Segue 1 is an ultra-faint Milky Way satellite with only a few hundred solar luminosities in stars but a measured line-of-sight velocity dispersion of order 3–4.5 km/s, implying an extreme dynamical mass-to-light ratio (M/L ? 10²–10³) if interpreted as an equilibrium, dark-matter-dominated system (Geha et al. 2009; Simon & Geha 2007). In ΛCDM, explaining such a high apparent dispersion and huge inferred dark-matter fraction in a barely resolved galaxy—while accounting for possible tidal disruption, contamination by Sagittarius stream stars, and the minimum halo masses expected from simulations—forces delicate assumptions about equilibrium, subhalo structure, and environment, so Segue 1’s velocity dispersion remains a contentious small-scale test of the standard paradigm (Niederste-Ostholt et al. 2009; Bonnivard et al. 2015).