Strange quark stars - A review.pdf

a r X i v : a s t r o - p h / 0 2 1 1 3 4 8 v 1 1 5 N o v 2 0 0 2 High Energy Processes and Phenomena in Astrophysics ASP Conference Series, Vol. ?, 2003 Xiang-dong Li, Zhen-ru Wang, Virginia Trimble Strange quark stars — A review Renxin Xu School of Physics, Peking University, Beijing 100871, China Abstract. A pedagogical overview of strange quark matter and strange stars is presented. After a historical notation of the research and an introduction to quark matter, a major part is devoted to the physics and astrophysics of strange stars, with attention being paid to the possible ways by which neutron stars and strange stars can be distinguished in astrophysics. Re- cent possible evidence for bare strange stars is also discussed. 1. Historical notes Soon after the Fermi-Dirac form (in 1926) of statistical mechanics was proposed for particles which obey Pauli’s exclusion principle (in 1925), Fowler (1926) realized that the electron degeneracy pressure can balance for those stars, called as white dwarfs, discovered by astronomers in 1914. By a numerical calculation (1931) for a polytropic gas of extremely relativistic electrons, Chandrasekhar found a unique mass, which was interpreted as a mass limit of white dwarfs. Landau (1932) presented an elementary explanation of the Chandrasekhar limit by considering the lowest total energy of stars, and recognized that increasing density favors energetically the formation of neutrons, discovered only several months before by Chadwick, through the action p + e? ? n + νe. A very massive object with much high density may have almost neutrons in the chemical equilibrium, which was then called as neutron stars (NSs). Detailed calculations of NS structures showed (e.g., Oppenheimer Volkoff 1939) that an NS can have a mass of ～ 1M⊙, but is only ～ 10 km in radius, which makes it hard to be observed by astronomers. However, on one hand, a few authors do investigate possible astrophysical implications of NSs. For example, Baade Z