Quote:
Originally Posted by Ken G
A binary neutron star can make gravitational radiation, but it won't produce the significant "kicks" that publius is talking about. That must happen from a very sudden and very powerful pulse at the moment highly compact objects merge, or from an integrated asymmetry over time in a very strong gravitational wave source (very compact fast orbits). I don't know which dominates but I would suspect the former.
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Ken,
Don't hold me to it exactly because I'm not sure of the details, but I think the kick does indeed occur during the last moments when they "hit" each other.
These things are a complex mess to say the least and can only be tackled numerically. And numerical GR solutions are something else. IIRC, it took some ridiculous amount of total CPU time on some big parallel processor farm specially designed to solve them just for the last orbit before merger.
I've forgotten the details, but I remember reading a description of just how difficult and numerically back-breaking the thing was. A big problem was sanity checks. They were going off in uncharted waters -- no analytical solutions or other simplified solutions to compare with and keep things between the ditches. It would be bad to waste wads of CPU time after some numerical hiccup through the solution into la-la land.
Another interesting thing I remember is the final "kick" depends strongly on the spin of the merging black holes (the mind boggles at the complexity of two merging Kerr holes!). You've apparently some highly complex "spin-orbit" interactions going on that contribute to the final linear kick.
-Richard