Can a hybrid star with constant sound speed parametrization explain the new NICER mass-radius measurements ?

TL;DR

This study reanalyzes NICER data on pulsars to evaluate hybrid star models with constant sound speed, highlighting how phase transition parameters influence the consistency with observed neutron star masses and radii.

Contribution

It constrains the CSS model parameters for hybrid stars using NICER observations, emphasizing the role of phase transition characteristics in matching astrophysical data.

Findings

Lower energy density discontinuities are consistent with observations.

Large energy density jumps are disfavored for supporting massive neutron stars.

Higher sound speeds in quark matter improve agreement with data.

Abstract

We present a reanalysis of NICER observations of PSR J0740+6620 and PSR J0030+0451 to test the consistency of various nuclear equations of state (EoS) within the framework of hybrid star models. In particular, we examine how different surface temperature models for PSR J0030+0451, categorized as Scenarios A, B, and C, lead to significantly different mass-radius estimates. We perform a comprehensive study constraining the parameters of the constant speed of sound (CSS) model based on representative observational categories. Our findings indicate that for certain hadronic equations of state, including both density-independent and density-dependent cases, the results remain consistent for lower values of the energy density discontinuity, while discrepancies emerge as the discontinuity increases. Scenarios involving large jumps in energy density are generally disfavored by the requirement of supporting massive neutron stars, whereas higher values of the speed of sound in the quark matter phase tend to yield better agreement with observational trends. These results underscore the importance of phase transition characteristics in aligning hybrid star models with current astrophysical observations. We further constrain the CSS parameters using observational data from PSR J0740+6620 and PSR J0952-0607 by computing the maximum mass supported by these parameter sets.