Neutron Stars

[John Clark]

A pulsar is a Neutron Star that is rotating hundreds of times a second and is sending out radio pulses when it does so. If the Neutron Star was perfectly spherical it would not generate any Gravitational Waves no matter how fast it was rotating and neither would it if it was flattened at the poles into a perfect oblate spheroid as long as it was still symmetrical, but if there was any irregularity it would generate Gravitational Waves. The waves would be far weaker than those generated by Black Hole collisions but nevertheless LIGO would still be able to detect them because unlike the Black Hole case the generation of these ways would be continuous and even more important because they know the frequency of the Gravitational waves if they existed because they already know the radio frequency of the pulsar. So they know what frequency to look for. A recent paper looked for these waves that must have been generated by several different pulsars if they were irregular and they didn't find any, they were able to conclude that any variation from being perfectly symmetrical for a Neutron Star 20 km across must be smaller than the width of a human hair.
By the way I've never seen a paper with that many authors.

Gravitational-wave constraints on the equatorial ellipticity of millisecond pulsars

  John K Clark

[Lawrence Crowell]

This neutron star must have a quadrupole distribution of matter or higher order. A neutron star is composed largely of neutron fluid. If this is rotating there may be set up by thermal gradients and Coriolis acceleration convection flows that would set up such a distribution of matter. It is one possible reason the millisecond pulsar is the upper limit on their spin.

LC