通过黑洞-黑洞星/索恩-齐特科夫天体碰撞形成高偏心率致密双星的动力学过程
Dynamical formation of high-eccentricity compact binaries through BH--BH*/TZO collisions
AI总结：
本研究通过流体动力学与半解析少体模拟，提出大质量主序星经连续捕获恒星级黑洞形成高偏心率致密双星的新通道，该双星或可成为对应形成场景的独特引力波标识。
AI中文摘要：
LIGO探测到的恒星质量黑洞（sBH）并合双星的发现正快速累积，为致密双星的形成与演化研究打开了新窗口，其中残余轨道偏心率可作为其形成通道的独特标识。本研究结合流体动力学与半解析少体模拟，探究大质量主序星通过连续捕获多个sBH形成高偏心率致密双星的场景：质量M_•≲0.2M_★的sBH可被大质量恒星捕获，并通过气体动力学摩擦稳定为准流体静力学平衡的黑洞星（BH*）；后续与第二个sBH相遇，会在恒星包层内形成致密双星。流体动力学模拟显示，通过小碰撞参数捕获，部分双星形成时即具有高偏心率（e≳0.5），其轨道频率已进入LISA探测波段；半解析模型进一步表明，气体动力学摩擦可将偏心率提升至e_10Hz>0.9，最终在并合的最后阶段，引力波辐射会使双星圆化，该双星形成后可在约10小时内快速并合。该通道可能在星团、活动星系核（AGN）盘等致密恒星环境中运行，相同机制也适用于索恩-齐特科夫（Thorne-Żytkow）天体，因此LIGO波段的高偏心率双星可作为该形成场景的独特标识。
英文摘要：
The rapidly accumulating discoveries of binary stellar-mass black-hole (sBH) coalescences, detected by LIGO, have opened a new window into the formation and evolution of compact binaries. In particular, residual orbital eccentricity may provide a distinctive signature of their formation channels. Here, we investigate a scenario in which high-eccentricity compact binaries form through the sequential capture of multiple sBHs by massive main-sequence stars, using a combination of hydrodynamical and semianalytic few-body simulations. We find that sBHs with $M_\bullet\lesssim 0.2\,M_{\star}$ can be captured by massive stars and settle into a quasi-hydrostatic black-hole star (BH*) through gas dynamical friction. A subsequent encounter with a second sBH can then produce a compact binary embedded within the stellar envelope. Our hydrodynamical simulations show that through captures with small impact parameter, some binaries are born with high eccentricity ($e\gtrsim 0.5$), with its orbital frequency already entering the LISA band. Our semianalytic models further demonstrate that gas dynamical friction can pump the eccentricity to $e_{\rm 10\,Hz}>0.9$ before gravitational-wave emission eventually circularizes the binary during the final stage of coalescence. Once formed, the binary can merge quickly in $\sim 10$ hours. This channel may operate in dense stellar environments, such as star clusters and active galactic nucleus (AGN) disks. The same mechanism can also be applied to Thorne-Żytkow objects. A high-eccentricity binary in the LIGO band could therefore provide a distinctive signature of this formation scenario.
