Studying the onset of deconfinement with multi-messenger astronomy of neutron stars

TL;DR

This paper explores how multi-messenger astronomy constrains neutron star equations of state, proposing hybrid models with quark matter cores that could explain high-mass neutron stars and the nature of merger remnants.

Contribution

It introduces a class of hybrid equations of state consistent with observations and predicts observable signatures distinguishing hybrid from purely hadronic neutron stars.

Findings

Hybrid EoS models fit current constraints.

Potential to identify hybrid stars via radius measurements.

High maximum mass possible for hybrid stars, affecting merger remnant interpretations.

Abstract

With the first multi-messenger observation of a binary neutron star merger (GW170817) new constraints became available for masses and radii of neutron stars. We introduce a class of hybrid EoS that fulfils all these constraints and predicts a region in the mass-radius diagram that could be populated only by hybrid neutron stars with quark matter cores. A confirmation of this conjecture would be provided when the NICER radius measurement for the high-mass pulsar PSR J0740+6620 yields a radius less than 11 km. Would this radius measurement yield a result in excess of 12 km, this would allow for both, a purely hadronic and a hybrid nature of this star. In the latter case the maximum mass could reach $2.6~M_\odot$ so that the lighter object in the asymmetric binary merger GW190814 could have been a hybrid star. We demonstrate that this high mass can be compatible with an early onset of deconfinement at star masses below $1~M_\odot$ and the occurrence of low-mass twin stars. In such a case the remnant of GW170817 could be a long-lived hypermassive pulsar.