发表机构
University of Oxford; University of Notre Dame; Institute of Science and Technology Austria (ISTA); Eötvös University（牛津大学; 圣母大学; 奥地利科学技术研究所; 厄特沃什大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过483个二维流体动力学模拟，发现小偏心率（约盘厚径比）可扩大AGN盘中黑洞捕获窗口，而大偏心率降低捕获率，首次近心点距离能有效预测直接捕获。
AI 中文摘要
我们研究了活动星系核（AGN）气态盘内恒星质量黑洞（BHs）之间的近距离遭遇，在此过程中可能形成双黑洞（BBHs）。我们使用欧拉网格代码Athena++，在剪切盒框架内进行了一组483个二维绝热粘性流体动力学模拟。我们将两个嵌入的黑洞与气体共同演化。为了探究非圆形初始条件对捕获的影响，我们改变了初始径向间距$b$、其中一个恒星黑洞围绕中心超大质量黑洞的偏心率$e$，以及偏心相位角$\phi_e$。我们考虑了从$e=0$到$e=0.1$的偏心率，并将其与局部盘厚径比$h=H/R_0\simeq0.005$进行比较。我们发现小偏心率会改变参数空间中的捕获窗口。量级为盘厚径比的偏心率，特别是$e\sim h$--$2h$，在圆形模型中无法捕获的初始间距下产生了成功捕获。相比之下，$e \gg h$的系统在遭遇前保留的气体较少，在采样参数网格上捕获率较低。我们发现首次近心点距离是直接捕获的有用预测指标。对于$r_{\rm p}<0.1r_H$的直接捕获预测，能正确分类$92.7\\\\%$的希尔球遭遇。希尔球气体质量有助于识别气体贫乏的失败案例，但在此套模拟中（初始盘密度、温度和粘性参数保持固定）未提供额外的清晰捕获边界。遭遇前偏心率通过其对首次遭遇几何结构和可用于轨道能量耗散的气体储库的综合影响，改变了气体辅助的BBH形成。
英文摘要
We investigate close encounters between stellar-mass black holes (BHs) in the gaseous discs of active galactic nuclei (AGNs), during which binary black holes (BBHs) may form. We perform a suite of 483 2D adiabatic viscous hydrodynamic simulations within a shearing box prescription using the Eulerian grid code Athena++. We co-evolve the two embedded BHs with the gas. To probe the dependence of capture on non-circular initial conditions, we vary the initial radial separation $b$, the eccentricity $e$ of one of the stellar BHs around the central supermassive black hole, and the eccentric phase angle $ϕ_e$. We consider eccentricities from $e=0$ to $e=0.1$ and compare them with the local disc aspect ratio $h=H/R_0\simeq0.005$. We find that small eccentricities shift the capture window in the parameter space. Eccentricities of order the disc aspect ratio, in particular $e\sim h$--$2h$, produce successful captures at initial separations that do not capture in the circular models. By contrast, systems with $e \gg h$ retain less gas before encounter and have lower capture fractions across the sampled parameter grid. We find that the first periapsis distance is a useful predictor of direct capture. Predicting direct capture for $r_{\rm p}<0.1r_H$ correctly classifies $92.7\%$ of Hill sphere encounters. The Hill sphere gas mass helps identify gas-poor failures, but provides no clear additional capture boundary within this suite, in which the initial disc density, temperature, and viscosity parameter are held fixed. Pre-encounter eccentricity modifies gas-assisted BBH formation through its combined effects on the first-encounter geometry and the gas reservoir available for orbital energy dissipation.
Comments15 pages, 10 figures, submitted to MNRAS
