<p>Gravitational waves should be redshifted.</p>
<p>The gravitational wave signal of an inspiralling binary system, which drifts across  a range of frequencies, does not however yield the redshift of the binary system, since changing the redshift is indistinguishable from changing the mass of the system.</p>
<p>In practice, what is usually done is to estimate the redshift from the luminosity-distance, which can be determined purely from the gravitational wave signal (the so-called &quot;standard siren&quot; technique), combined with a cosmological model.</p>
<p>Of course, where there is an optical counterpart - such as a kilonova - then the redshift of the gravitational wave source can then be estimated from its host galaxy. In which case this offers an independent route to determine cosmological parameters.</p>

CC BY-SA 4.0
2021-11-30T18:27:33.773Z
2021-11-30T18:27:33.773Z
ProfRob
<p>There is no reason to suspect that there are no spectral lines at GW. On the contrary: in binary systems like Algol, two stars have been orbiting each other with an almost constant period for millions of years. The frequency change is so small that you would see a clear spectral line if you could receive the emitted GW. There is no problem building a receiver for <span class="math-container">$f_{GW}=8.073073~\mu$</span>Hz, all that is missing is a suitable antenna.</p>
<p>If the Earth-Algol distance decreases for six months as the Earth orbits the Sun, the reception frequency must be blueshifted. Then follows six months of redshift.</p>

CC BY-SA 4.0
2023-11-12T15:53:09.373Z
"There is no problem building a receiver"  there are lots of problems, mostly that the signal is *so* weak.
James K
CC BY-SA 4.0
2023-11-13T17:28:41.737Z
@James: No, it's really not difficult. They know exactly how to successfully receive and demodulate the signals from extremely distant probes like voyager.
9herbert9
CC BY-SA 4.0
2023-11-13T18:13:48.040Z
Those are em signals.  Not the same.
James K
CC BY-SA 4.0
2023-11-14T10:14:10.710Z
A receiver responds to alternating voltage of a selectable frequency without thinking about the origin of the alternating voltage. The antenna's job is to convert changes in the signal (sound, EM, GW,...) into alternating voltage.
9herbert9
CC BY-SA 4.0
2023-11-14T21:11:59.880Z
There's no alternating voltage in a gravitational wave.
James K
CC BY-SA 4.0
2023-11-15T15:02:33.200Z
I never claimed that the GW has EM nature. It is the task of the antenna to convert the GW into an alternating voltage. Just like a microphone converts sound waves into alternating voltage.
9herbert9
CC BY-SA 4.0
2023-11-12T09:40:41.937Z
2023-11-12T09:40:41.937Z
9herbert9
<p>Gravitational waves originate from significant distances. Presumably they are red-shifted the same amount as the galaxies they originated in. In the absence of gravitational “spectral lines”, can this red shift be measured? And if it can be, is this information useful in calculating distance or inferring the event that created the gravitational waves?</p>

<redshift><gravitational-waves>
Are gravitational waves red-shifted?
Woody
# Are gravitational waves red-shifted?

(Asked by: username_0 on 2021-11-30)

Gravitational waves originate from significant distances. Presumably they are red-shifted the same amount as the galaxies they originated in. In the absence of gravitational “spectral lines”, can this red shift be measured? And if it can be, is this information useful in calculating distance or inferring the event that created the gravitational waves?

**Tags:** redshift, gravitational-waves

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## 2 answers

### Answer by username_1 on 2021-11-30. Score: 8

Gravitational waves should be redshifted.

The gravitational wave signal of an inspiralling binary system, which drifts across a range of frequencies, does not however yield the redshift of the binary system, since changing the redshift is indistinguishable from changing the mass of the system.

In practice, what is usually done is to estimate the redshift from the luminosity-distance, which can be determined purely from the gravitational wave signal (the so-called "standard siren" technique), combined with a cosmological model.

Of course, where there is an optical counterpart - such as a kilonova - then the redshift of the gravitational wave source can then be estimated from its host galaxy. In which case this offers an independent route to determine cosmological parameters.


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### Answer by username_2 on 2023-11-12. Score: 0

There is no reason to suspect that there are no spectral lines at GW. On the contrary: in binary systems like Algol, two stars have been orbiting each other with an almost constant period for millions of years. The frequency change is so small that you would see a clear spectral line if you could receive the emitted GW. There is no problem building a receiver for $f\_{GW}=8.073073~\mu$Hz, all that is missing is a suitable antenna.

If the Earth-Algol distance decreases for six months as the Earth orbits the Sun, the reception frequency must be blueshifted. Then follows six months of redshift.

> **Comments:**
> **username_3**: "There is no problem building a receiver"  there are lots of problems, mostly that the signal is *so* weak.  
> **username_2**: @James: No, it's really not difficult. They know exactly how to successfully receive and demodulate the signals from extremely distant probes like voyager.  
> **username_3**: Those are em signals.  Not the same.  
> **username_2**: A receiver responds to alternating voltage of a selectable frequency without thinking about the origin of the alternating voltage. The antenna's job is to convert changes in the signal (sound, EM, GW,...) into alternating voltage.  
> **username_3**: There's no alternating voltage in a gravitational wave.  
> **username_2**: I never claimed that the GW has EM nature. It is the task of the antenna to convert the GW into an alternating voltage. Just like a microphone converts sound waves into alternating voltage.  

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