Galaxy Merger: Dynamical Friction Sinking

Most galaxy mergers don't happen in one fast head-on smash — a small satellite galaxy orbits for millions to billions of years while Chandrasekhar dynamical friction quietly bleeds off its orbital energy and angular momentum, until it finally spirals into the host's core. This simulator integrates the real drag law for an isothermal-sphere halo, F_df = -4πG²M_sat²ρ(r)lnΛ/v³, alongside the host's own gravity, so you can watch the orbit decay in real time. Tune the satellite's mass ratio, the Coulomb logarithm and the starting radius, and compare the live orbital radius and speed against the analytic sinking-time prediction t_df ≈ (1.17/lnΛ)·(r_i²v_c)/(GM_sat) — the same physics governing the Milky Way's ongoing absorption of the Sagittarius and Magellanic dwarf galaxies.