[Paper Review] Neutron star cooling and GW170817 constraint within quark-meson coupling models

O. Lourenço, César H. Lenzi+7 more|arXiv (Cornell University)|May 17, 2019

Pulsars and Gravitational Waves Research126 references4 citations

TL;DR

This study evaluates five quark-meson coupling (QMC) models—two based on the original bag potential and three using a harmonic oscillator quark confinement—against GW170817 gravitational wave constraints and neutron star cooling observations. It finds no clear correlation between symmetry energy slope and GW170817 compliance, but a strong link between higher symmetry energy slope and faster cooling, with no single model simultaneously satisfying both constraints and cooling data.

ABSTRACT

In the present work we used five different versions of the quark-meson coupling (QMC) model to compute astrophysical quantities related to the GW170817 event and to neutron star cooling process. Two of the models are based on the original bag potential structure and three versions consider a harmonic oscillator potential to confine the quarks. The bag-like models also incorporate the pasta phase used to describe the inner crust of neutron stars. We show that the pasta phase always play a minor or negligible role in all studies. Moreover, while no clear correlation between the models that satisfy the GW170817 constraints and the slope of the symmetry energy is found, a clear correlation is observed between the slope and the fact that the cooling is fast or slow, i.e., fast (slow) cooling is related to higher (lower) values of the slope. We did not find one unique model that can describe, at the same time, GW170817 constraints and give a perfect description of the possible cooling processes.

Motivation & Objective

• To assess the consistency of five QMC model variants with GW170817 constraints on tidal deformability and mass-radius relations.
• To investigate the role of the pasta phase in neutron star inner crust and its impact on tidal polarizability and cooling.
• To determine whether a unique QMC model can simultaneously satisfy GW170817 constraints and reproduce observed neutron star cooling behavior.
• To explore the influence of symmetry energy slope on cooling dynamics and tidal properties across different QMC formulations.
• To evaluate the effect of accreted atmospheres on surface temperature evolution in cooling simulations.

Proposed method

• Employed five QMC model variants: two with bag potential (including ωρ interaction) and three with harmonic oscillator quark confinement.
• Calculated equations of state (EOS) using mean-field approximation, incorporating scalar (σ), vector (ω, ρ), and pseudoscalar (π) meson fields.
• Included the pasta phase in the inner crust for bag-based models to model inhomogeneous nuclear matter structures.
• Computed tidal polarizability (Λ) and Love number for 1.4 M☉ neutron stars to compare with GW170817 posterior constraints.
• Perfomed thermal evolution simulations using the URCA process, phonon emission, and photon emission mechanisms to model cooling.
• Tested the effect of a 10⁻¹⁰ M☉ accreted atmosphere on surface temperature to improve agreement with observations.

Experimental results

Research questions

• RQ1 Which QMC model variants satisfy the GW170817 constraints on tidal deformability and mass-radius relations?
• RQ2 How does the symmetry energy slope correlate with the ability of QMC models to reproduce GW170817 constraints?
• RQ3 What is the role of the pasta phase in determining tidal polarizability and cooling rates in neutron stars?
• RQ4 Is there a unique QMC model that simultaneously describes GW170817 constraints and observed neutron star cooling behavior?
• RQ5 How do accreted atmospheres affect the surface temperature evolution and cooling speed in QMC-based models?

Key findings

• Only two models—QMC ωρ and MQMC3—produced tidal deformability values within the 90% credible interval of GW170817’s canonical 1.4 M☉ neutron star.
• No clear correlation was found between the symmetry energy slope and the ability of models to satisfy GW170817 constraints.
• A strong correlation exists between symmetry energy slope and cooling speed: higher slope values lead to faster cooling, lower slopes to slower cooling.
• The pasta phase has a minor effect on both tidal polarizability and cooling, accelerating cooling by only about 3.5 years when superconductivity is excluded.
• The QMC (with pasta) and MQMC2 models show the best agreement with observed cooling data, though none fully reproduce the highest observed surface temperatures.
• A modest 10⁻¹⁰ M☉ accreted atmosphere improves surface temperature agreement but accelerates late-stage cooling due to enhanced black-body emission.