Convective Excitation of Inertial Modes in Binary Neutron Star Mergers

TL;DR

This study uses long-term simulations to show that convective instabilities in post-merger neutron stars excite inertial modes, which could be detected via gravitational waves to probe the remnant's internal state.

Contribution

First long-term general relativistic simulations demonstrating convective excitation of inertial modes in neutron star mergers and their potential observability.

Findings

Convective instability occurs 30-50 ms after merger.

Inertial modes are excited and sustained for tens of milliseconds.

Potential detection of inertial modes by future gravitational-wave detectors.

Abstract

We present the first very long-term simulations (extending up to ~140 ms after merger) of binary neutron star mergers with piecewise polytropic equations of state and in full general relativity. Our simulations reveal that at a time of 30-50 ms after merger, parts of the star become convectively unstable, which triggers the excitation of inertial modes. The excited inertial modes are sustained up to several tens of milliseconds and are potentially observable by the planned third-generation gravitational-wave detectors at frequencies of a few kilohertz. Since inertial modes depend on the rotation rate of the star and they are triggered by a convective instability in the postmerger remnant, their detection in gravitational waves will provide a unique opportunity to probe the rotational and thermal state of the merger remnant. In addition, our findings have implications for the long-term evolution and stability of binary neutron star remnants