Thermal evolution and light curves of young bare strange stars

We study numerically the cooling of a young bare strange star and show that its thermal luminosity, mostly due to e(+)e(-) pair production from the quark surface, may be much higher than the Eddington limit. The mean energy of photons far from the strange star is approximately 10(2) keV or even more. This differs both qualitatively and quantitatively from the thermal emission from neutron stars and provides a definite observational signature for bare strange stars. It is shown that the energy gap of superconducting quark matter may be estimated from the light curves if it is in the range from approximately 0.5 MeV to a few MeV.     

Quark core stars,quark stars and strange stars

A recent one flavor (zero temperature) quark matter equation of state is generalized to several flavors. It is shown that quarks undergo a first order phase transition. In addition, this equation of state depends on few parameters, one in the two flavor case, two in the three flavor case, and these parameters can be constrained by phenomenology. This equation of state is then applied to 1) the hadronquark transition in neutron stars and the determination of quark star stability, 2) the investigation of strange matter stability and possible strange star existence.     

On relativistic models of strange stars

The superdense stars with mass-to-size ratio exceeding 0.3 are expected to be made of strange matter. Assuming that the 3-space of the interior space-time of a strange star is that of a three-paraboloid immersed in a four-dimensional Euclidean space, we obtain a two-parameter family of their physically viable relativistic models. This ansatz determines density distribution of the interior self-gravitating matter up to one unknown parameter. The Einstein’s field equations determine the fluid pressure and the remaining geometrical variables. The information about mass-to-size ratio together with the conventional boundary conditions lead to the determination of total mass, radius and other parameters of the stellar configuration.      

Dark matter heating in strange stars

We study the effect of dark matter heating on the temperature of typical strange star(SS hereafter)(M=1.4 M⊙,R=10 km)in normal phase(NSS hereafter)and in a possible existing colour-flavour locked(CFL)phase(CSS hereafter).For NSS,the influence of dark matter heating is ignored until roughly 107yr.After 107yr,the dark matter heating is dominant that significantly delays the star cooling,which maintains a temperature much higher than that predicted by standard cooling model for old stars.Especially for CSS,the emissivity of dark matter will play a leading role after roughly 104yr,which causes the temperature to rise.This leads to the plateau of surface temperature appearing in～106.5yr which is earlier than that of NSS(～107yr).     

A new model for strange stars

In the present work, we attempt to find a new class of solutions for the spherically symmetric perfect fluid sphere by employing the homotopy perturbation method (HPM), a new tool via which the mass polynomial function facilitates to tackle the Einstein field equations. A set of interior solutions found on the basis of the simplest MIT bag model equation of state in the form \(p=\frac{1}{3}(\rho -4B)\) where B is the bag constant. The proposed interior metric for the stellar system is consistent with the exterior Schwarzschild spacetime on the boundary. In addition, we also conduct a detailed study on different tests, viz. the energy conditions, TOV equation, adiabatic index, Buchdahl limit, etc., to verify the physical validity of the proposed model. The numerical value of the used parameters are predicted for different strange star candidates, for different chosen values of the bag constant. In a nutshell, by exploiting HPM technique first time ever in the field of relativistic astrophysics, we have predicted in the present literature a singularity-free and stable stellar model which is suitable to describe ultra-dense objects, like strange (quark) stars.     

A new deterministic model of strange stars

Experiments using polarized \(^{3}\) He atom beams to search for short range spin dependent forces are proposed. High intensity, high polarization, small beam size \(^{3}\) He atom beams have been successfully produced and used in surface science researches. By incorporating background reduction designs as combination shielding by \(\upmu \) -metal and superconductor and double beam paths, the precision of spin rotation angle per unit length could be improved by a factor of \(\sim \!10^{4}\) . By this precision, in combination with a high density and low magnetic susceptibility sample source mass, and reversing one beam path if necessary, sensitivities on three different types of spin dependent interactions could be improved by as much as \(\sim \!\!10^{2}\) to \(\sim \!\!10^{8}\) over the current experiments at the millimeter range.     

Distinguishing newly born strange stars from neutron stars with g-mode oscillations

The gravity-mode (g-mode) eigenfrequencies of newly born strange quark stars (SQSs) and neutron stars (NSs) are studied. It is found that the eigenfrequencies in SQSs are much lower than those in NSs by almost 1 order of magnitude, since the components of a SQS are all extremely relativistic particles while nucleons in a NS are nonrelativistic. We therefore propose that newly born SQSs can be distinguished from the NSs by detecting the eigenfrequencies of the g-mode pulsations of supernovae cores through gravitational radiation by LIGO-class detectors.     

Edmund Stoner and white dwarf stars

The discovery of a limiting mass for white dwarf stars is today usually attributed to Subramanian Chandrasekhar. However, it would seem that an article by Edmund Stoner, which appeared in the Philosophical Magazine in 1930, was the first publication to give a convincing demonstration of the existence of a limiting mass for white dwarfs. We examine here why it is that the contributions of Stoner and others towards this discovery have been largely forgotten.     

模型参数对奇异星性质的影响

用有效质量口袋模型描述奇异夸克物质,研究了耦合常数和口袋常数的选取对奇异夸克物质的状态方程及奇异星性质的影响.结果表明,随着耦合常数和口袋常数的增大,奇异夸克物质的状态方程变软,相应的奇异星的引力质量和对应的半径均变小.当耦合常数从0.5增大到2.0时,奇异星的质量从1.43M_⊙(M_⊙=1.99×10³⁰ kg)减小到1.25M_⊙,相应的半径由8.3 km减小到7.7 km;当口袋常数B^1/4由160 MeV增大到175 MeV时,奇异星的质量和半径分别由1.47M_⊙和8.6 km减小到1.22M_⊙和7.4 km.这说明奇异夸克物质及奇异星的性质明显依赖于模型参数的取值. 关键词： 模型参数 奇异星 状态方程 质量-半径关系     

A realistic model for charged strange quark stars

We report a general approach to solve an Einstein-Maxwell system to describe a static spherically symmetric anisotropic strange matter distribution with linear equation of state in terms of two generating functions.It is examined by choosing Tolmann IV type potential for one of the gravitational potentials and a physically reasonable choice for the electric field. Hence, the generated model satisfies all the required major physical properties of a realistic star. The effect of electric charge on physical properties is highlighted.     

Bulk viscosity for interacting strange quark matter and r-mode instability windows for strange stars

We investigate the bulk viscosity of strange quark matter in the framework of the equivparticle model,where analytical formulae are obtained for certain temperature ranges,which can be readily applied to those with various quark mass scalings.In the case of adopting a quark mass scaling with both linear confinement and perturbative interactions,the obtained bulk viscosity increases by 1-2 orders of magnitude compared with those in bag model scenarios.Such an enhancement is mainly due to the large quark equivalent masses adopted in the equivparticle model,which are essentially attributed to the strong interquark interactions and are related to the dynamical chiral symmetry breaki ng.Due to the high bulk viscosity,the predicted damping time of oscillatio ns for a can on ical 1.4 M⊙ strange star is less than one millisecond,which is shorter than previous findings.Consequently,the obtained r-mode instability window for the canonical strange stars well accommodates the observational frequencies and temperatures for pulsars in low-mass X-ray binaries(LMXBs).     

Properties of color-flavor locked strange quark matter and strange stars in a new quark mass scaling

Considering the effect of one-gluon-exchange interaction between quarks,the color-flavor locked strange quark matter and strange stars are investigated in a new quark mass density-dependent model.It is found that the color-flavor locked strange quark matter can be more stable if the one-gluon-exchange effect is included.The lower density behavior of the sound velocity in this model is different from the previous results.Moreover,the new equation of state leads to a heavier acceptable maximum mass,supporting the recent observation of a compact star mass as large as about 2 times the solar mass.     

Dark matter, neutron stars, and strange quark matter

We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.     

One-gluon-exchange effect on the properties of quark matter and strange stars

We present a modified version of quark mass scaling via considering the important one-gluon-exchange interaction between quarks in the quark mass density-dependent model. The properties of strange quark matter and the structure of strange stars are then studied with the new scaling and a self-consistent thermodynamic treatment. It is found that the one-gluon-exchange effect lowers the system energy considerably, makes the equation of state stiffer, and the sound velocity tends to the ultra-relativistic value faster, which make the biggest value of the maximum mass of strange stars become as big as approximately 2 times the solar mass, in accordance with the latest astronomical observations.     

Phase structures of neutral dense quark matter and applicationto strange stars

In the contact interaction model,the quark propagator has only one solution,namely,the chiral symmetry breaking solution,at vanishing temperature and density in the case of physical quark mass.We generalize the condensate feedback onto the coupling strength from the 2 flavor case to the 2+1 flavor case,and find the Wigner solution appears in some regions,which enables us to tackle chiral phase transition as two-phase coexistences.At finite chemical potential,we analyze the chiral phase transition in the conditions of electric charge neutrality andβequilibrium.The four chemical potentials,μ_u,μ_d,μ_s and He,are constrained by three conditions,so that one inde-pendent variable remains:we choose the average quark chemical potential as the free variable.All quark masses and number densities suffer discontinuities at the phase transition point.The strange quarks appear after the phase trans-ition since the system needg more energy to produce a d.-quark than an s-quark.Taking the EOS as an input,the TOV equations are solved numerically,and we show that the mass--radius relation is sensitive to the EOS.The max-imum mass of strange quark stars is not susceptible to the parameter Aq we introduced.     

Single star evolution I. Massive stars and early evolution of low and intermediate mass stars

We survey the results of those model calculations of the early evolution of single stars that have been obtained over approximately the last decade, and compare some of these results with the observations, concentrating particularly on the comparison between theoretical predictions regarding surface abundances of red giants and Cepheids and abundance estimates obtained by an analysis of spectral data.For massive stars, we discuss the ramifications of the fact that the time scale for mass loss (via stellar winds) during main sequence and red supergiant evolution can be comparable to the nuclear burning timescale, noting in particular the unusual distribution of stars in the Hertzsprung-Russell diagram, and the probability that significant mass loss is responsible for the chemically highly evolved spectra of Wolf-Rayet stars. finally, we sketch (1) recent progresses in following the evolution of massive stars to the presupernova stage, which is described by a configuration consisting of a core of near-Chandrasekhar mass made up of iron peak elements and a series of “onion”-skin layers of less highly thermonuclearly processed matter and (2) recent progress in understanding the nature of the type II supernova phenomenon.For low and intermediate mass stars, we discuss postulated “extramixing” (beyond convective) processes, which may occur on the main sequence and on the first red giant branch, and continue on to a discussion of asymptotic giant branch evolution, placing considerable emphasis on the character of the thermal pulses that occur in such stars and, in particular, on the nucleosynthesis that occurs in the helium burning convective shells during these pulses and on the dredge-up phenomenon that brings fresh carbon and neutron-rich isotopes to the surface following pulse peak.