Gravitational Lensing of Fermion Stars

We discuss the fermion stars, the self-gravitating systems of Fermi gases, as possible gravitational lenses. It is supposed that the fermions interact with themselves and other particles only by gravity, so they are the candidates of dark matter. We calculate Einstein deflection angles, study the image configurations, and calculate the magnification factors for a number of fermion stars that range from strong relativistic configurations to nonrelativistic ones. We find that typically there are three images, one Einstein ring and one radial critical curve for both cases. Two of the images are within the Einstein ring, and the other is outside, which may be very far. All these lensing characteristics can help to identify fermion stars as potential lensing objects, thus might give direct evidence that dark fermion stars exist in the universe.     

The best detection conditions for pulsars in the Galactic disk

Radio detection of pulsars in the Galactic disk is strongly affected by the dispersion and scattering effect of the interstellar medium and the Galactic background radio emission. In order to know the best conditions for discovery of pulsars, we select and simulate pulsar samples in the Galactic disk, and calculate the detection probability with various observation conditions (such as observational frequency, telescope aperture, receiver bandwidth and integration time). We have found that the detection frac...     

GW170817与标准汽笛宇宙学

GW170817实现了基于“标准汽笛”的首次哈勃常数&;amp;lt;em&;amp;lt;H&;amp;lt;/em&;amp;lt;&;amp;lt;sub&;amp;lt;0&;amp;lt;/sub&;amp;lt;测量,开启了标准汽笛宇宙学的序幕。正在进行的双中子星并合引力波观测,有望在5年内测量&;amp;lt;em&;amp;lt;H&;amp;lt;/em&;amp;lt;&;amp;lt;sub&;amp;lt;0&;amp;lt;/sub&;amp;lt;到约2%精度,提供解决&;amp;lt;em&;amp;lt;H&;amp;lt;/em&;amp;lt;&;amp;lt;sub&;amp;lt;0&;amp;lt;/sub&;amp;lt;危机的独立而珍贵的数据。下一代的引力波实验,则将通过标准汽笛方法,精确测量宇宙膨胀速度和宇宙大尺度结构,限制暗能量状态方程,在宇宙学尺度上检验广义相对论。     

Thermodynamics of strange quark matter with the density-dependent bag constant

The thermodynamics of strange quark matter with density dependent bag constant are studied self-consistently in the framework of the general ensemble theory and the MIT bag model.In our treatment,an additional term is found in the expression of pressure.With the additional term,the zero pressure locates exactly at the lowest energy state,indicating that our treatment is a self-consistently thermodynamic treatment.The self-consistent equations of state of strange quark matter in both the normal and color-fla...     

路与星、扇、轮图的积图的邻点可区别I-全染色

图G的I-全染色是指若干种颜色对图G的顶点和边的一个分配,使得任意两个相邻顶点的颜色不同,任意两条相邻边的颜色不同.在图G的一个I-全染色下,G的任意一个点的色集合是指该点的颜色以及与该点相关联的全体边的颜色构成的集合.图G的一个I-全染色称为是邻点可区别的,如果任意两个相邻点的色集合不相等.对一个图G进行邻点可区别I-全染色所用的最少颜色的数目称为图G的邻点可区别I-全色数.应用构造具体染色的方法给出了路与星、扇、轮图的积图的邻点可区别I-全色数     

Dependence of the tidal deformability of neutron stars on the nuclear equation of state

Within the Bayesian framework, using an explicitly isospin-dependent parametric equation of state (EOS) for the core of neutron stars (NSs), we studied how the NS EOS behaves when we confront it with the tidal deformabilities \begin{document}$ \Lambda_{1.4} $\end{document} of canonical NSs with different error and different lower boundaries, and with the tidal deformabilities of massive NSs. We found that it does not significantly improve the constraints on the NS EOS but has a weak effect on narrowing down the slope parameter of the symmetry energy by decreasing the measurement errors of \begin{document}$ \Lambda_{1.4} $\end{document}. Both the isospin-dependent and isospin-independent parts of the NS EOS were significantly constrained and raised as the tidal deformabilities of massive NSs were adopted in the calculations, especially in high-density regions. We also found that \begin{document}$ \Lambda_{1.4} $\end{document} is more competent to limit the curvature parameter than the slope parameter of the symmetry energy, whereas the opposite occurs for the radius of canonical NSs \begin{document}$ R_{1.4} $\end{document}. The tidal deformability of an NS with two times the solar mass \begin{document}$ \Lambda_{2.0} $\end{document} is more sensitive to skewness than the curvature parameter of the symmetry energy, and \begin{document}$ \Lambda_{1.4} $\end{document} and \begin{document}$ R_{1.4} $\end{document} have no correlation with the former.     

Charged quark stars in f(R,T) gravity

Recent advances in nuclear theory and new astrophysical observations have led to the need for specific theoretical models applicable to dense-matter physics phenomena. Quantum chromodynamics (QCD) predicts the existence of non-nucleonic degrees of freedom at high densities in neutron-star matter, such as quark matter. Within a confining quark matter model, which consists of homogeneous, neutral 3-flavor interacting quark matter with \begin{document}$ \mathcal{O}(m_s^4) $\end{document} corrections, we examine the structure of compact stars composed of a charged perfect fluid in the context of \begin{document}$ f(R,T) $\end{document} gravity. The system of differential equations describing the structure of charged compact stars has been derived and numerically solved for a gravity model with \begin{document}$ f(R,T)= R+ 2\beta T $\end{document}. For simplicity, we assumed that the charge density is proportional to the energy density, namely, \begin{document}$ \rho_{\rm ch} = \alpha \rho $\end{document}. It is demonstrated that the matter-geometry coupling constant β and charge parameter α affect the total gravitational mass and the radius of the star.     

Equation of state in hybrid stars and the stability window of quark matter

Properties of hybrid stars with a mixed phase composed of asymmetric nuclear matter and strange quark matter are studied. The quark phase is investigated by the quark quasiparticle model with a self-consistent thermodynamic and statistical treatment. We present the stability windows of the strange quark matter with respect to the interaction coupling constant versus the bag constant. We find that the appearance of the quark–hadron mixed phases is associated with the meta-stable or unstable regions of the pure quark matter parameters. The mass–radius relation of the hybrid star is dominated by the equation of state of quark matter rather than nuclear matter. The contour plots of the maximum mass of the hybrid star are shown in the plane of the coupling constant and the bag constant.     

Towards an understanding of Type Ia supernovae from a synthesis of theory and observations

Motivated by the fact that calibrated light curves of Type Ia supernovae (SNe Ia) have become a major tool to determine the expansion history of the Universe, considerable attention has been given to, both, observations and models of these events over the past 15 years. Here, we summarize new observational constraints, address recent progress in modeling Type Ia supernovae by means of three-dimensional hydrodynamic simulations, and discuss several of the still open questions. It will be be shown that the new models have considerable predictive power which allows us to study observable properties such as light curves and spectra without adjustable non-physical parameters. This is a necessary requisite to improve our understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia as distance indicators for cosmology. We explore the capabilities of the models by comparing them with observations and we show how such models can be applied to study the origin of the diversity of SNe Ia.     

Knotted Solitons in an Interacting Mixture of a Charged and a Neutral Superfluid for Neutron Stars

By making use of the decomposition of U（1） gauge potential theory and the C-mapping method we discuss a mixture of interacting neutral and charged Bose condensates, which is supposed being realized in the interior of neutron stars in the form of a coexistent neutron superfluid and protonic superconductor. We propose that this system possesses vortex lines and two classes of knotted solitons. The topological charge of the vortex lines are characterized by the Hopf indices and the Brower degrees of φ-mapping, and the knotted solitons are described by nontrivial Hopf invariant and the BF action respectively.