2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/190000It is explicitly shown that if phase transition occurs at the core of a newborn neutron star with moderately strong magnetic field strength, which populates only the electron's Landau levels, then in the $β$-equilibrium condition, the quark core is energetically much more unstable than the neutron matter of identical physical condition.Six pages REVTEX file, one .eps file (included)Astrophysicstext