Black holes

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ramparts

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Well, the point of what you posted is exactly that no information is escaping - the flux is there from before the charges entered the horizon. So if the charges were to suddenly vanish (for some reason - that's not physical, but let's pretend) after entering the black hole, the outside world wouldn't know, and the electric field would remain.
 
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5hot6un

Guest
So the singularity is mathematical. What are the practical implications in terms a non scientist can understand?

What exactly is believed to happen to the protons and neutrons in a black hole? Are they reduced to sub-atomic particles? Does science know?

Infinitely dense, to me, means absolutely no space between particles.

We know that stars fuse atoms into bigger atoms.
We know that elements larger than iron absorb more energy than they release when fused.

Now allow me to speculate (and show my ignorance)

So the heavier elements and their energy absorption during fusion seem to be the mechanism by which all stars "die" The type of death is determined by the amount of mass present. On one end of the spectrum, the end result is the white dwarf. On the other end, the black hole.

Why then do we need to think of a black hole as anything more than a big dead star remnant made up of regular atomic particles crammed tightly together?
 
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ramparts

Guest
Well, because the gravitational force of a black hole will overwhelm any possible forces between atoms or subatomic particles. In fact, that's by definition - a black hole is an object where the escape velocity is larger than the speed of light, or the fastest speed at which anything can travel, meaning nothing can escape the black hole's pull. That means that no forces can counteract the black hole's gravity. So, general relativity (which is quite well-tested) predicts that everything should collapse to literally a single point.

That said, this contradicts both common sense and quantum mechanics. We know that whatever happens deep inside a black hole (at a much smaller than atomic level) has to obey both GR and quantum mechanics, and we have no idea how the two theories act together in such extreme cases, so it is entirely possible that quantum effects prevent the formation of a true singularity.
 
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5hot6un

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ramparts":1tzqg52j said:
Well, because the gravitational force of a black hole will overwhelm any possible forces between atoms or subatomic particles. In fact, that's by definition - a black hole is an object where the escape velocity is larger than the speed of light, or the fastest speed at which anything can travel, meaning nothing can escape the black hole's pull. That means that no forces can counteract the black hole's gravity. So, general relativity (which is quite well-tested) predicts that everything should collapse to literally a single point.

That said, this contradicts both common sense and quantum mechanics. We know that whatever happens deep inside a black hole (at a much smaller than atomic level) has to obey both GR and quantum mechanics, and we have no idea how the two theories act together in such extreme cases, so it is entirely possible that quantum effects prevent the formation of a true singularity.
I appreciate your patience with me. I realize that we touched on your point in another thread as well.

What I am trying now to understand is at what point does normal fusion give way to atomic particle annihilation. Is that what GR predicts? Regular atomic particles squeezed so hard they implode? Quark soup? Or one really big neutron? Since we can't see inside a black hole, could we not turn to the next smaller objects like neutron stars for answers?
 
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ramparts

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Nah, GR is a theory of gravity, it doesn't tell you anything about particle annihilations and the like ;) That's the realm of quantum field theory, which we have so much trouble mixing with GR.

I'm not sure what your question means, about fusion giving way to "atomic particle annihilation" - particularly, I don't see where you think particle annihilation (which really has nothing to do with atoms) fits. Neutron stars will definitely give us an idea of what happens to matter in such extreme conditions, but ultimately the inside of a black hole is a different game because gravity is believed to overwhelm everything. Physics as it stands now is ill-equipped to answer those questions.
 
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5hot6un

Guest
ramparts":2gut5whp said:
Nah, GR is a theory of gravity, it doesn't tell you anything about particle annihilations and the like ;) That's the realm of quantum field theory, which we have so much trouble mixing with GR.

I'm not sure what your question means, about fusion giving way to "atomic particle annihilation" - particularly, I don't see where you think particle annihilation (which really has nothing to do with atoms) fits. Neutron stars will definitely give us an idea of what happens to matter in such extreme conditions, but ultimately the inside of a black hole is a different game because gravity is believed to overwhelm everything. Physics as it stands now is ill-equipped to answer those questions.
I think we are delving into areas for which there is no known answer.

In a run of the mill star, atoms are fused. Protons and neutrons persist. No problem. This is what we know happens to normal matter under extreme pressure. And this is what I would suspect to go on in the black hole. The atomic particles remain atomic particles.

I am under the impression that physicist believe that the atomic particles are annihilated. If this is true, I am sure there is good reason.

If the atomic particles persist, the black hole is a giant atom unable to decay becasue of gravity. A super element.

If the atomic particles are annihilated, the black hole is a big particle. A super-neutron?

I am way out of my league I know.

just.... cannot.... resist.... thinking.... :D
 
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MeteorWayne

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I think that one problem is the use of the term annihilated. That has a specific meaning in matter/antimatter events. That is not the same as being smooshed (very technical term :) ) into non existence as is suspected to happen in the extreme conditions of a black hole.
 
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ramparts

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Nope, atoms definitely wouldn't stay put - the forces that it takes to hold atoms up would definitely be overwhelmed by the black hole's gravity. There's no way around that. The only possible way out of a true singularity forming is through quantum gravity, which takes place at the so-called Planck scale - a size scale many, many orders of magnitude smaller than the scale of atoms.
 
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skeptic

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ramparts":3rggq176 said:
[snip] A black hole can be a big conducting sphere, which attracts/repels using the electric force, rather than the magnetic.
Ramparts, I'm curious about this statement. Which theory says that a black hole can be a big conducting sphere? I'm also curious how it is that an object can fall through the event horizon but leave its gravitational or electrical field behind.
 
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ramparts

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Skeptic, see this post from earlier:

5hot6un":xsqkrlld said:
skeptic":xsqkrlld said:
In the sense that a gravitational field causes a curvature of spacetime and by removing the gravitational field the curvature is returned to zero, spacetime is elastic. My post however wasn't about spacetime being elastic but about it becoming plastic beyond some gravitational field strength and not returning to zero curvature when the gravitational field is removed.

I was suggesting that perhaps the reason the curvature hasn't returned to zero is because the gravitational field hasn't been removed i.e. the matter is still at the event horizon.
Indeed! According to wiki; "a black hole has only three independent physical properties: mass, charge, and angular momentum."

Interesting to me is "a charged black hole repels other like charges just like any other charged object, despite the fact that photons, the particles responsible for electric and magnetic forces, cannot escape from the interior region. The reason is Gauss's law, the total electric flux going out of a big sphere always stays the same, and measures the total charge inside the sphere. When charge falls into a black hole, electric field lines still remain, poking out of the horizon, and these field lines conserve the total charge of all the infalling matter. The electric field lines eventually spread out evenly over the surface of the black hole, forming a uniform field-line density on the surface. The black hole acts in this regard like a classical conducting sphere with a definite resistivity."

Am I understanding this correctly? It's a big magnet?
Can't say I completely understand the electrodynamics of black holes myself, but this explanation - that the electric field lines remain after the charge has crossed the horizon - seems reasonable to me. I suppose I'd need to learn some field theory to be able to say more.
 
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skeptic

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ramparts":1hlt8pkn said:
Can't say I completely understand the electrodynamics of black holes myself, but this explanation - that the electric field lines remain after the charge has crossed the horizon - seems reasonable to me. I suppose I'd need to learn some field theory to be able to say more.
My understanding of black holes is far from complete as well but to have electric field lines in the absence of electric charge and gravity in the absence of matter does not seem reasonable to me. I have a mental picture of the electric field lines protruding from the event horizon like so much hair but of course black holes have no hair.
 
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ramparts

Guest
Actually, I think you just answered your own question :) Clearly a black hole's mass is beyond its event horizon and thus unable to communicate with the world outside, but the black hole still exerts gravity outside the horizon, no? In the same way, a black hole with charge will still have an electric field outside the horizon.

Think about it, if you want, using Gauss's law. Take a charge outside the horizon and draw a Gaussian surface containing it and the black hole. The electric field outside that surface won't change, due to Gauss's law, as long as the charge doesn't leave the enclosed space (as you can agree it doesn't).
 
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5hot6un

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ramparts":2ippcduf said:
Actually, I think you just answered your own question :) Clearly a black hole's mass is beyond its event horizon and thus unable to communicate with the world outside, but the black hole still exerts gravity outside the horizon, no? In the same way, a black hole with charge will still have an electric field outside the horizon.

Think about it, if you want, using Gauss's law. Take a charge outside the horizon and draw a Gaussian surface containing it and the black hole. The electric field outside that surface won't change, due to Gauss's law, as long as the charge doesn't leave the enclosed space (as you can agree it doesn't).
I think I read that BHs radiate heat too.

Back to my line of questions regarding atomic particles; I am left wondering if it takes a black hole to 'squish' a proton or neutron into... whatever it would be (I used the term annihilated.) Or does this occur in smaller things like Neutron stars as well?

And what is the term to describe squishing a proton/neutron with gravity? How much E would that release? What would would you call the remnants? Why does my dog hunch some people's legs and not others? :lol:
 
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OleNewt

Guest
And what is the term to describe squishing a proton/neutron with gravity? How much E would that release? What would would you call the remnants? Why does my dog hunch some people's legs and not others?
1. Fusion
2. Lots. More than fission, I think, but I might be confusing the input/output ratio with the total amount of output.
3. Not sure what happens in a fusion process, but in fission if I remember some neutrons break off and go smashing into other atoms, starting a chain reaction.
4. it's a display of dominance, and the leg just a handy and accessible piece of flesh from the invader. By all means, though, continue teasing them about their choice of companion. :mrgreen:
 
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5hot6un

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OleNewt":3d0v83zz said:
1. Fusion
2. Lots. More than fission, I think, but I might be confusing the input/output ratio with the total amount of output.
3. Not sure what happens in a fusion process, but in fission if I remember some neutrons break off and go smashing into other atoms, starting a chain reaction.
4. it's a display of dominance, and the leg just a handy and accessible piece of flesh from the invader. By all means, though, continue teasing them about their choice of companion. :mrgreen:
Fusion is when you squash atoms together to make bigger atoms. Fission is breaking atoms apart. I get that.

What we are discussing is what happens to protons and neutrons in a black hole. Apparently they are squashed into a state where they are not longer protons or neutrons. This is not fusion or fission. It's something else entirely. And beyond what I can imagine. :?

The dog picks on one friend exclusively. Strange. :?
 
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skeptic

Guest
ramparts":2ioovce7 said:
Actually, I think you just answered your own question :) Clearly a black hole's mass is beyond its event horizon and thus unable to communicate with the world outside, but the black hole still exerts gravity outside the horizon, no? In the same way, a black hole with charge will still have an electric field outside the horizon.
This I think is the crux of our difference of understanding. To me it is a paradox that a black hole's mass can be "beyond its event horizon and thus unable to communicate with the world outside, but the black hole still exerts gravity outside the horizon". Exerting gravity outside the event horizon IS communicating with the world outside. That a black hole has mass or charge is the best indication that the matter has not passed through the horizon.

ramparts":2ioovce7 said:
Think about it, if you want, using Gauss's law. Take a charge outside the horizon and draw a Gaussian surface containing it and the black hole. The electric field outside that surface won't change, due to Gauss's law, as long as the charge doesn't leave the enclosed space (as you can agree it doesn't).
But it does leave the enclosed space as you mentioned above. The inside of an event horizon cannot be considered part of our universe. If electrostatic attraction and repulsion are cause by an exchange of virtual photons, once the charged particles have passed through the event horizon, where would those photons originate? ...from inside the event horizon?
 
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ramparts

Guest
I don't know what to tell you. Why can't the inside of the event horizon be considered part of our universe? There's nothing special about that region except for some communication issues.

As for your first point, are you claiming that when black holes have gravitational fields, it's only from mass that's outside the horizon? You realize that's patently untrue, right?

The field theory question is one I'm not equipped to answer. At that point I tell you, if you think that a century of scientists are wrong, go publish a paper about it ;) But understand that this would also necessarily involve you making the claim that black holes don't have gravitational fields, which seems untenable.
 
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darkmatter4brains

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ramparts":1r8cmgi8 said:
The field theory question is one I'm not equipped to answer. At that point I tell you, if you think that a century of scientists are wrong, go publish a paper about it ;) But understand that this would also necessarily involve you making the claim that black holes don't have gravitational fields, which seems untenable.
That is a good point he's raising though and Im failing to come up with an explanation as well. If a black hole is an area where nothing can escape, this should include gravitons, which is the particle that is supposed to mediate the gravitional force. If the mass is inside the event horizon, the gravitons should be unable to get out.

Now, if there were NO gravitons in reality, and gravity truly was just a curvature of spacetime, this doesn't seem like a problem. But, gravitons seem to be a popular way to go due to the success of other QFD theories.

One last catch - aren't most force-mediating field-quanta particles typically virtual particles?? There could be some subtelty here we're all missing that makes this a moot point.
 
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ramparts

Guest
Oh, I agree it's an interesting question. I'm sure an answer exists, but I haven't taken any QFT so I wouldn't know :) But the alternative is black holes having no gravity, which is just wrong.
 
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skeptic

Guest
ramparts":2wyir7uk said:
I don't know what to tell you. Why can't the inside of the event horizon be considered part of our universe? There's nothing special about that region except for some communication issues.

As for your first point, are you claiming that when black holes have gravitational fields, it's only from mass that's outside the horizon? You realize that's patently untrue, right?

The field theory question is one I'm not equipped to answer. At that point I tell you, if you think that a century of scientists are wrong, go publish a paper about it ;) But understand that this would also necessarily involve you making the claim that black holes don't have gravitational fields, which seems untenable.
I am not claiming that a century of physicists are wrong, merely trying to understand some aspects of black holes I never can find discussed anywhere.

If the gravity of a black hole is caused by the mass in the singularity and if the singularity is in the future of everything inside the event horizon, then the gravitational force or the cause of the curvature of spacetime would have to travel backwards in time to reach the event horizon, would it not? The same would be true of the virtual photons not to mention the problem of their escaping the black hole.

I'm not suggesting that black holes do not have any gravity, I just don't understand how that gravity could escape from inside the event horizon. How would the perception of a black hole be any different if all the mass were piled up in the infinitely contracted spacetime at the event horizon?
 
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skeptic

Guest
darkmatter4brains":17klzdlw said:
Re: http://helios.gsfc.nasa.gov/qa_sp_bh.html#gravitons

The author makes the point of the electrostatic field is constant and therefore does not convey any signal. However this may not always be the case.

If a charged particle, traveling at nearly c, were to encounter the event horizon tangentially and once it crossed the event horizon, spiral towards the singularity, what would an outside observer see? Would he see the electrostatic lines of flux frozen at the point the charged particle crossed the horizon resulting in a higher flux density at that point than any other, would he see the lines of flux rapidly orbit the event horizon (from the inside) a few times before becoming stationary or would he see the lines of flux instantly take on the unchanging value it will have at the singularity before it has even had a chance to reach the singularity?


Re: http://curious.astro.cornell.edu/questi ... number=264

The author writes: "The field can also be thought of (in classical mechanics) as a "fossil field," generated by the continuously collapsing star which, to an outside observer, never actually crosses the event horizon due to time dilation."

If the collapsing star which, to an outside observer, never actually crosses the event horizon, would not that alone explain the black hole's gravity and charge?
 
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Couerl

Guest
Hmm.. I'm a little lost here, but I am curious if it is or would be possible to measure the radius of the event horizon through outside observation? Is there a practical, measurable, physical disk of nothingness that we can see in the center of our own galaxy or perhaps another or does light simply curve all around it to make it appear or look like a disk?

I've never really understood how far out the singularity can "reach" out with its event horizon, perhaps a few million kilometers? Perhaps an AU? Perhaps many?

TIAFAI
 
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ramparts

Guest
DM, those are some good links. Thanks!

Couerl, you could definitely measure the event horizon through observation. One possibility is to find a black hole that happens to be in front of some large source, and see where there's no light. Another is to measure, in a black hole that's accreting, the radius at which the disk stops - the innermost stable circular orbit (ISCO). That's mathematically related to the event horizon. Those are just a couple of ways. They both involve some very good technology, though.
 
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