Self-Interacting Dark Matter in Brown Dwarfs

Brown dwarfs, being transitional objects between giant planets and low-mass stars, possess dense, cool interiors that provide optimal conditions to explore non-standard physics. Capture and accumulation of dark-matter particles can alter the thermal, structural and dynamic of these substellar objects. We aim to apply a self-consistent two-fluid framework to model the internal structure of self-gravitating brown dwarfs and to quantify how the presence of a dark-matter component modifies their mass--radius relations and dynamical properties. The brown dwarf is modeled as a composite system of a baryonic fluid, described by a polytropic equation of state, and an independent dark-matter fluid. Both components are coupled through their shared gravitational potential in hydrostatic equilibrium. We solve numerically the coupled Lane-Emden equations for a range of dark-matter mass fractions. We find that dark matter accumulating in the core reshapes the baryonic density profile, modifying both the radius and the second-order Love number. Radius and dynamical anomalies in brown dwarfs can serve as diagnostic tools to constrain dark-matter properties. Future high-precision astrometric missions could identify these structural signatures, establishing brown dwarfs as possible detectors of dark matter in the Galaxy.