Strange Matter

TL;DR

This paper proposes that pulsar-like objects are actually strange stars composed of strange matter, offering new models for their structure, properties, and observational signatures to better understand their nature and related astrophysical phenomena.

Contribution

It introduces the concept of strange matter as the core composition of pulsars, developing models for strange star structures and connecting them to observable phenomena.

Findings

Strange matter models explain pulsar mass-radius relations.

Observational data supports the strange star hypothesis.

Strange stars could account for dark matter and merger events.

Abstract

Pulsar-like objects are extremely compact, with an average density that exceeds nuclear saturation density, where the fundamental strong interaction plays an essential role, particularly in the low-energy regime. The internal structures and properties of those objects are profoundly connected to phenomena such as supernova explosions, gamma-ray bursts, fast radio bursts, high/low-mass compact stars, and even to issues like dark matter and cosmic rays. However, due to the non-perturbative nature of quantum chromodynamics, significant uncertainties remain in our current understanding of the composition and equation of state (EOS) for the dense matter inside them. Drawing on three-flavour symmetry and the strong coupling between light quarks, this paper presents a novel perspective on the nature of pulsars: they are actually composed of strange matter, in the form of either strange quark matter or strangeon (analogous to nucleons and representing multibaryon states with three-flavour symmetry) matter. As both strange quark matter and strangeon matter contain non-zero strangeness, we refer to them collectively as ``strange matter'', and to the corresponding compact stars as ``strange stars''. We then briefly introduce several physical models describing strange matter and present the resulting structures and properties of strange stars. This includes discussions on the EOSs, surface properties, mass-radius relations, glitches, binary compact star mergers, and dark matter. Furthermore, we will explore how observational properties of pulsar-like objects support the strange star model.