Quark stars with ‘realistic’ equations of state

Abstract

THE possibility of a phase transition between nuclear matter and quark matter has been discussed in recent work^1–13. Free quarks would presumably appear above a critical density pq, which is greater than the typical density ρ_n ≃ 2.5 × 10¹⁴g cm⁻³ within ordinary atomic nuclei. Such a transition might allow stable collapsed stars to exist wherein much of the matter is in the form of quark matter (quark stars). The maximum masses of collapsed stars have been investigated for the extreme case of ρ_q ≃ ρ_n and hard equations of state for quark matter⁵. However, it has been argued^6,8,9 that some equations of state for quark matter require ρ_q >> ρ_n and are therefore unlikely to permit the existence of stable quark stars. We investigate here the properties of collapsed stars in the context of another class of quark-matter models that has recently been proposed^11–13. These models¹², which are consistent with all experimental nuclear and high-energy physics data, are based on a quantum chromodynamic treatment of quarks that are assumed to be of low mass (≲100 MeV for the lightest quarks). We find that stable quark stars are possible (compare with refs 6, 8, 9). However, we also conclude (compare with refs 5, 14) that such stars need not have significantly different macroscopic properties from those of neutron-star models^15–17 based on conventional nuclear-matter equations of state.