The Tale of a Hungry Subgiant and Its Brown Dwarf: Interior Radiative Damping Dominates the Tidal Evolution of TOI-5882

Abstract We present a self-consistent tidal-evolution framework that couples binary evolution from MESA to the full linear tidal response from GYRE-tides . Applying this framework to TOI-5882, a subgiant hosting a short-period brown dwarf, we show that interior radiative damping dominates the system’s tidal evolution, with the classical equilibrium tidal model significantly underestimating the star’s angular-momentum evolution by several orders of magnitude. Consequently, our combined framework predicts a 2–6 fold reduction in the engulfment timescale, accelerating the companion’s inspiral by roughly 25–110 Myr. By modeling angular-momentum transport through the star as it evolves, we demonstrate that the early inspiral is driven by the nonresonant dissipation of internal gravity waves, before transitioning into a regime dominated by resonance crossings as the system approaches Roche-lobe overflow. We highlight the necessity of reframing the historical dichotomy between equilibrium and dynamical tides and instead propose categorizing tidal interactions around their dissipation mechanisms: radiatively damped tides, driven by radiative diffusion, and viscously damped tides, driven by turbulent viscosity. Our framework is broadly applicable to the tidal modeling of a wide class of star–companion systems, from binary stars to hot Jupiters, in a self-consistent and computationally feasible manner.