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I Wobbling BGC and Dark Matter

  1. Nov 16, 2017 #1
    I found an article https://arxiv.org/abs/1703.07365 and also it says that we should change current standart model about DM.
    Also I find this;
    "If this "wobbling" is not an unknown astrophysical phenomenon and in fact the result of the behaviour of dark matter, then it is inconsistent with the standard model of dark matter and can only be explained if dark matter particles can interact with each other -- a strong contradiction to the current understanding of dark matter. This may indicate that new fundamental physics is required to solve the mystery of dark matter." (https://www.sciencedaily.com/releases/2017/10/171026103110.htm says that, para. 7)

    It says that BGC are making some kind of oscillation in the galaxy cluster.Or I understand like that at least.
    1-What's the critical points in this article that we should be understand it ? ( like just asking the general idea cause I didnt quite get it).
    2- In the light of this new evidence, how it will effect properities of DM, DM Halo or DM density profiles ?
     
  2. jcsd
  3. Nov 17, 2017 #2

    ohwilleke

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    The really core point, from the abstract is that:

    Ten years ago, this would have been a really big deal since it contradicts the cold dark matter (CDM) hypothesis as an explanation for dark matter phenomena. But, at this point, it is really just piling onto an abundant collection of evidence showing contradictions between the CDM hypothesis and observation.

    One of these contradictions (there are several of them) is known as the cusp-core problem, which is that CDM theories, generically, predict that dark matter halos should have a cuspy density profile, but inferences about the distribution of dark matter from the dynamics of visible matter in galaxies and gravitational lensing observations demonstrate that this is not actually the shape of inferred dark matter distributions in galaxies. Instead, inferred dark matter halos distributions have what is known as an "isothermal" distribution of dark matter within the dark matter halo around a galaxy.

    So, this result really just confirms in a novel way something that was widely known from other evidence. This is still important, because it makes the conclusion that there really is a cusp-core problem that is not just an artifact of a flaw in some particular methodology that provides the evidence for the cusp-core problem much more robust. But, it doesn't really change the bottom line from existing data.

    To prevent a cuspy density profile from emerging in a halo you need some kind of feedback either between dark matter particles or between ordinary matter and dark matter that spreads it out when it gets too dense.

    But, that contradicts the assumption made in early cold dark matter theories that dark matter should be collisionless, which has strong support from the failure to direct dark matter detection experiments to see it, from the absence of a strong dark matter annihilation signal, and from the non-detection of dark matter at the Large Hadron Collider (LHC), and is consistent with the success of the lamdaCDM model of cosmology at scales much larger than galaxies and galaxy clusters, although these methods would often miss detect interactions between dark matter and other dark matter that does not result in annihilation of the interacting dark matter particles and take place at relative small distances relative to those important for cosmology.

    Warm dark matter proponents have suggested a quantum effect that only kicks in at masses of dark matter particles on the order of 2 keV/c2 or less. Others have proposed self-interacting dark matter (SIDM) models to address the issue. But, those models have their own problems beyond the scope of this discussion.
     
  4. Nov 17, 2017 #3
    First of all I want to thank your for your reply.Your explanation was so great.
    I thought this problem is the first or recent founded contradiction with the CDM model. I know that theres some DM density profiles that can explain some structers but in general yes theres still a lots of gaps and these discoveries show us that theres also something wrong with CDM model.So we have no explanation for DM again ? Like we should re-consider most of things or still our CDM theories applied in general ? Like do we need some adjusments or a whole new theory about it ?
    Isnt this make sense ? I mean why should expect more denser DM around small galaxies ? Or Its just about the problem of models ?
     
  5. Nov 18, 2017 #4

    ohwilleke

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    You were wrong. Serious problems with the CDM model were identified, overwhelming, and basically irrefutable at least as far back as six years ago. Consider an excerpt from this September 2011 paper:

    Even in 2011, the evidence that there were serious problems with cold dark matter models had been accumulating for years. So, this is really nothing new.

    You go on to state:

    As I note it has been clear that the CDM model was profoundly broken six years ago and subsequent efforts to cure it with more sophisticated simulations have not been successful. Instead, increased volumes of evidence have continued to provide more evidence that this is not the answer. The sub-type of CDM model that was once most popular, the supersymmetric WIMP, has been pretty definitively disproven.

    There is no currently outstanding dark matter model that is a good fit to the data. Some are better than others, but all of them have serious problems fitting the data.

    "Warm dark matter" models (in which dark matter particles have masses on the order of a keV instead of "Cold dark matter" models on the order of 1-100 GeV, are a better fit to the data, and direct dark matter models have not ruled out weakly interacting warm dark matter (mostly because the current experiments are incapable of distinguishing dark matter from ordinary neutrinos at low masses), but high energy physics experiments like LEP, Tevatron and the LHC strongly disfavor weakly interacting dark matter particles with masses of less than 45 GeV. So, any warm dark matter particle would have to be "sterile". Unfortunately for warm dark matter, even sterile warm dark matter models still share some significant problems with cold dark matter models.

    A host of other more complex dark matter models, such as self-interacting dark matter models, are also in trouble.

    Dark matter models still do much better at matching reality than a universe with only ordinary matter and only general relativity. And, not every possible dark matter model in "theory-space" has been ruled out yet. But, the house of dark matter models is starting to look like a horror movie. There are dead theories everywhere, every time you turn around another one dies, and the astronomers whose observations are killing them are churning out new data limiting dark matter parameter space faster than a horror movie can grow a zombie swarm.

    This isn't to say that the astronomers are only aiming their sights at dark matter models. The set of modified gravity theories was smaller than the set of dark matter theories in the first place, and several of them have also fallen prey to experimental falsification. For example, Verlinde's new "emergent gravity" theory was a case of infant mortality that was ruled out just months after it was proposed.

    Of course, like the dead dark matter theories, the falsified modified gravity theories are still better fits to observation than ordinary matter and general relativity alone. Better yet, they provide better intuition about dark matter phenomena and have been more successful at predicting new dark matter phenomena than dark matter models. But, there are now at least as many, if not more, viable modified gravity theories as there are viable dark matter particle theories (although, in fairness, this is partially because less effort has been devoted to comparing modified gravity theories to the data).
     
    Last edited: Nov 18, 2017
  6. Nov 18, 2017 #5
    It was very helpful thank you.
     
  7. Nov 18, 2017 #6
    Since current CDM is wrong, does it affect Friedmann Equations, somehow ?
     
  8. Nov 21, 2017 #7

    ohwilleke

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    Not really in the cosmology sense. CDM produces the right results as cosmology scales (as do pretty much all other viable models of DM or modified gravity).
     
  9. Nov 21, 2017 #8
    I see...seems awkward though
     
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