Color Ferromagnetic Quark Matter in Neutron Stars

We show that color ferromagnetic phase of quark matter is energetically more favored than color superconducting phases in neutron stars. Namely, increasing baryon density in neutron stars transforms nuclear matter into the quark matter of the color ferromagnetic phase. Further increase of the density makes the quark matter take the color superconducting phases. We find that a critical mass of the neutron star with such an internal structure is about $1.6M_{\odot}$. We stress that analysis of gluon dynamics is crucial for exploring dense quark matter.