Simulating extreme plasmas in neutron star mergers and beyond

Ranging from dense plasmas above nuclear saturation in their interiors to strongly magnetized pair-plasmas in their magnetospheres, neutron stars feature some of the most extreme plasmas in the universe. The delicate interplay between strong gravity, nuclear and plasma physics makes the collision of two neutron stars an ideal playground to study matter in its most extreme form. 

In this talk, I will present recent advances in the state-of-the-art modeling of relativistic plasmas applicable to neutron star mergers and beyond.

Starting from hot and dense plasmas formed during the collision of two neutron stars, I will present novel insights into how these plasmas might be obtainable in ground-based experiments. I will then discuss why dissipative effects (e.g., weak-interaction driven bulk viscosity) might be crucial for understanding the post-merger evolution of a binary neutron star coalescence. Going to plasmas at densities below saturation, I will comment on the importance of magnetic fields and relativistic turbulence during the collision. Furthermore, I will present a systematic study of the emission of electromagnetic (EM) flares from the inspiral that can drive powerful EM precursors to gravitational wave events.

The next-generation modeling of relativistic plasmas in these extreme regimes requires the consistent inclusion of dissipative effects into numerical magnetohydrodynamics (MHD) simulations. To this end, I will introduce a novel 14-moment based numerical approach to dissipative relativistic MHD. This 14-moment closure can seamlessly interpolate between the highly collisional limit found in neutron star mergers and heavy-ion collisions, and the weakly coupled Braginskii-like limit of extended MHD appropriate for the study of accretion disks around supermassive black holes. Going beyond these collisional limits, I will also provide an outlook on how to describe the collisionless dynamics of electron-ion/positron plasmas using dissipative two-fluid MHD.