标题： GW231123：来自$\sim 10 $个恒星级质量黑洞的连续合并产物 显示英文标题

标题： GW231123: a product of successive mergers from $\sim 10 $ stellar-mass black holes

摘要： GW231123是一个异常质量的双黑洞（BBH）合并事件，其组成部分具有异常高的自旋。 这种极端特性挑战了传统的恒星演化模型，该模型预测由于对不稳定超新星会导致黑洞质量间隙。 我们使用关于黑洞质量和自旋分布的人口信息先验来分析GW231123，以测试可能的形成情景：第一代恒星坍缩、分层（多代）合并和原初起源。 我们的分析强烈支持至少一个成分是更高代的黑洞的情景。 两个成分都被认为具有高自旋，这排除了它们都是第一代（低自旋）或原初（几乎无自旋）的情景。 我们得出结论，GW231123是一个分层合并，其成分可能分别源自$\sim 6$和$\sim 4$第一代黑洞的连续合并。 这表明重复合并可能很频繁，甚至可以产生更高质量的中等质量黑洞。 因此需要能够有效硬化BBH轨道的机制，例如活动星系核盘中的气体动力学分数。 显示英文摘要

摘要： GW231123 is an exceptionally massive binary black hole (BBH) merger with unusually high component spins. Such extreme properties challenge conventional stellar evolution models predicting a black hole mass gap due to pair-instability supernovae. We analyze GW231123 using population-informed priors on BH mass and spin distributions to test possible formation scenarios: first-generation stellar collapse, hierarchical (multi-generation) mergers, and primordial origin. Our analysis strongly prefers scenarios where at least one component is a higher-generation BH. Both components are favored to have high spins, which rules out scenarios in which they are both first-generation (low spin) or primordial (nearly non-spin). We conclude that GW231123 is a hierarchical merger, with components plausibly originate from the successive mergers of $\sim 6$ and $\sim 4$ first-generation BHs, respectively. This suggests that repeated mergers can be frequent and even more massive intermediate-mass black holes may be produced. Thus mechanisms that can efficiently harden the BBHs' orbits are required, e.g., gas dynamical fraction in the disks of active galactic nucleus.