Strange Quark stars: Observations & Speculations
  Two kinds of difficulties have challenged the physics community for many years: (1) knowing nature's building blocks (particle physics) and (2) understanding interacting many-body systems (many-body physics). Both of them exist in the research of quark matter and compact stars. This paper addresses the possibility that quark clustering, rather than a color super-conducting state, could occur in cold quark matter at realistic baryon densities of compact stars, since a weakly coupling treatment of the interaction between quarks might not be reliable. Cold quark matter is conjectured to be in a solid state if thermal kinematic energy is much lower than the interaction energy of quark clusters. Different manifestations of pulsar-like compact stars are discussed, as well as modeled in a regime of solid quark stars. 
Renxin Xu (PKU)