Structure Constrains And Rotochemical Heating Mechanism In The Hybrid Star

It is generally recognized that pulsar is the compact object (neutron star) composed of super dense matter, and its interior is still a mystery of astrophysics. The study of the neutron star theories compared with the observations provides an important tool to probe the dense matter in it. In section1, we introduced the inner structure and various theo-retical models of the neutron star, and discussed the constrains of observations (maximum mass, surface thermal radiation, mass-radius relation) on the models.Recently, some studies indicate that strange quark matter may exist in neutron star. The development of the high energy nuclear physics and high-energy heavy-ion collision experiments indicate the exist of quark matter and the importance of the neutron star model containing strange quark matter. In section2, we introduced the equations of state of quark matter, and studied the constrains of newly maximum mass observations on equations of state of quark matter in the strange star, combined with the physical condition of stable exist of strange quark matter. The results show that the strange star model is not in contradiction to the observations. Without the color-superconductivity, the maximum mass of unpaired quark stars is more sensitive to the parameter C, and the largest mass can reach2.25M⊙. For the strange stars composed of the quark matter in color-flavor locked(CFL) phase, we can obtain quite large maximum masses at a sufficiently high gap value, but the value of mso is very important in deciding the maximum mass of the CFL strange stars. Different from the former studies which use the mass-radius relation to exclude some equation of state, we calculated the maximum mass varying with two state parameters, and gave clear constrains on the parameters.The observation of the thermal radiations is an another important way to probe the inner matter and physical processes in the neutron star. With the help of Chandara X-ray Observatory, XMM-Newton Slew Survey, the observations and research of neutron thermal radiation get obvious progress. The new observation from XXM-Ncwton shows that a few old neutron stars (>105) still have high surface tcmperatures(PSR B2224+65, PSRJ2043-2740, PSR B0628-28, PSR B1929+10). Then the heating mechanisms are important in the explanations of the behaviors. In section3, we introduced the cooling theory of neutron star, and gave comparison of various heating mechanisms. The rotochemical heating mechanism is one of the most important.Rotochemical heating originates in the deviation from weak reaction equilibrium due to spin-down compression. As the star spins down, compression results in a displacement of the equilibrium concentration of each particle species and changes the chemical equilibrium state. The reaction rate is slower than the change of the equilibrium concentrations due to spin-down compression, the star is never exactly in chemical equilibrium and thus energy is stored. Excess of energy is dissipated by enhanced neutrino emission and heat generation. In section4, we introduced the physical process of the chemical deviation and heating in the star, and studied two main problems as following.We calculated the reaction rate and emissivity of weak reaction of superconduc-tive quark matter in non-equilibrium state. The numerical results show that the color-superconductivity dramatically suppress the Durca reaction rate and emissivity, and the reduction is also related to the chemical departure from the beta equilibrium. For small chemical departure, the reduction factor almost only depends on the gap. Until the de-parture reach a certain value, it enhances reaction rate and emissivity rapidly. These results above may be used in the cooling simulation of neutron stars, which contain color-superconductivity quark core in the non-equilibrium state.Furthermore, we studied the effect of deconfinement phase transition on chemical deviation. Through building the physical model, we calculated the chemical deviation and surface temperature evolution in a uniform hybrid, and found that the deconfinement phase transition enlarge the chemical deviation and enhance the heating efficiency obviously. The research of rotochemical heating hint us that the non-equilibrium state maybe is the normal state of a neutron star, although neutron star is considered to be in equilibrium state in former studies. The physical behavior in non-equilibrium state is very different and worth pursuing.