The LIGO team reported on June 15, 2016, their second confirmed detection of coalescing binary black hole pair generating a gravitational wave. This was published in Physical Review Letters,1 with an abstract that reads (with some editing in […]’s and emphases added):
We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of [about] 3.4 × 10-22. The inferred source-frame initial black hole masses are 14.2 and 7.5 [solar masses, i.e. mass of the sun], and the final black hole mass is 20.8 [solar masses]. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440 Mpc [about 1.4 billion light-years] corresponding to a redshift of 0.09±0.03. All uncertainties define a 90% credible interval.
Estimated gravitational-wave strain from GW151226 projected onto the LIGO Livingston detector with times relative to December 26, 2015 at 03:38:53.648 UTC. This shows the full bandwidth, without the filtering used for Fig. 1. Top: The 90% credible region for a nonprecessing spin waveform-model reconstruction (gray) and a direct, nonprecessing numerical solution of Einstein’s equations (red) with parameters consistent with the 90% credible region. Bottom: The gravitational-wave frequency f (left axis) computed from the numerical-relativity waveform. The cross denotes the location of the maximum of the waveform amplitude, approximately coincident with the merger of the two black holes. During the inspiral, f can be related to an effective relative velocity (right axis) given by the post-Newtonian parameter v/c=(GMπf/c^3)^1/3 , where M is the total mass. (Click on image for larger version.)
This result further strengthens the argument for stellar mass size black holes and for their correct prediction by Einstein’s general relativity. As I have written before this largely falls into the category of operational science. Some assumptions are necessarily required, but the waveform (see right) extracted from the received signal very precisely matches the expected waveform. Read What impact does the detection of gravitational waves have on biblical creation?2 Continue reading
The following is written as a rebuttal to an article titled “In Response to Hartnett’s Article”1, dated February, 2016, written by Mr Barry Setterfield. (This rebuttal is also available on creation.com.) The author states that he received the following email, along with a number of others with the same questions about the Hartnett article:2
I have a question regarding a CMI article by a Dr. John Hartnett entitled “What impact does the detection of gravitational waves have on biblical creation?” Dr. Hartnett makes the claim that the recent discovery of gravity waves uses a modern value for the speed of light to calculate the masses of the two black holes which collided to produce those waves, so he concludes (a bit too quickly in my opinion) that “the cdk idea is [to be] thoroughly rejected”. I wanted your take on this issue. Here’s the relevant portion of the article:
“Interestingly, the calculation used to determine the masses of the merging black holes in the analysis of this week’s discovery employed the standard canonical speed of light, c. That is, it used the same constant value that we measure today. Does that tell us something? I think it does.
Inspiral of black holes and associated waveform. Ref. 3. Click image for enlarged view.
Some biblical creationists favour a much higher value for the speed of light in the past, from a time soon after creation of the universe, after which it decreased or decayed down to its current value (the concept is known as cdk, from c-decay). They use this supposed much higher value of c in the past as a solution of the biblical creationist light-travel time problem. But now this new discovery shows that, at a time in the past representative of a distance in the cosmos of 1.3 billion light-years, the value of the speed of [sic] (c) was identical to today’s current value. Regardless of which creationist cosmology you like, the gravity waves observed in September 2015 must have left their source very soon after Creation week. Thus the cdk idea is thoroughly rejected.”
To which Setterfield responds. So I respond to his response (indented black text) with my comments (blue text) interspersed below his. Continue reading
The discovery of gravitational waves
Figure 1: The gravitational-wave event GW150914 observed by the LIGO Hanford (H1, left column panels) and Livingston (L1, right column panels) detectors. Times are shown relative to 14 September 2015 at 09:50:45 UTC. For visualization, all time series are filtered with a 35–350 Hz bandpass filter to suppress large fluctuations outside the detectors’ most sensitive frequency band, and band-reject filters to remove the strong instrumental spectral lines. Top row, left: H1 strain. Top row, right: L1 strain. GW150914 arrived first at L1 and 6.9 ms later at H1; for a visual comparison, the H1 data are also shown, shifted in time by this amount and inverted (to account for the detectors’ relative orientations). Second row: Gravitational-wave strain projected onto each detector in the 35–350 Hz band. Solid lines show a numerical relativity waveform for a system with parameters consistent with those recovered from GW150914 confirmed to 99.9% by an independent calculation (details in original). Shaded areas show 90% credible regions for two independent waveform reconstructions. One (dark gray) models the signal using binary black hole template waveforms. The other (light gray) does not use an astrophysical model, but instead calculates the strain signal as a linear combination of sine-Gaussian wavelets. These reconstructions have a 94% overlap. Third row: Residuals after subtracting the filtered numerical relativity waveform from the filtered detector time series. Bottom row: A time-frequency representation of the strain data, showing the signal frequency increasing over time. (Caption edited from the original, Ref. 6.)
On 14 September 2015 at 09:50:45 UTC the two gravitational wave detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO)—one at Hanford, Washington and the other at Livingston, Louisiana—simultaneously observed a transient gravitational-wave signal. The signal exhibited the classic waveform predicted by Einstein’s general relativity theory for a binary black hole merger, sweeping up in frequency from 35 to 250 Hz, and exhibited a peak gravitational-wave strain of 1.0 × 10−21 at the detectors.1
The two detectors recorded the same signal, which matched the predicted waveform for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a statistical significance greater than 5.1σ (where 1σ represents 1 standard deviation).2 In other words, the detection is highly likely to be real.
The source lies at a luminosity distance of about 1.3 billion light-years corresponding to a redshift z ≈ 0.09.3 The two initial black hole masses were 36 M⊙ and 29 M⊙,4,5 and the final black hole mass is 62 M⊙, with the equivalent of 3 M⊙ radiated as gravitational waves. The observations demonstrate for the first time the existence of a binary stellar-mass black hole system but, more importantly, the first direct detection of gravitational waves and the first observation of a binary black hole merger. Continue reading