We suggest a scenario where the three light quark flavors are sequentially deconfined under increasing pressure in cold asymmetric nuclear matter as , e.g . , in neutron stars .
The basis for our analysis is a chiral quark matter model of Nambu–Jona-Lasinio ( NJL ) type with diquark pairing in the spin-1 single flavor ( CSL ) , spin-0 two flavor ( 2SC ) and three flavor ( CFL ) channels .
We find that nucleon dissociation sets in at about the saturation density , n _ { 0 } , when the down-quark Fermi sea is populated ( d-quark dripline ) due to the flavor asymmetry induced by \beta -equilibrium and charge neutrality .
At about 3 n _ { 0 } u-quarks appear and a two-flavor color superconducting ( 2SC ) phase is formed .
The s-quark Fermi sea is populated only at still higher baryon density , when the quark chemical potential is of the order of the dynamically generated strange quark mass .
We construct two different hybrid equations of state ( EoS ) using the Dirac-Brueckner Hartree-Fock ( DBHF ) approach and the EoS by Shen et al . in the nuclear matter sector .
The corresponding hybrid star sequences have maximum masses of , respectively , 2.1 and 2.0 M _ { \odot } .
Two- and three-flavor quark-matter phases exist only in gravitationally unstable hybrid star solutions in the DBHF case , while the Shen-based EoS produce stable configurations with a 2SC phase component in the core of massive stars .
Nucleon dissociation due to d-quark drip at the crust-core boundary fulfills basic criteria for a deep crustal heating process which is required to explain superbusts as well as cooling of X-ray transients .