# Tag Info

36

The actual image isn't much. I was able to find it from Science, and this is all it is: It's just a ripple, seen at slightly different times from two different observatories. The shift fits perfectly by shifting it by the speed of light difference in their locations. Thus is the proof of gravity waves. It should be noted that the reason there are two ...

29

First of all, I think your question belies a misunderstanding of the nature of the LIGO observatories. The nature of the detectors is that they act like a microphone, as opposed to a camera. What that means is that they are sensitive to gravitational waves coming in from most directions, but don't have an ability to distinguish where the waves came from. ...

26

General relativity predicts that there are only two possible polarizations of gravitational waves, the so-called "tensor" polarizations $+$ and $\times$. It turns out you can show that the tensor polarizations actually don't lead to time dilation, making any attempted measurement of it pointless. The short answer, then, is that we don't expect to ...

14

LIGO didn't "see" anything. It monitors the relative lengths of the paths taken by two laser beams in vacuum pipes about 4km long (although the laser path consists of about 75 trips up and down the arms) and at right angles to each other. A gravitational wave, travelling at the speed of light, changes the ratio of these lengths (one gets shorter, one gets ...

11

No, for several reasons. The expected gravitational wave signature of a core collapse supernova looks nothing like that from a merging black hole binary system, so no sensible comparison can be done with GW150914. The maximum frequency of the gravitational waves from a merger decreases with increasing mass. The expected frequencies from a core collapse are ...

8

There are two issues: Would there be gravitational waves to be detected and would LIGO detect them. On the first issue, gravitational waves are quadrupolar, and a cylindrically symmetric system will not produce any. (Specifically, the second time derivative of the quadrupole moment of an isolated system's stress–energy tensor must be non-zero in order for ...

7

The answer by @HDE 226868 addresses the current attempts by LIGO/Virgo and PTAs to detect alternate gravitational wave (GW) polarization states, which have not been detected. In that answer, this SE question is cited, which shows that gravitational waves being interpreted as tensor perturbations of the flat (Minkowski) spacetime produces only two non-trivial ...

7

According to the GW150914 tutorial, this is what Advanced LIGO L1 and H1 detectors originally saw: You can download the raw data from this tutorial. The other answers show already processed (whitened, filtered, shifted by 7 ms, inverted) waveforms.

6

Updated to use reported timing confidence intervals instead of trying to infer those from reported sky location resolution uncertainties. The latter approach was misleading because the sky location has been further resolved using more information than just the arrival time difference. Beware that I am neither an astronomer nor involved with aLIGO. I ...

5

Here's how my non-scientist mind envisions it. I draw a straight line between the two LIGO sites on a map. Then I take another straight line (like a straight edge/ruler) that represents the GW coming in. If the GW line is coming from the south exactly parallel with the line I drew on the map, then both sites would detect the "chirp" at exactly the same time ...

5

This paper should tell you all you need to know about how LIGO observes and localizes gravitational waves, and in particular its blind spots. The map below is taken from the paper and shows the observability of the system when in the HLV configuration (Hanford-LIGO, Livingston-LIGO & Virgo). To triangulate a source by definition you need at least 3 ...

5

The actual mechanism of measurement that LIGO used is laser interferometry, so one reasonable interpretation of what LIGO "saw" would be the interference pattern caused by the gravity waves, which would "look" something like this: Unfortunately I could not find an image of the actual laser interference that LIGO mentioned; it's probably too small for ...

5

Yes. Gravitational wave observatories like the proposed eLISA laser interferometer may be able to detect gravitational waves that originate from the early moments of the big bang itself. If some part of the big bang energy goes into gravitational waves then those waves will be redshifted by expansion and waves produced in the first $<10^{-10}$ s should be ...

4

In Cartesian coordinates, the flat spacetime interval can be written in terms of invariant proper time $\tau$ as $$c^2 d\tau^2 = c^2dt^2 - dx^2 - dy^2 - dz^2\ ,$$ where $t$ is some universal time coordinate and the usual notation convention that $dt^2 = (dt)^2$ is used. For all stationary observers, in the frame of reference for which $x, y, z$ are defined, ...

4

The confusing language is due to wave-particle duality. At higher frequencies and larger distances, the particle model is more accurate: Ray-tracers can track photons as they reflect, refract and scatter (but not diffract) and photons arrive in discrete events. But at low frequencies the wave model is more accurate: individual photons are less important and ...

4

They are looking at one very specific degree freedom of the individual mirrors. The collective oscillatory motion the mirror in the direction of the laser beam. When isolated from the full equations of motion for the mirror, the effective equation of motion for this degree of freedom is a harmonic oscillator with an effective mass of 10 kg (remember the ...

4

Gravitational wave detectors have a frequency range that they are sensitive to. In the case of LIGO it is about 10Hz to 1kHz. The lower limit is imposed by seismic noise, the upper limit by "shot noise" (basically not having enough photons to sample the interferometer path difference at high frequencies). LISA is in space and doesn't have the problem with ...

4

There's a detailed graph of it here: https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves What is the most precise reference for your query is the Time-Frequency graphs in black and green, also called waterfall graphs, spectrographs, sonograms and so forth. On the Y axis, the width of the green smudge is about 30-50Hz, That's the ...

3

The signal does not travel from Livingston to Hanford. The signal comes in with an angle of about 45 degrees to the line joining the two, and has the same amplitude on planes perpendicular to the direction of travel (the peaks of water waves are not along the direction of travel of the water waves but perpendicular to the direction of travel). Thus if the ...

3

The addition of more detectors will immensly help event localization. To get an understanding of the calculation look at the old LORAN navigation system. This system used synchronized transmitters, and the receiver measured the difference in time. The receiving device measured the time between signals from multiple sources, that chirp at the same time. If ...

3

A fact sheet published by the LIGO collaboration at the time of the announcement of GW150914 (that's the official name of the first detection) gives the peak frequency as "~250 Hz". The Abbott et al. paper also quotes a value of 35 to 250 Hz in the abstract (I haven't checked for more precise measurements later in the paper, I'm sure the OP or other ...

2

The waveform of binary inspiral was about 100ms with a peak for every rotation, about 10 waves/rotations were measured, ranging from 30 to 200Hz. The average female voice has a fundamental frequency of about 200hz, to have some idea, and a typical pitchfork is about 440Hz. The waveform for a head on collision would about 5ms, probably less, kindof like a ...

2

The blind spots are caused by the way the detectors work. They are sensitive to a gravitational wave (GW) changing the relative path length along interferometer arms at right angles to each other. Gravitational waves come in two polarisations (plus and cross). These polarisations cause alternate perpendicular expansions and contractions in space, but are ...

1

The initial detections were made without using squeezed light. Squeezed light was introduced in early 2019. It has the effect of increasing the detection sensitivity by about 15% above 50 Hz (Tse et al. 2019). Since gravitational wave strain scales inversely with distance, this expands the surveyed volume by about 50%.

1

I don't know whether it's interesting for you, but here is the link of the paper that was published about those observations: http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102 Once the answer above is quite straightforward! What the paper says (in short) is that LIGO has observed a transient gravitational-wave signal, and these observations ...

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