# The structure of hybrid neutron star in Einstein-$\Lambda$ gravity

## TL;DR

This study examines how the cosmological constant influences the structure of hybrid neutron stars in Einstein-$\Lambda$ gravity, revealing that higher values reduce their maximum mass and size, with stability maintained.

## Contribution

It introduces a modified TOV equation in Einstein-$\Lambda$ gravity to analyze the impact of the cosmological constant on hybrid neutron star properties.

## Key findings

- Higher $\Lambda$ decreases maximum mass and radius of neutron stars.
- For small $\Lambda$, effects on star structure are negligible.
- An upper limit for $\Lambda$ is established based on gravitational redshift constraints.

## Abstract

In this paper, we investigate the structure of neutron stars by considering both the effects of the cosmological constant and the existence of quark matter for neutron stars in Einstein's gravity. For this purpose, we use a suitable equation of state (EoS) which includes a layer of hadronic matter, a mixed phase of quarks and hadrons, and a quark matter in the core. To investigate the effect of the cosmological constant on the structure of hybrid neutron stars, we utilize the modified TOV equation in Einstein-$\Lambda $ gravity. Then we drive the mass-radius relation for different values of the cosmological constant. Our results show that for small values of the cosmological constant ($\Lambda $), especially for the cosmological constant from the cosmological perspective $(\Lambda =10^{-52}$ $m^{-2})$, $\Lambda $ has no significant effect on the structure of hybrid neutron stars. But for higher values, for example, by considering $\Lambda >10^{-14}$ $m^{-2}$, this quantity affects the maximum mass and radius of these stars. We find an upper limit for the cosmological constant as $\Lambda <9\times 10^{-13}m^{-2}$, based on the fact that the gravitational redshift cannot be more than $1$ for stars. The maximum mass and radius of these stars decrease by increasing the cosmological constant $\Lambda$. Also, by determining and analyzing radius, the compactness, Kretschmann scalar, and gravitational red shift of the hybrid neutron stars with $M=1.4M_{\,\odot }$ in the presence of the cosmological constant, we find that by increasing $\Lambda$, they are contracted. Also, our results for dynamical stability show that these stars satisfy this condition.