双黑洞系统的不同起源及其参数分布

双黑洞组成的近密双星系统并合是激光干涉仪引力波天文台等地基引力波探测器的主要探测对象。随着探测器灵敏度的提高,大量该类信号的探测将成为进一步研究黑洞物理的有效工具。但是目前对双黑洞系统的起源机制和内禀参数分布等物理问题的研究还不够深入,例如由引力波探测得到的黑洞质量分布与X射线双星观测的结果存在较大差异,还未有很好的理论模型可解释该结果。目前普遍认为双黑洞系统主要有两种起源:大质量双星演化机制和动力学起源机制。基于这两类起源的双黑洞系统在质量、自旋分布等方面存在差异。因此可在贝叶斯理论框架下,利用引力波信号携带的波源质量和自旋等信息,推断波源起源,计算不同起源的双黑洞系统所占比例,以及检验质量自旋等参数分布的差异。

Formation Channels of Binary Black Hole and Their Parameter Distributions

The binary black hole(BBH)coalescence event GW150914 has been observed by LIGO detectors,and many more detections are expected once current advanced LIGO and Virgo detectors begin operating at designed sensitivity.Gravitational waves will provide us with a powerful tool for investigating the physics of BBHs,because it encodes information about the formation channel of this system.However,Many physical properties of BBH system is still unknown,especially mass,spin and other intrinsic parameter distributions of binary system from different formation channels.Mass distribution of black holes from gravitational-wave detection and X-ray observation are different,because of different formational channels.X-ray observation indicates that the black hole mass distribute mainly in(7:8±1:2)M⊙,which may come from dynamical capture.And mass estimation from gravitational waves is in the range 20M⊙~40M⊙,which is supposed to be field BBHs.This is because Jeans stability analysis provides corresponding Jeans radius and black hole mass which is smaller than dynamical binaries.Two formation channels are commonly considered for BBH coalescence:common envelope evolution and dynamical evolution mechanism which have the underlying uncertain intrinsic parameter distributions on mass and spin.The two formation channels have different mass and spin distributions,and due to Jeans stability analysis,black hole mass from common envelope evolution is smaller than the other case and spin aligned.BBHs from dynamical capture mechanism have random oriented spins commonly considered as isotropic distribution.Based on differences especially mass and spin distributions of BBHs from the two formation channels,using Bayesian hierarchical inference to distinguish the two formation channels is workable,more over,Bayes method can be used to calculate relative population of sources in each channel.Moreover,assuming the percentages of these two channels have been obtained,it can be used to compare mass distributions of different formation channels.