Anisotropic pressure effect on central EOS of PSR J0740+6620 in the light of dimensionless TOV equation

【摘要】 It is generally agreed upon that the pressure inside a neutron star is isotropic. However, a strong magnetic field or superfluidity suggests that the pressure anisotropy may be a more realistic model. We derived the dimensionless TOV equation for anisotropic neutron stars based on two popular models, namely, the BL and H models, to investigate the effect of anisotropy. Similar to the isotropic case, the maximum mass Mmax and its corresponding radius RMmax can also be expressed linearly by a combination of radial central pressure prc and central energy densityε_c, which is insensitive to the equation of state（EOS）. We also found that the obtained central EOS would change with different values of λ_BL（ λ_H）, which controls the magnitude of the difference between the transverse pressure and radial pressure. Combining with observational data of PSR J0740+6620 and comparing to the extracted EOS based on an isotropic neutron star, it is shown that in the BL model, for λBL = 0.4, the extracted central energy density ε_c changed from 546-1056 MeV/fm³ to 510-1005 MeV/fm³, and the extracted radial central pressure prc changed from 87-310 MeV/fm³ to 76-271 MeV/fm³. For λ_BL = 2, the extracted ε_c and prc changed to 412-822MeV/fm³ and 50-165 MeV/fm³, respectively. In the H model, for λH = 0.4, the extracted ε_c changed to 626-1164 MeV/fm³, and the extracted prc changed to 104-409 MeV/fm³. For λH = 2, the extracted ε_c decreased to894-995 MeV/fm³, and the extracted p_rc changed to 220-301 MeV/fm³.更多还原

【Abstract】 It is generally agreed upon that the pressure inside a neutron star is isotropic. However, a strong magnetic field or superfluidity suggests that the pressure anisotropy may be a more realistic model. We derived the dimensionless TOV equation for anisotropic neutron stars based on two popular models, namely, the BL and H models, to investigate the effect of anisotropy. Similar to the isotropic case, the maximum mass Mmax and its corresponding radius RMmax can also be expressed linearly by a combination of radial central pressure prc and central energy densityε_c, which is insensitive to the equation of state（EOS）. We also found that the obtained central EOS would change with different values of λ_BL（ λ_H）, which controls the magnitude of the difference between the transverse pressure and radial pressure. Combining with observational data of PSR J0740+6620 and comparing to the extracted EOS based on an isotropic neutron star, it is shown that in the BL model, for λBL = 0.4, the extracted central energy density ε_c changed from 546-1056 MeV/fm³ to 510-1005 MeV/fm³, and the extracted radial central pressure prc changed from 87-310 MeV/fm³ to 76-271 MeV/fm³. For λ_BL = 2, the extracted ε_c and prc changed to 412-822MeV/fm³ and 50-165 MeV/fm³, respectively. In the H model, for λH = 0.4, the extracted ε_c changed to 626-1164 MeV/fm³, and the extracted prc changed to 104-409 MeV/fm³. For λH = 2, the extracted ε_c decreased to894-995 MeV/fm³, and the extracted p_rc changed to 220-301 MeV/fm³.更多还原