[论文解读] Constraining neutron star properties and dark matter admixture with the NITR-I equation of state: Insights from observations and universal relations

Pinku Routaray, Harish Chandra Das+2 more|arXiv (Cornell University)|Jul 24, 2023

Pulsars and Gravitational Waves ResearchPhysics and Astronomy被引用 3

一句话总结

本研究提出了一种新的相对论性平均场（INRS）方程态，用于包含暗物质（DM）的中子星，基于PSR J0952-0607和HESS J1731-347的观测约束。结果表明，费米动量最高达0.045 GeV的暗物质与质量、半径、潮汐可变形性及NICER观测结果一致；同时，增加暗物质会提高非径向f模振荡频率并软化方程态，支持HESS J1731-347作为潜在的暗物质混合中子星。

ABSTRACT

A recent observational study has constrained the maximum mass of neutron stars (NSs), with particular attention to PSR J0952-0607 and the compact star remnant HESS J1731-347, especially in the low-mass regime. Building on our earlier work, which developed the NITR energy density functional (EDF) to reproduce the mass limit of PSR J0952-0607 but did not satisfy other observational constraints, this study introduces a refined EDF named ``NITR-I". NITR-I successfully reconciles the PSR J0952-0607 mass limit with observational data, including radius measurements from NICER+XMM and tidal deformability constraints from GW170817, demonstrating its robustness. The low-mass constraint associated with HESS J1731-347 indicates diverse NS compositions. Since NITR-I alone cannot satisfy this constraint, we explore the role of dark matter (DM) within NSs to bridge the gap. Incorporating DM, particularly at specific Fermi momentum values, enables the model to address this constraint. We further analyze the influence of DM on various NS properties, such as tidal deformability and non-radial $f$-mode oscillations, across multiple relativistic mean-field models. The presence of DM suggests a reduction in tidal deformability and shifts in oscillation frequencies, potentially offering detectable signatures in gravitational wave observations from neutron star mergers. Additionally, we investigate universal relations (URs) for DM-admixed NSs, focusing on correlations such as compactness versus tidal deformability and $f$-mode frequency versus tidal deformability. Canonical values for these properties are estimated using GW170817 data, offering further insights into the structure and composition of neutron stars.

研究动机与目标

• 利用PSR J0952-0607和HESS J1731-347的观测约束，研究暗物质混合中子星的可行性。
• 开发一种新的相对论性平均场（INRS）方程态，重现PSR J0952-0607（2.35 M☉）的质量并引入暗物质。
• 利用多信使数据（包括NICER、GW170817和GW190814）约束中子星中暗物质的含量。
• 分析暗物质对中子星潮汐可变形性和非径向f模振荡的影响。

提出的方法

• 提出一种新型相对论性平均场（RMF）模型，命名为INRS，用于重现PSR J0952-0607的质量，并通过单流体方法引入暗物质。
• 方程态由包含标量、矢量和rho介子场的INRS拉格朗日密度导出，包含非线性自耦合项和交叉耦合项。
• 暗物质被建模为费米气体，其费米动量k_f^DM可变，其对方程态的影响通过求解耦合的爱因斯坦方程与物质场方程计算得出。
• 利用观测数据对模型进行约束：NICER提供的质量与半径、GW170817和GW190814提供的潮汐可变形性，以及HESS J1731-347的低质量和小半径。
• 在相对论性Cowling近似下计算非径向f模振荡，以研究暗物质对恒星脉动的影响。
• 验证在所有暗物质混合水平下，方程态与手征有效场论约束的一致性。

Figure 1: Using the chiral EFT bound, which is shaded in pink color, the EOS for the INRS model is plotted with and without DM. The inset plot shows how the sound speed ( $c_{s}^{2}$ ) varies with the density.

实验结果

研究问题

• RQ1 基于INRS方程态的暗物质混合中子星模型能否满足PSR J0952-0607和HESS J1731-347的质量与半径约束？
• RQ2 在包含NICER、GW170817和GW190814等多信使观测数据的前提下，允许的最大暗物质费米动量k_f^DM是多少？
• RQ3 暗物质混合如何影响中子星的潮汐可变形性？其结果是否在引力波事件的可信区间内？
• RQ4 引入暗物质如何影响中子星的非径向f模振荡频率？
• RQ5 INRS模型在包含暗物质的情况下，是否与手征有效场论对方程态的约束一致？

主要发现

• INRS模型在包含暗物质时，中子星最大质量为2.343 M☉，与PSR J0952-0607的观测质量（2.35 ± 0.17 M☉）一致，且在NICER约束范围内。
• 当暗物质费米动量k_f^DM最高达0.045 GeV时，模型满足HESS J1731-347（0.77⁺⁰.²⁰₋₀.¹⁷ M☉，10.4⁺⁰.⁸⁶₋₀.⁷⁸ km）的质量与半径约束，以及Capano等人（2020）的典型半径约束。
• 暗物质混合星体的潮汐可变形性值位于GW170817和GW190814的90%可信区间内，表明与引力波观测一致。
• 引入暗物质会软化方程态，降低最大质量，同时随着k_f^DM增加，非径向f模振荡频率提高。
• 在所有k_f^DM取值下，模型均保持在手征有效场论约束范围内，证实其理论稳健性。
• 分析支持HESS J1731-347可能是暗物质混合中子星的假设，尤其在k_f^DM ≈ 0.03 GeV时更为成立。

Figure 2: The mass-radius relation for our novel RMF model INRS is shown with and without DM along with different observational constraints.