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Space Science

Simulation Predicts Clumps of Dark Matter Within Galaxies 131

A team of researchers has simulated the gravitational interaction of dark matter particles over the course of a hypothetical 13.7 billion years. They found that the particles tended to form clumps large enough to assist in the formation of galaxies. The results contradicted observations from previous, smaller studies, but they lent support to an unrelated simulation of how the Milky Way formed. UCSC's press release is also available. Quoting ScienceNews: "The clumps of dark matter in the simulation have densities that are remarkably similar to densities that a University of California, Irvine research group found when simulating the formation of the Milky Way and its satellite dwarf galaxies, says James Bullock, the astrophysicist who leads the UC-Irvine group and was not involved in the new study. 'This is a remarkable success of the particular model simulated and adds strong support to the idea that the dark matter is made up of particles that are "cold." There are a number of planned experiments aimed at detecting the dark matter that are betting on it being cold, so this is generally good news for the community,' Bullock says. And, [study co-author Piero Madau] notes, larger simulations that might help constrain the nature of dark matter even more are already in the works."
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Simulation Predicts Clumps of Dark Matter Within Galaxies

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  • by timmarhy ( 659436 ) on Saturday August 09, 2008 @03:30AM (#24535665)
    because MOND hasn't been verfied by any pyshical tests. it's MOND that lacks evidence not dark matter. all dark matter is, is visible gravitational effects of matter we can't see just yet. it IS crazy to go modifying a verified theory of newton's laws to fit our results without being able to explain why.
  • ha (Score:2, Insightful)

    by Johnny Chinpo ( 1340653 ) on Saturday August 09, 2008 @03:52AM (#24535707)

    More cruft to add to the bogus hypothesis that is dark matter.

    I am a physicist.

  • by jabithew ( 1340853 ) on Saturday August 09, 2008 @04:07AM (#24535757)
    All physics is most likely wrong. Some of it is *less* wrong than the rest of it. Even if we know of problems within the standard model, we don't currently have much better to explain things.
  • by Hektor_Troy ( 262592 ) on Saturday August 09, 2008 @04:28AM (#24535829)

    Say with MOND, why are we so scared to think that perhaps Newtonian mechanics aren't quite enough to calculate with on galactic scales?

    It's not about being scared - it's about the scope of that theory. Using "stuff falls down" as a theory of gravity works, but only in very specific situations. It's not something you can use as a usable replacement for any of the accepted theories, like GR and Newton.

    Talking about scientists being scared of MOND is silly. Especially when you bring in Newtonian mechanics, which have long since been proven to fail in a large number of ways. The reason we still use Newtonian mechanics is that it's "good enough" for most things. Just like "stuff falls down" works great here on Earth, but not so well inside the ISS.

  • Dark Matter.... (Score:1, Insightful)

    by Anonymous Coward on Saturday August 09, 2008 @05:00AM (#24535893)

    ..... aka the new aether

  • by YttriumOxide ( 837412 ) <> on Saturday August 09, 2008 @09:40AM (#24536889) Homepage Journal

    My beginnings of a hypothesis are that it's gravity from THIS universe from folded dimensions. "Parallel Universe", while possible, seems to require too many further assumptions.

    Fun, yes. False, almost certainly, but not necessarily - that's the point of trying to formulate a hypothesis.

  • by wanerious ( 712877 ) on Saturday August 09, 2008 @11:27AM (#24537431) Homepage
    What?? Where in the field equations is there an anomaly? If it *were* some anomaly in the field equations, we'd see really bizarre effects everywhere else there are strong gravitational fields. We don't.

    The point is that it's not a strange theoretical solution, but a real, physical deflection of light by a gravitating mass. It is certainly evidence of unseen matter --- were there a cloud of unseen matter, this is exactly the effect it would have on passing light. To attribute it instead to a non-specific flaw in a theory we know *very* well is far more speculative than what you criticize others for.

  • by Ambitwistor ( 1041236 ) on Monday August 11, 2008 @02:55PM (#24558853)

    Well Bullet Cluster or any other cluster is a problem for MOND. But the Bullet Cluster is also a problem for Dark Matter. The velocity of the Cluster is much faster than GR can provide, which MOND can easily handle.

    (GR doesn't have anything to do with it per se; Newtonian gravity predicts the same thing as GR on galactic scales.)

    The Bullet Cluster is a much more severe problem for MOND than dark matter; you can't even qualitatively explain the divergence between the galaxy and the lensing with MOND. The Brownstein and Moffat paper you're alluding do doesn't even attempt to address that elephant in the room, which is the problem with MOND and the Bullet Cluster by far. I've also read comments on Cosmic Variance that they assume some coincidental alignments of the galaxies and the result barely reaches statistical significance, but I'm no expert.

    Then again, there are the other problems with getting MOND to hold on a number of other scales, which myself and others have discussed elsewhere in these comments.

    I actually liken MOND to Keplers laws. It shows how the matter moves. If GR cannot reproduce it, then there is a need for a new theory.

    Er, no. MOND doesn't show anything about how matter moves. We observe how matter moves and theorize explanations of it (dark matter, MOND, etc.) There is more than one way to explain observations. And I don't see this as even remotely a thorn in the side of GR, or even much so for dark matter. Galaxies are messy. In the case of the Bullet Cluster, it happens to have a geometry which is a smoking gun against MOND (or at least MOND with no dark matter), but it's much less conclusive about dark matter.

    The other problem is that GR and QM don't work well.

    That almost certainly doesn't have anything to do with MOND, given the scales at which quantum gravity is relevant (which is not astrophysical!). It certainly doesn't imply something like MOND should be true.

    It could be that both MOND and DM are correct.

    That would be the most scientifically interesting outcome. But I don't think it's very likely. Even if GR needed to be modified on astrophysical scales, I highly doubt anything like MOND would be it.

    DM may exist in significant quantities in Clusters while MOND is sufficient at the Galactic levels.

    It's really hard to construct a hybrid theory like that, because if you reduce the amount of dark matter in galaxies by introducing MOND, you completely screw up early universe structure formation. Then you have to explain why all that dark matter in clusters didn't clump in galaxies. You can turn back to hot dark matter, but I think that's going to screw up cosmology. The reason why dark matter has become the dominant theory is because it consistently explains a lot of otherwise unrelated phenomena. It's hard to change one part of it without making things worse.

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