The Fault Is Not in Our Stars, It Is in Our Priors

Gravitational waves from mergers involving neutron stars enable inference of neutron star masses and tidal deformabilities. As tidal deformability depends on mass, using uninformative priors in both quantities introduces inconsistency and can shift posteriors significantly, leading to biased recovery of source properties and the inferred dense matter equation of state. These biases are already critical for ongoing and future gravitational wave analyses of neutron star mergers and can also affect the interpretation of several archival events involving neutron stars. We address this by constructing physics-informed priors that incorporate realistic mass–tidal deformability relationships and scale with detector sensitivity. In this work, we use systematic injection studies to explore how this framework yields unbiased parameter estimates, tighter credible regions, and efficient coverage of the tidal deformability space, making it a timely tool for current and future analyses. The approach is readily adaptable to upgrades such as the A# sensitivity and to next-generation observatories, including Cosmic Explorer and the Einstein Telescope.