Modeling neutron stars using first-order viscous relativistic hydrodynamics

Recent evidence suggests that weak interactions may noticeably impact the dynamics of binary neutron star mergers, potentially acting as an effective bulk viscosity in the process. Motivated by these results, we present progress toward the incorporation of dissipative fluid effects into neutron star models. To do so we make use of the so-called BDNK formalism, the only relativistic dissipative fluid theory to date rigorously proven to be causal, hyperbolic, and stable about thermodynamic equilibrium. In this talk, we briefly overview the construction of BDNK theory and contrast it with ideal (perfect fluid) hydrodynamics, summarize recent progress regarding numerical methods and the choice of model coefficients, and then discuss applications to neutron stars in spherical symmetry.