Schedule Aug 2, 2000
R-Modes in Superfluid Neutron Stars
Gregory Mendell (LIGO Hanford Observatory)
Scattering off quantized vortices causes an unique form of dissipation to occur in superfluids known as mutual friction. In superfluid neutron stars mutual friction is due to the scattering of normal-fluid electrons off quantized magnetic-flux carrying neutron vortices. The purpose of this talk is to explain exactly what mutual friction is, how one calculates the mutual friction damping rate, and what effects this has on the onset of the gravitational-radiation instability of the r-modes in superfluid neutron stars. The talk begins by reviewing the salient features of superfluidity in neutron stars. It then discusses mutual friction in detail. It ends with the results for the stability analysis of the r-modes. The last overhead is an estimate of the effects of mutual friction in a viscous boundary layer. The results shown here are published in L. Lindblom and G. Mendell, Phys. Rev. D61, 104003 (2000), and can be found online at gr-qc/9909084. The abstract from that paper follows. The analogs of r-modes in superfluid neutron stars are studied here. These modes, which are governed primarily by the Coriolis force, are identical to their ordinary-fluid counterparts at the lowest order in the small angular-velocity expansion used here. The equations that determine the next order terms are derived and solved numerically for fairly realistic superfluid neutron-star models. The damping of these modes by superfluid ``mutual friction'' (which vanishes at the lowest order in this expansion) is found to have a characteristic time-scale of about 10^4 s for the m=2 r-mode in a ``typical'' superfluid neutron-star model. This time-scale is far too long to allow mutual friction to suppress the recently discovered gravitational radiation driven instability in the r-modes. However, the strength of the mutual friction damping depends very sensitively on the details of the neutron-star core superfluid. A small fraction of the presently acceptable range of superfluid models have characteristic mutual friction damping times that are short enough (i.e. shorter than about 5 s) to suppress the gravitational radiation driven instability completely. Links to this, and related papers, follow.
gr-qc/9909084, gr-qc/9902052, astro-ph/9702032

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