Evolutionary tracks of binary neutron star progenitors – EVOLVE

The evolution of massive stellar binaries and the subsequent formation of binary neutron stars is an active field of research, powered by observations of Galactic binary pulsars as well as merging binary neutron stars that emit gravitational waves. The goal of this project is to explore the evolutionary tracks of the progenitors of binary neutron stars, their dependence on metallicity and hence redshift. The project will focus on the effect of these evolutionary tracks on two observables. The first is the amount of heavy (r-process) elements synthesized in the ejecta of merging binary neutron stars (kilonovae). These elements are observed in the spectra of metal-poor stars in the Galaxy, which indicates very early enrichment of the interstellar medium. If binary neutron stars contributed to this enrichment, the delay between system formation and merger had to be very short, as is the case in some specific evolutionary paths. The second observable that will be studied is the distribution of periods and eccentricities of Galactic binary pulsars that have a neutron star as a companion. The question that will be studied is whether the progenitors of these systems followed the same evolutionary paths as those of the merging population. Indeed, merging systems and binary pulsars probe different stages in the evolution of the same underlying population of binary neutron stars. The combination of these two observables as well as a range of numerical methods, including semi-analytic and hydrodynamical codes, will provide a new perspective on the origins of binary neutron stars.