arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2009.04696astro-ph.HEastro-ph.SRgr-qc
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根据大质量中子星和GW170817用实际状态方程研究$f(\mathcal{R,T})$引力中的中子星

Neutron stars in $f(\mathcal{R,T})$ gravity using realistic equations of state in the light of massive pulsars and GW170817

R. Lobato, O. Lourenço, P. H. R. S. Moraes, C. H. Lenzi, M. de Avellar, W. de Paula, M. Dutra, M. Malheiro

摘要:

本文研究了$f(\mathcal{R,T})$引力下的中子星(NS):$R+2λ\mathcal{T}$,$\mathcal{R}$是Ricci标量,$\mathcal{T}$是能量动量张量的迹.流体静力平衡方程求解考虑现实状态方程(EsoS)。所得到的NS质量和半径受到大质量恒星和事件GW 170817的联合约束。在以前的NS研究中,参数$λ$需要为负,但是我们发现它的最小值。该值应该是$|λ|\lesssim0.02$,与以前用简单EsoS获得的值相比,如此小的值的原因是由于NS地壳的存在。重力理论中的压力取决于声速$v_s$的倒数。由于$v_s$在地壳中的位置很低,因此PDMATHAMT需要非常小。我们发现,恒星质量的增量小于$1\%$,远小于以往不考虑实际恒星结构的结果,并且恒星半径不能变大,其相对于GR的变化在所有情况下都小于$3.6\%$.用几种相对论和非相对论模型计算的结果表明,对于所有的EsoS,NS质量和半径的变化几乎相同,这表明我们的结果对EsoS的高密度部分不敏感。它证实了恒星质量和半径的变化只取决于地壳,其中EoS基本上是相同的所有模型。NS地壳效应意味着非常小的$|λ|$值并不依赖于所选择的理论函数,因为对于任何其他函数,流体静力平衡方程总是依赖于$1/v_s$。最后,我们强调,我们的研究结果表明,从NS研究中得到的结论,在修改后的引力理论,而不使用现实的EsoS正确描述NS内部可能是不可靠的。

英文摘要:

In this work we investigate neutron stars (NS) in $f(\mathcal{R,T})$ gravity for the case $R+2λ\mathcal{T}$, $\mathcal{R}$ is the Ricci scalar and $\mathcal{T}$ the trace of the energy-momentum tensor. The hydrostatic equilibrium equations are solved considering realistic equations of state (EsoS). The NS masses and radii obtained are subject to a joint constrain from massive pulsars and the event GW170817. The parameter $λ$ needs to be negative as in previous NS studies, however we found a minimum value for it. The value should be $|λ|\lesssim0.02$ and the reason for so small value in comparison with previous ones obtained with simpler EsoS is due to the existence of the NS crust. The pressure in theory of gravity depends on the inverse of the sound velocity $v_s$. Since, $v_s$ is low in the crust, $|λ|$ need to be very small. We found that the increment in the star mass is less than $1\%$, much smaller than previous ones obtained not considering the realistic stellar structure, and the star radius cannot become larger, its changes compared to GR is less than $3.6\%$ in all cases. The finding that using several relativistic and non-relativistic models the variation on the NS mass and radius are almost the same for all the EsoS, manifests that our results are insensitive to the high density part of the EsoS. It confirms that stellar mass and radii changes depend only on crust, where the EoS is essentially the same for all the models. The NS crust effect implying very small values of $|λ|$ does not depend on the theory's function chosen, since for any other one the hydrostatic equilibrium equation would always have the dependence $1/v_s$. Finally, we highlight that our results indicate that conclusions obtained from NS studies done in modified theories of gravity without using realistic EsoS that describe correctly the NS interior can be unreliable.

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