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naturally occuring elements
- Thread starter fungle
- Start date
Deamiter
I just follow Christ.
from the American physical society:
"Its current value of roughly 1/137 could not have been very different in the past, as that would have spelled trouble for our very existence. A variation in alpha by more than a factor of ten would imply that carbon atoms could not be stable, and organic life could not have arisen."
however, some scientists analyzed the spectra in some cosmic clouds and found that alpha might have been smaller in the past. Now, don't jump all over this and say it 'proves' that alpha is not constant and scientists are simply ignoring it! There don't seem to be any articles (at least not in the APS journal) that confirm the finding - and if it were confirmed, it would have been a something to write about without a doubt! Can anyone with a bit more time find a source that discusses the constant after 2001? Otherwise, it seems likely that the error was easily explained by another group and the issue was dropped alltogether.
http://focus.aps.org/story/v8/st9
"Its current value of roughly 1/137 could not have been very different in the past, as that would have spelled trouble for our very existence. A variation in alpha by more than a factor of ten would imply that carbon atoms could not be stable, and organic life could not have arisen."
however, some scientists analyzed the spectra in some cosmic clouds and found that alpha might have been smaller in the past. Now, don't jump all over this and say it 'proves' that alpha is not constant and scientists are simply ignoring it! There don't seem to be any articles (at least not in the APS journal) that confirm the finding - and if it were confirmed, it would have been a something to write about without a doubt! Can anyone with a bit more time find a source that discusses the constant after 2001? Otherwise, it seems likely that the error was easily explained by another group and the issue was dropped alltogether.
http://focus.aps.org/story/v8/st9
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As we have it, the fine constant might have been the reason or the the the fine constant has changed.To the latter it may have changed by one billionth and to the former it is obvious that that the forces involved in the composition of an atom is strictly controlled by four forces
What happens to those forces in a black hole? Do elements exist?
Does the fine constant exist in extreme conditions.
What happens to those forces in a black hole? Do elements exist?
Does the fine constant exist in extreme conditions.
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J
Jet Black
Guest
barring the singularity, those forces are all still there. However the gravitational attraction overcomes all of these forces since the density is so high. However the gravity is so strong, that the forces cannot overcome the attraction of the gravity anymore, and everything just keeps collapsing. For example at the Chandrasekhar limit, the relativistic gravitational forces overcome the electron degeneracy pressure and then it collapses. The electrons merge with the protons to form neutrons, and then the collapse stops, because the neutron degeneracy pressure overcomes the gravity. however, keep on adding mass and even this will be overcome. then there is no known force that will stop the collapse of the object (a neutron star) into a black hole.
in short, elements do not exist within the hole, since the gravity is so great that the forces resisting the collapse of the elements are overcome.
in short, elements do not exist within the hole, since the gravity is so great that the forces resisting the collapse of the elements are overcome.
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Could we have the position where there is an absence of gravity? That would involve a state where no masses were being influenced by any other or all masses were cancelled.At some time after the big bang , gravity must have become constant under normal conditions. By normal I mean a constant which allows space craft to follow newtonian laws to reach other planets.
Just out of interest when does g=o. Does it happen when a stone is thrown into the air?
Getting back to the original point it seems that the alpha constant must be the same throughout the universe and the number of elements does not change
Just out of interest when does g=o. Does it happen when a stone is thrown into the air?
Getting back to the original point it seems that the alpha constant must be the same throughout the universe and the number of elements does not change
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J
Jet Black
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well you could have a position where there is no gravity, or at least any detectable gravity. remember however that the whole issue depends on what frame of reference you are in, and by gravity I mean acceleration, because relativistically they are the same thing.
The entire universe could be accelerating at a constant rate to the left right now, and we would never know it, because we are in the same frame.
as for your stone, the acceleration is the second derivitive with respect to time, and that is never zero. viewed from the stone's perspective hower, it cannot tell whether is being accelerated or not though, because it not feeling any force (barring friction). To imagine this, imagine, rather than a stone, being in a lift. It could be in outer space floating away really far away from any masses (where G is effectively 0) or you could be plummeting down a lift shaft to your doom. and there is no test to see which is true (forget noise and friction from outside again)*
Getting back to the original point. everything shows that alpha is the same everywhere, and the number of elements does not change (ignoring singularities, since they are sort of out of the remit of the problem) however alpha does determine the minimum sizes of objects that can gravitationally collapse into black holes, and hence the number/types of them.
*this is not quite true. If you really wanted, you could test for a slight difference in acceleration in an object dropped at the top of the lift, and an object at the bottom, but it is infinitessimal in a normal field like ours. a point particle could never tell though.
The entire universe could be accelerating at a constant rate to the left right now, and we would never know it, because we are in the same frame.
as for your stone, the acceleration is the second derivitive with respect to time, and that is never zero. viewed from the stone's perspective hower, it cannot tell whether is being accelerated or not though, because it not feeling any force (barring friction). To imagine this, imagine, rather than a stone, being in a lift. It could be in outer space floating away really far away from any masses (where G is effectively 0) or you could be plummeting down a lift shaft to your doom. and there is no test to see which is true (forget noise and friction from outside again)*
Getting back to the original point. everything shows that alpha is the same everywhere, and the number of elements does not change (ignoring singularities, since they are sort of out of the remit of the problem) however alpha does determine the minimum sizes of objects that can gravitationally collapse into black holes, and hence the number/types of them.
*this is not quite true. If you really wanted, you could test for a slight difference in acceleration in an object dropped at the top of the lift, and an object at the bottom, but it is infinitessimal in a normal field like ours. a point particle could never tell though.
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Jet Black said:
Aren't you getting confused with white dwarfs? When they go over the Chandrasekhar limit (e.g. by accreting from a companion star in a binary) they explode in a Type I supernove with no compact remnant i.e. no black hole. What you may be thinking of is when a star exhausts all of its hydrogen a sequence of events occurs that may or may not end in supernova. If sufficient mass loss occurs during expansion (to bring the mass below the Chandrasekhar mass) then the star collapses to a white dwarf. If not then the star will explode in a Type II supernova, which does leave a compact remnant which may either be a black hole (if the progenitor star had a mass greater than about 30 solar masses) or a neutron star.
Jet Black said:
However I agree with your main point. And I'm afraid I don't know much about the fine structure constant, though I will add that I remember reading about its possible variation with time and don't think it was ever resolved. So I'll be quiet now.
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J
Jet Black
Guest
sorry if my post was a bit confusing, yours is a better description of what goes on. I was really just illustrating how the physics affects bodies of different sizes. You are correct that a collapsing white dwarf would indeed result in a type 1 supernova, but the point I intended to put across was that a neutron star must be more massive than in the Chandresekhar limit case. anyway your post is better explained than minethomas the tank engine said:
I recall that too, though if I remember it was something really small, like one part in 10^10 or something silly like that.
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I have no knowledge of the level of physics you described. That is why I am picking your minds.
Elements in extreme conditions such as black holes do not exist as elements, is this correct.
By altering one of the four "forces" do the the others have to compensate.
By growing material, organic and inorganic, in zero gravity conditions would you expect variations to the normal?
Elements in extreme conditions such as black holes do not exist as elements, is this correct.
By altering one of the four "forces" do the the others have to compensate.
By growing material, organic and inorganic, in zero gravity conditions would you expect variations to the normal?
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J
Jet Black
Guest
strictly they cannot exist as elements. However all the rules are the same, it is just the extreme gravity that crushes them.fungle said:
Let me give a slightly different example, I did some experiments at my old university with a really powerful laser. The laser was so powerful in fact that the electromagnetic field between the nucleus and the electrons was just a perturbation (small effect) on the field of the laser. All the rules were the same, just the system was very very extreme, and so is the case with gravity: in a black hole, the effects of the strong force and EM force are just a small perturbation on the effects of the gravitational field. However the rules in the hole and outside it are the same.
Growing materials in a zero-G environment does produce differences, however these are just due to the lack of gravity, rather than any adjustment in the way the forces behave. This doesn't have any real effect on the production of atomic elements though, as the forces in the nucleus are so strong anyway.
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Back to black holes if you don't mind
As a giant red starts to become a black hole it goes through a series of expansions and contractions using up elements starting with the lighter ones and head to the heavier ones breaking them down. Is iron the last element and no others
As a giant red starts to become a black hole it goes through a series of expansions and contractions using up elements starting with the lighter ones and head to the heavier ones breaking them down. Is iron the last element and no others
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Iron has the most stable nuclei of any element, in that heavier elements will decay 'down' (nuclear fission) towards iron and release energy, and lighter ones will fuse (nuclear fusion) 'up' towards iron and release energy. Iron nuclei cannot undergo fusion or fission and release energy. Nuclei heavier than iron form in supernovae because of the enormous amount of energy that is released.
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ps. I'm not sure if red giants go supernovae - to be massive enough they might have to be a different colour giant (but I could be wrong).
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J
Jet Black
Guest
There might be occasions in the cores of these heavy stars where elements larger than iron are produced, however these will not be the norm, and a star cannot continue to burn by fusing iron.
But essentially yes, Iron is the last element produced by nuclear fusion in the cores of stars. This is a result of the binding energies, and is expected from the Semi Empirical Mass Formula (it has been a while since I used it, but my notes are at home if you want to ask more questions about it later) It is energetically preferable (i.e. an exothermic reaction) for elements smaller than this to fuse, and energetically preferable for larger elements to decay. Note I am not including in this the unstable isotopes of smaller elements, like C14 and so on which will just be the result of local energy spikes and so on, as in the case of any elements heavier than iron that might be produced. If I recall correctly though, some of the "paths" might include these smaller unstable elements, though I would have to check it out. for example A+B might fuse to create C, which is in itself unstable, but more energetically preferable than A and B. C would then decay to D+E, heading at all times towards iron.
But essentially yes, Iron is the last element produced by nuclear fusion in the cores of stars. This is a result of the binding energies, and is expected from the Semi Empirical Mass Formula (it has been a while since I used it, but my notes are at home if you want to ask more questions about it later) It is energetically preferable (i.e. an exothermic reaction) for elements smaller than this to fuse, and energetically preferable for larger elements to decay. Note I am not including in this the unstable isotopes of smaller elements, like C14 and so on which will just be the result of local energy spikes and so on, as in the case of any elements heavier than iron that might be produced. If I recall correctly though, some of the "paths" might include these smaller unstable elements, though I would have to check it out. for example A+B might fuse to create C, which is in itself unstable, but more energetically preferable than A and B. C would then decay to D+E, heading at all times towards iron.
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J
Jet Black
Guest
it is the type of star. I can't remember the classifications at the moment though.Timo said:
Black holes, generally speaking, originate from one of two sources: hot blue stars, which are gererally really big, about 30 solar masses, and Extra large gas clouds which achieve the critical density, for example, the supermassive black holes in the cores of galaxies. If I recall correctly, this is one of the ideas behind quasars, which were gas clouds large enough and dense enough to just collapse straight to a black hole without bothering with all the fusion jiggery pokery in the middle. I will do the calcs now.
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J
Jet Black
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I just did a back of the envelope calculation with
R=2GM/(c^2)
G= grav const
M is a billion solar masses
c is the speed of light.
and I get a density of about 10^-8 kg/m^3 as the density required for a billion solar mass object to collapse into a black hole. bear in mind I was quite sloppy with the numbers and did a fair bit of rounding since I couldn't be bothered with the calculator, so I might be an order of magnitude out either way.
R=2GM/(c^2)
G= grav const
M is a billion solar masses
c is the speed of light.
and I get a density of about 10^-8 kg/m^3 as the density required for a billion solar mass object to collapse into a black hole. bear in mind I was quite sloppy with the numbers and did a fair bit of rounding since I couldn't be bothered with the calculator, so I might be an order of magnitude out either way.
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Polycarp1
Born-again Liberal Episcopalian
The elements above nickel in the periodic table are produced by giant stars in the last stages of their fusion or in the supernova explosion/implosion that ends their life as giant stars. (Cobalt and nickel are so close to iron in binding energy that small quantities of each are produced in the fusion-to-iron phase.) Basically, the star is capable of supporting a miniscule amount of endothermic reactions by its predominant exothermic activity, and this serves to create iridium, mercury, gold, lead, etc., in cosmically small amounts prior to the supernova. But principally the explosion of the supernova will serve as an energy source to fuse iron and other bottom-of-the-curve elements to produce the "supraferrous" elements at that momnent -- and some of these will be expelled into the interstellar medium by the force of the supernova.
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