Measuring the Lense–Thirring Orbital Precession and the Neutron Star Moment of Inertia with Pulsars

Abstract

Neutron stars (NSs) are compact objects that host the densest forms of matter in the observable universe, providing unique opportunities to study the behaviour of matter at extreme densities. While precision measurements of NS masses through pulsar timing have imposed effective constraints on the equation of state (EoS) of dense matter, accurately determining the radius or moment of inertia (MoI) of an NS remains a major challenge. This article presents a detailed review on measuring the Lense–Thirring (LT) precession effect in the orbit of binary pulsars, which would give access to the MoI of NSs and offer further constraints on the EoS. We discuss the suitability of certain classes of binary pulsars for measuring the LT precession from the perspective of binary star evolution and highlight five pulsars that exhibit properties promising to realise these goals in the near future. Finally, discoveries of compact binaries with shorter orbital periods hold the potential to greatly enhance measurements of the MoI of NSs. The MoI measurements of binary pulsars are pivotal to advancing our understanding of matter at supranuclear densities, as well as improving the precision of gravity tests, such as the orbital decay due to gravitational wave emission, and of tests of alternative gravity theories.

Measuring a Gravitomagnetic Effect with the Triple Pulsar PSR J0337+1715

“…Intense efforts to measure it, not yet crowned with success, are currently underway [17,19,20]. The figure quoted in Equation ( 10) is inferred from 2 J A ≃ 4.5 × 10 40 kg m 2 s −1 (11) for the angular momentum of PSR J0737-3039A; it can be calculated by assuming for the pulsar's moment of inertia (MOI) the value [21] I A ≃ 1.6 × 10 38 kg m 2 (12) and recalling that the spin period of the A component of the double pulsar is 22.7 ms [5].…”