Conversion of a neutron star to a strange star: A two-step process

The conversion of a neutron star to a strange star is studied. Such a transition may be viewed as a two-step process in which the hadronic matter first gets converted to two-flavor quark matter, which, in turn, converts to strange quark matter in the second step of the process. Relativistic hydrodynamical equations are employed to obtain the velocity of propagation of the first conversion front. The second transition front, arising from the conversion of two-flavor to three-flavor quark matter, is studied by using an appropriate weak interaction rate. The propagation velocity of the first conversion front initially shoots up near the core of the star to eventually saturate to some ultrarelativistic value. The first conversion takes about a millisecond, during which the second conversion front is likely to be generated. The second process takes about a hundred seconds to convert the whole quark star into a strange star.