活动星系核吸积盘中白矮星碰撞及其观测效应  

White dwarf collisions in AGN disks and the observational effects

作　　者：张书瑞 罗沿 袁业飞[1,2] Shu-Rui Zhang;Yan Luo;Ye-Fei Yuan(School of Astronomy and Space Science,University of Science and Technology of China,Hefei 230026,China;CASKeyLaboraryr ReearchinGaaesand ComoogyparmentofAtromy,Universityof Scnceand TechogyofChnaHei 230026,China;Department of Physics and Earth Science,University of Ferrara,Ferrara I-44122,Italy)

机构地区：[1]中国科学技术大学天文与空间科学学院,合肥230026 [2]中国科学技术大学天文系,中国科学院星系与宇宙学研究重点实验室,合肥230026 [3]Department of Physics and Earth Science,University of Ferrara,Ferrara 1-44122,Italy

出　　处：《科学通报》2025年第3期423-431,共9页Chinese Science Bulletin

基　　金：平方公里阵列射电望远镜(SKA)专项(2020SKA0120300);国家自然科学基金(12393812);中国科学院基础与交叉前沿科研先导专项(B类)(XDB0550200)资助。

摘　　要：活动星系核(active galactic nuclei,AGN)盘中的白矮星(white dwarf,WD)很可能会迁移到内区,并形成由两白矮星与中心超大质量黑洞(supermassive black hole,SMBH)组成的限制性三体系统.多体模拟发现该三体系统通常是不稳定的,会导致两白矮星在近遇(close encounter)过程中相撞.该事件率可达300 Gpc^(-3)yr^(-1),相当于观测到的Ia型超新星的1%.白矮星相撞会引发热核爆炸,爆炸的能量主要转化为碎片的动能,碎片再与AGN吸积盘碰撞将动能转化为内能,并产生特征性光变:迅速上升后以L∝t^(-2.8)衰减,时标为几小时到月的量级,具体取决于SMBH质量.后续对盘的破坏还可能导致变脸AGN现象.回落碎片撞击盘物质产生的高能辐射主要在硬X射线到软γ波段,光度可达1043erg s^(-1),有望被未来的Me V探测器观测到.另外,AGN吸积盘可能是重元素产生的工厂,白矮星相撞产生的碎片将显著增加AGN吸积盘的金属丰度.White dwarfs(WDs)in the accretion disks of active galactic nuclei(AGN)are likely to migrate to the inner regions and form restricted three-body systems with two WDs moving around the central supermassive black hole(SMBH)in close orbits.Through N-body simulations,we find that such three-body systems are typically unstable,leading to collisions between the two WDs during close encounters.We explore the evolution of these systems with different initial orbital separations p,relative orbital inclinations i,and SMBH masses M.Our simulations show that close WD encounters predominantly occur within the range 1.1 R_(H)≤p≤2√3 R_(H),where R_(H)is the mutual Hill radius.For p<1.1 R_(H),most WDs occupy stable horseshoe or tadpole orbits,with only a few undergoing close encounters if their initial orbital phase difference is small.In cases where p=3.0 Rh,WD-WD collisions are observed in the majority of simulated systems within a timescale of 105 Pi,with numerous collisions occurring within t<62 Pr for smaller orbital radi,where Pr is the orbital period.The peak of the closest separation distribution increases,and the frequency of WD-WD collisions decreases as the relative inclination between orbits increases.This closest-separation distribution remains similar across different SMBH masses,but the fraction of WD collisions declines with increasing SMBH mass.The estimated collision rate for WDs in AGN disks reaches up to 300 Gpc^(-3) yr^(-1),which is approximately 1%of the observed Type la supernova rate.However,the observational effects of WD collisions in AGN disks could differ from those of typical Type Ia supernovae.When two WDs collide,they can trigger a runaway thermonuclear explosion,with most of the explosion energy stored in the ejecta in the form of kinetic energy.Typically,this ejecta escapes the AGN disk rapidly without significant deceleration.However,under the gravitational influence of the SMBH,most of the ejecta eventually falls back toward the disk.As this fallback ejecta disperses over time and space,it

关 键 词：活动星系核 吸积盘 白矮星 碰撞 

分 类 号：P157.6[天文地球—天文学] P145.5