论文标题
年轻明星簇中的二进制黑洞：金属性的影响
Binary black holes in young star clusters: the impact of metallicity
论文作者
论文摘要
年轻的恒星簇是巨大恒星的最常见的出生地，并且是动态活跃的环境。在这里，我们通过6000种N体仿真以及二元种群合成的6000个N体模拟研究了年轻恒星簇中黑洞（BHS）和二元黑洞（BBHS）的形成。我们探测了三种不同的恒星金属（z = 0.02、0.002和0.0002）和两个初始密度制度（在半径半径$ρ_{\ rm h} \ ge {} \ ge {} 3.4 \ times1010^4 $和$ \ ge {1.5 \ \ \ \ \ \ \ \ \ \ \ \ \ $ m $ m $ $ pc $ pc中，集群分别）。金属贫困簇倾向于形成比金属富含金属的BHS更大的BHS。我们找到$ \ sim {} 6 $，$ \ sim {} 2 $，以及$ <1 $ <1 $ bhs的质量$ $ m _ {\ rm bh}> 60 $ m $ _ \ odot $ at z = 0.0002、0.002、0.002和0.02。在金属贫穷的簇中，我们形成了中间质量BHS，质量最高为$ \ sim {} 320 $ m $ _ \ odot $。 BBH通过动力交流（交换BBH）出生的BBH合并比由二进制进化形成的BBH合并更大：前（后）达到总量高达$ \ sim {} 140 $ M $ _ $ _ \ odot $（$ \ odot $（$ \ sim {} 80 $ _ $ _ $ _ \ odot $）。在我们的模拟中，最庞大的BBH合并具有主要质量$ \ sim {} 88 $ m $ _ \ odot $，内部稳定质量差距，质量比为$ \ sim {} 0.5 $。只有来自金属贫穷祖细胞的年轻明星群中出生的BBH才能与GW170729的质量相匹配，这是O1和O2中最庞大的事件，以及GW190412的质量，这是第一次不等的质量合并。我们估计本地BBH合并速率密度$ \ sim {} 110 $和$ \ sim {} 55 $ gpc $^{ - 3} $ yr $^{ - 1} $，如果我们假设所有星星都以松散和密集的恒星簇形式形成。
Young star clusters are the most common birth-place of massive stars and are dynamically active environments. Here, we study the formation of black holes (BHs) and binary black holes (BBHs) in young star clusters, by means of 6000 N-body simulations coupled with binary population synthesis. We probe three different stellar metallicities (Z=0.02, 0.002 and 0.0002) and two initial density regimes (density at the half-mass radius $ρ_{\rm h}\ge{}3.4\times10^4$ and $\ge{1.5\times10^2}$ M$_\odot$ pc$^{-3}$ in dense and loose star clusters, respectively). Metal-poor clusters tend to form more massive BHs than metal-rich ones. We find $\sim{}6$, $\sim{}2$, and $<1$% of BHs with mass $m_{\rm BH}>60$ M$_\odot$ at Z=0.0002, 0.002 and 0.02, respectively. In metal-poor clusters, we form intermediate-mass BHs with mass up to $\sim{}320$ M$_\odot$. BBH mergers born via dynamical exchanges (exchanged BBHs) can be more massive than BBH mergers formed from binary evolution: the former (latter) reach total mass up to $\sim{}140$ M$_\odot$ ($\sim{}80$ M$_\odot$). The most massive BBH merger in our simulations has primary mass $\sim{}88$ M$_\odot$, inside the pair-instability mass gap, and a mass ratio of $\sim{}0.5$. Only BBHs born in young star clusters from metal-poor progenitors can match the masses of GW170729, the most massive event in O1 and O2, and those of GW190412, the first unequal-mass merger. We estimate a local BBH merger rate density $\sim{}110$ and $\sim{}55$ Gpc$^{-3}$ yr$^{-1}$, if we assume that all stars form in loose and dense star clusters, respectively.
