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The size or effective distortion field of a gravitational-wave perturbation at any given location in space-time is determined by the distance separating the source and that location. This describes a gradient of gravitational-wave intensity that ranges from the minuscule to the macroscopic. So, a confluence of gravitational sources sufficiently large within the Milky Way galaxy for example or within 1000 ly of the earth will yield a much larger gravity wave, a wave that may even cause damage. So why does no one speak of this?

Qmechanic
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debyton
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    Gravity waves are waves in a fluid driven by gravity. Presumably you meant gravitational waves? (they're a different concept, and yes, the difference in terminology does matter.) – Emilio Pisanty Aug 12 '19 at 15:22
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    The kinds of events that generate gravitational wave detectable over galactic or cosmological distances have two properties: (A) they are rare (so the probability of one happening in our own galaxy in any given year is small) and (B) the are exceedingly energetic (so that each has a worryingly long range over which they represent an existential threat to our species). The second point puts a limit on how large a magnitude event we need to worry about. Because a larger one would be accompanied by other effect that render publishing opportunities ... sparse. But I don't know what the limit is. – dmckee --- ex-moderator kitten Aug 12 '19 at 15:41
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    Possibly answered by this question; – Peter Shor Aug 12 '19 at 19:46

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Because even the strongest sources are fairly weak. The peak strain of GW150914 was only $10^{-21}$. Of course, it would be stronger if it had originate closer to the earth. However, since the strain is inversely proportional to distance, even putting it as close as our nearest star would only increase the strain by a factor of $10^9$ (a bit less actually). Hence, even a bh merger happend at our nearest neigbour in space, the observed strain on Earth would less than $10^{-12}$. This corresponds to a deformation of the Earth of maybe 10s of nanometers.

Hence, we simply do not know of any possible sources that would produce gravitational waves that would be "large" when they would reach Earth. Moreover, if such sources would exist (in the LIGO frequency band), they would have been observed. Hence, not observing any such sources confirms that they don't exist (or are at least extremely rare).

TimRias
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gravitational sources sufficiently large within the Milky Way galaxy for example

The problem comes down to "what example"? Generation gravitational waves requires massive and rapid changes in mass distribution. There are only a few events that can cause this, like black hole mergers. Colliding (normal) stars and even supernovas just don't have the oomph. I suspect the rebound in the later case might be detectable at close range, but likely only well within the ~1000 ly lethal range so it would be difficult to know for sure.

Maury Markowitz
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  • This answer does not address the question asked. Please reread the question more carefully and try again. Thanks – debyton Aug 12 '19 at 19:06