Imprints of the nuclear symmetry energy on the tidal deformability of neutron stars

Abstract

Applying an equation of state (EOS) with its symmetric nuclear matter (SNM) contribution and low-density symmetry energy $E_{sym}(\rho)$ constrained by heavy-ion reaction data, we calculate the dimensionless tidal deformability $\Lambda$ of neutron stars in coalescing binary systems. Corresponding to the partially constrained EOS that previously predicted a radius of 11.5 km $\leq R_{1.4} \leq$ 13.6 km for canonical neutron-star configurations, $\Lambda$ is found to be in the range of 292 $\leq\Lambda_{1.4}\leq$ 680, consistent with the very recent observation of the GW170817 event. We investigate the effect of the high-density behavior of $E_{sym}(\rho)$ on the tidal properties of neutron stars and find that while $\Lambda$ depends strongly on the details of the symmetry energy, different trends of $E_{sym}(\rho)$ lead to very similar values of $\Lambda$. In particular, the transition from stiff/soft to soft/stiff $E_{sym}(\rho)$ could yield the same $\Lambda$. Thus, measuring $\Lambda$ alone may not determine completely the density dependence of the symmetry energy. Coherent analyses of the dense neutron-rich nuclear matter EOS underlying both nuclear laboratory experiments and astrophysical observations are therefore necessary to break this degeneracy and determine precisely the details of the $E_{sym}(\rho)$.