  First-order phase transitions are a source of stochastic gravitational
radiation. Precision calculations of the gravitational waves emitted during
these processes, sourced by both the degrees of freedom undergoing the
transition and anisotropic stress of the coupled, ambient constituents, have
reached an age of maturity. Here we present high-resolution numerical
simulations of a scalar field coupled to a fluid and parameterize the final
gravitational wave spectrum as a function of the ratio of the energies of the
two sectors and the coupling between the two sectors for a set of models that
represent different types of first-order phase transitions. In most cases, the
field sector is the dominant source of gravitational radiation, but it is
possible in certain scenarios for the fluid to have the most important
contribution.
