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Dark matter vindicated?

  1. May 21, 2012 #1

    Chronos

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    Unsurprisingly, the conclusions of of Bidin, et al, on the apparent lack of dark matter in our galactic neighborhood have been challenged:
    On the local dark matter density
    http://arxiv.org/abs/1205.4033
     
  2. jcsd
  3. May 21, 2012 #2
    Does Dark Matter eventually resettle on the 'new' galaxy after a collision with another galaxy? And how long might this take? Might this give some discrepancies in local dark matter densities? And so how would observation match the data on small local scales?
     
  4. May 21, 2012 #3

    marcus

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    Re: Dark matter vindicated.

    Excellent! Chronos thanks for spotting this one!
    BTW both Bovy and Tremaine are at the Institute for Advanced Study.
    Jo Bovy has published 26 papers since 2008 and many were co-authored with David Hogg (formerly Princeton now NYU).
    Scott Tremaine (former chair of Astrophysics at Princeton, now IAS) has published 85 papers, some co-authored with David Spergel (Princeton) and some with Abraham Loeb (Harvard).
    http://en.wikipedia.org/wiki/Scott_Tremaine
    This is a quality rebuttal.

    Nice it came out roughly what the standard model predicts for DM density in our neighborhood.

    They got around 0.3 GeV/cm3 that is about 50 nanojoules per m3

    and the Holmberg Flynn prediction (from back in 2000) was around 0.38 which is about 60 nanojoules per m3.

    http://arxiv.org/abs/astro-ph/9812404
    The local density of matter mapped by Hipparcos
    Johan Holmberg, Chris Flynn
    (Submitted on 22 Dec 1998 (v1), last revised 1 Nov 2005 (this version, v2))
    We determine the velocity distribution and space density of a volume complete sample of A and F stars, using parallaxes and proper motions from the Hipparcos satellite. We use these data to solve for the gravitational potential vertically in the local Galactic disc, by comparing the Hipparcos measured space density with predictions from various disc models. We derive an estimate of the local dynamical mass density of 0.102 +/- 0.010 solar masses per cubic parsec which may be compared to an estimate of 0.095 solar masses per cubic parsec in visible disc matter. Our estimate is found to be in reasonable agreement with other estimates by Creze et al. and Pham, also based on Hipparcos data. We conclude that there is no compelling evidence for significant amounts of dark matter in the disc.
    9 pages, 7 figures, accepted by MNRAS

    EDIT TO REPLY TO PHYZGUY:
    Thanks! I will make the change in my post.

    Indeed about units if you put this into the google window:
    c^2*.102 mass of sun/pc^3
    you do get that 60 nJ per cubic meter, or 62 more precisely. So it works out.
     
    Last edited: May 21, 2012
  5. May 21, 2012 #4

    phyzguy

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    Re: Dark matter vindicated.

    FYI, David Hogg was at Princeton IAS, but is now at NYU.
     
  6. May 22, 2012 #5

    Chalnoth

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    While it's interesting that the previous result was wrong, this is a really cool result in and of itself.
     
  7. May 22, 2012 #6

    turbo

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    Negative results are essential to the progression of science. Still, negative results are not definitive, just exclusionary. Cosmology is a field that is reliant on observational astronomy and on interpretation, so we can't claim "vindication" for any cosmological concept based on a paper or two. The fact is that we are stuck here on Earth, relying on observations from orbiting and ground-based observatories. Just sayin'
     
  8. May 22, 2012 #7

    phyzguy

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    I agree. The authors also make the point that when the Gaia observations start pouring in (scheduled to launch next year), this will get a lot more accurate.
     
  9. May 22, 2012 #8

    Chalnoth

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    I don't see this as so much of a negative result, however, as they're showing that you can, indeed, measure the amount of dark matter in our local area. And that is, to me, pretty cool.
     
  10. May 22, 2012 #9

    marcus

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    More bad news for MOND (hence good news for DM):
    http://arxiv.org/abs/1205.4880
    Confronting MOND and TeVeS with strong gravitational lensing over galactic scales: an extended survey
    Ignacio Ferreras, Nick Mavromatos, Mairi Sakellariadou, Muhammad Furqaan Yusaf
    (Submitted on 22 May 2012)
    The validity of MOND and TeVeS models of modified gravity has been recently tested by using lensing techniques, with the conclusion that a non-trivial component in the form of dark matter is needed in order to match the observations. In this work those analyses are extended by comparing lensing to stellar masses for a sample of nine strong gravitational lenses that probe galactic scales. The sample is extracted from a recent work that presents the mass profile out to a few effective radii, therefore reaching into regions that are dominated by dark matter in the standard (general relativity) scenario. A range of interpolating functions are explored to test the validity of MOND/TeVeS in these systems. Out of the nine systems, there are five robust candidates with a significant excess (higher that 50%) of lensing mass with respect to stellar mass, irrespective of the stellar initial mass function. One of these lenses (Q0957) is located at the centre of a galactic cluster. This system might be accommodated in MOND/TeVeS via the addition of a hot component, like a 2 eV neutrino, that contribute over cluster scales. However, the other four robust candidates (LBQS1009, HE1104, B1600, HE2149) are located in field/group regions, so that a cold component (CDM) would be required even within the MOND/TeVeS framework. Our results therefore do not support recent claims that these alternative scenarios to CDM can survive astrophysical data.
    Comments: 13 pages, 2 figures
     
  11. May 22, 2012 #10

    Chronos

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    The bulk of very good observational evidence renders MOND and other alternative theories of gravity untenable.
     
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