Non-radial Oscillation And Gravitational Wave Emission Of Neutron Stars

Due to the lack of exact nonperturbative calculation of quantum chromodynamics(QCD),the structure of high-density nuclear matter remains an open theoretical problem.Neutron stars(NSs)are the currently known densest stars except black holes.The interior of a NS can reach several times the nuclear saturation with extreme high temperature and pressure.It is a natural laboratory for studying high-density nuclear matter and QCD.In 2017,the detection of the binary NS merger gravitational wave(GW)event GW170817 by the LIGO/Virgo Gravitational Wave Observatory greatly improve the study of NSs and GWs,starting the era of GW multi-messenger astronomy.GWs will become an important tool for astronomical observation in the future.The non-radial oscillation of NSs,which is one of the mechanisms of GW emission,has also become a hot topic in the current study of dense nuclear matter and NSs.The equation of state(EOS)of dense nuclear matter is a key input that determines the structure and properties of NSs.For dense nuclear matter,current EOS are highly model dependent,and one of the important assumptions is the emergence of deconfined quark matter(QM).In this work,we use the EOS of nuclear matter(NM)described by Brueckner-Hartree-Fock many-body theory,where the Bonn-B and Argonne-V18 potentials are used for the interaction potential.For QM,we use the Dyson-Schwinger equation model,which can simultaneously address both confinement and dynamical chiral symmetry breaking.For the hadron-quark phase transition,we adopt the Gibbs phase transition construction.On this basis,we investigate the structure and non-radial oscillations of pure NSs and hybrid stars(HSs).The two most direct and important physical quantities of NSs are mass and radius.The observations on mass and radius impose constraints on the EOS.Combining the EOS with the hydrostatic equilibrium equation(TOV equation)under the framework of general relativity,the mass-radius relationship of NSs can be obtained.The mass-radius relation obtained with our adopted EOSs satisfies the constraints of current observations of NS masses and radii.The observations of GWs from NSs can also impose constraints on the structure and components of the interior of NSs.We solve the non-radial oscillation equations of NSs with ? = 2 under the Cowling approximation and obtain the corresponding displacement perturbations and eigenfrequencies.We find that,compared with pure NSs,the appearance of QM in HSs will lead to much stronger decrease of the displacement perturbations from the center to the surface.Therefore,the oscillation in HSs occurs mainly in the inner core,and might reveal more information about the core.The appearance of QM in HSs also affects the Brunt-V?is?l? frequency and thus the-mode frequency.We find eigenfrequencies ～300 for pure NSs,which increase very slowly with the NS mass,while those of HSs increase very quickly,reaching above 700 Hz.All these frequencies are in the sensitivity range of current ground-based GW detectors.The clear difference of the-mode frequency between the pure NSs and HSs can thus be a good observable to distinguish them.We also calculate the damping time and the amplitude of GW strain emitted from non-radial oscillations.The concurrent shorter damping time of HSs correspond to larger GW strain and radiation power,and thus it is easier to detect GW of HSs than that of pure NSs.To sum up,the mode is the most suitable mode to provide an observational window on the internal components of NSs.The study of non-radial oscillations of NSs contributes to deeper understanding of NSs and GW,and is of great importance to both nuclear physics and astrophysics.