The GW170817 binary neutron star merger event in 2017 has raised great interest in the theoretical research f neutron stars. The structure and cooling properties of dark-matter-admixed neutron stars are studied here using relativistic mean field theory and cooling theories. The non-self-annihilating dark matter (DM) component is assumed to be ideal fermions, among which the weak interaction is considered. The results show that pulsars J1614-2230, J0348+0432 and EXO 0748-676 may all contain DM with the particle mass of 0.2-0.4 GeV. However, it is found that the effect of DM on neutron star cooling is complicated. Light DM particles favor the fast cooling of neutron stars, and the case is converse for middle massive DM. However, high massive DM particles, around 1.0 GeV, make the low mass (around solar mass) neutron star still undergo direct Urca process of nucleons at the core, which leads the DM-admixed stars cool much more quickly than the normal neutron star, and cannot support the direct Urca process with a mass lower than 1.1 times solar mass. Thus, we may conjecture that if small (around solar mass) and super cold (at least surface temperature 5-10 times lower than that of the usual observed data) pulsars are observed, then the star may contain fermionic DM with weak self-interaction.

BAO Tmurbagan() 1;1) LIU Guang-Zhou( ) 2;2) ZHU Ming-Feng( ) 2

No abstract

In this paper, we study the third family of compact stars with the color-flavor locked (CFL) quark core. The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter. The results of the calculation show a transitional behavior that goes from the hadron star range, through the transition range, into the CFL quark star range. In the transition range, the third family of compact stars with the CFL quark matter core is found in the wide range of the CFL energy gap 100 MeV≤<150 MeV. By comparing with early investigations, we argue that the greatest possible third family of compact stars may be the hybrid stars with the CFL quark core. Neutron stars are natural laboratories to study the properties of compact matter [1,2]. In the interior of a neutron star there exist phase transitions from hadronic matter to various exotic matter, such as hyperonic matter, meson condensation and quark matter [3][4][5]. It is widely accepted that hadronic matter undergoes a phase transition to strange quark matter at the high density range [6,7]. The study of quantum chromodynamics (QCD) indicates that quark matter might be in a color superconducting phase at quite high density range [8,9]. The essence of color superconductivity is based on the Bardeen, Cooper, and Schrieffer (BCS) pairing mechanism [10]. Theoretical researchers generally agree that the ground state of QCD with three flavors is the color-flavor-locked (CFL) phase [11,12]. At present, the hybrid stars with a CFL quark matter core have been extensively studied [13][14][15]. Two families of compact stars, white dwarfs and neutron stars, are known well. Almost 40 years ago, Gerlach [16] found that a third family of stable configurations of compact stars could exist in nature besides two families of white dwarfs and neutron stars. He noted that it was due to a large discontinuous behavior in the speed of sound (dp/dε) of the corresponding equation of state (EoS). Glendenning [17] also found that the practical physical mechanism was a phase transition from hadronic to quark matter. Schertler et al. [18] investigated the phase transition from hadronic to normal quark matter and the possibility of the third family of compact stars. They concluded that the third family could serve as a signature for a phase transition from hadronic to quark matter. This paper will investigate the influence of the CFL energy gap on the bulk properties of neutron stars and discuss