Constraining Population Synthesis Models via the Binary Neutron Star Population

The observed sample of double neutron-star (NS-NS) binaries presents a challenge to population-synthesis models of compact object formation: the input model parameters must be carefully chosen so the results match (1) the observed star formation rate and (2) the formation rate of NS-NS binaries, which can be estimated from the observed sample and the selection effects related to the discoveries with radio pulsar surveys. In this paper, we select from an extremely broad family of possible population synthesis models those few (2%) that are consistent with the rate implications of the observed sample of NS-NS binaries. To further sharpen the constraints the observed NS-NS population places on our understanding of compact object formation processes, we separate the observed NS-NS population into two channels: (1) merging NS-NS binaries, which will inspiral and merge through the action of gravitational waves within 10 Gyr and (2) wide NS-NS binaries, consisting of all the rest. With the subset of astrophysically consistent models, we explore the implications for the rates at which double black hole (BH-BH), black hole-neutron star (BH-NS), and NS-NS binaries merge through the emission of gravitational waves.