Physics Theory Seminar with François Foucart on Understanding Merging Neutron Stars

Mergers of compact objects such as black holes and neutron stars have recently risen as remarkable astrophysical laboratories to test the laws of physics in extreme environments. The strong spacetime curvature and rapid motion of these compact objects make them powerful emitters of gravitational waves, while the ejection of neutron rich matter from a disrupted neutron star provides a favorable environment for the production of many heavy nuclei (including gold, platinum, uranium,...). From the gravitational waves and electromagnetic signals produced by these events, we can learn about the unknown properties of dense neutron rich matter, study the laws of gravity and the expansion of the Universe, or attempt to constrain the origin of the heavy nuclei observed on Earth today. Neutron star mergers are however complex non-linear systems that can only be truly understood through costly numerical simulations modeling general relativity, relativistic magnetohydrodynamics, neutrino transport, and maybe even out-of-equilibrium nuclear reaction. In this talk, I will review the physics of neutron star mergers, and what we can learn from current and upcoming observations. I will then discuss recent progress in the numerical modeling of these systems, as well as important remaining limitations of our simulations.