Supercritical accretion in the evolution of neutron star binaries and its implications

Recently ∼ 2 M ⊙ neutron stars PSR J1614-2230 and PSR J0348+0432 have been observed in neutron star-white dwarf binaries. These observations ruled out many neutron star equations of states with which the maximum neutron star mass becomes less than 2 M ⊙ . On the other hand, all well-measured neutron star masses in double neutron star binaries are still less than 1.5 M ⊙ . In this article we suggest that 2 M ⊙ neutron stars in neutron star-white dwarf binaries are the result of the supercritical accretion onto the first-born neutron star during the evolution of the binary progenitors.