Nonrotating and rotating neutron stars in the extended field theoretical model

We study the properties of nonrotating and rotating neutron stars for a new set of equations of state (EOSs) with different high-density behavior obtained using the extended field theoretical model. The high-density behavior for these EOSs are varied by varying the ω-meson self-coupling and hyperon-meson couplings in such a way that the quality of fit to the bulk nuclear observables, nuclear matter incompressibility coefficient, and hyperon-nucleon potential depths remain practically unaffected. We find that the largest value for maximum mass for the nonrotating neutron star is $2.1M_{\odot }$. The radius for a neutron star with canonical mass is 12.8–14.1 km, provided only those EOSs are considered for which the maximum mass is larger than $1.6M_{\odot },$ the lower bound on the maximum mass measured so far. Our results for the very recently discovered fastest rotating neutron star indicate that this star is supramassive with mass $1.7M_{\odot }$–$2.7M_{\odot }$ and circumferential equatorial radius 12–19 km.

Figure 1

Variations of $X_{\sigma Y}$ with $X_{\omega Y}$ for $\Lambda ,\Sigma ,$ and Ξ hyperons. The values of $X_{\sigma Y}$ for a given value of $X_{\omega Y}$ are calculated by using Eqs. (24) and (26).

Figure 2

Variations of the symmetry energy coefficient $J$ (upper panel) and its linear density dependence $L$ (lower panel) as a function of $\Delta r$ for different parametrizations with $\zeta =0.0,$ 0.03, and 0.06.

Figure 3

Variations of the rms errors in the total binding energies (upper panel) and charge rms radii (lower panel) as a function of $\Delta r$ for different parametrizations with $\zeta =0.0,$ 0.03, and 0.06.

Figure 4

The EOSs for pure neutron matter (upper panel) and symmetric nuclear matter (lower panel). The solid and dashed curves correspond to $\Delta r=0.16$ and 0.28 fm, respectively. The shaded regions represent the experimental data taken from Ref. [61].

Figure 5

The chemical potentials for neutrons (upper panel) and electrons (lower panel) as a function of density.

Figure 6

Variation of neutron star mass as a function of its radius $R$ for selected EOSs. These EOSs are obtained by using the parameter sets LY (UY) correspond to combinations of $\Delta r=0.16$ (0.28), $\zeta =0.06$ (0.0), and $X_{\omega Y}=0.5$ (0.8). The parameter sets L0 and U0 are analogous to LY and UY, respectively, but with no hyperons. The various constraints as indicated by causality, rotation, and $\Delta I/I=0.014$ are discussed in the text.

Figure 7

The threshold density for various hyperons and central densities for a neutron star with the canonical mass and maximum mass obtained for the EOSs corresponding to the parameter sets LY and UY.

Figure 8

Particle fractions as a function of radial coordinate of the neutron star obtained at maximum mass for LY (upper panel) and UY (lower panel) parametrizations. The curves labeled as “n/3" should be multiplied by 3 to get the actual neutron fractions.

Figure 9

Variations of radius ($R_{1.4}$) and redshift ($Z_{1.4}$) for a neutron star with the canonical mass as a function of maximum neutron star mass obtained for the EOSs corresponding to the all different parametrizations of the extended FTRMF model as considered. The vertical line at $M_{max}=1.6M_{\odot }$ in the upper panel corresponds to the mass of the PSR J0751+1807 measured with a $95\%$ confidence limit.

Figure 10

Variations of radius ($R_{max}$) and redshift ($Z_{\text{max}}$) for a neutron star with the maximum mass as a function of maximum neutron star mass obtained for the EOSs corresponding to the all different parametrizations of the extended FTRMF model as considered. The horizontal line in the lower panel corresponds to the measured value of the redshift, $Z=0.35$, for the neutron star EXO 0748–676 [53].

Figure 11

The relationship between mass $M$ and the circumferential equatorial radius $R_{\mathrm{eq}}$ for Keplerian sequences for different EOSs obtained within the extended FTRMF model.

Figure 12

The mass $M$ verses the circumferential equatorial radius $R_{\mathrm{eq}}$ for neutron stars rotating at 1122 Hz for selected EOSs obtained within the extended FTRMF model. The minimum values for the radius indicated by open circles are determined by the setting-in of the instability with respect to axisymmetric perturbations. The maximum values for the radius indicated by open squares are determined by the mass-shedding instability. The values of maximum radius are well fitted by the solid curve obtained using Eq. (35).