Remnant massive neutron stars of binary neutron star mergers: Evolution process and gravitational waveform

TL;DR

This paper investigates the evolution and gravitational wave emission of remnant massive neutron stars formed after binary neutron star mergers, highlighting their quasiperiodic nature and dependence on the equation of state through numerical simulations.

Contribution

It provides a detailed analysis of the evolution process of remnant neutron stars and introduces a fitting formula for their gravitational waveforms, aiding data analysis.

Findings

Remnant hypermassive neutron star lifetime depends on total binary mass and equation of state.

Gravitational waves are quasiperiodic with approximately constant frequency, varying with time.

Frequency and variation of gravitational waves depend strongly on the equation of state.

Abstract

Massive (hypermassive and supramassive) neutron stars are likely to be often formed after the merger of binary neutron stars. We explore the evolution process of the remnant massive neutron stars and gravitational waves emitted by them, based on numerical-relativity simulations for binary neutron star mergers employing a variety of equations of state and choosing a plausible range of the neutron-star mass of binaries. We show that the lifetime of remnant hypermassive neutron stars depends strongly on the total binary mass and also on the equations of state. Gravitational waves emitted by the remnant massive neutron stars universally have a quasiperiodic nature of an approximately constant frequency although the frequency varies with time. We also show that the frequency and time-variation feature of gravitational waves depend strongly on the equations of state. We derive a fitting formula for the quasiperiodic gravitational waveforms, which may be used for the data analysis of a gravitational-wave signal.