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arXiv 2409.02147astro-ph.HEastro-ph.SRnucl-th
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基于无量纲TOV方程的各向异性压强对PSR J0740+6620中心状态方程的影响

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

Zhihao Yang, Dehua Wen

AI总结:

本文基于无量纲TOV方程研究各向异性压强对中子星中心状态方程的影响,结合PSR J0740+6620观测数据给出不同各向异性参数下中心能量密度和压强的变化范围。

摘要:

人们普遍认为中子星内部的压强是各向同性的。然而,强磁场或超流性表明压强各向异性可能是更符合实际的模型。我们基于两种常用模型,即BL模型和H模型,推导了各向异性中子星的无量纲TOV方程,以研究各向异性的影响。与各向同性情形类似,最大质量$M_{max}$及其对应半径$R_{Mmax}$也可以用径向中心压强$p_{rc}$和中心能量密度$\varepsilon_{c}$的线性组合来表示,并且这种表示对状态方程(EOS)不敏感。我们还发现,所得到的中心EOS会随着$λ_{BL}$($λ_{H}$)取值的不同而改变,该参数控制横向压强与径向压强之间差异的大小。结合PSR J0740+6620的观测数据,并与基于各向同性中子星提取的EOS进行比较,结果表明:在BL模型中,当$λ_{BL}$ = 0.4时,提取的中心能量密度$\varepsilon_{c}$从546 -- 1056 MeV/fm$^{3}$变为510 -- 1005 MeV/fm$^{3}$,提取的径向中心压强$p_{rc}$从87 -- 310 MeV/fm$^{3}$变为76 -- 271 MeV/fm$^{3}$;当$λ_{BL}$ = 2时,提取的$\varepsilon_{c}$和$p_{rc}$分别变为412 -- 822 MeV/fm$^{3}$和50 -- 165 MeV/fm$^{3}$。在H模型中,当$λ_{H}$ = 0.4时,提取的$\varepsilon_{c}$变为626 -- 1164 MeV/fm$^{3}$,提取的$p_{rc}$变为104 -- 409 MeV/fm$^{3}$;当$λ_{H}$ = 2时,提取的$\varepsilon_{c}$降至894 -- 995 MeV/fm$^{3}$,提取的$p_{rc}$变为220 -- 301 MeV/fm$^{3}$。

英文摘要:

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 model and the H model, to investigate the effect of anisotropy. Similar to the isotropic case, the maximum mass $M_{max}$ and its corresponding radius $R_{Mmax}$ can also be expressed linearly by a combination of radial central pressure $p_{rc}$ and central energy density $\varepsilon_{c}$, 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 the radial pressure. Combining with observational data of PSR J0740+6620 and comparing to the extracted EOS based on isotropic neutron star, it is shown that in the BL model, for $λ_{BL}$ = 0.4, the extracted central energy density $\varepsilon_{c}$ changed from 546 -- 1056 MeV/fm$^{3}$ to 510 -- 1005 MeV/fm$^{3}$, and the extracted radial central pressure $p_{rc}$ changed from 87 -- 310 MeV/fm$^{3}$ to 76 -- 271 MeV/fm$^{3}$. For $λ_{BL}$ = 2, the extracted $\varepsilon_{c}$ and $p_{rc}$ changed to 412 -- 822 MeV/fm$^{3}$ and 50 -- 165 MeV/fm$^{3}$, respectively. In the H model, for $λ_{H}$ = 0.4, the extracted $\varepsilon_{c}$ changed to 626 -- 1164 MeV/fm$^{3}$, and the extracted $p_{rc}$ changed to 104 -- 409 MeV/fm$^{3}$. For $λ_{H}$ = 2, the extracted $\varepsilon_{c}$ decreased to 894 -- 995 MeV/fm$^{3}$, and the extracted $p_{rc}$ changed to 220 -- 301 MeV/fm$^{3}$.

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