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Astron. Astrophys. 361, 795-802 (2000) 2. Glitches driven by the spheroidality mechanismIn the first years after the problem of accounting for neutron star
"crustquakes" was posed, attention was concentrated on what is
describable as the "spheroidality mechanism" (Ruderman 1969). This
mechanism depends on the supposition that the solidity forces will not
be strong enough to allow the stellar equilibrium configuration to
differ very much from a perfectly fluid equilibrium state, which would
be spherical in the absence of rotation, but which will actually have
the form of an oblate spheroid with ellipticity proportional to
where For a perfectly fluid star model, a continuous angular momentum
variation Due to the solidity of the crust, which tends to preserve the more highly elliptic initial configuration, the actual change in the moment of inertia will fall short of what is predicted by this formula, but at some stage the strain will build up to the point at which the solid structure will break down (see Fig. 1). It is predicted that there will then be a "crustquake" in which the solid structure suddenly changes towards what the perfect fluid structure would have been, thereby changing the moment of inertia by an amount where
Since the amount of angular momentum loss during the very short duration of the glitch will be negligible, the corresponding discontinuous angular velocity change will be given by Its value will therefore be expressible in terms of the order of
unity efficiency factor in which it is to be recalled that the magnitude predicted by (7) is much too low for such a mechanism to be able to account for the comparatively large glitches that are frequently observed in cases such as that of the Vela pulsar. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 2000 Online publication: October 2, 2000 ![]() |