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Idea: Dark Matter - Supergas

  1. Jan 15, 2009 #1
    Suppose dark matter is normal matter, in an exotic state.

    Superfluids have some interesting properties in common with "dark matter". Superfluids are quite restricted in how they interact with their surroundings. Because a superfluid is, quantum mechanically, a single entity, all of its interactions are quantized. For example, if the container of a superfluid is spun, the superfluid will not spin until the speed of rotation of the container matches the "critical speed" of the superfluid; at which point the entire bulk of superfluid will immediately start spinning at that speed.

    Superfluids can be extremely transparent.

    Consider this:

    At extremely low temperatures, the quantum wavelength of a particle (particularly (no pun intended) a very light particle, like hydrogen) becomes quite long. There could be a process in which sufficiently cold hydrogen (or helium or something) interstellar or intergalactic gas that is dense enough becomes a superfluid or a supergas or something.

    Maybe there would be a way to look for this sort of thing. The fact that any transitions would be bulk-quantized should give it some odd properties. Spin, EM absorption, ...

    Somebody better versed in QM than I would have a better sense for whether transitions into or out of such a state would be observable.

    Such a cloud of supergas in the vicinity of a supernova could be expected to suddenly change from invisible dark matter to ionized normal matter when the radiation hits.

    The fact that dark matter outweighs 'normal' matter by 5-to-1 (according to the WMAP 5-year report) suggests that it might have a visible influence, if it does behave in a bulk-quantized fashion. Considering the fact that dark matter seems to be considerably more common than 'normal' matter, maybe I should refer to dark matter as 'normal' and the baryonic matter we're more familiar with as exotic. :smile:

    Suppose a galaxy were surrounded by a ring of dark matter. If (however unlikely) the surrounding ring had a critical rotational speed, then it would likely be a multiple of the rotational rate of the galaxy. A dark matter ring around a galaxy would tend to keep galaxies spinning at constant rates. At least, the outer-most reaches of galaxies would tend to have more stable rotational rates than the rest of the galaxy. Over the long term, this could alter the shape of a galaxy. I'm having trouble visualizing how this might change the appearance, but I'm sure it would.

    Anyway, just an idea I wanted to toss out there.
     
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  3. Jan 15, 2009 #2

    ZapperZ

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    But the fact that we DO know a lot of "superfluids" and "supergas" (as in both the atomic BE condensate and the fermionic gas condensates) should imply that we do know how to detect them and how they should behave. After all, we have shown our ability to study them very closely here on earth.

    So it is inconceivable that such detection has escaped us so far. This is before we consider the validity of your idea, and what possible mechanism one can come up with for something that is not confined in vacuum to end up with such large coherence length to condense into such a state. It isn't that easy for that to happen when the atomic and fermionic condensates were created. Low temperature isn't the ONLY constraint.

    Besides, atomic gas, even neutral gas, CAN be detected via the spectral lines that it can absorb.

    Zz.
     
    Last edited: Jan 15, 2009
  4. Jan 16, 2009 #3
    "Inconceivable"? Really. You can't conceive of the possibility that some material that is well-studied in the lab might exist in interstellar or intergalactic space but not be noticed until we specifically look for it?

    I bet I can find some examples.

    How would you go about observing an optically transparent superfluid millions of lightyears away, in regions of space of low radiance.

    Low temperature isn't the only constraint. The constraint for superfluids is that the component parts (e.g. atoms) lose identity and become a single entity.

    The fact that matter in normal states doesn't behave the same way that matter in exotic states behave is irrelevant.
     
  5. Jan 16, 2009 #4

    ZapperZ

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    You are missing the location on where I put that "inconceivable" quality on. It is inconceivable to me, as a condensed matter physicists, that you can have just the right geometry of the magnetic field to somehow cause these particles to form a BE condensation and maintain that long of a coherence length. Since you can find "examples", find me an example of a region of space that has JUST the right magnetic field to form such condensates.

    Do you get my point now?

    It is moot to discuss a superfluid doing this and that IF there is no conceivable mechanism for its formation in the first place. You are putting the cart before the horse. Besides, where do you get the idea that ALL superfluids are optically transparent?

    But an even larger issue here is the fact that baryonic matter has been ruled out by almost all accounts as being dark matter. Where is your argument that such "supergas" is the source? So there are really two horses being put before the carts here.

    Zz.
     
  6. Jan 16, 2009 #5

    Nereid

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    In addition to what's in the posts after the OP, here are a few things I thought of:

    * the distribution of CDM (cold dark matter) is reasonably well constrained, at least to distance scales of ~kpc and up, in the sense of its mass density per cubic pc (say).
    -> can any baryonic superfluid exist at such low densities? Recall that their densities are lower than those of the hardest vacua we can create in labs here on Earth.

    * the universe seems to be bathed in a uniform radiation field, whose SED is a blackbody (to ~ppm), and whose temperature in the local universe is 2.73K.
    -> can any baryonic superfluid exist at this temperature?

    * zillions of high energy particles pass through each cubic metre of the universe every {insert unit of time here}; these particles range from electrons and positrons, through protons and anti-protons, to the nuclei of Fe and even Th and U; their energies are as high as ~EeV.
    -> how stable is any baryonic superfluid under these conditions? Consider stability over billions of years

    * objects like the Earth and Voyager spacecraft have speeds of many km/sec wrt the local standard of rest (a circular orbit around SgrA*, at our distance from it), the velocity vector of this motion changes in complicated ways.
    -> how stable could any baryonic superfluid be to massive (baryonic) objects moving through it at high speeds?
    -> what is the effect of a blob of baryonic superfluid colliding with an object the mass of the Earth, at a relative speed of some dozens of km/sec?

    ... and so on.
     
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