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More evidence for Dark Matter?

  1. May 15, 2007 #1

    ZapperZ

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    NASA just had a press release today of new evidence that supports the presence of Dark Matter. I think this would be the most direct detection so far if verified.

    http://www.nasa.gov/home/hqnews/2007/may/HQ_07114_Hubble_Dark_Matter_Rings.html

    We still have to wait for the publication of the paper. I don't particular like how they do science via press conferences like this.

    Zz.
     
  2. jcsd
  3. May 15, 2007 #2
    Well, it wasn't far behind and it has been accepted by ApJ.

    Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
    Authors: M.J. Jee, H.C. Ford, G.D. Illingworth, R.L. White, T.J. Broadhurst, D.A. Coe, G.R. Meurer, A. Van Der Wel, N. Benitez, J.P. Blakeslee, R.J. Bouwens, L.D. Bradley, R. Demarco, N.L. Homeier, A.R. Martel, S. Mei
    (Submitted on 15 May 2007)

    Abstract: We present a comprehensive mass reconstruction of the rich galaxy cluster Cl 0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies (~120 per square arcmin) across the cluster enables the derivation of a high-resolution parameter-free mass map. The strongly-lensed objects tightly constrain the mass structure of the cluster inner region on an absolute scale, breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17 obtained in such a way is remarkable. It reveals a ringlike dark matter substructure at r~75" surrounding a soft, dense core at r~50". We interpret this peculiar sub-structure as the result of a high-speed line-of-sight collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated by the cluster velocity distribution. Our numerical simulation with purely collisionless particles demonstrates that such density ripples can arise by radially expanding, decelerating particles that originally comprised the pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56, but viewed $along$ the collision axis at a much later epoch. In addition, we show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and lensing can be resolved by treating the cluster X-ray emission as coming from a superposition of two X-ray systems. The cluster's unusual X-ray surface brightness profile that requires a two isothermal sphere description supports this hypothesis.

    Comments:
    To appear in the June 1 issue of The Astrophysical Journal. Color version of Figure 8 is availalble at this http URL
    Subjects:
    Astrophysics (astro-ph)
    Cite as:
    arXiv:0705.2171v1 [astro-ph]
     
  4. May 15, 2007 #3

    EnumaElish

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    Does anyone have the link to the simulation (per the NASA news piece)?
     
  5. May 15, 2007 #4

    Kea

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    OK, I've skimmed through the paper, and am confused about one thing (well, that's assuming I buy LCDM, which I don't). Why a Ring? Is the filament structure of the supercluster scale somehow responsible for containing the ripple to the orthogonal plane?
     
  6. May 16, 2007 #5
    Dark Matter Ring

    APOD for 5/16/2007 shows a simulated dark matter ring around Galaxy Cluster CL0024+17. The work is the product of Jee and Ford, et al, of Johns Hopkins University.

    In a separate NY Times article, it was reported "Richard Massey, an astronomer at the California Institute of Technology, said the findings were facing skepticism within the astronomical community."

    Why is the work by Gee and Ford considered controversial?
     
  7. May 16, 2007 #6

    George Jones

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    From the NASA release:

    "Computer simulations of galaxy cluster collisions, created by the team, show that when two clusters smash together, the dark matter falls to the center of the combined cluster and sloshes back out. As the dark matter moves outward, it begins to slow down under the pull of gravity and pile up, like cars bunched up on a freeway."

    The simulation videos are here. Two views are shown:

    1) motion perpendicular to line of sight;

    2) motion along line of sight.

    Apparently, 2) is right for Earth.
     
  8. May 16, 2007 #7

    George Jones

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    A friend just pointed me towards a CBC article, and it reports

    "Richard Massey, a postdoctoral scholar at California Institute of Technology, who was not part of the research, said the discovery is exciting if it's correct. 'But in order to be convinced, astronomers would need to see it at a different angle or with another camera,' he said during a NASA teleconference of the announcement."

    This seems reasonable.

    It seems that, in paraphrasing, the NY Times distorted what Massey said in the teleconference.
     
  9. May 16, 2007 #8

    hellfire

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    I guess that it might be necessary to remove some uncertainties, such as possible undetected baryonic mass (gravitational lensing gives only a 2D "image"), but even from this perspective I don't understand this claim. The postulated ring is not in a photograph, but seams to be inferred from gravitational lensing of more than thousand background galaxies as well as from N-body simulations. May be he is trying to make some public pressure for an optical substitute for the HST?
     
  10. May 16, 2007 #9

    Kea

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    Note from the (non LCDM) Quantum Gravity point of view: Matti Pitkanen has correctly calculated the radius of the ring using his TGD model. See

    http://matpitka.blogspot.com/
     
  11. May 16, 2007 #10
    Which cosmology did the "non-LCDM" scientist use to convert the angular radius of the ring to a physical one? One would think the choice of cosmology would affect this conversion and thus the calculation using a TGD model.
     
  12. May 16, 2007 #11

    Kea

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    Yes, sure, so let's call it the TGD cosmology. You'll have to read a fair bit, or ask Matti, to clarify this point. The real point is that TGD says a lot more about Dark Matter than just "it is stuff".
     
  13. May 16, 2007 #12
    Ok, so the TGD cosmology must then predict the same physical radius as LCDM (0.4Mpc). If the TGD cosmology does not measure the same radius, then his calculation is a bit misleading.
     
  14. May 16, 2007 #13

    Kea

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    You are right that a more careful analysis should consider possible sources of error on the estimate for core radius. This will come in time, but I think the LCDM radius is a reasonable estimate since (eg.) the redshift is not too high.
     
  15. May 17, 2007 #14
    Acronyms

    In this thread, there are two acronyms used that are not known to me. I would greatly appreciate having them expanded and explained:

    1) LCDM
    2) TGD model

    as well as any other related acronyms. Thank you.
     
  16. May 17, 2007 #15

    Garth

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    LCDM = Lambda Cold Dark Matter, the standard cosmological model - it requires Dark non-baryonic non-relativistic matter, the CDM, and Dark Energy, which is possibly a non-zero cosmological constant, the Lambda.

    You will also see it written as [itex]\Lambda[/itex]CDM.

    TGD = Topological GeometroDynamical model. In general these are theories that account for sources as well as fields in terms of topological-geometrical structure. This non-standard model referred to by Kea is proposed by Matti Pitkanen. I cannot find a published reference for Pitkanen's theory, perhaps Kea can oblige?

    Garth
     
    Last edited: May 17, 2007
  17. May 17, 2007 #16

    Kea

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    Published? You've gotta be kidding! Anyway, there's plenty of material on his webpage:

    http://www.helsinki.fi/~matpitka/

    :smile:
     
  18. May 17, 2007 #17

    Garth

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    Yes I have read it, however there is just the small matter of the PF global guidelines....
    Garth
     
  19. May 17, 2007 #18

    Kea

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    Well, I apologise if this is against the Astro guidelines. In the Beyond SM forum, for example, we discuss such things frequently. On the other hand, I believe TGD qualifies as being part of 'current professional scientific discussion', given that many professionals (eg. Sir Roger Penrose) have been discussing it.
     
    Last edited: May 17, 2007
  20. May 18, 2007 #19

    Garth

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    Then where is it published? I am happy to discuss an endorsed eprint on the physics ArXiv, if the Moderators are, and if Pitkanen's ideas have substance then it is an easy matter to submit it there, so has he?

    Garth
     
  21. May 18, 2007 #20

    Wallace

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    No, I think not. He has also not submitted his ideas about the 'TGD Inspired Theory of Consciousness' :eek: Methinks there are many better non-LCDM models out there for those interested in alternatives to the standard model (which should be everyone right?) :cool:
     
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