Possible Formation Scenario of the Quark Star of Maximum Mass around 0.7   solar mass
  If there exists the quark star of maximum mass $\sim 0.7\sol$ as suggested by recent Chandra observations, we show that the general relativistic collapse of a neutron star of mass greater than the maximum mass of the neutron star with angular momentum parameter $q\equiv cJ/GM^2 > 1$ may lead to such a strange star. Here $J$ and $M$ are the angular momentum and the gravitational mass of the neutron star, respectively. Under the cosmic censorship hypothesis, such a star can not be a black hole directly. The jet formed in the soft core might explode the outer envelope and leave the quark star of mass $\sim 0.7\sol$. The remnant quark star has $\lesssim 10^{53}$ erg rotational energy so that the formation of the quark star may be related to the central engine of GRBs. The detailed numerical simulations are urgent to confirm or refute this scenario. 
Takashi Nakamura (Dept. Phys. Kyoto Univ.)