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I am not an expert on GR or gravitational waves but i have been reading about them and i wondered about where and how do these gravitational waves dump their energy? I read that the black hole collision detected by LIGO had energy equivalent to the mass of 3 solar masses in the form of gravitational waves. So, my question is where does this energy end up going?

Aniansh
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The energy propagates circularly (if far enough like we are), and if it runs into some matter it interacts very weakly. We detected it because it transformed some amount (a very small part of its energy, that's why it was so hard to detect, people have tried for over 50 years, and only now have our detectors become sensitive enough) of its energy in moving, ever so slightly, the mirrors used in the detection apparatus, so it lost some energy. Without some energy transfer we would not have detected it ever. Equivalently, it shortened the distance traveled by the light in one leg, and increased it in the other leg of the interferometer used to detect the gravitational wave.

Bob Bee
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  • Doesn't the energy spread out radially instead oh circularly which would limit the energy transfer to a single plane and would severely decrease our chances of detecting such an event. Also, can you please explain the process by which the wave transferred the energy to the detectors? Is it the only way by which gravitational waves may impart energy to matter? – Aniansh Feb 15 '16 at 06:05
  • Did the wave actually physically move the interferometer or did it just temporarily decrease and increase the space between the atoms of the legs? – Aniansh Feb 15 '16 at 06:07
  • @Aniansh it created a type vibrations. That is why great care is taken to diminish external vibrations by suspending the detectors , so as not to get confused with the sought signal . The distances between the hanging detectors temporarily changed , the space between them. – anna v Feb 15 '16 at 06:43
  • @Aniansh watch the first 45 minutes of this web cast https://www.youtube.com/watch?v=_582rU6neLc . The detectors are suspended, the distance of kilometers changed with the passing of the wave – anna v Feb 15 '16 at 06:46
  • @annav okay I understand that part but what about the propagation? Doest the propagation happen in a single plane? – Aniansh Feb 15 '16 at 08:29
  • it is like light, very very weak light coming at the detector. plane wave at such distance from source. – anna v Feb 15 '16 at 09:09
  • Yes, it is radially out, when you are so far away. Sloppy wording, circularly. And yes, it is as Anna said, when you receive it so far away, like a plane wave, that's also why you can do a level of triangulation like you would with far-off IR, RF or light sources -- in reality you'd need 3 or 4 separated interferometers to locate in 3D, and if there's little separation in some dimension the accuracy in that dimension will suffer. For the GW150914 there were just two interferometers, so the location errors had a geometrical banana shaped form (it's been posted online, not here). – Bob Bee Feb 15 '16 at 21:14