Why does Ligo's reported second detection of gravitational waves and a black hole merger look absolutely nothing like the first detection announced in Februaray?

Here is the data from the first LIGO detection of a black hole merger: enter image description here

And here is the data from the second LIGO black hole merger and gravitational waves announced today (note the solid black line was drawn on the noisey plots by the LIGO team):enter image description here

Both of these cases supposedly represent the same phenomena of a black hole merger. So why are they so very different?

More here: https://ligoskeptic.wordpress.com/2016/06/15/ligo-detects-second-gravitational-waves-ligo-detects-another-black-hole-merger-ligo-bags-new-black-hole-ligo-detects-gravitaional-wave/

It is almost as if LIGO is desperate to call any bump a “black hole merger,” so as to demonstrate reproduicble results.

But the thing about reproducible results is that the actual results must be reproduced, which, in fact, they weren’t. Not even close.

Well, why does Ligo's second detection of gravitational waves and a black hole merger look absolutely nothing like the first? Does anyone harbor any doubts about the LIGO announcements?


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    $\begingroup$ So, should all black hole merger events look exactly the same? Plus, I would edit your post to remove wording that gives a strong impression that you are accusing the facilities of scientific fraud. $\endgroup$ – Jon Custer Jun 15 '16 at 18:18
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    $\begingroup$ 1. Linking to a blog called "ligoskeptic" is not the best way to convince people this is a question they should treat seriously. 2. They explained in the very press conference where these images were shown how they know it was a merger and why it looks different. $\endgroup$ – ACuriousMind Jun 15 '16 at 18:19
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    $\begingroup$ They look the same to me in terms of having an decreasing wavelength (orbital period) until finally reaching the point where no further signal is detected. Beyond that broad match to what we expect to see in a black hole merger, why should they look any more similar? Different black hole masses, different orbital parameters, different black hole rotation rates, different orientation of the system to our line of sight, different distance away. That can affect all manner of things about the signal. But the most important, characteristic feature is clearly present in both. $\endgroup$ – PhillS Jun 15 '16 at 18:20
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    $\begingroup$ In addition it is like asking "why does a violin show different waveforms than a Tuba" $\endgroup$ – anna v Jun 15 '16 at 18:21
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    $\begingroup$ Did you watch the webcast? LIGO have dozens of different templates they use to search the experimental data. Each template covers different masses, energies, spins, etc, etc, and all give a different signal. $\endgroup$ – John Rennie Jun 15 '16 at 18:23

Check out this figure from the most recent LIGO paper. This is the reconstructed gravitational wave signal determined by the analysis. Focus on the zoom of the end of the signal. This is the merger.

enter image description here

The merger part of the GW151226 looks a lot like the merger of GW150914.

The differences tell us about the sources of the gravitational waves in each case. One obvious difference is the length of the signal. LIGO is only sensitive to a range of frequencies about 30Hz to about 1000 Hz. GW150914 is short because the merger occurred at a lower frequency (about 150 Hz). The signal starts at low frequency and "chirps", increasing in frequency over time until merging. Most of the inspiral part of GW150914 was too low frequency for LIGO to detect.

GW151226 merged with a frequency closer to 500 Hz. We can see many cycles of inspiral in this signal. The merger frequency is related to the total mass of the system. GW151226 was produced by a lower mass system (about 20 solar masses total) than GW150914 (about 60 solar masses total).

The next difference is the signal amplitude. Owing to the system's larger mass, GW150914 was higher amplitude. Just looking at the band-pass filtered data in the question, you can say "there's something there". Of course, you can't know its a gravitational wave without the detailed analysis.

GW151226 is much lower amplitude, so you can't just see it in the data. The data just looks like a bunch of noise. It takes a sophisticated analysis to pull GW151226 out from under the noise.

You may also want to check out LIGO's science summary for this paper.

  • $\begingroup$ Thanks! You write, "This is the reconstructed gravitational wave signal determined by the analysis." Correct me if I'm wrong, but it seems that the first detection didn't require such an elaborate "reconstructed gravitational wave signal determined by the analysis." For the first detection, it seemed that the signal was just there. :) Is this correct? $\endgroup$ – Astrophysics Math Jun 15 '16 at 18:34
  • $\begingroup$ @AstrophysicsMath They saw it in September and were analyzing until February. It took them a lot of time to be sure. This was seen last december and is published now $\endgroup$ – anna v Jun 15 '16 at 18:36
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    $\begingroup$ GW150914 was also reconstructed from the analysis in exactly the same way. It was higher amplitude making it easier to see "by eye" in the data. $\endgroup$ – Paul T. Jun 15 '16 at 18:37
  • $\begingroup$ Thanks @PaulT. ! Is there any way to post the original, pre-processed data of the two events side-by-side? Thanks! That would be great! $\endgroup$ – Astrophysics Math Jun 15 '16 at 18:39
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    $\begingroup$ @AstrophysicsMath -- check out the LIGO Open Science Center: losc.ligo.org/about. All of the data from both detections is public. $\endgroup$ – Paul T. Jun 15 '16 at 18:44

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