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As I know, neutron stars are almost perfect sphere and no net moments, does it mean it is not possible to tidally lock it?

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  • $\begingroup$ How much time and money do you have? :-) Now, seriously... of course it is theoretically possible to tidal lock a neutron star, gravity itself will cause the necessary asymmetry, like in any other object, the problem is the incredibly large angular momentum that you are trying to transfer... to what... exactly? Another neutron star or a black hole sounds like the best alternative. $\endgroup$ – CuriousOne Mar 10 '16 at 9:44
  • $\begingroup$ For a more technical answer, see e.g. "The coupled effect of tides and stellar winds on the evolution of compact binaries", Serena Repetto, Gijs Nelemans. $\endgroup$ – CuriousOne Mar 10 '16 at 9:51
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If a neutron star were a perfect sphere with a monopole moment and zero quadrupole, etc., moments, it would be impossible to observe its rotation. For example, observe the rotation of Earth's roundest object (whose rotational symmetry is broken by its crystalline structure).

We are able to observe that neutron stars rotate. Therefore neutron stars have nonzero moments of inertia and are subject to tidal locking. However it might take a very long time. A commenter links to a paper on the subject.

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  • $\begingroup$ I think its important to note that even a neutron star which is on its own spherical would not be spherical in the presence of another mass, which is necessary anyway for there to be something to tidally lock to. $\endgroup$ – Asher Mar 21 '16 at 19:19
  • $\begingroup$ @Asher Also true; my point was that that the asker's premise (that neutron stars don't have any non-spherical moments) is flawed. $\endgroup$ – rob Mar 21 '16 at 19:53
  • $\begingroup$ Ah, yes. I read the title and paid little attention to the actual question, so I hadn't realized the root of the question. $\endgroup$ – Asher Mar 21 '16 at 20:00

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