a weapon? I...

Hello everyone, I have a homework question for general relativity that is driving me nuts. It goes like this: An observer falls from rest at radius 10GM in the spacetime of a black-hole of mass M (in natural units). What time does it take for them to travel from a radius of 6GM to 4GM...

Is the theory that inflatons become dominate when gravity is strong (as in right after the big band) and when gravity is weak (as in driving the current expansion of the observable universe)?

I read that time dilation near a black hole's event horizon causes the infalling matter to "freeze" just above the event horizon and never cross it (in a distant observer's frame of reference). Doesn't the same phenomenon prevent the event horizon and singularity from being formed in the first...

Having discussed recently https://www.physicsforums.com/threads/rod-falling-radially-towards-the-center-of-a-mass.871169/ I'm now puzzled by the question, what happens to the rod during his radial fall through the event horizon and what would the hypothetical observer at ##r=2M## measure...

Hi! We have a projekt at the university and I have been thinking of creating a tiny tiny black hole after I've read some articles. I know one can create an artificial black hole with polarized laser pulses at a block of glass. And then one can measure a lot of things, usually hawkingradiation...

HI, I am looking to find a table of galaxies, their masses, types, black hole mass and dark matter content. Does anyone know if such a place exists anywhere on the internet? I'm trained in physics but is not a physicist - more a hobbyist. Any suggestion that you might have will be greatly...

I get that if you drop a tennis ball and a 10 lb medicine ball from the top of a tower they will both reach the ground at the same time. But what if I dropped a softball and a black hole with the radius of a softball (and the mass of a small planet)? Wouldn't the tremendous gravity of the black...

What happens to the Singularity when a Black Evaporates out of existence?

One of the enemies of SGI is the Ori, how does their black hole drive work?

In the paper Advanced LIGO they published some figures with chances. I would like to know how they know that there's a 90% chance for something to be in a specific value. https://dcc.ligo.org/public/0122/P1500218/014/PhysRevLett.116.241102.pdf paper here also have some other questions: What...

I have some questions about the first discovery paper that was released about gravitational waves, especially some of the maths. How did they: 1. Calculate the masses of the black holes that merged 2. Calculate the energy radiated away in gravitational waves 3. Calculate how far away the event...

If the Earth were hollow and we only had the shell could a black hole at the center take the place of all the mass and provide us with gravity to keep us from floating away?

The event horizon of a black hole appears to be plastered with 'afterimages' of everything that ever fell into it. (Because gravitational time dilation makes every such object appear to stop at the event horizon.) Now, suppose an event horizon is 'full' as defined by the Pauli exclusion...

According to this video, , if a black hole is large enough you could actually travel for some time within the event horizon without dying because the event horizon is so far from the actual singularity. So, assuming that's true, what would you see while you were inside the black hole? Here's...

I know that the accretion disk of a black hole gets hot enough for powerful emission of x-rays, but does that disk get hot enough for certain elements to fuse?

I refer to a Schwarzschild Black Hole as the simplest example, and a well defined time outside the hole, say the Schwarzschild time. The information paradox of BH deals with the question of what stuff has fallen into the hole, but I am not aware that it deals with the question when the...

There's lots of other questions on the forum about 2 black holes, but I think this is different - and I can't get my head around which outcome is consistent with GR. Black holes here are simplistic - non-rotating and let's assume with a tiny accretion disk; just enough grains of matter to allow...

What if our quantum eraser was a black hole? There's talk of event horizons preserving all the information that crosses them? Could we test this hypothesis by seeing whether or not black holes make good quantum erasers? Depending on the distance to the black hole - it might be hundreds...

I am a retired Physicist (Ph.D. U of NM 1977 in Astrophysics) who has spent most of his working life as a systems engineer and computer modeler. I now video conference Fridays with 4 friends to talk about the things we learned to calculate in grad school, but were never quite got the reason...

Hi I hope this is the right place for this questions, I started to think about this several years ago but had has a hard time finding anyone that's been interested in discussing this. As far as I understand time travel is not ruled out by modern physics at least if you limit yourself to go into...

If not why does the event horizon grow as more matter falls in?

Hello I am little bit confused about calculating Ricci tensor for schwarzschild metric: So we have Ricci flow equation,∂tgμν=-2Rμν. And we have metric tensor for schwarzschild metric: Diag((1-rs/r),(1-rs]/r)-1,(r2),(sin2Θ) and ∂tgμν=0 so 0=-2Rμν and we get that Rμν=0.But Rμν should not equal to...

The Schwarzschild Metric (with ##c=1##), $$ds^2 = -\Big(1-\frac{2GM}{r}\Big)dt^2+\Big(1-\frac{2GM}{r}\Big)^{-1}dr^2+r^2d\Omega^2$$ can be adjusted to a form involving three rectangular coordinates ##x##, ##y##, and ##z##: $$ds^2 =...

Near a black hole spacetime gets contracted, more and more as we get closer to it. At the event horizon the contraction (pull of spacetime towards the singularity) equals the speed of light, we could say that space is falling into the black hole at precisely the same rate as light trying to...