# The structure of cold neutron star with a quark core within the MIT and NJL models

## TL;DR

This paper models the internal structure of cold neutron stars with quark cores using MIT and NJL models, calculating their equations of state and comparing the results with observational data.

## Contribution

It introduces a combined approach using MIT and NJL models with density-dependent parameters to better understand neutron star structure with quark cores.

## Key findings

- Mass and radius predictions align with observed neutron stars.
- Equation of state models match observational data.
- Quark matter effects significantly influence neutron star properties.

## Abstract

Neutron star due to their high interior matter density are expected to be composed of a quark core, a mixed quark-hadron matter, and a layer of hadronic matter. Thus, in this paper, we compute the equation of state of these parts of neutron star to evaluate its structure properties. We use two models for describing EOS of quark matter, NJL and MIT bag models, and employ three approaches in this work. A density dependent bag constant satisfy the quark confinement in the simple MIT bag model. We also study the interaction behavior of quarks, firstly one gluon exchange within MIT bag model and the secondly dynamical mass will be held as effective interaction that roles between particles. Density dependence of quark mass is obtained from NJL self consistent model. NJL model is a effective manner for justify the chiral symmetry. Applying the Gibbs conditions the equation of state of the quarks and hadrons mixed phase is obtained. Since the hadronic matter is under the influence of strong force of nucleons, we calculate the equation of state of this phase using a powerful variational many-body technique. Finally, we calculate the mass and radius of a cold neutron star with a quark core by numerically solving the TOV equation. To check our used EOS, we compare our results with the recent observational data. Our results are in a good agreement with some observed compact objects such as $SAXJ1748.9-2021$, $4U1608-52$ and $Vela X-1$.