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Featured I 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.
     
  10. Sep 27, 2017 #30

    Jonathan Scott

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    I was very excited to hear about the new LIGO/Virgo announcement today, but it wasn't the neutron star event I was hoping for. It was a new black hole merger event, GW170814, which for the first time was seen by Virgo as well as both LIGO locations. Lots more details, including papers, on both www.virgo-gw.eu and https://www.ligo.caltech.edu/.
     
  11. Sep 27, 2017 #31

    phyzguy

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    I was disappointed as well. Since this announcement was about GW170814, I think the announcement about the 170817 event must still be forthcoming. Recalling the J Craig Wheeler tweets (below), today's announcement is probably about the event that triggered the Aug 15 tweet. I'm still expecting a merging NS announcement.

    J Craig Wheeler‏ @ast309 Aug 18
    New LIGO. Source with optical counterpart. Blow your sox off!

    J Craig Wheeler‏ @ast309 Aug 15
    Rumor of exciting new LIGO source.
     
  12. Sep 27, 2017 #32

    DaveC426913

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    Not the first time I've heard an expression of disappointment about this.
    Why is a neutron star merger more exciting than a black hole merger?
     
  13. Sep 27, 2017 #33

    mfb

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    We can learn a lot about the interior of neutron stars. We can't do that for black holes.
     
  14. Sep 27, 2017 #34

    Jonathan Scott

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    A neutron star merger is expected to be visible in various parts of the electromagnetic spectrum, providing a huge amount of additional information compared with a black hole merger.
     
  15. Oct 4, 2017 #35

    phyzguy

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    The latest I'm hearing is that there will be a press conference on this event on Oct 16. Stay tuned.
     
  16. Oct 11, 2017 #36

    phyzguy

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  17. Oct 12, 2017 #37

    mfb

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    From the panel:

    * Vicky Kalogera is an expert for binary neutron stars and white dwarfs.
    * Andy Howell and Ryan Foley use supernovae to study dark energy and work on quick optical follow-up observations for the supernovae.
    * Marcelle Soares-Santos studies dark energy and cosmological gravitational waves
    * David Sand is another supernova expert
    * Nial Tanvir studies gamma ray bursts, and found evidence that short GRBs are caused by binary mergers
    * Edo Berger studies GRBs and other supernovae
    * Eleonora Troja studies GRBs
    * Alessandra Corsi studies GRBs
    * Various LIGO/Virgo people, of course.

    We get a very consistent picture here. I predict that LIGO and Virgo measured a binary neutron star or neutron star black hole merger, which was also seen as short-duration gamma ray burst.
     
  18. Oct 13, 2017 #38

    Jonathan Scott

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    It's difficult to keep secrets with so many people involved. A Google search already finds a two web pages containing abstracts of papers about this event from the electromagnetic point of view (X-ray and optical); the pages themselves have been removed, but Google has cached them!

    Also, Francis Villatoro "emulenews" has tweeted a brief summary at https://twitter.com/emulenews/status/917302944990728193 as follows:

    Non-official GW170817 = time coincidence with short GRB170817A (Fermi GBM, INTEGRAL); optical counterpart localization in NGC4993 (40 Mpc)
    Official press-conference LIGO/Virgo on Oct 16 – keep tuned!
     
  19. Oct 15, 2017 #39

    mfb

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    ESO announced a press conference "to present groundbreaking observations of an astronomical phenomenon that has never been witnessed before" at the same time as the LIGO press conference. Is this the same conference, or do they announce the same thing in separate conferences, or is this unrelated? The timing is very suspicious.

    16:00 CEST, 14:00 UTC, 10:00 EDT, or 11:20 after this post.
     
  20. Oct 16, 2017 #40

    Borek

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    16th October, day of two important announcements: one astronomical and the other related to WiFi security (google KRACK).
     
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