Astronomy departmental seminar - Mattia Bulla (University of Ferrara)

Let there be light: Illuminating neutron star mergers with radiative transfer simulations
On Aug 17, 2017, the detection of an electromagnetic counterpart to the gravitational-wave source GW 170817 marked year zero of the multi-messenger gravitational-wave era. The combination of gravity and light from the same event provided the smoking gun for historically debated conjectures on e.g. the nature of “short Gamma-Ray Bursts” and the origin of heavy elements we see on Earth (including gold and platinum). This event was generated by the coalescence of two neutron stars and gave rise to an electromagnetic transient, dubbed a “kilonova”, powered by the radioactive decay of heavy (r-process) nuclei synthesised during the merger. In this talk, I will show how radiative transfer simulations can illuminate neutron star mergers and provide a connection between numerical models of the mergers and observational data. I will present POSSIS, a 3D Monte Carlo radiative transfer code to model kilonovae, and show how viewing-angle dependent predictions – such as spectra, light curves and polarization – can be used to interpret data, place constraints on models and guide future follow-up campaigns of gravitational-wave events.