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Featured I Rumors of merging neutron stars

  1. Aug 26, 2017 #21

    Jonathan Scott

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    Certainly it's the details that matter, and I agree "any" may be an exaggeration depending on the distance. However, when Fermi saw evidence of a possible GRB at exactly the same time as the first GW detection it was dismissed as a coincidence by most, as even with accretion disks involved the theoretical expected amount of EM energy emitted by a black hole merger was orders of magnitude too small to have triggered the apparent GRB detection, which would have needed a significant amount of the collision energy to be radiated in the EM spectrum. So the theory was felt to be stronger than the apparent observation in that case.
    If we have evidence this time of a significant amount of energy being emitted in the EM spectrum but the masses turn out to be too large not to be black holes according to standard theory then that would again suggest that something is wrong with the standard theory, which is always interesting.
    It would be interesting to know why this is being described as a binary neutron star merger; is this because the initial analysis of the GW signal shows relatively light masses (in which case it seems surprising that anything was detected at all) or because the SGRB and other EM emissions suggest that it wasn't a black hole, regardless of the masses?
     
  2. Aug 26, 2017 #22
    I think you meant to say "binary neutron stars" rather than "black holes"...
     
  3. Aug 26, 2017 #23

    Jonathan Scott

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    Actually I lost the word "not" when reordering my words, which I've now edited to correct, thanks.
     
  4. Aug 26, 2017 #24

    mfb

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    Binary neutron star mergers are among the signals LIGO and VIRGO want to find. The range is not as good as for large black holes, but there is a huge volume in space where the sensitivity is sufficient. It wouldn't be surprising to find such an event.
     
  5. Aug 26, 2017 #25

    Jonathan Scott

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    If they really have GW and EM detections of the same binary neutron star merger event, that's pretty amazing regardless. I thought the chances of that with current sensitivities were considered quite small, although obviously they were hoping for it.
     
  6. Aug 26, 2017 #26

    George Jones

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    From "Using Gravitational-Wave Standard Sirens" by Holz and Hughes (The Astrophysical Journal)
    http://iopscience.iop.org/article/10.1086/431341/pdf

     
  7. Aug 27, 2017 #27

    Vanadium 50

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    I just read the paper - I'm not sure I completely buy their argument, but will check with a GR expert Tuesday. It seems to be that even if the signals are scale independent, the transitions won't be (except by accident) - i.e. the inspiral to merge transition and the merge to ringdown.
     
    Last edited: Aug 28, 2017
  8. Aug 28, 2017 #28

    Jonathan Scott

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    I see there are mentions on the web of the gravitational wave event being provisionally referred to as GW170818, which isn't even the same day as GRB 170817A. Someone has created a Wikipedia page for it under that name, saying it occurred on 18th and referring to the Nature article, which as far as I can see doesn't say when the event occurred. I don't know what that date is based on - perhaps simply the day of J Craig Wheeler's "Blow your sox off!" tweet? But he posted about "Rumor of exciting new LIGO source" on 15th August, suggesting more than one event in that case. I wish we could get some more detail!
     
  9. Aug 28, 2017 #29

    phyzguy

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    As @mfb pointed out in post #13, LIGO has confirmed that they are investigating more than one event. The fact that the Chandra archive specifically refers to SGR170817A, the Dark Energy Camera, and aLIGO/Virgo strongly suggests that they all saw this same event, so I think Wheeler's post on 15-Aug must refer to a different event. But we'll have to wait and see.
     
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