文章基本信息

标题：The black hole retention fraction in star clusters
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作者：Václav Pavlík ; Tereza Jeřábková ; Pavel Kroupa 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2018
卷号：617
DOI：10.1051/0004-6361/201832919
语种：English
出版社：EDP Sciences
摘要：Context.Recent research has been constraining the retention fraction of black holes (BHs) in globular clusters by comparing the degree of mass segregation withN-body simulations. They are consistent with an upper limit of the retention fraction being 50% or less.Aims. In this work, we focus on direct simulations of the dynamics of BHs in star clusters. We aim to constrain the effective distribution of natal kicks that BHs receive during supernova (SN) explosions and to estimate the BH retention fraction.Methods. We used the collisionalN-body codenbody6to measure the retention fraction of BHs for a given set of parameters, which are: the initial mass of a star cluster, the initial half-mass radius, andσBH, which sets the effective Maxwellian BH velocity kick distribution. We compare these directN-body models with our analytic estimates and newest observational constraints.Results.The numerical simulations show that for the one-dimensional velocity kick dispersionσBH< 50 km s−1, clusters with radii of 2 pc and that are initially more massive than 5 × 103M⊙retain more than 20% of BHs within their half-mass radii. Our simple analytic model yields a number of retained BHs that is in good agreement with theN-body models. Furthermore, the analytic estimates show that ultra-compact dwarf galaxies should have retained more than 80% of their BHs forσBH≤ 190 km s−1. Although our models do not contain primordial binaries, in the most compact clusters with 103stars, we have found evidence of delayed SN explosions producing a surplus of BHs compared to the IMF due to dynamically formed binary stars. These cases do not occur in the more populous or expanded clusters.
关键词：enmethods: numericalmethods: analyticalgalaxies: star clusters: generalstars: black holes