Contraction of cold neutron star due to in the presence a quark core

Abstract

Motivated by importance of the existence of quark matter on structure of neutron star. For this purpose, we use a suitable equation of state (EoS) which include three different parts: i) a layer of hadronic matter, ii) a mixed phase of quarks and hadrons, and, iii) a strange quark matter in the core. For this system, in order to do more investigation of the EoS, we evaluate energy, Le Chatelier's principle and stability conditions. Our results show that the EoS satisfies these conditions. Considering this EoS, we study the effect of quark matter on the structure of neutron stars such as maximum mass and the corresponding radius, average density, compactness, Kretschmann scalar, Schwarzschild radius, gravitational redshift and dynamical stability. Also we find an upper limit for the maximum mass of these stars. Indeed, our results show that there is no any massive neutron star with mass more than 2M ⊙ ( M ⊙ is solar mass), when we consider a quark core for this object. This means that in the center of massive neutron stars with mass more than 2M ⊙ (for example 4U 1700 − 377 and J1748 − 2021B with masses about 2.4M ⊙ and 2.7M ⊙ , respectively), there is no any quark core. In addition, our analyze indicates that neutron stars are under a contraction due to the existence of quark core.

The structure of hybrid neutron star in Einstein-$Λ$ gravity

“…The obtained results in ref. [75], showed that, the existence of quark matter at center of neutron stars (or hybrid neutron stars) led to unstable against the radial adiabatic infinitesimal perturbations, while by applying the effect of cosmological constant to these stars, the dynamically stability keeps inside it.…”

“…It is worthwhile that energy conditions (the null energy condition, weak energy condition, strong energy condition and dominant energy condition at the center of neutron star), stability and Le Chatelier's principle of this EoS have been investigated in ref. [75].…”