Learning GRT: Why the High Frequency Search?

[Bill_K]

In particular, two orbiting neutron stars emit gravity waves mostly in their "equatorial" rotation plane and not at the "poles". The wave intensity angular characteristic is similar to that of the dipole antenna radiation pattern. Am I right?)

Thanks to the quadrupole nature of gravitational waves, dipole waves do not exist. This can also be understood as the result of momentum conservation. For a binary star system, the leading source term is a rotating quadrupole moment.

As I pointed out above in #14, there is radiation in the polar direction as well, although the polarization is different.

 

[Bill_K]

That said, could we see some effect of gravity waves in some distant stars light characteristics or in some exotic phenomena like gravity lensing pictures?

You haven't specified which directions the gravitational wave and the light are traveling, but if they're traveling more or less parallel to each other, the effect most easily observable at a distance will be that the light ray is deflected sideways.

PS - It's helpful to call them by their proper name, gravitational waves. Gravity waves are something else.

 

[haael]

Thanks to the quadrupole nature of gravitational waves, dipole waves do not exist. This can also be understood as the result of momentum conservation. For a binary star system, the leading source term is a rotating quadrupole moment.

As I pointed out above in #14, there is radiation in the polar direction as well, although the polarization is different.

OK, I understand, but please correct me if I'm wrong.

Gravitational waves, just as electromagnetic waves, have amplitude, frequency and polarization. Now: is it possible to arrange such an emitter that radiates waves in non-isotropic way? For example a setup, where the amplitude is maximal near the equator and zero near the poles?

You haven't specified which directions the gravitational wave and the light are traveling, but if they're traveling more or less parallel to each other, the effect most easily observable at a distance will be that the light ray is deflected sideways.

So if we happen to observe two merging stars at least one of is bright, then we would see the effects of the gravitational waves in the image? Have such experiments ever been performed?

 

[Bill_K]

Now: is it possible to arrange such an emitter that radiates waves in non-isotropic way? For example a setup, where the amplitude is maximal near the equator and zero near the poles?

The wave must have a polarization, and so from the viewpoint of the detector, the source must have a preferred direction - it must look asymmetric.

For any source that is cylindrically symmetric, an observer along the polar direction will NOT see a preferred direction, so there can't be any waves coming at him. E.g. if two stars collide directly, this is a cylindrically symmetric situation, and an observer situated right along the collision axis won't see any radiation.

 

[haael]

For any source that is cylindrically symmetric, an observer along the polar direction will NOT see a preferred direction, so there can't be any waves coming at him. E.g. if two stars collide directly, this is a cylindrically symmetric situation, and an observer situated right along the collision axis won't see any radiation.

Thanks, that is the clear answer.

 

[lsume]

I am trying to learn GRT so I can answer questions for myself. But I might croak first, so I’ll ask here. That gravity wave interferometer they are building out in Richland, Washington - I obviously haven’t read all the technical papers on their web site, but I am pretty sure one I did read showed a spectrogram or PSD with search frequencies of 40 Hz and above. I understand that the behavior of the Taylor-Hulse binary is the only empirical evidence we have so far of gravity waves - and its orbital period is around 8 hours. Can anyone explain why they are looking at such high frequencies? Shouldn’t we be looking for ultra-low frequency waves with periods like 8 hours (or maybe half that for these type waves)? Do we expect stuff falling into a black hole to emit broad-band high frequency gravity waves? Thanks for any enlightenment.

With the recent discovery of gravitational waves, I have a question. Knowing the frequency and wave length of these waves, can a harmonic wave increase gravity in the sphere of influence and conversely can gravitational force be eliminated or reduced by generating a wave 180 degrees out of phase with the gravity wave. I suppose there are many wondering the same thing.

 

[haael]

No. Gravity waves don't cancel the gravity attraction, just as light doesn't cancel magnetic attraction.

What gravity waves could cancel are tidal forces. In a pretty boring way.