Self-Consistency of Relativistic Observables with General Relativity in the White Dwarf-Neutron Star Binary PSR J1141-6545

Here we report timing measurements of the relativistic binary PSR J1141-6545 that constrain the component masses and demonstrate that the orbital period derivative P_b=(-4+/-1)×10^-13 is consistent with gravitational wave emission as described by the general theory of relativity. The mass of the neutron star and its companion are 1.30+/-0.02 and 0.986+/-0.02 M_solar, respectively, suggesting a white dwarf companion and extending the range of systems for which general relativity provides a correct description. On evolutionary grounds, the progenitor mass of PSR J1141-6545 should be near the minimum for neutron star production. Its mass is 2 standard deviations below the mean of the other neutron stars, suggesting a relationship between progenitor and remnant masses.