Population Properties Of Compact Binaries Via Gravitational Waves

Since the first detection of the gravitational wave signal from the coalescing of two black holes by Advanced LIGO,gravitational waves have gradually become an important means for people to understand the universe and study astrophysical phenomena.Compact stars（including black holes and neutron stars）have become the main objects of gravitational wave observation.How are the compact binary stars formed and able to merge within the age of the universe?What types of binary systems are included in gravitational wave sources?Does the mass and spin of black holes and neutron stars reveal the evolution process of their progenitors?These are important questions to be answered in the age of gravitational wave astronomy.In the first chapter,we firstly introduce how to extract the information of combined double dense stars from gravitational wave signals,which provides technical support for inferring the properties of the compact binary coalescing from an individual gravitational wave signal in the Chapter 4;Then we also introduce some important gravitational wave signals detected by LIGO,Virgo and KAGRA,and talk about their applications in the astrophysics;Finally,the formation and evolution of the compact binary stars as gravitational wave sources are introduced in detail,as well as some population properties of compact binary stars that are expected to be reflected in gravitational wave observation samples.In Chapter 2,we firstly introduce in detail the methods of studying the population properties of compact binary star via gravitational waves,including the nonparametric methods and the parametric methods.Then we use the nonparametric method via Gaussian process to study the mass distribution of binary black holes.We find that there is an obvious structure in the mass spectrum of binary black holes,i.e.,there is an obvious peak in the interval of M～20-30M⊙,which is associated with the pulsational pairinstability supernova or the dynamical assembly of binary black holes.We also use the parameterized model to explore the mass ratio distribution correlated with the mass distribution of binary black holes.We found that the binaries with m1>29M⊙（m1 is the primary mass of binary system）,are more likely to be symmetric systems than the binaries with m1<29M⊙.This means that there are more than one evolution channel.The formation of low-mass binary black holes may be dominated by the common-envelop evolution;while the formation of high-mass binary black holes may be dominated by the chemical homogeneous evolution and the dynamical capture,which are more likely to form symmetric binary black holes.In addition,we also found that the binary black holes near the peak of m1～34M⊙ may have a stronger trend to be symmetry than the other binary black holes.Different formation mechanisms（i.e.,the field binaries and the dynamic capture）may leave different information in the spin distribution of binary black holes in the whole mass range.Therefore,we constructed a simple phenomenological model to study the joint distribution of mass and spin for the binary black holes to explore their population properties.First of all,we find that the maximum mass of the stellar formed black holes is tightly constrained:mmax=39.3-2.5+2.3 M⊙,the maximum mass of stellar formed black holes reveals the existence of the high-mass gap caused by the pairinstability supernova,and the tight constraint can also help to estimate the metallicity of the progenitors of the binary black holes.Then we find that 4-17%of dynamical events were hierarchical mergers,and these black holes have an average spin magnitude significantly larger than the first-generation black holes.We also find that the spin orientations of the dynamical events are not exactly isotropic or perfectly aligned,and it is likely that the AGN disk environment has contributions to the dynamical assembly.In Chapter 3,we use the hierarchical Bayesian inference to analyze the population properties of the compact binary systems including at least one neutron star.Both the mass and spin may bring the information about the formation and evolution of neutron stars,additionally,there are great degeneracy between the mass and spin in the parameter estimation.Therefore,we jointly model the mass distribution and spin distribution of neutron stars in our analysis.We find that although the specific shape of neutron star mass distribution cannot be determined exactly by the current observation samples,there may be a peak at 1.35M⊙,which is consistent with the mass distribution of neutron stars in the Milky way.Simultaneously,we find that the masses of black holes in the neutron star-black holes are distributed in～5-10M⊙,which is consistent with the mass distribution of black holes in the X-ray binary stars in the Milky way.Additionally,the ratio of the merger rate densities between neutron star-black holes and binary neutron stars is estimated to be～3:7.Through simulation,we find that in the O4 and O5 stages,100 observations of compact binaries containing neutron stars will be able to accurately determine the mass distribution of extragalactic neutron stars,which will help to study the formation and evolution of coalescing low-mass compact binaries,and it is also possible to independently constrain the Hubble constant.In Chapter 4,we use the Bayesian parameter estimation of gravitational wave signals to mainly analyze a special source,GW190426₁52155 detected by LIGO and Virgo,because the observation of some special gravitational wave sources can provide data support for the research of compact stars related Astrophysics from different perspective.We find that the GW190426₁52155 may originate from a merger of neutron star-black hole,but the possibility that it comes from a merger of low mass binary black holes can not be ruled out.As a neutron star-black hole,we find that the system is unlikely to produce bright electromagnetic radiation;If it is a low mass binary black hole,we find that the black holes in this system have significantly large spins and the spin orientations are anti-aligned with respect to the orbital angular momentum,we speculate it may come from the a hierarchical merger of the previously merged binary neutron stars.If we do not consider the prior probability,we find that the Bayes factor of the hierarchical merger to the coalescence of neutron star-black hole is In B～2,In the Chapter 5,I summarize the dissertation,and look into the gravitational wave observation in the next few years,which may help better understand the formation and evolution of coalescing compact binary stars.