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This paper deals with an investigation of the properties of hypothetical strange-matter stars, which are composed of u, d, s quark matter whose energy per baryon number lies below the one of 56Fe (Witten's strange matter hypothesis). Observable quantities which allow to distinguish such objects from their ''conventional'' counterparts, neutron stars and white dwarfs, are pointed out.
(Uncorrected OCR) Abstract of thesis entitled THEORIES OF STRANGE STARS submitted by NG Chi Yung for the degree of Master of Philosophy at The University of Hong Kong in September 2001 Properties of strange stars were investigated using the Cloudy Bag Model, in which a pion cloud coupled to the quark-confining bag is introduced such that chiral symmetry is conserved. As chiral symmetry is widely recognized as an important driver of the strong interaction dynamics, it is expected to obtain more realistic results using this model. Emphasis is given on the observation properties of strange stars so that they can be distinguished from neutron stars. The parameters in the model, namely the bag constant and strange quark mass are determined self-consistently by fitting the mass spectrum of baryons. Then the equation of state is obtained by evaluating the energy-momentum tensor of the system. According to this model, the strange star is surrounded by a pion cloud. However, the result indicated that the pion cloud is not significant in global stellar properties. The stellar mass and radius of the Cloudy Bag strange stars are similar to that of MIT ones. It was found that the maximum static mass of a Cloudy Bag strange star is about 1.9 M0. The rotation properties of the strange stars were also investigated. By the approximate mass and radius formulae, the Kepler limit of Cloudy Bag strange stars was found to be ~ 6500 s"1, which is lower than the MIT one. The maximum mass of a stable rotating Cloudy Bag strange star is about 2.3 M0. The pion cloud surrounding a Cloudy Bag strange star provides a new cooling mechanism. The decay of pions is a very efficient cooling method. The decay product in the form of a fireball may be a possible energy source of?-ray bursts. Numerical results indicate that the temperature of a Cloudy Bag strange star is much lower than a MIT one. Also, the surface luminosity of a strange star is lower than that of a neutron star. This cooling behaviour.
This paper gives an overview of the properties of all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from strange stars to strange dwarfs. In contrast to their non-strange counterparts--neutron stars and white dwarfs--their properties are determined by two (rather than one) parameters, the central star density and the density at the base of the nuclear crust. This leads to stellar strange-matter configurations whose properties are much more complex than those of the conventional sequence. As an example, two generically different categories of stable strange dwarfs are found, which could be the observed white dwarfs. Furthermore the authors find very-low-mass strange stellar objects, with masses as small as those of Jupiter or even lighter planets. Such objects, if abundant enough, should be seen by the presently performed gravitational microlensing searches.
In this paper the following items will be treated: The present status of dense nuclear matter calculations and constraints on the behavior of the associated equation of state at high densities from data on rapidly rotating pulsars. Recent finding of the likely existence of a mixed phase of baryons and quarks forming a coulomb lattice in the dense cores of neutron stars. Review of important findings of recently performed calculations of rapidly rotating compact stars. These are constructed in the framework of general relativity theory for a representative collection of realistic nuclear equations of state. Establish the minimum-possible rotational periods of gravitationally bound neutron stars and self-bound strange stars. Its knowledge is of fundamental importance for the decision between pulsars that can be understood as rotating neutron stars and those that cannot (signature of hypothetical self-bound matter of which strange stars are the likely stellar candidates. Investigate the properties of sequences of strange stars. Specifically, we answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.
This paper gives an overview of the properties of all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from strange stars to strange dwarfs. In contrast to their non-strange counterparts--neutron stars and white dwarfs--their properties are determined by two (rather than one) parameters, the central star density and the density at the base of the nuclear crust. This leads to stellar strange-matter configurations whose properties are much more complex than those of the conventional sequence. As an example, two generically different categories of stable strange dwarfs are found, which could be the observed white dwarfs. Furthermore the authors find very-low-mass strange stellar objects, with masses as small as those of Jupiter or even lighter planets. Such objects, if abundant enough, should be seen by the presently performed gravitational microlensing searches.
The book gives an extended review of theoretical and observational aspects of neutron star physics. With masses comparable to that of the Sun and radii of about ten kilometres, neutron stars are the densest stars in the Universe. This book describes all layers of neutron stars, from the surface to the core, with the emphasis on their structure and equation of state. Theories of dense matter are reviewed, and used to construct neutron star models. Hypothetical strange quark stars and possible exotic phases in neutron star cores are also discussed. Also covered are the effects of strong magnetic fields in neutron star envelopes.