质量超过0.98M_(TOV)的中子星的内核呈现奇异新物态

Plausible presence of new state in neutron stars with masses above 0.98M_(Tov)

本文综合利用GW170817、PSR J0030+0451以及PSR J0740+6620的多信使数据及最新的手征有效场论和微扰量子色动力学计算信息,研究了中子星的状态方程.利用贝叶斯非参数推理中使用的单层前馈神经网络模型对各种状态方程结构进行采样,以非模型依赖的方式研究了中子星物质声速的结构.发现声速曲线中峰结构非常普遍,通常出现在2.4~4.8倍核饱和密度处,且声速平方在90%置信水平下超过真空中光速平方的1/3.这种非单调行为表明质量非常大的中子星中的物态偏离了纯强子物质.如果新的/奇异的物态比典型的强子模型甚至含有超子的模型都要软,作者发现引力质量在0.98M_(TOV)以上的中子星很可能存在一个超过10^(-3)M⊙的极可能由夸克物质组成的奇异核,这里的M_(TOV)=2.18_(-0.13)^(+0.27)M⊙(90%置信区间)是限制得到的慢转中子星的最大引力质量,它与GW170817/GRB 170817A/AT2017gfo的暂现超重中子星遗迹模型得到的2.17_(-0.12)^(+0.15)M⊙高度一致.对于迄今为止探测到的质量最大的中子星PSR J0740+6620,研究发现它含有一个奇异内核的概率约为36%.

We investigate the neutron star(NS)equation of state(EOS)by incorporating multi-messenger data of GW170817,PSR J0030+0451,PSR J0740+6620,and state-of-the-art theoretical progresses,including the information from chiral effective field theory(χEFT)and perturbative quantum chromodynamics(pQCD)calculation.Taking advantage of the various structures sampling by a single-layer feed-forward neural network model embedded in the Bayesian nonparametric inference,the structure of NS matter's sound speed csis explored in a model-agnostic way.It is found that a peak structure is common in the c_(s)^(2) posterior,locating at(2.4-4.8)ρ_(sat)(nuclear saturation density)and c_(s)^(2) exceeds c^(2)/3 at 90%credibility.The non-monotonic behavior suggests evidence of the state deviating from the hadronic matter inside the very massive NSs.Assuming the new/exotic state is featured as it is softer than typical hadronic models or even with hyperons,we find that a sizable(≥10^(-3)M_⊙)exotic core,likely made of quark matter,is plausible for the NS with a gravitational mass above about 0.98M_(TOV),where M_(TOV)represents the maximum gravitational mass of a non-rotating cold NS.The inferred M_(TOV)=(2.18_(-0.13)^(+0.27))M_⊙(90%credibility)is well consistent with the value of(2.17_(-0.12)^(+0.15))M_⊙estimated independently with GW170817/GRB170817A/AT2017gfo assuming a temporary supramassive NS remnant formed after the merger.PSR J0740+6620,the most massive NS detected so far,may host a sizable exotic core with a probability of≈0.36.