Constraining radii and stability of neutron stars in 4D Einstein–Gauss–Bonnet gravity

Abstract

In this paper, we have investigated the effects of Gauss–Bonnet extension on Einstein gravity in 4-dimensions. Four different equation of state, namely SLy4, APR4, FPS and Togashi are considered. These equation of state are used to model the massive neutron stars like PSR J0740+6620, PSR J1959+2048, PSR J1810+1744, PSR J2215+5135 and GW190814, which are in the neutron star-black hole mass gap. We have calculated the mass and radius through the $M-R$ curves for different values of the Gauss–Bonnet coupling parameter for four different equation of state to examine the upper limit of masses that fall within the mass gap. Our results show that the positive branch of $\alpha$ is suitable for explaining the existence of massive neutron stars in the mass gap. Bondi’s and static stability criteria confirm the stability of these massive neutron stars. In fact, an increase in Gauss–Bonnet coupling strength improves the stability of these massive neutron stars. Furthermore, the surface redshift of these massive neutron stars is below the maximum limit, i.e. $Z_s\le 2$. Finally, we have used the $M-R$ curves with the observed masses to predict the radii of PSR J2215+5135, PSR J1959+2048, PSR J1810+1744, PSR J0740+6620 and GW190814 in general relativity and 4D Einstein–Gauss–Bonnet gravity. The predicted radii are in agreement with the constraints from the GW170817 event. Lastly, the maximum observed NS mass fits in the $M-R$ curves, implying that the range of $\alpha$ should be somewhere around 0 to 5 ${\text{km}}^2$.