A new state of dense matter in neutron stars with nucleon structure

TL;DR

This paper proposes a new model of dense matter in neutron stars using a chiral soliton framework, predicting a novel superdense state of overlapping composite nucleons with implications for neutron star stability and astrophysical phenomena.

Contribution

It introduces a topological cubic crystal model of superdense matter in neutron stars based on composite nucleons with bound quarks, differing from traditional quark matter models.

Findings

Identifies a new superdense state of matter in neutron stars.

Predicts a density threshold for instability leading to quark matter transition.

Suggests implications for neutron star mergers and gamma-ray bursts.

Abstract

The existence of stars with a large mass of 2 solar masses means that the equation of state is stiff enough to provide high enough pressure at large central densities. Previous work shows that such a stiff equation of state is possible if the ground state has nucleons as its constituents. We find this to be so in a chiral soliton ( skyrmion ) model for a composite nucleon which has bound state quarks. The strong binding of the quarks in this composite nucleon is plausibly the origin of the nucleon-nucleon hard core. In this model we find a new state of superdense matter at high density which is a 'topological'cubic crystal of overlapping composite nucleons that are solitons with relativistic quark bound states. The quarks are frozen in a filled band of a unique state, which not an eigenstate of spin or isospin but an eigenstate of spin plus isospin, $ \vec S + \vec I = 0$. In this alternative model we find that all neutron stars have no regular `free'quark matter. Neutron stars whose central density crosses a threshold baryon density of approximately, $n_b \sim 1/fm^3 $, will become unstable and go through a decompression (sudden) density discontinuity to conventional quark matter. Sequentially, this contraction of the core of the star will soften the equation of state release a large amount of gravitational potential energy which can give rise to a shock wave and matter ejection. Since the merger of two neutron stars gives a compact state whose mass is larger than the allowed maximum mass, this will be followed by a jet and a short gamma ray burst while transiting into a black hole.