<p>This question is difficult to answer. If GW behave like &quot;normal&quot; waves, obstacles in the inner <a href="https://en.wikipedia.org/wiki/Fresnel_zone" rel="nofollow noreferrer">Fresnel zone</a> are the main nuisance. The diameter of possible objects should be larger than <span class="math-container">$\lambda/10$</span>. Even big stars are smaller. The possibility of strengthening GW with <a href="https://en.wikipedia.org/wiki/Zone_plate" rel="nofollow noreferrer">zone plates</a> is illusory.</p>
<p>Are GW &quot;normal&quot; waves?</p>

CC BY-SA 4.0
2023-11-17T17:42:10.503Z
2023-11-17T18:10:56.453Z
2023-11-17T18:10:56.453Z
9herbert9
<p>Firstly, gravitational waves (GWs) are not an echo - we measure the direct signal.  </p>

<p>The process you describe here is known as <a href="https://en.wikipedia.org/wiki/Gravitational_lens" rel="noreferrer">gravitational lensing</a>, the deviation of (usually) light rays due to massive objects between the source and the observer.  This also applies to GWs.  The result will be similar - the direction of the waves can be changed, resulting in a distorted image of the source and possibly a 'brighter' image (stronger signal) due to 'gravitational focussing'.</p>

<p>However, LIGO and Virgo do not image GWs, they detect point sources.  Hence, there is no distorted image, but the 'luminosity' of the signal may be affected, resulting in a (somewhat) misjudged distance (although they use a 'luminosity distance', which is not necessarily the same as a current physical separation).</p>

<p>Just as in the case of light, a black hole could trap some of the GW signal that would have reached the observer (gravitons that fall directly into the black hole), if it is directly between the source and the observer, but the gravitational focussing makes it likely that the resulting signal will be stronger rather than weaker.</p>

CC BY-SA 4.0
2019-12-26T14:03:34.420Z
Wait, "they detect point sources" not so much as "the analysis assumes point sources*.  If there were a known lensing or distorting effect along the way, that could probably be added to the simulation. Currently it may not make a difference or may correlate with other fitted parameters and so be impossible to resolve at this time, but that's not the same as saying it can't happen.
uhoh
CC BY-SA 4.0
2020-01-02T04:11:43.580Z
LIGO, like a single-dish radio telescope has only a single "pixel", a "point-sink". A RT can scan an extended source to generate an image, but LIGO, while "directional", can't be scanned during the short (~0.1 sec) event.
user38715
CC BY-SA 3.0
2016-08-23T06:55:43.700Z
2016-08-23T06:55:43.700Z
AstroFloyd
<p>Given that the gravitational wave detected by LIGO was a very weak echo of a very distant event, could it have been "deviated" and distorted on its way here by a sufficiently massive black hole in between?</p>

<p>Would a black hole, since it traps even light, and since gravitational waves travel at the speed of light, absorb some portion of the gravitational wave and leave a "shadow" in its propagation such that if a black hole was between your instrument and an incoming gravitational wave you would have no way to detect it?</p>

<p>If so wouldn't the mass distribution in the Universe look less homogeneous at larger scales (as observed), since gravitational waves would not deform space uniformly and would instead need to "equalize" by forming voids like the <a href="https://en.wikipedia.org/wiki/Bo%C3%B6tes_void" rel="nofollow noreferrer">Boötes void</a>, and filament structures like the <a href="https://en.wikipedia.org/wiki/Pisces%E2%80%93Cetus_Supercluster_Complex" rel="nofollow noreferrer">Pisces–Cetus Supercluster Complex</a> or <a href="https://en.wikipedia.org/wiki/Sloan_Great_Wall" rel="nofollow noreferrer">Sloan Great Wall</a>?</p>

<p>If not, how could a gravitational wave from a distant event possibly affect the gravity well of a black hole closer to the observer? It doesn't seem possible to me that the attenuated ripple in space time from an event so far away could pass right through the gravity well of a closer local black hole like a galactic supermassive black hole.</p>

<black-hole><mass><gravitational-waves><galaxy-cluster><gravitational-lensing>
Would gravitational waves be subject to external gravitational perturbations?
Drunken Code Monkey
# Would gravitational waves be subject to external gravitational perturbations?

(Asked by: username_0 on 2016-08-14)

Given that the gravitational wave detected by LIGO was a very weak echo of a very distant event, could it have been "deviated" and distorted on its way here by a sufficiently massive black hole in between?

Would a black hole, since it traps even light, and since gravitational waves travel at the speed of light, absorb some portion of the gravitational wave and leave a "shadow" in its propagation such that if a black hole was between your instrument and an incoming gravitational wave you would have no way to detect it?

If so wouldn't the mass distribution in the Universe look less homogeneous at larger scales (as observed), since gravitational waves would not deform space uniformly and would instead need to "equalize" by forming voids like the [Boötes void](https://en.wikipedia.org/wiki/Bo%C3%B6tes_void), and filament structures like the [Pisces–Cetus Supercluster Complex](https://en.wikipedia.org/wiki/Pisces%E2%80%93Cetus_Supercluster_Complex) or [Sloan Great Wall](https://en.wikipedia.org/wiki/Sloan_Great_Wall)?

If not, how could a gravitational wave from a distant event possibly affect the gravity well of a black hole closer to the observer? It doesn't seem possible to me that the attenuated ripple in space time from an event so far away could pass right through the gravity well of a closer local black hole like a galactic supermassive black hole.

**Tags:** black-hole, mass, gravitational-waves, galaxy-cluster, gravitational-lensing

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## 2 answers

### Answer by username_2 on 2016-08-23. Score: 7 | Accepted answer

Firstly, gravitational waves (GWs) are not an echo - we measure the direct signal.

The process you describe here is known as [gravitational lensing](https://en.wikipedia.org/wiki/Gravitational_lens), the deviation of (usually) light rays due to massive objects between the source and the observer. This also applies to GWs. The result will be similar - the direction of the waves can be changed, resulting in a distorted image of the source and possibly a 'brighter' image (stronger signal) due to 'gravitational focussing'.

However, LIGO and Virgo do not image GWs, they detect point sources. Hence, there is no distorted image, but the 'luminosity' of the signal may be affected, resulting in a (somewhat) misjudged distance (although they use a 'luminosity distance', which is not necessarily the same as a current physical separation).

Just as in the case of light, a black hole could trap some of the GW signal that would have reached the observer (gravitons that fall directly into the black hole), if it is directly between the source and the observer, but the gravitational focussing makes it likely that the resulting signal will be stronger rather than weaker.

> **Comments:**
> **username_3**: Wait, "they detect point sources" not so much as "the analysis assumes point sources*.  If there were a known lensing or distorting effect along the way, that could probably be added to the simulation. Currently it may not make a difference or may correlate with other fitted parameters and so be impossible to resolve at this time, but that's not the same as saying it can't happen.  
> **username_4**: LIGO, like a single-dish radio telescope has only a single "pixel", a "point-sink". A RT can scan an extended source to generate an image, but LIGO, while "directional", can't be scanned during the short (~0.1 sec) event.  

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### Answer by username_1 on 2023-11-17. Score: -1

This question is difficult to answer. If GW behave like "normal" waves, obstacles in the inner [Fresnel zone](https://en.wikipedia.org/wiki/Fresnel_zone) are the main nuisance. The diameter of possible objects should be larger than $\lambda/10$. Even big stars are smaller. The possibility of strengthening GW with [zone plates](https://en.wikipedia.org/wiki/Zone_plate) is illusory.

Are GW "normal" waves?


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