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26 votes
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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 ...
HDE 226868's user avatar
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14 votes
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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 ...
James K's user avatar
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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 ...
ProfRob's user avatar
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12 votes
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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 ...
pela's user avatar
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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 ...
ProfRob's user avatar
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10 votes
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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 ...
Mark Olson's user avatar
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9 votes

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 ...
TimRias's user avatar
  • 2,720
8 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 ...
planetmaker's user avatar
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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 ...
ProfRob's user avatar
  • 155k
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 ...
Daddy Kropotkin's user avatar
5 votes
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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 ...
ProfRob's user avatar
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5 votes
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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 ...
Kevin Kostlan's user avatar
5 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 ...
TimRias's user avatar
  • 2,720
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 ...
ProfRob's user avatar
  • 155k
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 ...
bandybabboon's user avatar
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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 ...
TimRias's user avatar
  • 2,720
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 ...
ProfRob's user avatar
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3 votes

At the intersection of engineering and astronomy in its structure as a scientific discipline

It is quite common. For example, ASTRON, the Netherlands Institute for Radio Astronomy, has astronomers and engineers at work. They work together, since an astronomer should not need to know about ...
Mast's user avatar
  • 223
3 votes

Telling bounces in LIGO interferometer

This number is the "effective number" of times the light bounces up and down, as judged by the sharpness of the resonance in the Fabry Perot arms of the interferometer. The arms consist of a ...
ProfRob's user avatar
  • 155k
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 ...
planetmaker's user avatar
  • 19.9k
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 ...
W Unruh's user avatar
  • 31
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. ...
FJC's user avatar
  • 1,324
2 votes

Does LIGO have a blind spot?

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. ...
ProfRob's user avatar
  • 155k
2 votes
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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?

A discussion of the analysis of LISA data is given by Boileau et al. (2021). Specifically, they provide an in depth analysis of exactly the point you are interested in - to what extent is LISA able to ...
ProfRob's user avatar
  • 155k
2 votes

Would LIGO Detect Head-On Collision?

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 ...
bandybabboon's user avatar
  • 4,268
1 vote
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Was quantum metrology important for gravitational-wave astronomy?

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 ...
ProfRob's user avatar
  • 155k
1 vote

Expected nature of LISA's data; will it be more like a forest of static peaks, or a series of individual events?

Our galaxy hosts probably more than $10^6$ binary stars with periods ranging from one day to about 100 days. Each is thought to have at least six planets orbiting it. Each planet has a different ...
9herbert9's user avatar
  • 101
1 vote

What did LIGO Actually See? (Gravitational waves discovery)

It sees waveforms as shown in the drawns above. Some examples you can get and explore by yourself from here: BH-NS merger dataset NS-NS merger dataset
circassia_ai's user avatar

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