  In this work, under the hypothesis that quark matter may not be strange
[Phys. Rev. Lett. 120, 222001 (2018)], we adopt a modification of the coupling
constant of the four-quark scalar interaction $G\rightarrow
G_1+G_2\langle\bar{\psi}\psi\rangle$ in the 2-flavor Nambu-Jona-Lasinio model
to study nonstrange hybrid stars. According to lattice QCD simulation results
of the critical temperature at zero chemical potential, $G_1$ and $G_2$ are
constrained as $G_1\in(1.935, 1.972)$ GeV$^{-2}$, and $G_2\in(-1.582, -0.743)$
GeV$^{-5}$, respectively. To obtain hybrid equation of states, the Maxwell
construction is used to describe the first-order confinement-deconfinement
phase transition in hybrid stars. With recent measurements on neutron star
mass, radius, and tidal deformability, the hybrid equation of states are
constrained. The result suggests that pure nonstrange quark matter cores can
exist in hybrid stars, possessing 0.014-0.026 solar mass with the bag constant
$B^{1/4}$ in a range of 148-161 MeV. It is argued that the binary neutron stars
in GW170817 should be hadron stars.
