AI 中文总结
本研究提出年轻超高速星源于核星团的偏心不对称盘，通过SMBH-IMBH双星的引力弹弓效应产生，其产生率与观测一致，且年轻超高速星的分布与旧星族存在差异。
AI 中文摘要
在银河系晕中，已发现约20颗晚B型超高速星（HVS），其运动速度超过银河系逃逸速度，其中多数源自银河系中心（GC）。近期研究提出，这些HVS最可能形成于1.5亿至5亿年前的核星团（NSC），主要通过绕超大质量黑洞（SMBH）人马座A*（Sgr A*）运行的中等质量黑洞（IMBH）的引力弹弓效应被抛出。本研究探讨年轻HVS产生率对NSC恒星形成区的约束，提出年轻HVS的前身星诞生于与NSC半径相当的偏心不对称盘。通过数值追踪盘星的轨道演化，发现盘星因偏心盘不稳定性在形成时发生快速角动量弛豫，其与SMBH-IMBH双星在约100天文单位（au）距离处的弹弓相互作用，产生HVS的速率为10⁻⁵至10⁻⁴年⁻¹。该速率可反映盘的形成历史，随盘星积累而增加，在1.5亿年前恒星形成停止后迅速下降。此速率与观测结果一致，且比文献中旧弛豫星族的预期速率高出数个数量级，提升原因来自非球形GC引力矩及盘星的径向速度各向异性。研究结果表明，年轻HVS应具有与旧HVS不同的径向和角分布。
英文摘要
About twenty late B-type hypervelocity stars (HVSs) traveling faster than the Galactic escape velocity have been discovered in the Galactic halo, many of which were ejected from the Galactic center (GC). Recently, we have advocated that these HVSs most likely formed in the nuclear star cluster (NSC) $150$--$500\, \rm{Myr}$ ago and were predominantly ejected via the gravitational slingshot of a past intermediate-mass black hole (IMBH) orbiting the supermassive black hole (SMBH) Sgr~A$^{*}$. Here we explore the constraints of the production rate of young HVSs on the star formation region of the NSC. We propose that the young HVS progenitors are born in a lopsided eccentric disk that is comparable in radius to the NSC. By numerically tracking the orbital evolution of disk stars, we find that they undergo rapid angular momentum relaxation at formation due to eccentric disk instability, and that their slingshot interactions with the SMBH-IMBH binary at distances $\simeq 100\, \rm{au}$ produce HVSs at a rate of $10^{-5}$--$10^{-4}\, \rm{yr}^{-1}$. The rate is expected to trace the disk formation history, increasing with the accumulation of disk stars and dropping rapidly after the star formation stopped at $150\, \rm{Myr}$ ago. The rate is consistent with the observation and orders of magnitude higher than that expected for an old relaxed population in the literature, enhanced due to the gravitational torque from the non-spherical GC potential and radial velocity anisotropies of the disk stars. Our results imply that young HVSs should have a distinct radial and angular distribution from old ones.
Comments11 Pages, 5 figures, accepted for publication in ApJL
