Lense-Thirring effect from spinning neutron stars in double neutron star binaries contribute to the periastron advance of the orbit. This extra term involves the moment of inertia of the neutron stars. Moment of inertia, on the other hand, depends on the mass and spin of the neutron star as well as the equation of state of the matter. If at least one member of the double neutron star binary (better the faster one) is a radio pulsar, then accurate timing analysis might lead to the estimation of the contribution of Lense-Thirring effect to the periastron advance, which will lead to the measurement of the moment of inertia of the pulsar. Combination of the knowledge on the values of the moment of inertia, mass, and spin of the pulsar, will give a new constraint on the equation of state. Pulsars in double neutron star binaries are the best for this purpose as short orbits and moderately high eccentricities make Lense-Thirring effect substantial, whereas tidal effects are negligible (unlike pulsars with main sequence or white-dwarf binaries). The most promising pulsars are PSR J0737-3039A and PSR J1757-1854. The spin-precession of pulsars due to the misalignment between the spin and the orbital angular momentum vectors affect the contribution of Lense-Thirring effect to the periastron advance. This has been explored for both PSR J0737-3039A and PSR J1757-1854, and as the misalignment angles for both of these pulsars are small, the variation in the Lense-Thirring term is not much.
Fri, 8 Dec 17
Comments: To appear in the special issue of `Universe’ dedicated to the conference: “Compact Stars in the QCD Phase Diagram VI” held at The Joint Institute for Nuclear Research (JINR), Dubna, Russia; during 26 – 29 September, 2017