Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Poppa Oomowmow on 25/08/2011 21:40:28
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A black hole is often shown spewing matter out as it eats a star or something simlar. How is that possible if nothing can escape a black hole once it reaches the event horizon? Is that because the black hole is full and can't contain it all so it spits it out. If so, I guess something can escape a black hole. Thanks.
Mod edit: Please phrase your post titles as question. Thanks!
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The visible stuff is outside the event horizon - otherwise, by definition, we would not be able to see it.
Matter that comes close to the black hole is accelerated immensely causing it to heat up and radiate light from the visible spectrum upwards.
Just because an object (including interstellar matter) gets very close to a highly dense gravity source (even one that is a singularity) it doesn't automatically follow that the object will fall into it.
It comes down to vectors. If you've seen a golf ball skirt round the hole on a golf-course - seemingly against the laws of motion - you will have some idea of what happens to matter near to a black hole.
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This could degenerate into a highly debated topic. My view is that black holes do not exist, or at least have not been proven to exist. But I will concede that something is at the center of many Galaxies that is very massive and produces extremely powerful electromagnetic fields. And you are right, mega matter does escape from the center of Galaxies in a perpendicular stream to Galactic plane that travels, ALMOST, the speed of light. This is a distinct clue of what is actually happening in the center of many mature Galaxies.
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Ppprcrn - simultaneity and what we can see really breaks down and leaves normal intuition at the event horizon. An outside observer in an accelerated frame, which is what we would be in if observing, will see objects that have already passed through the event horizon almost frozen in time, massively red-shifted and smeared over the EH even after they have crossed the event horizon.
Soulsurfer (methinks) in a previous thread made the very good point that whilst in a simulation and in imagination stuff falls endlessly into the blackhole - in reality nothing/very little is heading directly at the incredibly small object and much will thus end up in a very small and fast, and destructive orbit.
Rob - per the other thread, whilst other solutions to the equations that satisfy observations might be found in the future, the best explanation at present is the existence of blackholes
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Soulsurfer (methinks) in a previous thread made the very good point that whilst in a simulation and in imagination stuff falls endlessly into the blackhole - in reality nothing/very little is heading directly at the incredibly small object and much will thus end up in a very small and fast, and destructive orbit.
In my own peculiar way, that was more or less the point I was trying to make as well - In terms of super-accelerated matter near to the E-H is what gives off the most energy but all the interactions of gigatonnes of matter getting whizzed round the central small infinite (can we truly say it's infinite?) gravity well is far more likely to go in other arced near-luminal-slingshots rather than into the hole itself.
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Quasar.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.starstryder.com%2Fwp-content%2Fuploads%2F2007%2F09%2Fquasar_simonnet.jpg&hash=d23f85d92228ba0b161568d43d09a14a)
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Fair, as black holes have not been proven not to exist. Someday, perhaps when mainstream science allows that gravity itself is an artifact of electromagnetism, it will bring new light to the 'black hole/super massive object' debate. Maybe the mechanics of the interior of these objects will show a singularity, maybe not. But what a wonderful journey it will be, to see the future discoveries yet to be made.
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Hawking radiation escapes from black holes. For a tiny black hole, such as those theoretically produced by the LHC, the Hawking radiation will evaporate all the mass in a tiny fraction of a second. For a supermassive black hole, it takes many billions of years to evaporate all the mass.
The stuff that we can see around a black hole is from masses colliding with each other as they approach the event horizon.
After matter crosses the event horizon, its gravity is still felt outside the event horizon. Whether gravity "escapes" from a black hole is a matter of semantics. In the language of general relativity, gravity is not a thing that can radiate; it is a property of space.
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If it has past the Event horizon, it has only HUP to lean against. and HUP doesn't discus macroscopic objects, yet at last, even though some might argue against that. But for very small particles uncertainty will allow them to tunnel even when passed that EV, as I understands it. All macroscopic trajectories passing it though should only have one way to go and that is in a 'straight line' into the center of that Black Hole.
The straight line here is a conceptual description of that 'space' it will find inside it, 'folded out', sort of :) No different from any light path described in SpaceTime. All paths are thought to be 'straight' from that point of view, although gravity shows them as bent to the observer.
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And what a lovely painting teknix.
Very cool indeed.
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Fract -
Is the LHC actually producing tiny blackholes? I thought that was a theoretical possibility when the energies involved were notched up much more than at present.
It is also worth remembering that the heat of the background means that any black hole worthy of the name is a net absorber of radiation and is actually growing in size and getting colder rather than evaporating and getting hotter (ie their blackbody equiv temperature is lower than cmbr).
GR predicts gravitational waves - which allow the radiation of gravitational energy at c.
Yoron -
Both HUP and quantum tunnelling apply to macro objects - but the maths and probabilities make it worth ignoring and near impossible to calculate
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Fract -
Is the LHC actually producing tiny blackholes? I thought that was a theoretical possibility when the energies involved were notched up much more than at present.
I shall edit my earlier post to insert "theoretically".
It is also worth remembering that the heat of the background means that any black hole worthy of the name is a net absorber of radiation and is actually growing in size and getting colder rather than evaporating and getting hotter (ie their blackbody equiv temperature is lower than cmbr).
Ordinary black bodies radiate or absorb radiation, depending on whether they are hotter or colder than their surroundings. A net emitter would grow colder until it matches the temperature of the surroundings——unless it contains an energy source. In the case of a black hole, I suppose gravitational contraction must be the energy source which is predicted to make it get hotter as it evaporates. The hotter it gets, the faster it evaporates and the faster it shrinks; shrinking under the influence of gravity makes it hotter still. BANG!
"Because Hawking radiation allows black holes to lose mass and energy, black holes that lose more matter than they gain through other means are expected to dissipate, shrink, and ultimately vanish. Smaller micro black holes (MBHs) are predicted to be larger net emitters of radiation than larger black holes; thus, they tend to shrink and dissipate faster." Wikipedia (http://en.wikipedia.org/wiki/Hawking_radiation)
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Whilst micro black holes are predicted to evaporate at ever increasing rate (it is positive feedback) - black holes that we actually think exist (ie 3-4 solar masses or more) are far colder than the background. FYG a blackhole of temperature 2.725k is about 10^-8 solar masses. Any actual blackholes that were created by collapsing stars will not even start evaporating till the background radiation of the universe is less than a hundred millionth of a degree above abs zero - and even then will take at least 10^69 years to evaporate
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Nope, give a experiment with a macro object tunneling and I will stand corrected though.
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Nope, give a experiment with a macro object tunneling and I will stand corrected though.
So Yoron no can do. As I said the probabilities are mindboggling, the chances of it happening in the lab are not worth considering - but the theory applies. There is no magic line where quantum events start happening because things are getting smaller, similarly no line where gravity stops applying - they just become so small and insignificant that we can ignore them.
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I know Imatfaal, the theory doesn't really stop at the microscopic plane. But for all practical purposes it seems to do just that, although there are some trying to show that it goes in all 'scales'.
What's interesting to me is why and where.
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I know Imatfaal, the theory doesn't really stop at the microscopic plane. But for all practical purposes it seems to do just that, although there are some trying to show that it goes in all 'scales'.
What's interesting to me is why and where.
I once heard Anthony Legett, a Nobel laureate, give a talk on the idea that quantum effects might, in fact, stop at some size/mass scale. I believe I've read that Roger Penrose has proposed that gravity causes quantum effects to collapse at around the Planck mass, but I could be mistaken about that.
The thing is that there is no good reason yet to assume that quantum effects do stop on some level. It would definitely be via some new mechanism, because as the theory stands, quantum effects should still exist for large objects--it's just the large numbers of particles involved that makes things look classical to us.
Still, I think it's an interesting question.
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What's interesting to me is why and where.
Oh Yes without doubt its interesting. As JP said above there are serious people talking about there being different regimes - but as JP also said "there is no good reason yet to assume" that there are transitions and cut offs. I just feel that the current system with quantum effects at very small sizes, with GR at cosmological scales and each resolving to a classical limit in between is highly indicative of a more general plan that encompasses both - whether this will be found through string theory, another exotic theory, or something currently unthought of we just dont know
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Yes, it's a very interesting question :)
And I didn't mention the most important question there either.
How?
If we assume that there is a 'arrow of time' existing through all of what we see macroscopically, pointing only one way as far as we can measure. Then 'scale' definitely will have to do with it as I see it.
You can think of it as a composite, consisting of one 'layer' of QM interwoven at all points with one layer of 'macroscopic effects'. As far as we observe macroscopically they don't meet. QM stays in each point where it, from our point of view, doesn't 'exist'.
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BTW Imatfaal. I'm partly wrong in saying that we can't observe macroscopic effects of QM.
"When liquid helium becomes a superfluid, at temperatures below 2.176K, Chan noted, it can flow without friction. The lack of friction means the superfluid has no viscosity. If a droplet is caused to rotate inside a container, it can continue to rotate forever as if it were in a vacuum. To Chan, these are examples of macroscopic quantum phenomena -- quantum mechanics operating on a macroscopic scale."
Well, yes. but it is also at a temperature that is near one of the 'borders' of SpaceTime, and with a 'material' that becomes weirdly 'bosonic' in its composition. Still, it's a macroscopic behavior, but of something having become a 'super atom' containing no distinguishable parts (atoms) any longer. But scale wise its possible to do it macroscopically. So although tunneling is an effect I've never heard of macroscopically, we might still be able to produce it although then laboring close to the borders of SpaceTime, as it seems to me.
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It's almost like QM in some mysterious way have a existence outside what we can observe, also possibly unbound by our classical arrow. And the only thing combining those two is the way we 'scale it up'.
Statistics is a very powerful tool.
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Maybe it has to do with where we are in 'time'.
Assuming there is a arrow of time for the whole of SpaceTime, also assuming a beginning, then at that beginning QM must have ruled, if we use our standard for finding such effects, namely 'scale'.
Maybe everything was possible at that first state, but as it 'inflated' it also cooled down to a possible SpaceTime, with a arrow and measurable 'scales' becoming. This is assuming that scale is what QM is about. Then we have temperature also, and there I don't know. Absolute zero is quantum mechanically a place of absolute uncertainty, meaning that there alway exist a possibility of 'motion' 0r 'fluctuations' invalidating any such concept. And if it becomes very very hot then? What transitions happens then? It's not unreasonable to assume a symmetry to temperature(motion/fluctuations) existing both ways. And as there can be no classical definition coming true of a state where all motion has 'stopped' so there might be transitions the other way when very hot that will change it into another state?
It's incredibly interesting, and confusing, symmetries.
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But there is one more thing, if motion is measured by a ruler and a clock, then calling that state where we can't define what's happening, other than statistically (based on repeatable experiment in time), a 'motion' or 'fluctuations' must be incorrect. It is not a motion, because we cannot measure it. And to have it 'fluctuating' introduce the concept of a measurable duration. I would rather call it a state of becoming, only measurable after it arrived.