Causality Bounds on Dissipative General-Relativistic Magnetohydrodynamics

We derive necessary and sufficient conditions under which a large class of relativistic generalizations of Braginskii’s magnetohydrodynamics with shear, bulk, and heat diffusion effects is causal and strongly hyperbolic in the fully nonlinear regime in curved spacetime. We find that causality severely constrains the size of nonideal effects and the onset of kinetic instabilities. Our results are crucial for assessing the regime of validity of fluid dynamical simulations of plasmas near supermassive black holes.