Neutron star mergers have recently become a tool to study extreme gravity,
nucleosynthesis, and the chemical composition of the Universe. To date, there
has been one joint gravitational and electromagnetic observation of a binary
neutron star merger, GW170817, as well as a solely gravitational observation,
GW190425. In order to accurately identify and interpret electromagnetic signals
of neutron star mergers, better models of the matter outflows generated by
these mergers are required. We compare a series of ejecta models to see where
they provide strong constraints on the amount of ejected mass expected from a
system, and where systematic uncertainties in current models prevent us from
reliably extracting information from observed events. We also examine 2396
neutron star equations of state compatible with GW170817 to see whether a given
ejecta mass could be reasonably produced with a neutron star of said equation
of state, and whether different ejecta models provide consistent predictions.
We find that the difference between models is often comparable to or larger
than the error generally assumed for these models, implying better constraints
on the models are needed. We also note that the extrapolation of outflow models
outside of their calibration window, while commonly needed to analyze
gravitational wave events, is extremely unreliable and occasionally leads to
completely unphysical results.
