Theories of strange stars
Abstract of thesis entitled
THEORIES OF STRANGE STARS
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 may provide a possible way to distinguish a compact object between a neutron star, MIT strange star and Cloudy Bag strange star by observations.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Date of Publication:01/01/2001