Constraining the p-Mode-g-Mode Tidal Instability with GW170817

Area of Science:

• Astrophysics
• Gravitational Wave Astronomy
• Neutron Star Physics

Background:

• Neutron stars possess complex internal structures with various oscillation modes.
• Tidal interactions in binary neutron star systems can excite these internal modes, potentially affecting their inspiral.

Purpose of the Study:

• To analyze the impact of a proposed tidal instability coupling p-modes and g-modes in neutron stars on the gravitational wave signal of GW170817.
• To quantify the influence of this p-g mode instability on the gravitational wave phasing and energy dissipation during binary neutron star inspiral.

Main Methods:

• Modeling the effect of p-g mode instability on gravitational wave signals using three parameters per star: amplitude, saturation frequency, and spectral index.
• Computing Bayes factors to compare models with and without p-g effects.
• Performing signal injections to assess the probability of observing similar results when the instability is absent.

Main Results:

• The observed GW170817 signal is consistent with models neglecting p-g effects, with a Bayes factor lnB_{!pg}^{pg}=0.03_{-0.58}^{+0.70}.
• There is approximately a 50% chance of obtaining similar Bayes factors even without p-g effects.
• Constraints on the p-g amplitude for 1.4 solar mass neutron stars are less than a few tenths of the theoretical maximum, with a saturation frequency around 70 Hz.

Conclusions:

• The study rules out extreme values for the p-g instability parameters.
• The energy dissipated by this instability is less than a few percent of the total gravitational wave energy radiated.
• Further observations and refined models are needed to definitively probe the role of p-g mode instabilities in neutron star mergers.