Numerical-relativity simulations of long-lived remnants of binary neutron star mergers

TL;DR

This study uses numerical relativity simulations to analyze long-lived neutron star merger remnants, identifying distinct post-merger phases and potential gravitational wave signals detectable by future observatories, which could reveal properties of neutron star matter.

Contribution

It introduces a detailed analysis of post-merger gravitational wave phases and inertial modes, highlighting their detectability and implications for neutron star equation of state studies.

Findings

Post-merger phase subdivided into three distinct stages.

Inertial modes have frequencies below quadrupole modes.

Potential detection of inertial modes by third-generation gravitational wave detectors.

Abstract

We analyze the properties of the gravitational wave signal emitted after the merger of a binary neutron star system when the remnant survives for more than a 80 ms (and up to 140ms). We employ four different piecewise polytropic equations of state supplemented by an ideal fluid thermal component. We find that the post-merger phase can be subdivided into three phases: an early post-merger phase (where the quadrupole mode and a few subdominant features are active), the intermediate post-merger phase (where only the quadrupole mode is active) and the late post-merger phase (where convective instabilities trigger inertial modes). The inertial modes have frequencies somewhat smaller than the quadrupole modes. In one model, we find an interesting association of a corotation of the quadrupole mode in parts of the star with a revival of its amplitude. The gravitational wave emission of inertial modes in the late post-merger phase is concentrated in a narrow frequency region and is potentially detectable by the planned third-generation detectors. This allows for the possibility of probing not only the cold part of the equation of state, but also its dependence on finite temperature. In view of these results, it will be important to investigate the impact of various type of viscosities on the potential excitation of inertial modes in binary neutron star merger remnants.