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I Dark matter/energy, why must it be there?

  1. Sep 9, 2017 #26
    The section "Lensing Constraints" on page 15 speaks directly about how little PBHs would contribute to the overall DM equation. My understanding is PBHs, if they existed, would be detected as a twinkling from microlensing, which is not observed.
     
  2. Sep 11, 2017 #27

    kimbyd

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    Bear in mind that there are two distinct classes of MACHOs:
    1. As normal matter collapses, some percentage of the collapsed matter becomes effectively invisible because it's too dim to detect.
    2. Some amount of matter started out as compact objects.

    Option (1) has been completely ruled out by the CMB data, which shows very clear evidence of dark matter long before any compact objects formed due to gravitational collapse. Option (2) is primordial black holes. Yes, they are a possibility. But they should still be considered an exotic possibility.
     
  3. Sep 11, 2017 #28

    kimbyd

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    My understanding is that those constraints still allow PBH's within a certain mass range, which is incidentally also the mass range of the observed black hole-black hole mergers that LIGO detected.
     
  4. Sep 12, 2017 #29

    Buzz Bloom

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    Hi kimbyd:

    I agree that PBHs seem to be "an exotic possibility". However, at the present time, the other ideas previously discussed about what dark matter might be (e.g., neutrinos, WIMPs) seem to no longer be plausible candidates at all.

    What seems particularly odd about the PBH idea, based on the https://arxiv.org/abs/1607.06077 article, is that the only sizes for PBHs that have not yet been eliminated as a dark matter possibility are those that cannot with the present technology be detected. This would require a physical mechanism for PBH creation that by an odd coincidence would create only PBHs of a size that we cannot now detect.

    Regards,
    Buzz
     
  5. Sep 12, 2017 #30

    PeterDonis

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    Thread closed for moderation.

    Edit: The thread topic has been sufficiently addressed. The thread will remain closed.
     
    Last edited: Sep 12, 2017
  6. Sep 12, 2017 #31

    Drakkith

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    For clarification, this thread has been attracting some problematic posts that have now been deleted. Thread will remain locked since it is one of those topics that seems to inherently invite personal speculation.
     
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