大质量黑洞周围的恒星级天体及动力学演化  

The stellar-mass objects and their dynamics around supermassive black hole

作　　者：范霄 王梦叶 吴庆文 Xiao Fan;Mengye Wang;Qingwen Wu(Department of Astronomy,School of Physics,Huazhong University of Science and Technology,Wuhan 430074,China)

机构地区：[1]华中科技大学物理学院天文系,武汉430074

出　　处：《科学通报》2025年第3期338-352,共15页Chinese Science Bulletin

基　　金：国家重点研发计划(2023YFC2206702);国家自然科学基金(12233007)资助。

摘　　要：黑洞吸积是活动星系核(active galactic nuclei,AGNs)的能量之源.理论研究表明吸积盘外区一般是引力不稳定的,该不稳定区域可能会形成大量恒星.这些恒星通过星风、超新星爆发等可实现AGN核区元素的快速增丰.AGN发射线观测表明其pc尺度金属丰度的确远超过太阳金属丰度,支持星系核区存在大量恒星活动.这些核区恒星会演化为白矮星、中子星和恒星级黑洞等致密天体.当AGN吸积盘存在时,核区恒星级天体会与AGN吸积盘产生复杂的相互作用,比如穿越吸积盘的恒星在气体阻力作用下可能会落入吸积盘,吸积盘的引力势也会扰动恒星运动轨道(如Kozai-Lidov机制),盘中的恒星或恒星级致密天体会快速向内迁移,外区恒星级天体通过两体或多体相互作用可能被散射到中心大黑洞周围从而被潮汐瓦解(tidal disruption event,TDE)或形成极端质量比旋近系统(extreme mass ratio inspiral,EMRI)等.近几年发现TDE偏向于发生在后暴星系中,表明中心黑洞活动或星系演化影响或决定了TDE事件率.在多信使时代,特别是未来空间引力波时代(天琴/太极/LISA),星系核区TDE、EMRI相关研究将为理解星系核心环境、黑洞与星系共同演化等提供全新信息.The accretion process plays a key role in releasing the gravitational energy of accreting matter in high-energy objects(e.g.,active galactic nuclei,AGNs).It is well known that the accretion disk is gravitationally unstable in the outer part of the AGN disk,where many stars may form.Considering these stars stay in a dense environment,they will evolve quickly in a much different way compared to isolated stars.These stars will evolve into compact sources(e.g.,white dwarf,neutron star,and stellar-mass black hole),which will themselves accrete matter and continue to evolve.Observations indicate that the metallicity,estimated from broad emission lines of AGNs,ranges from solar to supersolar and does not evolve with redshift up to around 7.This metallicity is also correlated with the mass of the supermassive black hole(SMBH)or the luminosity of the AGN.We discuss the possibility of star formation and evolution in the outer unstable AGN disk and find that it can roughly reproduce the observed correlation between the SMBH mass and metallicity if the stellar mass distribution is‘top-heavy’.The model also predicts that the metal enrichment is very fast,which can explain why there is no strong redshift evolution for the metallicity in AGNs.During the AGN phase,both stars and stellar-mass compact objects interact with the AGN disk.The SMBH at the center of our Galaxy may have been in an active phase millions of years ago.If Sgr A^(*)was active in the past,the accretion disk may have had a significant impact on the dynamics of stars in the Galactic center,where the drag force exerted on stars during star–disk interaction could lead some of them to sink into the accretion disk.These embedded stars will rapidly migrate inward and eventually be disrupted within several thousand years.The presence of an AGN disk could also explain the absence of stars within 1000 AU,the possible bimodal distribution of S-star inclinations,and their high-eccentricity orbits.Tidal disruption events(TDEs)also provide a valuable probe for studyi

关 键 词：活动星系核 恒星 金属丰度 恒星动力学 引力波 

分 类 号：P14[天文地球—天体物理]