Constraining the dense matter equation-of-state with radio pulsars

TL;DR

This paper discusses how radio pulsar observations, especially of the Double Pulsar system, can constrain the dense matter equation-of-state by measuring neutron star properties like mass and moment of inertia, with projections for future improvements.

Contribution

It introduces a method to measure the neutron star moment of inertia via pulsar timing, including spin-down mass loss, and provides future projections with MeerKAT and SKA.

Findings

Lower limit of 1.98 M_sun for maximum NS mass constrains EOSs.

Potential to measure the NS moment of inertia with 11% accuracy by 2030.

Possible tests of relativistic effects like Lense-Thirring precession with 7% precision.

Abstract

Radio pulsars provide some of the most important constraints for our understanding of matter at supranuclear densities. So far, these constraints are mostly given by precision mass measurements of neutron stars (NS). By combining single measurements of the two most massive pulsars, J0348$+$0432 and J0740$+$6620, the resulting lower limit of 1.98 $M_\odot$ (99% confidence) of the maximum NS mass, excludes a large number of equations of state (EOSs). Further EOS constraints, complementary to other methods, are likely to come from the measurement of the moment of inertia (MOI) of binary pulsars in relativistic orbits. The Double Pulsar, PSR J0737$-$3039A/B, is the most promising system for the first measurement of the MOI via pulsar timing. Reviewing this method, based in particular on the first MeerKAT observations of the Double Pulsar, we provide well-founded projections into the future by simulating timing observations with MeerKAT and the SKA. For the first time, we account for the spin-down mass loss in the analysis. Our results suggest that an MOI measurement with 11% accuracy (68% confidence) is possible by 2030. If by 2030 the EOS is sufficiently well known, however, we find that the Double Pulsar will allow for a 7% test of Lense-Thirring precession, or alternatively provide a $\sim3\sigma$-measurement of the next-to-leading order gravitational wave damping in GR. Finally, we demonstrate that potential new discoveries of double NS systems with orbital periods shorter than that of the Double Pulsar promise significant improvements in these measurements and the constraints on NS matter.