LIGO Seminar

Gravitational waves from neutron star mergers are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal called a kilonova. The gravitational wave source GW170817 rose from a binary neutron star merger in the nearby Universe with a relatively well confined sky position and distance estimate. In this talk, we use gravitational-wave observations to make predictions about the ejecta properties and lightcurves expected from dynamical ejecta, in addition to the contribution of kilonovae to r-process element production in the universe. In addition, using observations and physical modelling of the identified optical counterpart SSS17a, we show the transient has physical parameters broadly matching the theoretical predictions of blue kilonovae from neutron star mergers. The emitted electromagnetic radiation can be used to estimate the ejecta mass, velocity, and opacity. The power source is shown to have a power law slope consistent with radioactive powering from r-process nuclides.  We identify line features in the spectra that are consistent with light r-process elements. As it fades, the transient rapidly becomes red, and emission may have contribution by a higher opacity, lanthanide-rich ejecta component. This indicates that neutron star mergers produce gravitational waves, radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements. Finally, we compare the gravitational-wave predictions to observations, and conclude with future plans for further research.