Impact of massive neutron star radii on the nature of phase transitions in dense matter

Univ Lyon, Univ Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon - UMR 5822, F-69622, Villeurbanne, France

^(a) r.somasundaram@ipnl.in2p3.fr (corresponding author)

Received: 3 September 2021
Accepted: 4 April 2022

Abstract

The last few years have seen tremendous progress in the observation of the global properties of neutron stars (NSs), e.g., masses, radii and tidal deformabilities. Such properties provide information about possible phase transitions in the inner cores of NSs, provided the connection between observed masses and radii and the equation of state (EoS) is well understood. We focus the present study on first-order phase transition, which often softens the EoS and consequently reduces the maximum mass as well as the radii of NSs. Here, we challenge this conventional expectation by constructing explicit examples of EoSs undergoing a first-order phase transition, but which are much stiffer that their purely hadronic counterparts. We also provide comparisons with the recently proposed quarkyonic EoS which suggests a strong repulsion in the core of NSs, and we show that their stiffness can be realistically masqueraded by stiff first-order phase transitions to exotic matter.