Session G05: Dynamics of Relativistic Plasmas

Simulations of relativistic plasma processes in neutron star magnetospheres relevant for fast radio bursts

Fast radio bursts (FRBs) are mysterious, bright, millisecond duration radio bursts of cosmological origin. Although we have not yet figured out the progenitors of FRBs, recent detection of FRB-like bursts from a galactic magnetar coincident with its X-ray bursts lends support that magnetars may be responsible for producing at least some of the FRBs. The FRBs and X-ray bursts from the galactic magnetar may be triggered by a magnetar quake that launches Alfven waves into the magnetosphere, an extremely magnetized relativistic plasma environment surrounding the magnetar. We have carried out detailed, systematic numerical simulations of the Alfven wave dynamics that are relevant for FRB production, including Alfven waves becoming nonlinear and breaking out from the magnetosphere, as well as charge starvation of the Alfven waves. In this talk, I will present results from our first-principles simulations, and discuss the implications for FRB production.   

Computational Challenges for Multi-Messenger Heavy-ion Physics

High energy relativistic nuclear collisions create matter in an extremely hot and dense environment. Such matter exhibits near-perfect fluidity that emerges from many-body interactions among deconfined quarks and gluons, known as the Quark-Gluon Plasma (QGP). A wealth of high precision measurements at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC) have been driving our field to an era of multi-messenger characterization of the QGP properties. Like multi-messenger astronomy, different types of particles emitted from heavy-ion collisions carry unique dynamical information, complement each other. Hadrons with transverse momenta below 2 GeV interact collectively. Their momentum distributions and correlations encode QGP's thermal and transport properties. QCD jets and heavy quarks probe the color degrees of freedom of the QCD medium at different length scales. Electromagnetic (EM) radiation, such as photons and dileptons, is a unique soft penetrating probe for the entire medium evolution in heavy-ion collisions with a high sensitivity to the collisions' early-stage. This talk will lay out the computational challenges in theoretical aspects of multi-messenger heavy-ion physics. I will highlight recent theoretical and numerical advancements in 3+1D relativistic viscous hydrodynamics and the treatments of stochastic fluctuations. Such computational frameworks serve as a powerful tool to unravel QCD many-body physics from the complex dynamics of relativistic heavy-ion collisions.   

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.