Fully general-relativistic simulations of isolated and binary strange quark stars

TL;DR

This paper introduces a novel numerical technique for simulating binary strange quark stars in full general relativity, revealing key differences from hadronic stars in merger dynamics and ejecta properties.

Contribution

The authors develop a new method to model quark stars with smooth equations of state, enabling the first fully relativistic simulations of their binary mergers and detailed comparison with hadronic stars.

Findings

Quark-star binaries show suppressed dynamical mass loss.

Merger and post-merger frequencies follow similar relations to hadronic stars when scaled by tidal deformability.

Ejected matter from quark stars has smaller velocity and entropy tails.

Abstract

The hypothesis that strange quark matter is the true ground state of matter has been investigated for almost four decades, but only a few works have explored the dynamics of binary systems of quark stars. This is partly due to the numerical challenges that need to be faced when modelling the large discontinuities at the surface of these stars. We here present a novel technique in which the EOS of a quark star is suitably rescaled to produce a smooth change of the specific enthalpy across a very thin crust. The introduction of the crust has been carefully tested by considering the oscillation properties of isolated quark stars, showing that the response of the simulated quark stars matches accurately the perturbative predictions. Using this technique, we have carried out the first fully general-relativistic simulations of the merger of quark-star binaries finding several important differences between quark-star binaries and hadronic-star binaries with the same mass and comparable tidal deformability. In particular, we find that dynamical mass loss is significantly suppressed in quark-star binaries. In addition, quark-star binaries have merger and post-merger frequencies that obey the same quasi-universal relations derived from hadron stars if expressed in terms of the tidal deformability, but not when expressed in terms of the average stellar compactness. Hence, it may be difficult to distinguish the two classes of stars if no information on the stellar radius is available. Finally, differences are found in the distributions in velocity and entropy of the ejected matter, for which quark-stars have much smaller tails. Whether these differences in the ejected matter will leave an imprint in the electromagnetic counterpart and nucleosynthetic yields remains unclear, calling for the construction of an accurate model for the evaporation of the ejected quarks into nucleons.