Measurability of the tidal deformability by gravitational waves from coalescing binary neutron stars

TL;DR

This study assesses how well gravitational wave observations can measure neutron star tidal deformability, using hybrid waveforms and advanced detectors, to constrain neutron star radii and differentiate from black hole signals.

Contribution

The paper combines numerical-relativity and EOB waveforms to evaluate tidal deformability measurability and neutron star radius constraints with advanced gravitational-wave detectors.

Findings

Tidal deformability difference of ~100-800 at 1-3 sigma for 200 Mpc events.

Neutron star radius can be constrained within ~1 km at 2-sigma if R ≥ 13 km.

Binary neutron star signals can be distinguished from black hole signals at >2 sigma.

Abstract

Combining new gravitational waveforms derived by long-term (14--16 orbits) numerical-relativity simulations with waveforms by an effective-one-body (EOB) formalism for coalescing binary neutron stars, we construct hybrid waveforms and estimate the measurability for the dimensionless tidal deformability of the neutron stars, $\Lambda$, by advanced gravitational-wave detectors. We focus on the equal-mass case with the total mass $2.7M_\odot$. We find that for an event at a hypothetical effective distance of $D_{\rm eff}=200$ Mpc, the distinguishable difference in the dimensionless tidal deformability will be $\approx 100$, 400, and 800 at 1-$\sigma$, 2-$\sigma$, and 3-$\sigma$ levels, respectively, for advanced LIGO. If the true equation of state is stiff and the typical neutron-star radius is $R \gtrsim 13 $ km, our analysis suggests that the radius will be constrained within $\approx 1$ km at 2-$\sigma$ level for an event at $D_{\rm eff}=200$ Mpc. On the other hand, if the true equation of state is soft and the typical neutron-star radius is $R\lesssim 12$ km , it will be difficult to narrow down the equation of state among many soft ones, although it is still possible to discriminate the true one from stiff equations of state with $R\gtrsim 13$ km. We also find that gravitational waves from binary neutron stars will be distinguished from those from spinless binary black holes at more than 2-$\sigma$ level for an event at $D_{\rm eff}=200$ Mpc. The validity of the EOB formalism, Taylor-T4, and Taylor-F2 approximants as the inspiral waveform model is also examined.