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  1. #1
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    Default Dark Matter May Not Exist



    Reference: [1102.2622] Misaligned And Alien Planets From Explosive Death Of Stars "Misaligned and Alien Planets for Explosive Death of Stars" by Shlomo Dado et al.

    Very interesting paper and one that is likely to become controversial. Puts forth a single theory that explains unusual extrasolar planetary systems and the missing mass of the Galaxy along with a proposed verification experiment. If true, the theory accounts for a large proportion of the missing baryons, or "dark matter" in galaxies like our own Milky Way. A synopsis of the paper is in the June issue of Sky at Night. Interestingly, the objective of the study by Dado was not to explain dark matter but to determine why some exoplanets have orbits contrary to that expected from standard models of planet formation.

    Their theory asserts that these puzzling planets form elsewhere and are captured by passing stars. The planets are formed from hot gases ejected by super novae or planetary nebulae. Calculations show that perhaps as many as a 1000 ejections are from Cassiopeia A, a supernova remnant and more than 40,000 launched from the Helix Nebula. Hubble photographed the hot gas ejecta from the Helix Nebula. If these observations are typical of supernovae and planetary nebulae in general, then the number of free floating Jupiter mass objects may be 100 times higher than the number of stars in the galaxy. If true, this will explain both the misaligned alien planets and the missing matter in galaxies. Two different means to verify are proposed ... a microlensing survey or perhaps infrared telescopes for recently formed planets.
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  3. #2
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    Default

    You jumped the gun. The paper doesn't say what you think it says. You mixed together "missing baryons" and "missing mass" / "dark matter". These are not the same thing and the paper says nothing about dark matter.

    I found a web page that explains the concept of "missing baryons":

    Missing Baryons

    It is now well established that that the baryon to dark matter mass ratio is 15-20%. On scales of galaxy clusters, the observed baryons fall just slightly short of this prediction, but on galaxy scales the observed baryons fall well short. For instance, an inventory of baryons in and around the Milky Way reveals at best one-quarter of the expected baryons...
    So you see, the "missing baryon" problem is independent of the "missing mass" or "dark matter" problem.

    Here is another pop-science article that discusses the concept of missing baryons:

    Astronomers find missing baryons - physicsworld.com
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    Default

    I agree that you have misinterpreted what the Author was saying. Easy to do with the nature of the paper. Excellent paper, thanks for the link.
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  6. #4
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    Default

    Regarding dark matter, do it actually have mass, or could the amount of mass
    that is assumed to be missing in regards to the behavior of the visible mass
    in galaxies be caused by something else?

    I would guess its possible that there could be several different things
    contributing their share to the total amount of missing matter that
    dark matter amounts to. What i have in mind though is if a part of it
    could be explained by the effect of a force, that would make the observable
    matter behave like its under the influence of the missing mass known
    as dark matter?


    PS: Would appreciate an explanation if i got the wrong idea of
    some the physics involved wrong here.



    Regards


    Dustworm

  7. #5
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    Quote Originally Posted by Dustworm View Post
    Regarding dark matter, do it actually have mass, or could the amount of mass
    that is assumed to be missing in regards to the behavior of the visible mass
    in galaxies be caused by something else?
    Dark matter, if it exists, has mass. But dark matter itself is just a candidate solution to the problem of galaxies moving too fast. Another proposed solution is that we just got the law of gravity wrong and that it is actually stronger at large distances. This is the "MOND" hypothesis. However, observational evidence and simulations strongly favour the dark matter hypothesis.


    I would guess its possible that there could be several different things
    contributing their share to the total amount of missing matter that
    dark matter amounts to. What i have in mind though is if a part of it
    could be explained by the effect of a force, that would make the observable
    matter behave like its under the influence of the missing mass known
    as dark matter?
    What you have described is more or less the MOND idea. Basically, it makes gravity stronger in the "weak gravity" regime. This is not the most popular idea, but it is still actively explored by several people.

    Some of the problems with MOND include:

    1. It doesn't try to explain *why* gravity would behave in this way, so it is not very satisfactory from a scientific point of view.

    2. There is one important observation that favours dark matter versus MOND. I'll try to explain it:

    There is a galaxy cluster called the "bullet cluster". It is actually two galaxy clusters that are colliding. When two clusters collide, the stars and the gas in the cluster become separated, because the gas feels pressure and stars do not. This allows you to test dark matter vs MOND:

    (a) If MOND is correct, most of the gravity should be coming from where most of the visible mass is, which in this case means the gas.

    (b) If dark matter is correct, most of the gravity should be in the dark matter halos that are attached to the galaxies.

    A team of researchers used microlensing to make a "gravity map" of the bullet cluster, and they found that most of the gravity is in the galaxies, even though most of the visible mass is in the gas. This is a strong piece of evidence in favour of dark matter rather than MOND.

    That said, until we know what's causing the gravity, astronomers continue to explore options including MOND.
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  9. #6
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    Default

    Most two arm spiral galaxies have asymmetry in brightness of spiral arms. It is essential in Fourier transformation of brightness of galaxies – first harmonic is much bigger than second one. This is not big deal, but analysis of light-of-sight velocities also shows that such one arm wave has larger amplitude and correlated with one arm structure in brightness. For one sub stellar subsystem is not good – center of mass is shifted for one arm structure. Gas has not so big mass (especially in the center) and also follow to stars. For standalone galaxies without satellites, to keep the center mass you need one more subsystem – for example dark matter. But in this case this is completely different mechanism of generation of spiral arms than classical.

    Does somebody investigate generation of one spiral arm in galaxies by dark matter?

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  10. #7
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    Thanks for the good reply DanielC

    This kinda makes sense to me.

    That being said, the rotational behavior of galaxies
    really puzzle me.

    Even if you have the missing mass accounted for
    how will that explain the strange result on the galaxy rotation curves?


    Regards

    Dustworm

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    Quote Originally Posted by Dustworm View Post
    Thanks for the good reply DanielC

    This kinda makes sense to me.

    That being said, the rotational behavior of galaxies
    really puzzle me.

    Even if you have the missing mass accounted for
    how will that explain the strange result on the galaxy rotation curves?
    That's a bit harder to explain, but I'll try. Here is a sketch of the galaxy rotation problem. Curve "A" is what we'd predict based on the mass we see and curve "B" is what we actually observe.





    The speed of an orbit depends on the mass inside that orbit and the size of the orbit. The first thing to note is that the shape of this galaxy rotation curve depends not only on the mass of the galaxy but how it is distributed. For example, if all the mass of the galaxy was concentrated at one point in the centre, the speed of the orbits would drop uniformly from the centre. The speed of the orbits would have the formula:

    V = sqrt( GM/R )

    But the galaxy is not a point mass, it is a distributed mass. Looking through a telescope, most of the visible mass is concentrated in a buldge at the centre and then the galactic arms have less mass.



    If you start very close to the centre the speed is small because there is not much mass inside the orbit. As you move outward through the buldge, the mass inside the orbit initially increases very fast and the speed of the orbit increases. Once you are out of the bulge, as you continue to move outward, the mass inside the orbit continues to increase, but more slowly. So now the speed of the orbit decreases, but more gradually than with the "v = sqrt( GM/R )" law.

    What I have described here is curve "A". To explain curve "B" we postulate that there is more mass outside the bulge than we can see. So as you move outward, the mass inside the orbit increases more rapidly than we thought, which would explain why the speed of the orbits is not dropping.

    This is the dark matter postulate. It proposes that the galaxy is immersed inside a huge ball of matter that is unseen. In the WIMP dark matter version, this matter is a new undiscovered particle that doesn't produce light. The dark matter "halo" is spread out as a sphere, so when you move outward, the mass inside an orbit increases more rapidly than if it were a disk.

    I hope that answers your question.
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    Yeah it does answer my question and it is raising new ones as well but,
    that is how physics works i guess.




    Regards


    Dustworm

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    Quote Originally Posted by Dustworm View Post
    Yeah it does answer my question and it is raising new ones as well but,
    that is how physics works i guess.
    Yeah. Welcome to science ;-)
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