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#21
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LCDM and rotation of DM
In article , Nicolaas Vroom
writes: Not much non-baryonic matter is needed to explain galaxy rotation. Does that mean that only a small percentage of the total mass of a galaxy is non-baryonic ? I think Steve meant "not much" as compared to the total amount of non-baryonic matter. The general argument is that if we cannot observe it (being visible) than it should be non-baryonic. Not really. About half of the baryons have been unaccounted for. Recently there is evidence the "missing baryons" are in very hot intra-cluster gas, but I don't know whether that's yet confirmed. Which seems to indicate that the necessity for non-baryonic seems to decrease. Not necessarily. From big-bang nucleosynthesis, we no the baryon density. From various cosmological tests, we know the total density. The difference is non-baryonic. 100% correct and seems to most logical explanation (part of). This immediatly implies that there also could be much more baryonic matter outside (but part of) the disk. You can't exceed the nucleosynthesis constraint, though. IMO, both, based on observations indicate a missing mass issue which could be either baryonic or non-baryonic. You can't exceed the nucleosynthesis constraint, though. Nowadays there is far more evidence than either of these. The CMB radiation fluctuations seem to indicate that roughly 20% of all the mass in the present day is baryonic and 80% is non-baryonic. The detailed reasoning how these numbers are derived is not clear to me. It is well documented. You could read the CMBFAST or CAMB code, or the papers describing them and references therein, or any of the vast number of theoretical papers describing how the power spectrum (from which the conclusions you mentioned) is derived. It's not easy; it's not necessarily intuitive, but it is straightforward physics with no fudge factors. Specific if this balance all ready existed immediate after the BB and stayed constant there after untill present. Not immediately after the big bang, but after nucleosynthesis. |
#22
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LCDM and rotation of DM
On 8/27/14, 1:52 AM, Phillip Helbig---undress to reply wrote:
In article , Nicolaas Vroom writes: Which seems to indicate that the necessity for non-baryonic seems to decrease. Not necessarily. From big-bang nucleosynthesis, we no the baryon density. From various cosmological tests, we know the total density. The difference is non-baryonic. Big Bang baryon nucleosynthesis calculations are based on theoretical models developed during the Manhattan Project and follow-on efforts. These models were used to define nuclear reactions at the National Ignition Facility https://lasers.llnl.gov/ such that there was confidence for 'over unity' energy creation. This did not happen. I would not be 100% confident that the same models are accurate in expressing nuclear dynamics at the much more complex first minutes of the Big Bang. |
#23
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LCDM and rotation of DM
In article , "Richard D. Saam"
writes: Big Bang baryon nucleosynthesis calculations are based on theoretical models developed during the Manhattan Project and follow-on efforts. These models were used to define nuclear reactions at the National Ignition Facility https://lasers.llnl.gov/ such that there was confidence for 'over unity' energy creation. This did not happen. Reference, please. I would not be 100% confident that the same models are accurate in expressing nuclear dynamics at the much more complex first minutes of the Big Bang. A large part of the literature on BBN is concerned with refining the "laboratory values". Even if early estimates were based on sources which, for whatever reason, were not completely correct, these days are long since gone. |
#24
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LCDM and rotation of DM
On 8/28/14, 3:07 AM, Phillip Helbig---undress to reply wrote:
In article , "Richard D. Saam" writes: Big Bang baryon nucleosynthesis calculations are based on theoretical models developed during the Manhattan Project and follow-on efforts. These models were used to define nuclear reactions at the National Ignition Facility https://lasers.llnl.gov/ such that there was confidence for 'over unity' energy creation. This did not happen. Reference, please. NIF did achieve break even 'over unity' in February, 2014 http://newenergyandfuel.com/http:/ne...ion-breakeven/ with reference to Nature article http://www.nature.com/nature/journal...ture13008.html "The experimental results have matched computer simulations much better than previous experiments, providing an important benchmark for the models used to predict the behavior of matter under conditions similar to those generated during a nuclear explosion, a primary goal for the NIF." but the science continues: “There is more work to do and physics problems that need to be addressed before we get to the end, but our team is working to address all the challenges, and that’s what a scientific team thrives on." I would not be 100% confident that the same models are accurate in expressing nuclear dynamics at the much more complex first minutes of the Big Bang. A large part of the literature on BBN is concerned with refining the "laboratory values". Even if early estimates were based on sources which, for whatever reason, were not completely correct, these days are long since gone. But the science continues: Hints of Mysterious Particle Detected in 'Big Bang Soup' http://www.livescience.com/47506-hea...ons-found.html Big Bang Soup conditions were experimentally studied at 7.2 trillion degrees Fahrenheit (4 trillion degrees Kelvin) This temperature conforms to a radiation dominated universe at 1.02E-08 sec. References are made to analogous chemical phase relationships in explaining the Big Bang Soup. "Now, the team is hoping to create a map of how different types of matter, such as quark-gluon plasma, change phases at different temperatures. Just as the chemical symbol H20 represents water in the form of a liquid, ice or steam depending on the temperature and pressure, the subatomic particles in an atom's nucleus take different forms at different temperatures. So, the team is hoping the new results could help them to create a map of how nuclear matter behaves at different temperatures." These physical chemistry references to liquid, solid and gas phases and salting out effect are not addressed in the standard model. Further physical chemistry logic anticipates the existence of critical points between phases and then there is the Bose Einstein Condensate phase. And then: how is gravity addressed? "Refining Laboratory Values" to BBN theory is a continuing process and will add to understanding the BBN contribution to the present understanding of galactic formation, dark matter and dark energy and in particular the baryonic and non baryonic content in the universe. Richard D Saam |
#25
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LCDM and rotation of DM
In article ,
Nicolaas Vroom writes: Does that mean that only a small percentage of the total mass of a galaxy is non-baryonic ? This is hard to study, and it probably varies by galaxy type and mass. A good guess is perhaps half and half. The early history of dark-matter is explained in this document: http://arxiv.org/pdf/astroph/9904251.pdf 1999. Looks like a nice historical article. What you need is an excel spreadsheet showing based on 2014 information for all the galaxies of the coma cluster what the baryonic masses are of each and what the total is, Yes, that's the sort of approach needed, though there's nothing magic about Coma. The complication is that measuring the galaxies is not enough. Intra-cluster gas probably makes up half or more of the baryonic mass but is very hard to measure. Total mass can come from velocity dispersions or gravitational lensing. There's some uncertainty converting velocity dispersion to mass because it depends on how velocities are distributed. There is a vast literature on all these questions. The document shows a sigma value of 706 +- 267 km/sec2 which implies that the total mass has a large uncertainty range. I'm not sure what document you refer to, but I'd expect a much better value to be known now. See also http://arxiv.org/pdf/1110.2649v1.pdf (2011) which gives a very mixed picture. That's for the ratio in individual dwarf galaxies. The problem is similar, but the region being studied differs. Not really. About half of the baryons have been unaccounted for. Recently there is evidence the "missing baryons" are in very hot intra-cluster gas, but I don't know whether that's yet confirmed. Which seems to indicate that the necessity for non-baryonic seems to decrease. No. The total baryon density is known from the CMB, nucleosynthesis, and I think from baryon acoustic oscillations. Or does that last not give a density? The question is where those baryons reside. No matter where they are, there just aren't enough of them to explain cluster velocity dispersions. And some of the peaks in the CMB fluctuation power spectrum cannot be explained by baryons at any density. The CMB radiation fluctuations seem to indicate that roughly 20% of all the mass in the present day is baryonic and 80% is non-baryonic. The detailed reasoning how these numbers are derived is not clear to me. It's far from obvious! Try playing with the simulator at http://lambda.gsfc.nasa.gov/education/cmb_plotter/ and look at the related documentation. The "lambda" site has huge amounts of information. Specific if this balance all ready existed immediate after the BB and stayed constant there after untill present. Current theory says the amounts of baryonic and non-baryonic matter have stayed fixed at all times since the Universe became matter dominated. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#26
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LCDM and rotation of DM
In article , Steve Willner
writes: Current theory says the amounts of baryonic and non-baryonic matter have stayed fixed at all times since the Universe became matter dominated. Right. There are actually quite strong limits on this, as some theories predicted proton decay (which would violate baryon-number conservation) and people have looked for it. They didn't find it. This rules out those theories and also indicates that the ratio hasn't changed. (Of course, one cannot rule out that it has change via some other mechanism, but there is absolutely no evidence for this observationally, and no reason to expect it theoretically.) |
#27
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LCDM and rotation of DM
On 9/7/2014 11:02 AM, Phillip Helbig---undress to reply wrote:
In , Steve Willner writes: Current theory says the amounts of baryonic and non-baryonic matter have stayed fixed at all times since the Universe became matter dominated. Right. There are actually quite strong limits on this, as some theories predicted proton decay (which would violate baryon-number conservation) and people have looked for it. They didn't find it. This rules out those theories and also indicates that the ratio hasn't changed. For the *ratio* to be unchanged you also would need to rule out decay of the other component. At the moment we are not yet in the era of "precision dark matter theories" (although it will come, of course!) but suppose, for the sake of argument, and also because I find it convenient, that it consists of axions (the dark matter, I mean) then our current theory certainly does predict certain decay modes. In fact, physicists are actively trying to induce those decays right now: http://www.phys.washington.edu/groups/admx/home.html (Of course, one cannot rule out that it has change via some other mechanism, but there is absolutely no evidence for this observationally, and no reason to expect it theoretically.) But axions do decay (or get created) in a magnetic field! So theoretically at least it is possible. (I admit that observationally you may have a point, or else the headlines would be all over the planet by now, I'm sure..) -- Jos |
#28
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LCDM and rotation of DM
On 9/7/14, 4:02 AM, Phillip Helbig---undress to reply wrote:
In article , Steve Willner writes: Current theory says the amounts of baryonic and non-baryonic matter have stayed fixed at all times since the Universe became matter dominated. Right. There are actually quite strong limits on this, as some theories predicted proton decay (which would violate baryon-number conservation) and people have looked for it. They didn't find it. This rules out those theories and also indicates that the ratio hasn't changed. (Of course, one cannot rule out that it has change via some other mechanism, but there is absolutely no evidence for this observationally, and no reason to expect it theoretically.) Ref: First Direct Measurement of the H2Li6 Cross Section at Big Bang Energies and the Primordial Lithium Problem http://physicsworld.com/cws/article/...n-of-lithium-6 Such studies continue to confirm the accepted baryonic and non-baryonic ratio. But this experiment with hydrogen nuclei (atomic weight 1) does not study the colligative properties of primordial nucleosynthesis such as when much higher nuclei number are present, expressed in gold (atomic weight 196.97) atom collisions simulating the near infinity Big Bang nucleosynthetic(BBN) atomic weight: Hints of Mysterious Particle Detected in 'Big Bang Soup' http://www.livescience.com/47506-hea...ons-found.html These BBN colligative properties may provide a reason to expect a different baryonic and non-baryonic ratio. |
#29
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LCDM and rotation of DM
In article , Jos Bergervoet
writes: For the *ratio* to be unchanged you also would need to rule out decay of the other component. Right, of course. At the moment we are not yet in the era of "precision dark matter theories" (although it will come, of course!) but suppose, for the sake of argument, and also because I find it convenient, that it consists of axions (the dark matter, I mean) then our current theory certainly does predict certain decay modes. Of course, if it decays to some other non-baryonic particle, then the ratio stays the same. If it decays completely to radiation (or to something baryonic) then, yes, the ratio would change. However, if the ratio substantially changed with time, then this would probably contradict some observation the interpretation of which assumes a constant ratio. |
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