The amount of crustal entrainment and the type of Vela-like pulsars

TL;DR

This paper investigates how crustal entrainment affects the internal structure and classification of Vela-like pulsars, using advanced equations of state and observational data to clarify the role of superfluid neutrons.

Contribution

It assesses the impact of crustal entrainment on neutron star models and distinguishes between hybrid and non-hybrid Vela-like pulsars based on entrainment levels.

Findings

Large entrainment implies Vela-like pulsars are likely non-hybrid stars.

The amount of entrainment influences the fractional moment of inertia.

Vela data constrains hyperon-meson coupling parameters.

Abstract

The "glitch crisis" of Vela-like pulsars has been a great debate recently. It might challenge the standard two-component glitch model, because large fractions of superfluid neutrons are thought to be entrained in the lattices of the crust part, then there is not enough superfluid neutrons to trigger the large glitches in Vela-like pulsars. But the amount of entrainment which could effectively constrain the fractional moment of inertia of a pulsar, is very uncertain. In order to examine the importance of this parameter on the inner structures of neutron stars, we relax the "glitch crisis" argument, employ a set of most developed equations of state derived within microscopic many-body approaches that could fulfill the recent 2-solar-mass constraint, and evaluate their predictions for the fractional moment of inertia with two extremes of crustal entrainment. We find a final determination of the amount of entrainment could be closely related to the type of neutron star. If a large enough fraction of neutrons are entrained, a Vela-like pulsar could not be a hybrid star, namely no free quarks would be present in its core. In addition, we use the Vela data to narrow the parameter space of hyperon-meson couplings in the popular phenomenological relativistic mean field model.