With the dawn of the multi-messenger astronomy era marked by the detection of a binary neutron star merger, it became imperative to understand how extremely dense fluids behave under very strong gravitational fields. In this talk I will critically review the foundations of relativistic viscous fluid dynamics and its formulation in curved spacetime. I will present the first set of fluid dynamic equations that satisfies all of the following properties: (a) the system when coupled to Einstein’s equations is causal and strongly hyperbolic (the initial value problem is well-posed); (b) equilibrium states are stable; (c) all leading dissipative contributions are present, i.e., shear viscosity, bulk viscosity, and thermal conductivity; (d) effects from non-zero baryon number are included; (e) entropy production is non-negative in the regime of validity of the theory. The properties above hold in the nonlinear regime without any simplifying symmetry assumptions and are mathematically rigorously established. This is achieved using a new formulation of relativistic fluid dynamics containing only the hydrodynamic variables and their first-order derivatives. The framework presented here provides the starting point for systematic investigations of general-relativistic viscous phenomena in neutron star mergers.

Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.