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A In LIGO’s pulse, how much comes from BH merging/ inspiraling

  1. Apr 7, 2016 #1
    The inspiralling oscillations of ~20ms period (reducing to ~5ms) appear much stronger than the ringdown of ~ 3ms period (noisy, at resolution limit). Merger happens at ~440ms in the figure of Abbott et al. (Phys Res Lett link.aps.org/doi/10.1103/PhysRevLett.116.061102). This would agree with published calculations of the black-hole merger process giving under 0.1% of the mass released in gravitational energy, while the LIGO studies found ~ 5% of the total mass (of ~60 solar masses) in the whole pulse. Yet descriptions tend to say the energy comes from the merger itself. Doesn’t most of the merger energy disappear in the black hole; while LIGO cannot be said to verify that under 0.1% comes out, but does verify the 5% release in the inspiralling?
     
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  3. Apr 7, 2016 #2

    mfb

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    "Binary black hole merger [event]" usually includes the inspiralling directly before as well.
     
  4. Apr 8, 2016 #3
    Yes, but the modelling of the gravitational waves from inspiralling applies to a binary neutron star system as well as a black-hole binary. The merging process for black-holes meeting head-on (no inspiralling) give 0.055% and 0.089% (two models) release of the mass-equivalent in gravitational wave energy (http://blackholes.ist.utl.pt/fp-content/attachs/thesis_helviwitek.pdf). Does this mean that the "ring-down" tail in the LIGO signal cannot be said to be energy released in the actual merging of the model calculations? Could it be an after-pulse of the 5% released in the inspiralling, eg. ringing of the gravitational field outside the event horizon of the merged body?
     
  5. Apr 11, 2016 #4

    Dale

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    It sounds like you are trying to say that an "actual merging" can only be head-on. I don't believe that "actual merging" is a defined term in the literature, so you are free to define it that way if you like. Should you define it that way then I doubt anyone will consider it to be a particularly important concept.
     
  6. Apr 14, 2016 #5
    The LIGO team paper interprets their signal as inspiralling, followed by merging after the event horizons touch, and then ring-down as the system relaxes. The instant of touching is important as defining the event horizon sizes and thus constraining the masses (29 and 33 times the solar mass) I never said merging can only be head-on; but such calculations do exclude the inspiralling pulse - the published models do take the simplified head-on case and their results show relatively little energy in the gravitational pulse from the relaxation (ringing-down) of the gravitational field outside the event horizon. If this ring-down is below the resolution of the LIGO instrument, if follows that LIGO was unable to detect the merging of the two black holes. The team could then not sustain their claim to first direct detection of black holes - which is surely of pretty high importance ! It's a surprise than no-one from the huge LIGO team has yet popped up on this Forum to justify their claim.
     
  7. Apr 14, 2016 #6

    PeterDonis

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    I'm not sure I understand; are you claiming that there are no published models of the case of a black hole merger that is not head-on?
     
  8. Apr 14, 2016 #7

    mfb

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    LIGO calculated the case of two black holes orbiting each other, coming closer and finally merging. Those events generate a large amount of gravitational waves, and the predicted shape matches closely what LIGO observed. I don't understand where you see a problem.

    LIGO probably has calculations for head-on mergers without orbiting as well, but those do not match the observations.

    The chirp mass, the critical part of the mass estimate, comes from the time before the black holes merge.
     
  9. Apr 14, 2016 #8

    Dale

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    @MaxWallis if you have any specific scientific reference which supports your criticism of the LIGO results, then I suggest you produce it. Otherwise you should review the forum rules on personal speculation.

    No, the instant of touching is not particularly important, no single instant is. The entire inspiral/merge/ring-down waveform is important, that is what was predicted by GR and detected by their matched filter.

    Obviously. The quadrupole moment of a head-on collision changes relatively little so little energy will be radiated. That is precisely the reason that the detectors will preferentially detect spiral-in collisions. Comments about the low GW energy of head on collisions are simply irrelevant to the LIGO results.

    Why would the LIGO team do that? They have justified their claim in the scientific literature. Anyone who wishes to criticize their claim may do so in the scientific literature also. Until that happens neither the criticism nor the justification is suitable for PF anyway.
     
  10. Apr 14, 2016 #9

    George Jones

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    Yes, there is ring-down phase during/after a black hole merger caused by a head-on collision of black holes. This is discussed in section 10.2 "Head-on collision of two black holes" of the advanced book "Numerical Relativity: Solving Einstein's Equation's on the Computer". As mentioned above, this scenario almost certainly could not be matched to the actual data.
     
  11. Apr 17, 2016 #10
    Thanks, as the team describe, most of the G-wave pulse is from the spiralling in - the orbit-chirp frequency and its rate of change determine the sizes around 30 solar masses. What I suspected is that the ring-down signal from the spiralling is likely to swamp any small signal from merging (at <0.1% compared with the tail of ~5%).
    Picturing the merger as preceding the ring-down part of the signal (Abbott et al. paper) does not mean that the latter was a consequence of merger, so their statement "GW150914 demonstrates the existence of black holes more massive than ~25M⊙" depends on excluding other compact stellar objects (reg. neutron or quark stars) of sizes comparable to the Schwarzschild radius, a topic the study doesn't really address.
     
  12. Apr 17, 2016 #11

    mfb

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    The different processes have a nice time-ordering.
    No ring-down without merger. I don't think it is useful to talk about "consequences" here. Also, how is that related to anything else?
    The study does, and black holes are the only option consistent with observations.
    If you think you have an alternative explanation for the signal, publish it. We cannot discuss unpublished material here, this is against the forum rules.
     
  13. Apr 17, 2016 #12

    Dale

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    You speak as though these are two distinct features of the GW. The are not. The waveform that they detected using their matched filter included both.

    You also speak as though the GW energy for a spiral in collision can be separated into a spiral in ringdown and a head on merger. The head on merger energy is irrelevant for the spiral in GW energy.

    The distinctions you are drawing are artificial.
     
  14. Apr 17, 2016 #13
    Don't wave theories from a finite source give a decay train due to the front and back parts; otherwise can the ring-down part of the pulse not be interpreted as from the pre-merger G-field over a few times the radial scale relaxing?

    Only if you dismiss other explanations of 30Ms condensed stellar bodies. They dismiss neutron stars on the basis of the TOV limit of 2Ms, whereas there are published theories raising this limit significantly and published astrophysical data implying heavier pulsar-binaries. Also published theories of quark stars and other exotic options. I wouldn't expect the LIGO team to model the merging of these, but they might consider specifically if the ring-down part of the pulse is consistent with black-hole merging and if the merging part is below the instrument threshold or not.
     
  15. Apr 17, 2016 #14

    mfb

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    Gravitational waves do not have dispersion.
    No, not at all.
    They violate relativity. You can always say "okay, but what if GR is invalid", but then you need an alternative model that fits to all the observations. Do you have that?
     
  16. Apr 17, 2016 #15

    PeterDonis

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    The highest limit I'm aware of is about 3 Ms. Do you have a reference for a higher limit?

    If the neutron star limit is 3Ms, the limit on a pulsar binary is 6 Ms. To get to 30 Ms you would need a compact system of 10 pulsars. That is extremely unlikely, and I'm not aware of anyone claiming that as an explanation of compact 30 Ms objects.

    I'm not aware of any published theory of quark stars that claims that as an explanation of a 30 Ms compact object.

    By "other exotic options" do you mean the papers we are discussing by PM, or is there something else? If the latter, do you have a reference?
     
  17. Apr 18, 2016 #16
    The Maurya et al. paper I've cited and others related/cited find higher limits depending on pressure anisotropy. BTW, I don't buy their instability argument based on dp/d(rho) [elsewhere called causality condition]; as far as gravitational energy exerts a pressure-force, that has to be included.

    It would surely be dynamically unstable. And not produce the binary orbiting signal of LIGO.

    I haven't seen numbers - the Maurya etc. people have charged quark-star models. Gravastars http://en.wikipedia.org/wiki/Gravastar and Mitra-Glendinning's eternally contracting models.
     
  18. Apr 18, 2016 #17

    Dale

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    OK, so since there seems to be no published alternative source that could produce the signal, this thread is closed.

    If such a publication becomes available in the near future then let me or PeterDonis know and we can reopen it.
     
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