Three-dimensional hydrodynamic simulations of the combustion of a neutron star into a quark star

TL;DR

This paper presents three-dimensional hydrodynamic simulations of neutron star conversion into quark stars, revealing turbulence-driven acceleration of the process and the persistence of an outer hadronic layer due to non-exothermic conditions.

Contribution

It introduces a novel 3D simulation approach for neutron star conversion, incorporating turbulence modeling and a level-set method for front propagation.

Findings

Conversion becomes turbulent and faster than laminar in large parameter regions.

An outer hadronic layer remains due to non-exothermic stopping conditions.

Turbulence significantly influences the conversion dynamics.

Abstract

We present three-dimensional numerical simulations of turbulent combustion converting a neutron star into a quark star. Hadronic matter, described by a micro-physical finite-temperature equation of state, is converted into strange quark matter. We assume this phase, represented by a bag-model equation of state, to be absolutely stable. Following the example of thermonuclear burning in white dwarfs leading to Type Ia supernovae, we treat the conversion process as a potentially turbulent deflagration. Solving the non-relativistic Euler equations using established numerical methods we conduct large eddy simulations including an elaborate subgrid scale model, while the propagation of the conversion front is modeled with a level-set method. Our results show that for large parts of the parameter space the conversion becomes turbulent and therefore significantly faster than in the laminar case. Despite assuming absolutely stable strange quark matter, in our hydrodynamic approximation an outer layer remains in the hadronic phase, because the conversion front stops when it reaches conditions under which the combustion is no longer exothermic.