Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Eric A. Taylor on 30/05/2011 05:39:35
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Very often on NS they've talked about spinning black holes. A black hole is not an object in the way a planet or star is, rather it's a region of space so highly curved that it is curved back on itself, so what, exactly, is spinning?
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The singularity is spinning. At least according to current theory.
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If the singularity is of quasi zero dimensions then its peripheral speed must be superluminal ?
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If the singularity is of quasi zero dimensions then its peripheral speed must be superluminal ?
The potential for superluminal rotation has bothered me as well.
If I recall correctly, the concept of the ergosphere is that it is the region of space surrounding a rotating black hole where the rotation cannot be resisted. I believe the idea is that it is because the frame-dragging effect of the singularity causes space to be pulled around the black hole at or exceeding the speed of light in this region. Logically, the singularity must be spinning even faster than that...surely I've misunderstood something.
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Nothing will break the speed of light in a vacuum. We can only see to the Event Horizon though, so if you want you might assume that past that there can be some other region with different laws of physics. I think it was SoulSurfer(?) that gave a beautiful explanation of where the black hole is thought to get its 'rotational energy' from? It was the direct result of all objects 'spinning', with the angular momentum growing relative its 'size' as it compressed into a 'point'. As it becomes that 'point' all laws of physics breaks down, and its mass becomes 'infinite' as i understands it. The Event horizon is the last outpost for our laws of physics, at least as we can measure, so assuming this is right then it would surprise me if we ever found any black Holes that didn't spin relatively close to light. It must have to do with what mass they had before they collapsed and their 'spin' at that time.
Wonder if there are Black Holes of opposite spins?
I mean, if there was, and they were close enough we should have us a really cool lab for watching relativity at play:)
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If the singularity is of quasi zero dimensions then its peripheral speed must be superluminal ?
The potential for superluminal rotation has bothered me as well.
If I recall correctly, the concept of the ergosphere is that it is the region of space surrounding a rotating black hole where the rotation cannot be resisted. I believe the idea is that it is because the frame-dragging effect of the singularity causes space to be pulled around the black hole at or exceeding the speed of light in this region. Logically, the singularity must be spinning even faster than that...surely I've misunderstood something.
Nothing can travel through space faster than light.
The catch here is that space itself can travel faster than light.
An analogy I've seen used for (non-rotating) black holes is that of a boat on a river. There's a strict speed limit to how fast your engine can propel your boat with respect to the water right around you--that's analogous to the speed of light. But there's no speed limit on the flow of the water itself. If it's rushing over a waterfall at faster than the speed limit, you have no option but to be sucked along with it, even running your engines at full throttle. That's exactly what happens past the event horizon of a black hole. Space itself is being "pulled" at faster than the speed of light, and no matter how fast you go, you can't escape. The same thing is happening with rotating black holes.
In addition to black holes, we see this with the expansion of the universe. Distant galaxies are rushing away from us and at some point, they move away at faster than the speed of light due to space itself expanding at faster than the speed of light. A ship trying to reach them would never be able to do so since it's engines limit it to moving at the speed of light with respect to the region right around itself. There is no such limit on the expansion of space itself.
The other problem--that the mass at the singularity is moving faster than light--would actually be a problem, since that mass lives within space-time. I'm less sure on what happens there. I think most physicists would argue that it probably isn't actually a physical singularity--just that our theories break down there. I also don't know how fast it moves even if it is a singularity.
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Heh :)
JP
And now I will disagree, the EV is what lies inside SpaceTime as I see it. The rest are theories over what lies behind. That is, if we by SpaceTime define where all physics experiments are expected to deliver us the same outcomes? Although maybe? Maybe we can expect a same physics inside the EV? I like your idea on space although 'expansion' still gives me a headache, it should accelerate with greater 'areas', and very quickly become superluminous, as defined by measuring the stars 'moving' away? I don't see why we expect it to accelerate at a stately pace, as all new areas should be as ready for further expansion as any old 'space'? That one has disturbed me for quite some time.
And there's one more thing, to me it's the gravity that has 'directions', not space as such. And as 'gravity propagates' at 'c'?
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You lost me there, yor_on. What's an EV?
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Eh, Event Horizon :)
I know, everyone else define it as a EH, but I learnt to write it that way a long way ago, and old dogs :)
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And now I will disagree, the EV is what lies inside SpaceTime as I see it. The rest are theories over what lies behind. That is, if we by SpaceTime define where all physics experiments are expected to deliver us the same outcomes? Although maybe? Maybe we can expect a same physics inside the EV?
You can expect the same physics inside the event horizon. One of the points of GR is that it tells you what changes when you move from one place to another in space-time. It also tells you that you can't move out of the event horizon once you're inside of it.
Of course what goes on inside the event horizon isn't accessible experimentally, so it's "just a theory," but we also don't have 100% proof that black holes exist so they're "just a theory," too. The thing is that if you trust general relativity enough to work in other cases, why would you suddenly assume that it's wrong about what goes on inside the event horizon of a black hole?
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Simple, as I know it we have strong evidence for massive Black Holes, but we define the EV as the last place we can do any measuring on. Is that wrong?
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Simple, as I know it we have strong evidence for massive Black Holes, but we define the EV as the last place we can do any measuring on. Is that wrong?
That's true, but that's not exactly what you said earlier.
And now I will disagree, the EV is what lies inside SpaceTime as I see it. The rest are theories over what lies behind. That is, if we by SpaceTime define where all physics experiments are expected to deliver us the same outcomes? Although maybe? Maybe we can expect a same physics inside the EV?
Like I said, general relativity predicted black holes, and we have good evidence that they exist. General relativity also predicts what happens past the event horizon. Everything inside of the event horizon also lies in space-time, it's just not causally connected to whatever's outside the event horizon. If you say that general relativity doesn't cover what goes on inside a black hole, no one can prove you wrong, since they can't go in and send back information, but general relativity works so well at predicting everything else...
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Yeah JP, I know, and I keep changing my point of view on that subject. What we don't know is the singularity in itself, that mysterious 'point' whatever, depending on view. I agree that 'space' should be 'space' if we assume that there is a distance. So you're most probably correct, although the 'space' metrics will be different from the 'metrics' measured outside. Why I stop at the measurement is most probably a result of my new and wobbling definitions of 'interactions' as what will make the 'rules'. Before I have had no problems with associating the 'space' inside the EV with the 'space' outside it. But if I want to make sense of my idea of 'interactions' I will have to look at those we can measure first, and I guess that's also why I disagreed.
If you look at it that way then the question becomes if a Black Hole is a singularity or not, and what defines it. To me it's the EV that defines the limit of our knowledge, so to be consistent I will stop there :) But if the Hawking radiation ever get proved we will have a loophole, possibly? I'm still not sure on that one, it seems to depend on if entanglements can be said to bring out information to me? Entropy as such may be satisfied with the system getting back what it otherwise would have 'lost' irrecoverably but, isn't SpaceTime also a informational system, where all 'bits' have a defined relation? As I said, that's where my headache starts.
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Look at this way, how many combinations of one 'SpaceTime' can there be? Take all particles in one SpaceTime, do they have to be in certain combinations? What are the combinations? How can the Black Hole know those combinations? Is the Hawking radiation a 'communication' or is it just a 'entropic process', containing no information. Is the compositions of a SpaceTime infinite?
I don't know?
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Furthermore, why would entropy exist if it didn't fulfilled a informational need.
What is a equilibrium and why do we think SpaceTime need it?
Weird stuff.
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As things collapse gravitationally both energy and angular momentum (spinning) are conserved and this means that things spin faster. There is nothing special about crossing the event horizon when this forms. Very High coherent velocities of material will cause frame dragging and other gravitomagnetic effects but the critical factor in the Kerr solution to the equations is that it does not form a singularity at a mathematical point but along an orbital line sometimes called a "ring singularity". The material is essentially orbiting around its own centre of mass. This will be the state of ALL black holes because it is virtually inconceivable that a black hole will form without there being any angular momentum trapped within the event horizon. For a black hole of a given mass there is a maximum amount of angular momentum that it can contain before this ring singularity becomes too large to be contained within the event horizon and it is highly probable that most black holes are pretty close to this maximum. That is where the generally accepted analysis stops as far as I know.
It is I believe in theory possible for angular momentum to be "shed" by the creation of more particles. Now these are usually produced as particle antiparticle pairs so the net angular momentum is conserved but we are now aware of a small asymmetry in this relationship associated with the production and decay of K mesons. This allows there to be a slight imbalance between antimatter and matter and therefore an excess of angular momentum in one sense.
The conventional analysis can be taken further because as the material collapses towards this ring singularity angular momentum that is present in the two other dimensions than the rotation axis will also be conserved and this will cause the eventual state to become a toroidal surface or membrane.
I feel quite strongly that the conventional analysis (ie non quantum gravity) of this rotational collapse inside an event horizon could easily be taken much further and could produce very significant insights into both theories of everything and big bang theory. I am looking very hard for work in this field and have found very little as yet.
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Very often on NS they've talked about spinning black holes. A black hole is not an object in the way a planet or star is, rather it's a region of space so highly curved that it is curved back on itself, so what, exactly, is spinning?
There is talk here of a spinning singularity? How does that work like?
Singularities are like pointlike particles, they are without dimension and form, so there can be no classical spinning. If it were spinning, the singularity would not even be pointlike, it would be like a ring... in theory I believe.
A stagnant black hole, one which does not spin, does not have any magnetic fields. So a black hole spins because it contains magnetic fields. This is converted to an understanding of angular momentum for these exotic objects.
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The term "singularity" in reference to black holes is a very bad misnomer. For a non rotating (entirely theoretical) Swartschild black hole it just means, "we have not got a model to describe it" and not a mathematical point. For a "rotating" black hole, that is one containing angular momentum, that is all the black holes that have ever formed in our universe outside of the Cosmic Microwave Background observational limit, the Kerr solution applies, where the mass is in the form of a ring rotating at the velocity of light. This does in fact mean that any black hole can only absorb a limited amount of angular momentum otherwise the ring would get bigger than the event horizon.
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The term "singularity" in reference to black holes is a very bad misnomer. For a non rotating (entirely theoretical) Swartschild black hole it just means, "we have not got a model to describe it" and not a mathematical point. For a "rotating" black hole, that is one containing angular momentum, that is all the black holes that have ever formed in our universe outside of the Cosmic Microwave Background observational limit, the Kerr solution applies, where the mass is in the form of a ring rotating at the velocity of light. This does in fact mean that any black hole can only absorb a limited amount of angular momentum otherwise the ring would get bigger than the event horizon.
A very safe yet accurate reply.
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Had to pass on this beauty. Apropos theories and Black Holes. (http://www.skyandtelescope.com/news/124868524.html)
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Had to pass on this beauty. Apropos theories and Black Holes. (http://www.skyandtelescope.com/news/124868524.html)
Quote from the above article.
"At the heart of the quasar, however, lies a conundrum. The black hole that powers it is a monster. With a mass of two billion Suns, it strains currently accepted theories on black-hole formation and evolution."
I know this isn't the right place to say this but if it's a white hole, (a left over black hole from the previous antimatter cycle of the universe) all will become clear.
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according to Relativity the perception of time, how long it takes for a second to elapse, depends on the relative velocity of the observers. Two people travailing at different speeds will not agree on the amount of time that has passed. This is also true of gravity. A person standing on the surface of the moon will not agree with a person standing on Earth as to how much time has passed. Though it will take a very long time for them to notice the difference, the event horizon of a black hole has a much more powerful gravity field. So powerful that an observer at the event horizon would never say "when", as viewed from Earth, to signal the elapse of his first second. From that idea there should be no observable spin from outside the black hole.
This is just my own theory, but I imagine that if we were able to see below the event horizon of the black hole we'd see the surface of the star that collapsed to form it, still slowly (to us) collapsing. Should you decide to try and find this star you won't though. Assuming you can get passed the stretch you'd cross the event horizon after the star's surface, so you won't see it. However your own time perception will be slowed down. If billions of years later someone comes along and looks in they'll see you, still there just above the surface of the star.
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well, I think I can say one thing. If we assume that at the 'heart' of a Black hole there is a non dimensional 'singularity', then I believe it can have any spin it wants. It should behave just a strange as a photon at least. Both are 'point less' in main stream theory, so to speak. What differs them is the 'gravity' expected to act in their vicinity and that is then a result of a 'mass' getting so compressed (BH) that it surpass any mathematical descriptions, just as a photon seems to do in other ways.
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Please listen. At the heart of any rotating black hole there is NOT a non dimensional singularity! That has been proved and accepted by experts for many years, see my earlier post for details of the simplest model of its structure. Also there is absolutely no such thing as a non rotating black hole. So all this talk about mysterious non dimensional singularities at the middle of black holes is just rubbish talked about by "gee whiz" scientists and publicity idiots who really do not understand the theory. Scwartschild black holes are just so improbable that you might as well think that they don't exist. I really do wish that the text books would get it right.
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I like your idea in place, although the "expansion" still gives me a headache, it should speed up with larger "zones", and quickly became superluminous as defined by measuring the movements of the stars " on? I do not see why we expect to accelerate at a pace stately, like all new areas should be as ready for further expansion as any old "space"? If anyone has bothered me for some time.
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DM613 Your post is a slight re-write of Yo-rons post above.
Please stop this immediately! It is against forum rules and will result in a ban
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All the mystery of Black holes stems from the belief that matter cannot be compressed to a higher density than that found in a Neutron star, what is the evidence for this ?
Neutron stars can have an escape velocity c/2 so why not beyond the EV a Neutron star like object but of higher density
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I'm trying to understand what JP wrote there?
" Space itself is being "pulled" at faster than the speed of light, and no matter how fast you go, you can't escape. The same thing is happening with rotating black holes."
would that be a 'force' acting on SpaceTime? If you have one that can 'propel' space ftl, doesn't that imply that what creates that 'force' acting on space would be of a even greater magnitude? A 'infinite Gravity' in this case?
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A 'force' is one way to describe it, as in a waterfall (gravity) driving a mill, or wind doing the same. But it seems a limited case to me. If one want a 'field' then forces disappear. You need to add time to make them appear.
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Or if you like, a 'clock'. That's 'local'
Time is more of a property to me
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All the mystery of Black holes stems from the belief that matter cannot be compressed to a higher density than that found in a Neutron star, what is the evidence for this ?
The surface density of a neutron star is somewhere around the density of a Lead nucleus (just zillions of times bigger, physically).
If you want to see what happens under higher pressures (like the center of a neutron star), you have to do experiments like smash lead nuclei together in a particle accelerator, and just such experiments are done at the LHC. The problem is that with no gravity to confine the results, the lead nuclei shatter into a cloud of other particles, so physicists have to rely on theory.
One theory is that the "strange" quark might be stable under the immense pressure at the center of a neutron star. The strange quark has much higher mass than the more familiar light quarks making up protons and neutrons. So maybe a "strange star" could be denser than a "neutron star"?
See: https://en.wikipedia.org/wiki/Strange_star
There are a few experiments proposed or underway now that may be able to test these theories on neutron stars and pulsars:
LIGO has detected its first neutron star merger. In this case, the final product became a black hole, rather than a bigger neutron star. With increased sensitivity and more detections, astronomers should be able to place tighter bounds on the size of neutron stars before they collapse into black holes.
See: https://en.wikipedia.org/wiki/GW170817#Astrophysical_origin_and_products
I saw a proposed satellite-based experiment measuring the radius and density of neutron stars by studying the spectrum of light emitted by pulsars, with very high resolution in time. By monitoring the red and blue shift, the surface velocity can be measured, and the pulse rate gives the rotation speed. Together, it should be possible to work out the size of the neutron star.
Yet another method proposes to use neutron star seismology to study the interior of neutron stars.
See: https://en.wikipedia.org/wiki/Neutron-star_oscillation
But once the central density of a neutron/strange star reaches a critical value where the escape velocity exceeds the speed of light, current theory suggests that nothing can withstand the plunge into a singularity at the center of a black hole.