عنوان مقاله [English]
In this paper, we assume that the core of the neutron star consists of nucleons, leptons, and hyperons. We investigate the equation of state of neutron star matter using the LOCV method with AV18 potential,, TNI and also excluded volume effect (VE). We obtain the mass-radius relation of twin neutron stars in the presence of hyperons. The obtained results demonstrate that the threshold density of sigma hyperon lies in the range of (0.243-0.552) fm^-3 and that of lambda hyperon exists in the range of (0.353-0.940) fm^-3 . It is obvious that the appearance of hyperons softens the equation of state of neutron star matter, which is largely compensated by considering the radius for nucleons. The comparison of the results obtained for the mass-radius relation of neutron stars shows that the presence of hyperons using potential reduces the maximum mass of neutron stars from 2.11 to 1.12 M_sun . However, this parameter reaches the value of 1.5 M_sun by including the VE which indicates stiffening of the equation of state. In addition, excluded volume effect leads to instability after the appearance of hyperons, which implies the existence of a twin neutron star, two stars of the same mass but different radii.
 J. Zdunik, P. Haensel, Maximum mass of neutron stars and strange neutron-star cores, Astronomy and Astrophysics 551 (2013) A61. https://doi.org/10.1051/0004-6361/201220697