Modelling a $2.5 \, M_{\odot}$ Compact Star with Quark Matter

TL;DR

This paper explores models of a 2.5 solar mass compact star with quark matter, analyzing whether such stars can exist within current observational constraints and implications for universal matter density limits.

Contribution

It evaluates the feasibility of quark matter models for massive neutron stars and discusses constraints from recent radius measurements and maximum mass.

Findings

Quark matter models struggle to meet radius constraints from NICER data.

Self-bound quark stars cannot account for the 2.5 solar mass object under current models.

A very massive star implies an upper limit on universal matter density.

Abstract

The detection of an unexpected $\sim 2.5 M_{\odot}$ component in the gravitational wave event GW190814 has puzzled the community of High-Energy astrophysicists, since in the absence of further information it is not clear whether this is the heaviest "neutron star" ever detected or either the lightest black hole known, of a kind absent in the local neighbourhood. We show in this work a few possibilities for a model of the former, in the framework of three different quark matter models with and without anisotropy in the interior pressure. As representatives of classes of "exotic" solutions, we show that even though the stellar sequences may reach this ballpark, it is difficult to fulfill simultaneously the constraint of the radius as measured by the NICER team for the pulsar PSR J0030+0451. Thus, and assuming both measurements stand, compact neutron stars can not be all made of self-bound quark matter, even within anisotropic solutions which boost the maximum mass well above the $\sim 2.5 M_{\odot}$ figure. We also point out that a very massive compact star will limit the absolute maximum matter density in the present Universe to be less than 6 times the nuclear saturation value.