恒星-黑洞碰撞形成黑洞恒星
Formation of black hole stars via star--black hole collisions
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中文总结 AI 辅助
该研究通过多种方法探究恒星质量黑洞与大质量恒星的碰撞过程，发现低质量黑洞与恒星碰撞可形成黑洞恒星，或为致密系统中黑洞增长及JWST发现的小红点起源提供解释。
中文摘要 AI 辅助
在球状星团和活动星系核（AGN）盘等致密恒星环境中，恒星质量黑洞（sBH）可能频繁与大质量恒星发生碰撞。我们利用半解析模型、三维流体动力学模拟以及一维恒星演化计算对该过程展开研究，重点关注sBH与100倍太阳质量主序星的碰撞。研究发现，除非碰撞速度超过约2√[G(M★+M●)/R★]，气体阻力会将黑洞束缚在恒星包层内。碰撞后的结果主要取决于黑洞与恒星的质量比：当M●≥30倍太阳质量时，被束缚的包层要么呈准球形，要么呈盘状，但因激波加热而保持动力学不稳定；相反，当M●≤10倍太阳质量时，碰撞会形成“黑洞恒星”（BH*），即嵌入黑洞周围的准流体静力学平衡的延展恒星包层。这些结果与我们的分析预测一致，即BH*的形成必然要求M●≤0.2M★。后续的MESA计算进一步表明，对于这些低质量黑洞，经激波加热的残余体会发生热弛豫，不会触发失控膨胀。我们探讨了BH*的若干天体物理意义，包括其演化、恒星包层内形成的黑洞双星产生引力波事件的可能性，以及恒星-sBH多次碰撞作为致密恒星系统中黑洞快速增长的一种途径。该机制可能有助于高红shift核星团中大质量黑洞的形成，且可能与詹姆斯·韦布空间望远镜（JWST）发现的“小红点”的起源有关。
英文摘要
In dense stellar environments such as globular clusters and active galactic nucleus (AGN) disks, stellar-mass black holes (sBHs) may frequently collide with massive stars. We investigate this process using semi-analytic models, three-dimensional hydrodynamical simulations, and one-dimensional stellar evolution calculations, focusing on collisions between sBHs and a $100\,M_\odot$ main-sequence star. We find that gas drag retains the BH within the stellar envelope unless the impact velocity exceeds $\sim2\sqrt{G(M_\star+M_\bullet)/R_\star}$. The post-collision outcome depends primarily on the BH-to-star mass ratio. For $M_\bullet\gtrsim30\,M_\odot$, the retained envelope is either quasi-spherical or disc-like, but remains dynamically unstable because of shock heating. In contrast, for $M_\bullet\lesssim10\,M_\odot$, the collision forms a ``black hole star'' (BH*): a quasi-hydrostatic, extended stellar envelope surrounding the embedded BH. These results agree with our analytic prediction that BH* formation necessarily requires $M_\bullet\lesssim0.2\,M_\star$. Follow-up \texttt{MESA} calculations further show that, for these low-mass BHs, the shock-heated remnant thermally relaxes without triggering runaway expansion. We discuss several astrophysical implications of BH*s, including their evolution, the possibility of gravitational-wave events from BH binaries assembled within a stellar envelope, and repeated star--sBH collisions as a pathway for rapid BH growth in dense stellar systems. This mechanism may contribute to the formation of massive BHs in high-redshift nuclear star clusters and may be relevant to the origin of the ``little red dots'' discovered by JWST.
