Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!


  1. Nov 15, 2015 #1
    I have been thinking about this quite often, and I know that usually WIMPs are taken more seriously than MACHOs, and I know it is because MACHOS don't exist in such huge amounts, but why are they considered better candidates for Dark Matter?
  2. jcsd
  3. Nov 15, 2015 #2


    User Avatar
    Science Advisor

    The evidence of dark matter is seen clearly in the CMB, which was emitted before any compact objects could have formed.
  4. Nov 15, 2015 #3
    Aha, I had been wondering about this quite a while, why have MACHOs been discounted as a DM candidate by most people working on it.
    The idea that DM could be explained by there being a large amount of small material objects which simply are not visible to us because they are too small and dark always did seem like a simplest explanation to me.
    Is the evidence of DM existing in the CMB data a hard certainty, or is it the 'strongly likely' category?
  5. Nov 15, 2015 #4


    User Avatar
    Science Advisor
    Gold Member

    There are certain asumptions used that could affect our interpretations regarding dark matter. For example, it is assumed radiation density in the early universe was fixed. If you relax that assumption other interpretations are possible. See http://background.uchicago.edu/~whu/intermediate/driving2.html for discussion. There was a time it was speculated primordial black holes could account for dark matter, but, after extensive study and analysis of the permissible mass range for PBH's has nearly exhausted any possibility of them as a dark matter candidate.
  6. Nov 16, 2015 #5


    User Avatar
    Science Advisor
    Gold Member

  7. Nov 16, 2015 #6


    User Avatar
    Science Advisor

    Also, Big Bang Nucleosynthesis very tightly constrains the baryon content of the universe, and the required baryon content is quite consistent with what is derived from the CMB. So the dark matter can not be made of ordinary atoms. This pretty much eliminates MACHOS as a possibility.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - WIMPs MACHOS Date
I No Axions or Wimps Oct 5, 2015
Decoupling condition for dark matter WIMP Jul 5, 2014
Resurrection of the WIMP as DM candidate Jan 15, 2014
The W in WIMP Jul 20, 2012
Dark matter as micro - MACHOs? Jan 3, 2011