Compact Object Modeling in the Globular Cluster 47 Tucanae
Compact Object Modeling in the Globular Cluster 47 Tucanae
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DOI：
10.3847/1538-4357/ac5b0b
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发表时间：
2021-10
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影响因子：
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通讯作者：
Claire S. Ye;K. Kremer;C. Rodriguez;N. Z. Rui;Newlin C. Weatherford;S. Chatterjee;G. Fragione;F. Rasio
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作者：
Claire S. Ye;K. Kremer;C. Rodriguez;N. Z. Rui;Newlin C. Weatherford;S. Chatterjee;G. Fragione;F. Rasio
球状星团 47 Tucanae (47 Tuc) 是银河系中质量最大的星团之一，并且拥有异常丰富的奇异恒星群。几十年来，它一直是观测者最喜欢的目标，但由于其恒星数量众多（N ≳ 106）且密度高，建模在计算上非常具有挑战性。在这里，我们提出了使用 Cluster Monte Carlo 代码 (CMC) 计算的详细且自洽的 47 个 Tuc 模型。这些模型包括与恒星和双星演化耦合的所有相关动力学相互作用，并重现各种观测结果，包括表面亮度和速度色散剖面、脉冲星加速度和致密天体的数量。我们表明，通过采用相对于标准假设（例如，Kroupa 2001）的底部重和顶部轻的初始恒星质量函数以及溢出星团潮汐半径的初始埃尔森剖面（Elson et al. 1987），可以最好地再现 47 Tuc 的当前特性。我们在 CMC 中纳入了通过巨星碰撞和潮汐捕获形成双星的新方案，并且我们表明这些机制在 47 Tuc 中中子星双星和毫秒脉冲星的形成中发挥着至关重要的作用；我们的最佳拟合模型包含约 50 毫秒的脉冲星，其中 70% 是通过巨大碰撞和潮汐捕获形成的。我们的模型还表明，47 Tuc 目前包含多达 ∼200 个恒星质量黑洞、∼5 个双黑洞、∼15 个低质量 X 射线双星和∼300 个灾难变星。
The globular cluster 47 Tucanae (47 Tuc) is one of the most massive star clusters in the Milky Way and is exceptionally rich in exotic stellar populations. For several decades it has been a favorite target of observers, and yet it is computationally very challenging to model because of its large number of stars (N ≳ 106) and high density. Here we present detailed and self-consistent 47 Tuc models computed with the Cluster Monte Carlo code (CMC). The models include all relevant dynamical interactions coupled to stellar and binary evolution, and reproduce various observations, including the surface brightness and velocity dispersion profiles, pulsar accelerations, and numbers of compact objects. We show that the present properties of 47 Tuc are best reproduced by adopting an initial stellar mass function that is both bottom-heavy and top-light relative to standard assumptions (as in, e.g., Kroupa 2001), and an initial Elson profile (Elson et al. 1987) that is overfilling the cluster’s tidal radius. We include new prescriptions in CMC for the formation of binaries through giant star collisions and tidal captures, and we show that these mechanisms play a crucial role in the formation of neutron star binaries and millisecond pulsars in 47 Tuc; our best-fit model contains ∼50 millisecond pulsars, 70% of which are formed through giant collisions and tidal captures. Our models also suggest that 47 Tuc presently contains up to ∼200 stellar-mass black holes, ∼5 binary black holes, ∼15 low-mass X-ray binaries, and ∼300 cataclysmic variables.