2018ApJ...868L..22L

Continued observation of PSR J0737-3039, the double pulsar, is expected to yield a precise determination of its primary component's moment of inertia in the next few years. Since the moment of inertia depends sensitively on the neutron star's internal structure, such a measurement will constrain the equation of state of ultra-dense matter, which is believed to be universal. Independent equation-of-state constraints have already been established by the gravitational-wave measurement of neutron star tidal deformability in GW170817. Here, using well-known universal relations among neutron star observables, we translate the reported 90% credible bounds on tidal deformability into a direct constraint, I_*=1.15_–0.24^+0.38×10⁴⁵gcm², on the moment of inertia of PSR J0737-3039A. Should a future astrophysical measurement of I_* disagree with this prediction, it could indicate a breakdown in the universality of the neutron star equation of state.