Low-Mass Quark Stars or Quark White Dwarfs

An equation of state is considered that, in superdense nuclear matter, results in a phase transition of the first kind from the nucleon state to the quark state with a transition parameter > 3/2 ( = _Q /( _N + P ₀/c ²)). A calculation of the integrated parameters of superdense stars on the basis of this equation of state shows that on the stable branch of the dependence of stellar mass on central pressure (dM/dP _c > 0), in the low-mass range, following the formation of a tooth-shaped break (M = 0.08 M , R = 200 km) due to quark formation, a new local maximum with M _max = 0.082 M and R = 1251 km is also formed. The mass and radius of the quark core of such a star turn out to be M _core = 0.005 M and R _core = 1.7 km, respectively. Mass accretion in this model can result in two successive transitions to a neutron star with a quark core, with energy release like supernova outbursts.     

Space-Time Geometry of Quark and Strange Quark Matter

We study quarkand strangequarkmatter in the contextof generalrelativity.For this purpose,we solve Einstein's field equations for quark and strange quark matter in spherical symmetric space-times. We analyze strange quark matter for the different equations of state (EOS) in the spherical symmetric space-times,thus we are able to obtain the space-time geometries of quark and strange quark matter. Also,we discuss the features of the obtained solutions. The obtained solutions are consistent with the results of Brookhaven Laboratory,i.e. the quark-gluon plasma has a vanishing shear (i.e. quark-gluon plasma is perfect).     

Low-Mass Quark Stars

More and more observational hints of quark stars are proposed these years though pulsars are considered conventionally to be normal neutron stars. The existence of low-mass quark stars is a direct consequence of the possibility that pulsar-like stars are actually quark stars, because of the ability that quark matter can confine itself by color interaction. After a brief introduction to the study of quark stars, the various astrophysical implications of low-mass quark stars are investigated. It is addressed that some of the transient unidentified γ -ray sources are probably merging quark stars. The observability of low-mass quark stars is discussed.     

早期中子星和夸克物质

夸克禁闭的解除与夸克物质的存在一直是物理学家极感兴趣的问题。尽管理论上已指出在超高温或超高密的条件下可以有夸克物质存在,但是由于地面实验室的条件所限,目前还不能通过实验证实这一点.宇宙中被观测到的中子星(例如crab和Vela脉冲星)的中心密度大于4倍的核物质密度,其中心温度也可以达到10~8—10~9K,于是人们希     

An Exact Anisotropic Quark Star Model

We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a linear equation of state, while the tangential pressure is a complicated function of the radial coordinate. In order to obtain the general solution of the field equations a particular density profile inside the star is also assumed. The anisotropic pressure distribution leads to an increase in the maximum radius and mass of the quark star, which in the present model is around three solar masses.     

Neutron Stars With a Quark Core

Models of neutron stars with a quark core are calculated on the basis of an extensive set of equations of state for superdense matter. The possible existence of a new branch of stable layered neutron stars is revealed for some realistic equations of state of neutron matter.     

夸克物质与夸克星

二十世纪六七十年代强子结构研究的进展使人们认识到了亚核子--夸克--的存在,随后,实验和理论上关于夸克之间作用渐近自由性质的发现使学者们明确地提出了"夸克物质"的概念.理论上预言的这种物质是否真的存在将在很大程度上检验目前基本强作用的理论.夸克星就是夸克物质的可能存在形式之一,相关研究也是人们探索超核密度物质状态的重要途径,该文简述脉冲星、中子星及夸克星的研究历史,总结了近年来夸克物质与夸克星研究的重要成果,指出了夸克星与一般中子星的异同以及若干夸克星候选体.     

Quark nova model for fast radio bursts

Fast radio bursts(FRBs) are puzzling, millisecond, energetic radio transients with no discernible source; observations show no counterparts in other frequency bands. The birth of a quark star from a parent neutron star experiencing a quark nova- previously thought undetectable when born in isolation- provides a natural explanation for the emission characteristics of FRBs. The generation of unstable r-process elements in the quark nova ejecta provides millisecond exponential injection of electrons into the surrounding strong magnetic field at the parent neutron star's light cylinder via β-decay. This radio synchrotron emission has a total duration of hundreds of milliseconds and matches the observed spectrum while reducing the inferred dispersion measure by approximately 200 cm~(-3)pc. The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of β-decay chains of unstable neutron rich nuclei. Using this model, we can calculate expected FRB average energies(~10~(41)erg) and spectral shapes, and provide a theoretical framework for determining distances.     

轻夸克物质团、奇异子和致密矮星

相对于核物质和奇异夸克物质, 仅由两味夸克构成的轻夸克物质(即ud夸克物质)有可能更稳定. 而对于由这三类物质构成的典型物质集团, 研究发现如果ud夸克物质具有较大的对称能, 那么其物质团会在特定大小(重子数$A\approx1000$)时最稳定. 在这种情况下, 就可能存在由ud夸克物质团和电子构成的致密矮星, 即ud夸克矮星. 通过进一步研究这类ud夸克矮星的结构可知: 相较于传统的由原子核和电子构成的白矮星, ud夸克矮星通常具有较小的半径, 而被正常物质覆盖的ud夸克矮星的半径则在它们之间, 这与最近观测到的质量和半径都异常小的白矮星相符.     

Meissner Effect for “Color” Superconducting Quark Matter

The behavior of the magnetic field inside the superconducting quark matter core of a neutron star is investigated in the framework of the Ginzburg-Landau theory. We take into account the simultaneous coupling of the diquark condensate field to the usual magnetic and to the gluomagnetic gauge fields. We solve the problem for three different physical situations: a semi-infinite region with a planar boundary, a spherical region, and a cylindrical region. We show that Meissner currents near the quark core boundary effectively screen the external static magnetic field.     

On Low-Mass, Strange Quark Stars with a Crust

Low-mass strange stars with a crust are investigated within the framework of the bag model. The crust, which consists of degenerate electrons and atomic nuclei, has a limiting boundary density _cr , which is determined by the mass of the crust, and it cannot exceed the value _drip = 4.3·10¹¹ g/cm³, corresponding to the density at which neutrons drip from nuclei. For different values of _cr in the low-mass range (M 0.1 M) we calculate several series of configurations: we find the dependence of the stellar mass M on the central density _c for _cr = const, with 10⁹ g/cm³ _{cr drip} , and for each series we determine the parameters of the configuration for which the condition dM/d _c > 0 is violated. When the boundary density of the crust decreases to 10⁹ g/cm³, the minimum mass of a strange star decreases to M _min 10^-3 M, while the radius reaches 600 km.     

Strange Quark Matter in Cosmic Ray Flux and Exotic Events

There have been several reports of exotic nuclear fragments, with highly unusual charge to mass ratio, in cosmic ray experiments. Although there exist experimental uncertainties which make them, at best, only candidate `exotic' events, it is important to understand what they could be, if they are eventually confirmed. Among other possible explanations, some authors have interpreted them to be lumps of strange quark matter (strangelets).A major problem with such an interpretation is that to reach the earth's surface, they must possess an unusually high penetrability through the terrestrial atmosphere. We show that a recently proposed mechanism for the propagation of strangelets through the earth's atmosphere, together with a proper account of charge capture and ionisation loss, would solve this problem. We also argue that this could lead to viable strategies for definitive detection of strange quark matter in cosmic ray flux using aground based large area array of passive detectors. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Structure of the Free Surface of Self-Binding Quark Matter

The distributions of electrons and of electrical potential at the free surface of strange quark matter are determined within the framework of the MIT bag model. It is shown that, with allowance for the decay of quarks near the surface due to the outward escape of electrons, the electric charge density of quarks at the surface increases by a factor of 17-25, the thickness of the transitional layer decreases from 230 Fm to 15 Fm, and the field strength increases by a factor of 1.7. The difference between the chemical potentials of electrons at the surface and in deep layers decreases from 7 MeV to 0.8 MeV, which increases the limiting possible density of ordinary matter above a strange quark star.     

Properties of Hot Quark Matter with Neutrino Confinement in the NJL Model

Astrophysics - The thermodynamic characteristics of hot β-equilibrium three-flavor quark matter with neutrino confinement are studied in terms of the local SU(3) Nambu-Jona-Lasinio (NJL)...     

Magnetic Field of a Neutron Star With Color Superconducting Quark Matter Core

The behaviour of the magnetic field of a neutron star with a superconducting quark matter core is investigated in the framework of the Ginzburg-Landau theory. We take into account the simultaneous coupling of the diquark condensate field to the usual magnetic and to the gluomagnetic gauge fields. We solve the Ginzburg-Landau equations by properly taking into account the boundary conditions, in particular, the gluon confinement condition. We found the distribution of the magnetic field in both the quark and hadronic phases of the neutron star and show that the magnetic field penetrates into the quark core in the form of quark vortices due to the presence of Meissner currents.