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

TL;DR

This study explores how the nuclear symmetry energy influences the tidal deformability of neutron stars, showing that different symmetry energy behaviors can produce similar observational signatures, thus requiring combined analyses to constrain nuclear matter properties.

Contribution

It demonstrates that the tidal deformability of neutron stars is sensitive to the symmetry energy but not uniquely determined by it, highlighting the need for integrated nuclear and astrophysical data.

Findings

Tidal deformability $\Lambda$ ranges from 292 to 680 for certain EOS.

Different symmetry energy trends can produce similar $\Lambda$ values.

Measuring $\Lambda$ alone cannot fully constrain the symmetry energy behavior.

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 $E_{sym}(\rho)$.