Quark matter in compact stars: astrophysical implications and possible signatures

TL;DR

This paper reviews the properties of strange quark matter in compact stars, discusses recent observational data suggesting its presence, and explores the implications of metastability and stable quark stars on the maximum mass of such stars.

Contribution

It provides a comprehensive overview of recent advances in understanding quark matter in compact stars and extends the classical concept of limiting mass considering quark star stability.

Findings

Neutron stars above a certain mass threshold may be metastable to decay into quark stars.

Existence of stable hybrid and strange stars impacts the classical mass limit of compact stars.

Recent observations could indicate the presence of quark matter in some compact stars.

Abstract

After a brief non technical introduction of the basic properties of strange quark matter (SQM) in compact stars, we consider some of the late important advances in the field, and discuss some recent astrophysical observational data that could shed new light on the possible presence of SQM in compact stars. We show that above a threshold value of the gravitational mass a neutron star (pure hadronic star) is metastable to the decay (conversion) to an hybrid neutron star or to a strange star. We explore the consequences of the metastability of "massive" neutron stars and of the existence of stable compact "quark" stars (hybrid neutron stars or strange stars) on the concept of limiting mass of compact stars, and we give an extension of this concept with respect to the "classical" one given in 1939 by Oppenheimer and Volkoff.