Kilohertz gravitational waves from binary neutron star remnants: Time-domain model and constraints on extreme matter

Abstract

The remnant star of a neutron star merger is an anticipated loud source of kiloHertz gravitational waves that conveys unique information on the equation of state of hot matter at extreme densities. Observations of such signals are hampered by the photon shot noise of ground-based interferometers and pose a challenge for gravitational-wave astronomy. We develop an analytical time-domain waveform model for postmerger signals informed by numerical relativity simulations. The model completes effective-one-body waveforms for quasi-circular nonspinning binaries in the kiloHertz regime. We show that a template-based analysis can detect postmerger signals with a minimal signal-to-noise ratios (SNR) of 8, corresponding to GW170817-like events for third-generation interferometers. Using Bayesian model selection and the complete inspiral-merger-postmerger waveform model it is possible to infer whether the merger outcome is a prompt collapse to a black hole or a remnant star. In the latter case, the radius of the maximum mass (most compact) nonrotating neutron star can be determined to kilometer precision. We demonstrate the feasibility of inferring the stiffness of the equation of state at extreme densities using the quasiuniversal relations deduced from numerical-relativity simulations.

Binary Neutron Star Merger Simulations with a Calibrated Turbulence Model

“…We found this feature to be robust against turbulence: deviations in the peak frequency with mix were typically small and of the same order of the nominal uncertainty of the Fourier transform of the time domain data. Thus, our results confirmed that the measurement of the postmerger peak frequency was a promising avenue to constrain the EOS of dense matter using third-generation detectors, e.g., see [119]. Models with turbulent viscosities larger than those of our calibrated model, i.e., mix = 25 m and mix = 50 m, also showed an overall decrease in the power of the GW signal, suggesting that turbulence might suppress GW emission, as also found in [81,120].…”

Neutron star merger remnants

“…with γ 3200. Similar relations exists for all the relevant dynamical quantities, such as the binding energy, the angular momentum, or the GW luminosity at merger [64,75,79]. The effects due to the NS rotation can also be included in this picture.…”

“…where ν = μM ∈ [0, 1/4] and γ is a fitting parameter [75]. 5 A more precise and formal argument is discussed in [75,78].…”

Parameter estimation for strong phase transitions in supranuclear matter using gravitational-wave astronomy

“…However, due to the missing sensitivity of existing GW detectors in the high-frequency range [9,88] and the absence of high-quality GW models describing the postmerger evolution of BNS mergers-see Refs. [89][90][91][92][93][94] for some first attempts-it seems natural to investigate, at the current stage, possible phase transition effects that can be extracted from the GW signal during the inspiral.…”