Which first order phase transitions to quark matter are possible in neutron stars?

TL;DR

This paper investigates which first order phase transitions to quark matter in neutron stars are compatible with current astrophysical constraints, using a parameterized equation of state and recent NICER data to identify potential signatures.

Contribution

It introduces a systematic framework to analyze phase transition parameters in neutron stars using relativistic mean field models aligned with chiral effective field theory and recent observational data.

Findings

Certain regions in the transition pressure-energy density space may reveal phase transitions.

Strongly constrained mass-radius data could limit the ability to detect phase transitions.

Mass and radius alone may be insufficient indicators of quark matter transitions in neutron stars.

Abstract

We examine which first order phase transitions are consistent with today's astrophysical constraints. In particular, we explore how a well-constrained mass-radius data point would restrict the admissible parameter space and to this end, we employ the most likely candidates of the recent NICER limits of PSR J0030+0451. To systematically vary the stiffness of the equation of state, we employ a parameterizable relativistic mean field equation of state, which is in compliance with results from chiral effective field theory. We model phase transitions via Maxwell constructions and parameterize them by means of the transitional pressure $p_{\rm trans}$ and the jump in energy density $\Delta\epsilon$. This provides us with a generic setup that allows for rather general conclusions to be drawn. We outline some regions in the $p_{\rm trans}$-$\Delta\epsilon$ parameter space that may allow for a phase transition identification in the near future. We also find that a strongly constrained data point, at either exceptionally large or small radii, would reduce the parameter space to such an extent that mass and radius become insufficient indicators of a phase transition.