37
votes
Accepted
What did LIGO Actually See? (Gravitational waves discovery)
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 ...
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30
votes
What did LIGO Actually See? (Gravitational waves discovery)
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 ...
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26
votes
Accepted
Why are there not yet any instruments dedicated to registering time dilation caused by passing gravitational waves?
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 ...
- 36k
15
votes
What did LIGO Actually See? (Gravitational waves discovery)
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 ...
- 146k
14
votes
Accepted
Can the Hubble constant be measured directly?
The universe doesn't expand on such small scales. In fact there is no expansion even on the scale of the local group of galaxies. It is only when you look at more distant galaxies that you see the ...
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12
votes
Are gravitational waves emitted equally in all directions?
The gravitational wave strain is not isotropic. More power is emitted (per unit solid angle) along the orbital axis of the binary than in the orbital plane.
For a circular orbit (and they tend to be ...
- 146k
11
votes
Is a Hertz ratio to 65M ☉ proof that Betelgeuse had a core collapse in 1491 from a gravitational wave on January 14, 2020?
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 ...
- 146k
11
votes
At the intersection of engineering and astronomy in its structure as a scientific discipline
Yes, there is an intersection between astronomy and engineering. In my experience, it will mostly be astronomers who have a flair for technology and instrumentation who at some point, either from the ...
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9
votes
Accepted
Would LIGO Detect Head-On Collision?
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 ...
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9
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Expected nature of LISA's data; will it be more like a forest of static peaks, or a series of individual events?
LISA's data will be very different from LIGO's. It will typically "see" many sources at the same time. Most prominently:
Mergers of pairs of supermassive blackholes. These will be very much like a ...
- 2,511
8
votes
What did LIGO Actually See? (Gravitational waves discovery)
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 (...
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8
votes
Can LIGO distinguish rotating and non rotating black hole collisions?
Yes it can - well, to some extent. If you look at any of the merging black hole discovery papers you will see that they try and put constraints on the dimensionless spin parameter and orientations of ...
- 146k
7
votes
Why are there not yet any instruments dedicated to registering time dilation caused by passing gravitational waves?
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 ...
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7
votes
At the intersection of engineering and astronomy in its structure as a scientific discipline
Yes, this intersection exists, in the instrumentation, and somewhat in mission design.
When it gets to designing instruments, it needs knowledge of both worlds: what does science want, how and in what ...
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6
votes
Accepted
Gravitational wave detection time difference between LIGO Livingston and LIGO Hanford
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 ...
- 1,052
6
votes
Gravitational wave detection time difference between LIGO Livingston and LIGO Hanford
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 ...
- 161
6
votes
What did LIGO Actually See? (Gravitational waves discovery)
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 ...
- 253
5
votes
Can Gravitational astronomy look beyond the CMB?
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 ...
- 146k
5
votes
Accepted
Does LIGO have a blind spot?
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 ...
- 1,481
5
votes
Accepted
Which things can LIGO see that LISA can't, and vice-versa?
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 ...
- 146k
4
votes
LIGO gravitational wave chirp signal frequency
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 ...
- 4,188
4
votes
Accepted
How can there only be "11 phonons" in the mirrors of LIGO interferometers?
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 ...
- 822
4
votes
How can there only be "11 phonons" in the mirrors of LIGO interferometers?
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 ...
- 2,511
4
votes
Why are there not yet any instruments dedicated to registering time dilation caused by passing gravitational waves?
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 ...
- 146k
4
votes
Are gravitational waves emitted equally in all directions?
As a supplement to @ProfRob's answer.
The answer there only takes into account the leading order contribution coming from $\ell=m=2$ quadrupole mode. For binaries that are far from merger, and merging ...
- 2,511
3
votes
Accepted
Response function of LIGO
This is a brief and very general answer which points to some papers which deal with LIGO calibration in detail. More detailed answers might be possibly given on either point, but can easily cover ...
- 17.7k
3
votes
LIGO gravitational wave chirp signal frequency
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. ...
- 1,274
3
votes
Gravitational wave detection time difference between LIGO Livingston and LIGO Hanford
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 ...
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3
votes
Gravitational wave detection time difference between LIGO Livingston and LIGO Hanford
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, ...
- 31
2
votes
What did LIGO Actually See? (Gravitational waves discovery)
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 ...
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