Binary neutron star formation and the origin of GW170817

Understand

The first neutron star-neutron star merger was detected in by LIGO/Virgo in a galaxy in which the majority of star formation was taking place a long time ago (11 Gyr).

• LIGO/Virgo estimated that local cosmic NS-NS merger rate is 110-3840 Gpc^-3 yr^-1.
• Only some extreme evolutionary models can generate NS-NS merger rates in old host galaxies consistent with the LIGO/Virgo estimate.
• However, we show that these models generate rates exceeding empirical Galactic NS-NS merger rates based on the large population of Milky Way NS-NS binaries.