Relativistic simulations of the phase-transition-induced collapse of neutron stars

TL;DR

This paper presents general relativistic 2D simulations of neutron star phase transitions to hybrid stars, analyzing gravitational wave emissions and their detectability with current and future interferometers.

Contribution

It advances previous Newtonian models by implementing 2D relativistic simulations and improved initial phase transition treatment, providing new insights into gravitational wave signals from neutron star collapse.

Findings

Gravitational wave spectrum dominated by fundamental pulsation modes

Strain amplitudes smaller than previously estimated

Nonlinear mode resonance enhances gravitational wave emission

Abstract

An increase in the central density of a neutron star may trigger a phase transition from hadronic matter to deconfined quark matter in the core, causing it to collapse to a more compact hybrid-star configuration. We present a study of this, building on previous work by Lin et al. (2006). We follow them in considering a supersonic phase transition and using a simplified equation of state, but our calculations are general relativistic (using 2D simulations in the conformally flat approximation) as compared with their 3D Newtonian treatment. We also improved the treatment of the initial phase transformation, avoiding the introduction of artificial convection. As before, we find that the emitted gravitational-wave spectrum is dominated by the fundamental quasi-radial and quadrupolar pulsation modes but the strain amplitudes are much smaller than suggested previously, which is disappointing for the detection prospects. However, we see significantly smaller damping and observe a nonlinear mode resonance which substantially enhances the emission in some cases. We explain the damping mechanisms operating, giving a different view from the previous work. Finally, we discuss the detectability of the gravitational waves, showing that the signal-to-noise ratio for current or second generation interferometers could be high enough to detect such events in our Galaxy, although third generation detectors would be needed to observe them out to the Virgo cluster, which would be necessary for having a reasonable event rate.