A note on the discovery of a 2M_\odot pulsar

TL;DR

This paper proposes that clustering in cold quark matter can stiffen the equation of state, allowing pulsars to reach masses over 2 solar masses, challenging previous assumptions about quark stars.

Contribution

It introduces a Lennard-Jones model of clustered quark matter showing that high-mass pulsars are compatible with quark stars, and constrains quark cluster size using recent observations.

Findings

Supports maximum pulsar mass > 2 solar masses with clustered quark matter

Constrains quark cluster size to less than approximately 1000 quarks

Revises the standard view on quark star equations of state

Abstract

It is conventionally thought that the state equation of dense matter softens and thus cannot result in high maximum mass if pulsars are quark stars, and that a recently discovered $2M_\odot$ pulsar (PSR J1614-2230) may make quark stars to be unlikely. However, this standard point of view would be revisited and updated if quark clustering could occur in cold quark matter because of the strong coupling between quarks at realistic baryon densities of compact stars, and it is addressed that the state equation of clustering quark matter stiffs to support compact stars with maximum mass $M_{\rm max}>2M_\odot$. In this brief note, it is demonstrated that large parameter spaces are allowed for $M_{\rm max}>2M_\odot$ in a Lennard-Jones model of clustered quark matter, and the newly measured highest mass of PSR J1614-2230 would be meaningful to constrain the number of quarks inside single quark-cluster, to be $N_q<\sim 10^3$.