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Thread: DM clumping

  1. #1
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    DM clumping

    There have been a few articles on Hubble finding support for cold dark clumping.

    I thought in std cosmology, DM does not to give of EM radiation so can not clump by losing kinetic energy as normal matter does.

    So is this clumps of DM not expanding with the universe and maintaining its density from an earlier time?
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

  2. #2
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    Quote Originally Posted by PetTastic View Post
    There have been a few articles on Hubble finding support for cold dark clumping.

    I thought in std cosmology, DM does not to give of EM radiation so can not clump by losing kinetic energy as normal matter does.

    So is this clumps of DM not expanding with the universe and maintaining its density from an earlier time?
    Good question. The answer is hard to know so far, and so there aren't lots of papers making clear claims about it. In short, if there are clumps of dark matter, either there must have been a time when dark matter was cool enough that it was easy for it to gravitate and get some dense areas at the expense of throwing off a fraction of the dark matter to give away energy... OR another possibility is that Dark Matter is a remnant of something that had an ability to self-interact and clump (in the very early universe) before decaying out of existence, or that perhaps in the very early universe there were particles with a mass of about 10^70 eV (size of a DM clump) that decayed (directly or through some path) into a mixture of dark matter and normal matter that didn't have a lot of energy per particle, so they self gravitated (similar to globular clusters, but larger and with many more much smaller particles). There may be other answers too, but no answer is mainstream yet. Finding, and sizing DM clumps is basically step one toward eventually developing a model to explain it.
    Forming opinions as we speak

  3. #3
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    In my 'toy' models it extremely tricky to find a particle behaviour that both produces large voids and small scale clumping they are opposite ends of the behaviour spectrum.
    I either get large voids resulting in hot DM filaments or beads of cold DM.

    It is like modelling a critically thin layer of water beading into droplets on a water repellent surface.
    With low friction the tiniest imperfect produces a rapidly expanding hole (void with fast moving water)
    With surface & air resistance you get many small beads of water.
    There is very little middle ground.

    Looking at high velocity DM collisions making more DM. Trying 2 particles colliding at high speed forming 4 slow moving particles.
    Is this too silly to pursue?
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

  4. #4
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    Is the recent article about cold and warm dark matter a new situation or is it something that always existed and they are just finding out. Reading the universe today article and I am not sure if dark matter has just started clumping or has always and we just noticed?

  5. #5
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    If dark matter is not homogenous it has always been not homogenous. Talk of cold, warm, and hot dark matter has been around since the term dark matter was created. Note: neutrinos are an example of hot dark mater.
    Forming opinions as we speak

  6. #6
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    When it comes to dark matter, it is getting harder these days to know what is main stream any more.

    If you ignore things like gravity leaking in from parallel universes, you still have increasing unknown factors in how much DM we are looking for and where it is concentrated.


    Doubts over value of Hubble constant effect age of the universe & therefore formation speed of large scale structure & the scale factors in baryon acoustic oscillations.
    Early galaxies without DM?
    Super size galaxies that are possibly growing faster than they are rotating. (or have a very strange formation history)
    Then there are reports form Voyager probes etc. of the interstellar medium having more structure than expected, with suggestions of cold gas between hot filaments have a large impact on estimates of ISM mass & inter cluster medium mass.
    Changes in our understanding of the size of molecular cloud complexes along with multiple supermassive black holes wandering around dwarf galaxies.
    Some proposals for how early supermassive black holes formed look to be in conflict with DM models. ( A large proportion of DM would bullseye the SMBH and be swallowed)

    These only effect how much DM we are looking for and where.

    Then there is the nasty idea that we are looking for an overly simplified solution. What if DM is like normal matter and is a mixture of many different particles that only interact with normal matter via gravity?

    So what is rubbish, just unknown or main stream?
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

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