Impact of nuclear reactions on gravitational waves from neutron star mergers

Nuclear reactions may affect gravitational-wave signals from neutron-star mergers, but the impact is uncertain. To indicate the significance of this effect, we compare two numerical simulations representing intuitive extremes. In one case, reactions happen instantaneously. In the other case, they occur on timescales much slower than the evolutionary timescale. We show that, while the differences in the two gravitational-wave signals are small, the mismatch between them satisfies the condition for distinguishability using the Einstein Telescope noise curve, assuming that the neutron-star equation of state can be well constrained by experiments or by the postmerger signal of the event. This suggests that, to avoid systematic errors in equation of state parameters inferred from observed signals, we need to accurately implement nuclear reactions in future simulations.

Figure 1

Upper: square-root power spectral density (PSD) plots of the recovered waveforms from slow- and fast-reaction-limit simulations (blue and orange curves, respectively). Lower: the same comparison for the high- and low-resolution simulations (blue and green curves, respectively), both in the slow-reaction limit. Upper and lower: peak frequencies for each curve calculated using the Macleod method [36] are shown with dashed lines. The ET-D design sensitivity curve for the Einstein Telescope [5] is shown in red. The waveforms are normalized to a distance of 40 Mpc and assume the source and detector are perfectly aligned.

Figure 2

Upper: evolution of the total moment of inertia [see Eq. (12)] ignoring matter with rest mass density below ${\rho }_{\text{cutoff}}$ for slow- and fast-reaction-limit simulations (labeled OOE for out of equilibrium and NSE for in equilibrium, solid and dotted lines, respectively). Lower: relative difference between results for slow- and fast-limit simulations.