To differentiate neutron star models by X-ray polarimetry

TL;DR

This paper proposes using thermal X-ray polarimetry as an observational method to distinguish between neutron stars and quark/quark-cluster stars, based on their differing polarization signatures.

Contribution

It introduces the idea that thermal X-ray polarization can effectively differentiate quark/quark-cluster stars from neutron stars, providing a new observational approach.

Findings

Normal neutron stars show >10% polarization

Quark/quark-cluster stars exhibit near-zero polarization

X-ray polarimetry can identify star types

Abstract

The nature of pulsar is still unknown because of non-perturbative effects of the fundamental strong interaction, and different models of pulsar inner structures are then suggested, either conventional neutron stars or quark stars. Additionally, a state of quark-cluster matter is conjectured for cold matter at supranuclear density, as a result pulsars could thus be quark-cluster stars. Besides understanding different manifestations, the most important issue is to find an effective way to observationally differentiate those models. X-ray polarimetry would play an important role here. In this letter, we focus on the thermal X-ray polarization of quark/quark-cluster stars. While the thermal X-ray linear polarization percentage is typically higher than ~10% in normal neutron star models, the percentage of quark/quark-cluster stars is almost zero. It could then be an effective method to identify quark/quark-cluster stars by soft X-ray polarimetry. We are therefore expecting to detect thermal X-ray polarization in the coming decades.