Inference of the Neutron Star Equation of State from Cosmological Distances

Finite-size effects on the gravitational wave signal from a neutron star merger typically manifest at high frequencies where detector sensitivity decreases. Proposed sensitivity improvements can give us access both to stronger signals and to a myriad of weak signals from cosmological distances. The latter will outnumber the former and the relevant part of the signal will be redshifted towards the detector’s most sensitive band. We study the redshift dependence of information about neutron star matter and find that single-scale properties, such as the star radius or the postmerger frequency, are better measured from the distant weak sources from $z\sim 1$.

Figure 1

Charachteristic strain [61] of a source-frame $1.362+1.362{\mathrm{M}}_{\odot }$ BNS signal at different redshifts (shaded blue or green) and planned or proposed detectors (black lines). Top: late-inspiral signal assuming the H4 EoS [62]. The orange line represents 400 Hz in the source frame; the tidally corrected signal is always observed with $f>10\mathrm{Hz}$. Bottom: postmerger signal assuming EoS7 from [50]. Vertical lines mark the dominant postmerger frequency.

Figure 2

Total premerger SNR distribution per year per redshift slice, as a function of redshift for two mass distributions, three EoSs, $D=\{1,2\}$, and the 40 km CE detector. For $D=1$, the available SNR is dominated by BNSs at cosmological distances. For $D=2$, the accumulated information peaks at $z\sim 0$, suggesting a main contribution from local sources.

Figure 3

Total postmerger SNR distribution per year per redshift slice as a function of redshift for two mass distributions, three EoSs and the 40 km CE detector ($D=1$). The distribution peaks at $z\sim 1$, suggesting a significant contribution from nonlocal sources on the total postmerger information.

Figure 4

Total premerger SNR distribution per year per redshift slice, as a function of redshift for the bimodal mass distribution, the H4 EoS, and for different planned or proposed detectors. We show results for $D=1$.