What would happen if you threw honey really hard at a black hole as opposed to water?
Mathematicians and physicists of the field studying Einstein’s Field Equations in hopes of explaining physical phenomena know so much about ideal fluids. However, the community requires research into viscous fluids of different types, i.e. admitting different types of viscosity.
We encounter those of bulk and shear viscosity in the hopes of either expanding the viscous terms of the stress-energy tensor and/or changing the physical background. Analysing the dynamical systems is a large focus point for the qualitative understanding of the fluids.