Intermediate-mass black holes (IMBHs) could form via runaway merging of massive stars in a young massive star cluster (YMC). We combine a suite of numerical simulations of YMC formation with a semi-analytic model for dynamical friction and merging of massive stars and evolution of a central quasi-star, to predict how final quasi-star and relic IMBH masses scale with cluster properties (and compare with observations). The simulations argue that inner YMC density profiles at formation are steep (approaching isothermal), producing some efficient merging even in clusters with relatively low effective densities, unlike models which assume flat central profiles resembling those of globular clusters (GCs) {\em after} central relaxation. Our results can be approximated by simple analytic scalings, with $M_{\rm IMBH} \propto v_{\rm cl}^{3/2}$ where $v_{\rm cl}^{2} = G\,M_{\rm cl}/r_{\rm h}$ is the circular velocity in terms of initial cluster mass $M_{\rm cl}$ and half-mass radius $r_{\rm h}$. While this suggests IMBH formation is {\em possible} even in typical clusters, we show that predicted IMBH masses for these systems are small, $\sim 100-1000\,M_{\odot}$ or $\sim 0.0003\,M_{\rm cl}$, below even the most conservative observational upper limits in all known cases. The IMBH mass could reach $\gtrsim 10^{4}\,M_{\odot}$ in the centers nuclear star clusters, ultra-compact dwarfs, or compact ellipticals, but in all these cases the prediction remains far below the present observed supermassive BH masses in these systems.
From Dense Gas Clouds to Supermassive Black Hole Seeds: Hybrid Hydro/Direct $N$-body Simulations of Runaway Collision-driven Intermediate-mass Black Hole Formation
Seoul National University（首尔大学）；Northwestern University（西北大学）；Korea Institute of Science and Technology Information（韩国科学技术信息研究所）
Merging stellar and intermediate-mass black holes in dense clusters: implications for LIGO, LISA and the next generation of gravitational wave detectors
研究了由两个恒星黑洞（BH）和一个中等质量黑洞（IMBH）之间的相互作用触发的中等质量比螺旋（IMRIs）的形成。我们利用$N$体模型改变IMBH质量，恒星BH质谱，和星团的属性。这些模拟再加上半解析的过程来解释残余IMBH的演变。IMRI形成概率达到值$\sim 5-50\%$，较大的值对应于较大的IMBH质量。IMRIs绘制出恒星BH的质谱，因此它们可能被用来解开恒星星团中的BH人口窝藏IMBH。在IMRI阶段之后，最初接近最大值（几乎不旋转）的IMBH倾向于减少（增加）其自旋。如果IMBH增长主要是通过重复的IMRI，我们表明，只有IMBH种子足够大（$M_{\rm seed} > 300$ M $_\odot$）可以增长到$M_{\rm imbh} >10^3$ M $_\odot$在密集的球状星团。假设这些种子在红移$z\sim 2-6$处形成，我们发现它们中的$1-5\%$在红移$z=0$处将达到质量$\sim 500-1500$ M $_\odot$，并将表现出低自旋$S_{\rm imbh} < 0.2$。测量IMRI中涉及的IMBH的质量和自旋可以帮助解开它们的形成机制。我们表明，LISA可以检测IMBHs在银河系球状星团的信噪比$=10-100$，或在大麦哲伦星云的信噪比$=8-40$。我们提供了LIGO（$Γ_{\rm LIG} = 0.003-1.6$ yr…
Three-dimensional radiation hydrodynamics simulations of wandering intermediate-mass black holes considering the anisotropic radiation and dust sublimation
Tracers of Discs and Winds around Intermediate and High Mass Young Stellar Objects
我们提出了一个小样本的近红外明亮的大质量和中等质量的年轻恒星天体的运动学性质的研究，使用敏感的光盘和风的发射线。我们第一次表明，广泛的（$\sim500$公里$^{-1}$）对称线翼HI布拉开系线是由于斯塔克展宽或电子散射，而不是纯粹的多普勒展宽由于高速运动。结果与非常致密的星周环境的存在是一致的。此外，这些线中的许多线显示出弱线自吸收的证据，这表明吸收材料的那部分是风或盘风的起源。自吸收的弱点表明，这种流出的开口角度很大。我们还研究了荧光1.688 $μ$ m Fe Ⅱ线，这是敏感的致密材料。我们拟合开普勒光盘模型，这条线，并找到合理的适合在所有酒吧的一种情况下，与以前发现的经典Be星，荧光铁过渡是合理的光盘示踪剂。总的来说，这些恒星仍然有吸积盘，有一个非常致密的内部环星环境，可能是跟踪盘的内部区域，或恒星风，其中电离流出也存在。与低质量恒星的相似性是惊人的，这表明至少在这个质量范围内，它们以类似的方式形成。
