Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 03/03/2008 16:42:41
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What happens to all of the material swallowed by a black hole? Does the black hole continue to grow forever, or does it reach a critical mass and then alter its behaviour?
Chris
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There are no theoretical limits to the size of black holes.
Taking things to the limit the ultimate fate of any simply expanding universe is to contain just one single black hole because it has swallowed all the other black holes stars planets and atoms.
This however does not take into account the acceleration of the expansion of the universe that appears to be happening. This could result in there being isolated atoms or assemblies of atoms around for a long time.
What happens to an isolated black hole then depends on whether the expansion of the universe has taken the microwave background temperature below the temperature of the black hole. If the universe is cold enough it will evaporate incredibly slowly. If the background is warmer it will grow slowly until the temperature drops low enough for the hole to start to evaporate. This evaporation will also warm the universe a bit and will take vast orders of magnitude longer than the universe has existed since the big bang.
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If a black hole was sufficient large would we notice much difference whether we were inside or outside it?
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Taking things to the limit the ultimate fate of any simply expanding universe is to contain just one single black hole because it has swallowed all the other black holes stars planets and atoms.
This however does not take into account the acceleration of the expansion of the universe that appears to be happening. This could result in there being isolated atoms or assemblies of atoms around for a long time.
Is that actually the case?
Surely, if the universe were expanding fast enough then you wouldn't just have "...isolated atoms or assemblies of atoms around for a long time.". there would be whole galaxies (or are you classing a galaxy as an assembly of atoms?) moving further & further away from each other's gravitational influence.
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" a black hole was sufficient large would we notice much difference whether we were inside or outside it?"
We might be in one, we call it the universe.
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A galaxy is an assembly of atoms but it could be disrupted if the acceleration of expansion got too great.
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But space inside galaxies isn't expanding, so why should that be?
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The current rate of expansion of the universe is so small that it is just not detectable on the sacale of anything as small as a galaxy or even a cluster of galaxies. It's not that it doesn't happen, you need distances of hundreds of millions of light years for it to be reliably detectable against the background "noise" of things moving about under gravity.
If this accelerates in the future by a significant amount this may not be the case.
To put the current rate of expansion of the universe in a galactic/stellar scale it is about 0.2 millimetres per second over a distance of one light year.
Many people misunderstand astronomical observations because the numbers are "astronomical" and they do not put them into the context of scales that they can understand and visualise.
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To put the current rate of expansion of the universe in a galactic/stellar scale it is about 0.2 millimetres per second over a distance of one light year.
Can we really measure distances that accurately, or is it just theory?
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It's a real measurement, albeit not a very accurate one (wiki tells me the error margin is about 15%).
BTW, it seems the general fate of a black hole is to be speculated about endlessly by physicists.
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Conversely, it's the ultimate fate of physicists to endlessly speculate about the ultimate fate of black holes [:D]
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The figure for the current expansion rate of the universe on a stellar scale is obviously totally unmeasurable. I just gave you the figures to show you how tiny this expansion coefficient really is. Its just that the visible universe is a very big place and we can see a very long way so the velocites get quite big and become quite significant with respect to the velocity of light.
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Its just that the visible universe is a very big place and we can see a very long way so the velocites get quite big and become quite significant with respect to the velocity of light.
I'm aware of that; but I thought that within galaxies gravity was holding the expansion in check.
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That is effectively what is happening the expansion is far too tiny to affect even the orbits of stars in the galaxy the intereactions between the stars totally dominate their motions It does not even have much effect on the motion of galaxies in clusters of galaxies.
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hmm maybe once all other matter in the univers is engulfed by one black hole the black hole itself could devour itself, maybe resulting in an explosion of hurrendous preportions, which could result in the re-creation of the universe. this being a very vague theory..
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hmm maybe once all other matter in the univers is engulfed by one black hole the black hole itself could devour itself, maybe resulting in an explosion of hurrendous preportions, which could result in the re-creation of the universe. this being a very vague theory..
I don't see how a black hole could devour itself. The black hole's gravity will already have caused the matter inside to be compressed to its ultimate state. However, something happening inside the black hole to make it explode could be the cause of an oscillating universe.
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OK matter trying to fall into a black hole can create some spectacular effects getting rid of its excess angular momentum but in the whole black hole event horizons are pretty boring things. It's what might be going on inside where the interesting stuff might happen. unfortunately however violent things are inside nothing will appear on the outside. That is the nature of event horizons.
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The universe, as a whole, fits the requirements of a black hole....
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Dear me! I hope that pun was intentional.
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hmm maybe once all other matter in the univers is engulfed by one black hole the black hole itself could devour itself, maybe resulting in an explosion of hurrendous preportions, which could result in the re-creation of the universe. this being a very vague theory..
isnt this essentially the big crunch theory? (universe collapses under its gravitatonal force, vets very small, explodes, expands, ect.)
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The fate of a black hole is it starts consuming everything in its gravity. our milky way has a black hole in it,black holes make galaxies and all galaxies have been made by black holes. After a couple of hundred million years the black hole becomes dormant and just sits there waiting for a unfortunate planet or comet to come to close for its gravity to suck it in. We don't know for sure what will happen to the black holes in every galaxy,maybe they will last forever,nobody knows but they do know that the universe is expanding so maybe you can figure out whats going to happen and have it printed in a famous magazine with a title saying( Physics boy wonder has broken the secret of black holes)
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What happens to all of the material swallowed by a black hole? Does the black hole continue to grow forever, or does it reach a critical mass and then alter its behaviour?
Chris
I thought I saw a Discovery Channel show regarding Black Hole and Steven Hawkings, where he suggested a possible "Black Hole Radiation", which according to what I understood if a black hole is not getting constant materials the expelled radiation would eventually deplete the Black Hole and space around it will go back to normal.
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What happens to all of the material swallowed by a black hole? Does the black hole continue to grow forever, or does it reach a critical mass and then alter its behaviour?
Chris
I thought I saw a Discovery Channel show regarding Black Hole and Steven Hawkings, where he suggested a possible "Black Hole Radiation", which according to what I understood if a black hole is not getting constant materials the expelled radiation would eventually deplete the Black Hole and space around it will go back to normal.
That's the theory - sort of. Strangely enough, it's called Hawking Radiation (or Bekenstein-Hawking radiation) [;D]
Energy fluctuations in the vacuum cause particle-antiparticle pairs to be created near the event horizon of the black hole. One of the particles gets sucked into the black hole and the other escapes. To an outside observer, it would look as if the black hole had emitted a particle.
The particle that is emitted has to have positive energy, so the particle that gets sucked into the black hole must have negative energy (conservation of energy blah blah blah). By absorbing the negative energy of the particle the black hole loses energy, and, due to E=mc2, also loses mass.
Obviously, the lost mass is miniscule so the black hole would take quite a long time to evaporate; longer even than it takes my mate Bob to buy a round of drinks!
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As I have detailed in the thread " Is a black hole a point " Id like to postulate that the fate of a black hole greatly depends on the forces acting upon it !
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I have a question.
If space and time co-exist and matter creates space, then if a black hole sucks in everything in the entire universe does time and space cease to exist outside of the black hole? Or does dark matter not get sucked into a black hole and keeps time and space outside of the black hole?
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Don't forget that a black hole is, essentially, a local phenomenon. However massive it happens to be, it will only affect distant objects in the same way as an equivalent 'not-a-black-hole' in the same place. It is reckoned that we are orbiting a super massive black hole in the centre of our Galaxy. But it's only the total mass which is determining our orbit.
A black hole won't 'suck in' all the material of the Universe because there is too much angular momentum in the region around it to allow this to happen. The attractive force is just not great enough to do more than to keep stuff in orbit around it. (I am referring to distances way beyond any event horizon or any region where GR might come into play - not far, in cosmological terms, actually)
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"What happens to an isolated black hole then depends on whether the expansion of the universe has taken the microwave background temperature below the temperature of the black hole. If the universe is cold enough it will evaporate incredibly slowly. If the background is warmer it will grow slowly until the temperature drops low enough for the hole to start to evaporate."
what does microwave background temperature have to do with something as strong as a black hole?
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If a black hole is near other matter, like an accretion disk, or the center of a galaxy, the black hole will grow through matter falling in, and you can ignore much smaller effects like:
- Hawking Radiation, which would reduce the mass of a black hole over cosmological timescales. Assuming this effect really exists, the equivalent temperature of a solar-mass black hole is around 0.0000001 degrees absolute. This radiates mass extremely slowly.
- Photons from the Cosmic Microwave Background radiation falling in. These photons currently have an equivalent temperature around 2.7 degrees absolute, so they carry very little mass. With an accelerating expansion of the universe, this equivalent temperature will reduce, contributing even less mass to the black hole in future.
Assuming that there are no infalling matter particles (eg electrons or protons), no light from stars falling in, and no neutrinos being absorbed by the black hole, the balance between Hawking Radiation and CMB is determined by which has the higher effective temperature - at the moment, the photons from the Cosmic Background radiation have a higher temperature than the Hawking temperature of a solar-mass black hole, so such a black hole will grow, extremely slowly.
Hawking radiation could be significant on very tiny black holes, from the atom-mass black holes that might one day be created in the LHC, up to black holes with the mass of a small asteroid.
See: http://en.wikipedia.org/wiki/Black_hole#Evaporation
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http://www.livescience.com/27811-creating-mini-black-holes.html
"Still, conventional physics suggest it would take a quadrillion, or a million-billion, times more energy to form a microscopic black hole than the Large Hadron Collider is capable of, so even a third of that is beyond human reach. Scenarios based on extra dimensions could have black holes form at a lower energy, "but they make no concrete predictions on what it should be,"
I don't think we should worry too much !
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BTW, it seems the general fate of a black hole is to be speculated about endlessly by physicists.
And to that endless debate, I'll add my own tidbit.
The mass/energy that falls into the black hole passes from our Brane to one of the adjacent branes that lie one either side of ours. We still recognize the influence of gravity because gravitational forces can pass unimpeded between those branes.
Or own big bang was such a passage creating our universe from a supermassive black hole in the brane lying next to ours.
To clarify: Like so many other speculations, this is just one in a multitude of others that may never be proven. Nevertheless, I think M theory is one of the best speculations defining the unexplainable.
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Black hole will eventually eat more and more matter to increase it's mass and then split into two.
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Black hole will eventually eat more and more matter to increase it's mass and then split into two.
Never heard that explanation before. Where did you get your information and can you explain why a black hole should ever split into as you have suggested? According to general consensus, black holes will continue to grow as long as they have local matter upon which to feed. Nowhere have I ever read that black holes would divide or split into multiple parts. If you have a link to any information regarding this assertion, I would like for you to post it here so we could read about it.
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What is the nature of a black hole without any space time outside the event horizon?
Is that how you make one go pop?
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As long as we agree on what direction gravity has inside matter, which should be to some sort of a center, it seems most probable that a black hole won't split into two. To get it to split you need to introduce some 'force', able to split it, as for example tidal forces, overwhelming the gravitational 'infinite force' inside that event horizon, splitting it. That should then be a analogue to the idea of greater and smaller infinities, acting upon each other. So you need to make the angular momentum of a black hole infinite, relative the infinity of directional gravity described inside the event horizon. And if you really want to insist on it, making the angular momentum of a greater infinity :) to get to one infinity ripping another infinity apart :)
I know there is a theorem of lesser and greater infinity's, and that it seems logically sound, or mathematically as it is. But in a one to one correspondence, lifting out the 'bits', it then must end in a lesser infinity disappearing before a greater. Which to my eyes make for a definition in where a infinity has an end, either making a one to one correspondence meaningless as a foundation for describing a infinity, or making the ideas of infinity meaningless, as we always can introduce a greater infinity, then using a one to one correspondence to kill of the lesser, lifting 'bits' out.
Either way, using a one to one correspondence my way, it should never end, no matter what size of infinity you define. If you want there to exist infinity's? Defining it that way there is no way to define a magnitude of 'force' to a infinity, because if there was, there would be no infinity's.
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There is a way around it though. the one assuming there is no end to any infinity, lifting out 'bits' in a one to one correspondence, from two infinity's of different magnitude. You then need to assume that as soon as we get to a definition of a infinity, the sum of its parts stop having a meaning. If you assume this, then there can't be any meaningful definition of greater and smaller infinity's. Which makes the mathematics into a dog biting its tail.
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Or should that be a cat? :)
Ouch.