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Is Dark Matter a solid, gas or liquid?

  1. Jan 23, 2008 #1
    I was simply wondering if dark matter is most-likely a Solid, Liquid, Gas, or Plasma.
  2. jcsd
  3. Jan 23, 2008 #2
    If plasma is hot, it emits light.
    If plasma is cold, it recombinates and becomes gas.
  4. Jan 23, 2008 #3
    It is pretty much guaranteed to be a gas. The interactions that allow materials to form solid and liquid phases are electromagnetic in nature; and, plasmas are formed when there's enough energy that charged particles can remain unbound from each other. All of these are electromagnetic effects. Dark matter cannot be electrically charged. If it were, not only would it be unable to form large halos around galaxies and clusters, as it would tend to radiate away energy as light, but it would interact with light passing through it and we'd see blurring of distant objects.
  5. Jan 23, 2008 #4
    So it'd most likely resemble an ideal gas?
    Or is there the possibility that it is a new classification all-together?
  6. Jan 24, 2008 #5


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    It depends what type of dark matter, there are two main theories:
    MACHOS (Massive astrophysical compact halo object) are regular star/planet stuff that is too cool to glow in visible light. So these are solids (dust/planets/rocks) or gas (brown dwarfs) or degenerate matter (neutron stars)

    WIMPS (weakly interacting massive particles) are undiscovered heavy sub atomic particles like neutrinos that have mass but no charge or other properties that would have an easily detectable effect in telescopes.
    I don't know what 'state' you would call a single neutrino all by itself in space?

    To be honest the states of matter thing isn't very useful in astronomy. Solid/liquid/gas is really a statistical description of how a large number of particles behave when they are together - it's cold enough and empty enough in momst of space that most molecules are just drifiting along on their own.
    Last edited: Jan 24, 2008
  7. Jan 24, 2008 #6
    If this were the case and there were enough of these to account for the missing mass in our own galaxy, we should expect to see some amount otherwise inexplicable gravitational lensing of light from outside our galaxy. We don't.
  8. Jan 24, 2008 #7
    Indeed, I think the latest results from the microlensing surveys is that only 25-50% of dark matter can be accounted for by MACHOs.
  9. Jan 24, 2008 #8


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    It depends on the mass of the individual 'particles'.

    If much larger then the dark mass would require fewer of these objects and fewer lensing events would be detected.

    If MACHOs do not fit the bill then IMBHs might.

  10. Jan 24, 2008 #9
    There would be fewer lensing events; but, wouldn't the lensing in what events there were be stronger?
  11. Jan 25, 2008 #10


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    They would also be further away on average.

    The interpretation of lensing event is model dependent and you have to make certain assumptions about the lensing object that has been detected. Depending on how tightly the parameters are determined there might be a degeneracy in that model in which two different scenarios would yield the same data.

  12. Jan 25, 2008 #11
    I don't think that's quite right, because "cold plasma" and "hot plasma" have special meanings in plasma physics. For example, the plasma created in a fluorescent light tube is defined as a cold plasma, yet it emits light.(Ref)

    Conversely, the Solar Wind is classed as a hot plasma, but as far as I'm aware, produces no light.(Ref) It's not until the Solar Wind interacts with the Earth's magnetic field, do we get the aurora.

    But plasmas are indeed prodigious producers of electromagnetic radiation across the entire spectrum, from radio waves, visible light, to x-rays and gamma rays.
  13. Jan 25, 2008 #12
    It's not something I'm well versed on at all, but couldn't dark matter be manipulated into any state of matter?
  14. Jan 26, 2008 #13
    No. That's the whole point I was making. All of the usual phases of matter other than gas come about because of electromagnetic interactions between the particles. If the particles have no electric charge, they can't interact electromagnetically and, hence, cannot form solids, liquids, or plasmas.
  15. Jan 26, 2008 #14

    George Jones

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    I am surprised that no one has mentioned Big Bang nucleosynthesis.

    The theory of Big Bang nucleosynthesis together with measurements of, e.g., the ratio of the primordial density of deuterium to the primordial density of hydrogen put the baryonic (protons and neutrons and their exotic cousins) content of the universe at about 15% of the total matter content of the universe given by standard interpretation of http://map.gsfc.nasa.gov/m_ig/060916/UniversePie150.jpg" [Broken] like those from WMAP.

    According to the standard cosmological model, the majority of dark matter is not normal matter.
    Last edited by a moderator: May 3, 2017
  16. Jan 28, 2008 #15
    The theory of Nucleosynthesis is not only a guide to the quantities of cosmic components as George well pointed out, but it also immediately shows that Dark Matter, not only is not baryonic, but it cannot also be made up of Leptons and/or Quarks. This is because with the Standard Model (or other viable alternatives) these states must (by known physics) form familiar baryonic matter (at a certain epoch) unless ad hoc undefined conditions are invoked. This means at the very least, for Dark Matter (DM) the standard “Standard Model” needs “some” modification. Not to push alternative concepts here, BUT, a whole cosmology exists that can define and provide calculated values for diverse topics (from the DE, DM, BM, to the Pioneer Anomaly) that are either, validated, or can be checked by observations. One of the fundamental basis for this cosmology is the definition and details of what is spacetime (continuum) and how it makes the universe expand. A book published in 1984 deals with this general concept of Continuum Creation and Annihilation (CCA). The “creation” part (“chronogenesis” in the book) behaves as the more recently discovered Dark Energy (DE). To compare it with GR, it prevents the Einstein (Ricci) tensor from vanishing. This means that there is no such thing as classical empty space, or “simple” cosmological “constant”. From this (actually CCA insists) the continuum is forced to have an inherent (calculable equivalent mass) energy density (vacuum energy, not of 120 orders of magnitude too large). Another big part for this cosmology is a possible (third family state) candidate for DM (considered over the last 15 yr) that seems to predict observed DM characteristics, but has a couple of very strange (compared to baryonic matter) behaviors.
    To come back to Nucleosynthesis, by use of the NASA WMAP inferred age (13.7 x10^9 yr) one can precisely calculate the amount of baryonic matter, then by the above chronogenesis, calculate the equivalent DE contribution. Then by summation (as shown below) calculate the Dark Matter component and that means all the component contributions are defined as shown and can be checked with observations.
    The total “critical” density Dt is equal to the sum of component densities of DE (dark energy) and DM (dark matter) and BM (baryonic matter) and (photon) Dcmb (small)
    Dt = DE + DM + BM +Dcmb
    When all the rather simple math and substitution is done one obtains (details can be provided):
    rhoc = rhoDE + (rhoDM + rhoBM)
    9.60 x10-30 = 7.0 x10-30 +(2.18 x10-30 + 4.16 x10-31) g-cm-3
    For total critical value of (100%)
    omega = 100% ~ 72.9% + (22.7% + 4.33%)
    and can compared to the graph George has.
  17. Jan 29, 2008 #16
    Jury's still out on that one...as far as I've looked into it.

    The theory I think most plausible is that it's a reaction created by dark energy on matter. That creates a discernible pattern of affect.

    It's changed so much from what I once studied, and I don't try to keep up. As, many great Physicists and Theorists are in a ever-changing state on their theories.

    I'll wait till the dust settles. Then get back into it.

    But, yeah: Right now I'd say it behaves like matter in that it influences motions of visible matter somehow. Like gravity does. Only, it ain't really there. Like matter. But, causes similar behaviors, as matter.

    Beyond that, I don't know what to tell you. Only there's too many things that can't be accounted for by visible areas being observed now, that are "REALLY" there.

    Maybe optics will provide the answer before the lead of the pencil.
  18. Jan 29, 2008 #17
    Hhhhm... would be cool if it were to include a 5th force.
  19. Jan 30, 2008 #18
    Before wondering what dark matter could be, it is probably wise to ask first whether it exists at all. As everybody knows, there is no direct evidence for this. The fact that galaxy rotation curves are flat for instance is no proof of dark matter, it could equally well mean there is something badly wrong with the description of the gravitational force. There exist several alternatives, such as the MOND theory and also a number of other alternatives (which I am not allowed to provide in this forum).

    Rudi Van Nieuwenhove
  20. Jan 30, 2008 #19


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    You are if the alternative theories fly enough to have been published in peer reviewed journals.

    The problem is with the mountain of crackpot 'theories' out there. We haven't the strength to point out the obvious flaws with all of them and discussion about them might well mislead newbies who come to these Forums to actually learn some science.

    The evidence that something, which is labelled 'Dark Matter', is out there does not just depend on galactic rotation curves, but also galactic cluster binding masses, cluster gravitational lensing masses, large scale structure formation and the CMB anisotropy power spectrum.

    Last edited: Jan 30, 2008
  21. Jan 30, 2008 #20

    covers it somewhat, but there again I'm not that familiar with it. It says that the Dark Energy interacts through gravity, but of course it is not clearly defined. As of yet.

    And, since there both hard to detect; right now they're lumped together. That is Dark Energy and Dark Matter.

    This other force, as I'd say there is, would explain a lot on the current observation and why many of the models of the Universe would not fit. When the observations were made.


    is a patch at a model that some are working on. I'm still gonna' wait till more is resolved to, before I jump in, if I do. Lord, it's even changed since last I looked at it about 3 months ago. As far as my reference material.
  22. Jan 30, 2008 #21
    Accepting dark matter as a proven entity (such that one can start studying its properties) can be considered to be misleading as well :devil:
    The other indirect evidence you mentioned (galactic cluster binding masses, lensing, etc.) in fact also relate to the effect of the gravitational force. So, if the gravitational force is calculated wrong, this evidence disappears as well. I'm not sure about the CMB anisotropy spectrum. The interpretation of the latter is of course depending an a cosmological model which might be wrong as well ...
    At some point in time, I will come back with some peer reviewed altnerative theory.

    Rudi Van Nieuwenhove
  23. Jan 30, 2008 #22


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    We must always be critical of our conceptual models, especially while DM remains undiscovered in the laboratory. But something is out there.
    Gravitational lensing does not depend on 'gravitational force' but space-time curvature. For example, if GR is wrong and space-time is flat, so gravitational forces are some Newtonian force effect, then you could model galactic rotation curves with a suitable MOND type force but you might have no gravitational lensing at all.

    If you then invoked a pseudo Newtonian-SR light bending effect it would produce only half the observed light deflection by the Sun.

    Remember you have to fit local experimental data as well as astrophysical and cosmological data.

  24. Jan 30, 2008 #23
    Yes, I was wrong to use the term "gravitational force" but that does not really change the argumentation. I could equally well argue that GR does not describe well gravitation at large distances. Both Newton's law (of gravitation) and GR have only been verified experimentally at relatively short distances (size of solar system) and assuming that the same laws hold when extrapolating to distances which are much much larger represents a very optimistic point of view. I agree of course that one has to fit the astrophysical data. Regarding the "cosmological data", things are (in my view) much more confuse. The interpretation (such as of the CMB) depends on the chosen cosmological model which in turn depends on GR or on assumptions whether or not inflation actually is a valid theory.

    Not so many years ago, (nearly) everybody was convinced that 99 % of the mass in the universe was in the form of dark matter and you would be attacked strongly to claim otherwise. Now, this is reduced to 23 % (with the invention of dark energy). This demonstrates the loose ground on which the concept of dark matter rests.

    Rudi Van Nieuwenhove
  25. Jan 30, 2008 #24


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    I agree that the need for DM and DE to make the standard [itex]\Lambda[/itex]CDM model fit the data may indicate that GR breaks down at cosmological distances.

    However, the change in the consensus model over the last ten years from 96% to 23% exotic (non-baryonic) DM has been a consequence of new data being observed; viz: the distant SNe Ia together with the data from the CDM power spectrum that yields [itex]\Omega_{total} = 1[/itex].

    And yes that latter result is model dependent, but then so is everything else in cosmology.

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