  We study the deconfinement transition of hadronic matter into quark matter
under neutron star conditions assuming color and flavor conservation during the
transition. We use a two-phase description. For the hadronic phase we use
different parameterizations of a non-linear Walecka model which includes the
whole baryon octet. For the quark matter phase we use an SU(3)_f
Nambu-Jona-Lasinio effective model including color superconductivity.
Deconfinement is considered to be a first order phase transition that conserves
color and flavor. It gives a short-lived transitory colorless-quark-phase that
is not in beta-equilibrium, and decays to a stable configuration in tau ~
tau_{weak} ~ 10^{-8} s. However, in spite of being very short lived, the
transition to this intermediate phase determines the onset of the transition
inside neutron stars. We find the transition free-energy density for
temperatures typical of neutron star interiors. We also find the critical mass
above which compact stars should contain a quark core and below which they are
safe with respect to a sudden transition to quark matter. Rather independently
on the stiffness of the hadronic equation of state (EOS) we find that the
critical mass of hadronic stars (without trapped neutrinos) is in the range of
~ 1.5 - 1.8 solar masses. This is in coincidence with previous results obtained
within the MIT Bag model.
