On the potential of probing the neutron star composition in accreting X-ray binaries

TL;DR

This paper evaluates the potential of using deep crustal heating in accreting neutron stars to distinguish their core compositions, considering uncertainties and analyzing observational data to differentiate between various theoretical models.

Contribution

It provides a statistical assessment of deep crustal heating as a probe for neutron star core composition, accounting for uncertainties and demonstrating the possibility to distinguish different matter states.

Findings

Certain compositional scenarios can be statistically distinguished despite uncertainties.

Extended compositions like direct Urca and quark matter are distinguishable within current uncertainties.

Large data sets and additional mass measurements enhance the discrimination capability.

Abstract

Transiently accreting Low Mass X-Ray Binaries have the potential to probe the core composition of their neutron stars via deep crustal heating caused by nuclear reactions. We statistically assess this deep crustal heating scenario, taking into account the various microphysical and astrophysical uncertainties. We find that despite the sizable uncertainties there is the chance to discriminate different compositional scenarios. Several observed sources statistically challenge a minimal hadronic matter composition, where cooling proceeds exclusively via slow modified Urca reactions. Considering here two exemplary extended uniform compositions, namely ultra-dense hadronic matter with direct Urca emission and ungapped quark matter, we find that they are even within uncertainties distinguishable. We show that although exotic forms of matter are generally only expected in an inner core, which could in principle have any size, sufficiently large astrophysical data sets nonetheless have the potential to statistically discriminate compositional scenarios, in particular when further mass measurements become available.