Matched-radius slope comparison eliminates apparent cusp-core tension in Milky Way satellites

The arXiv preprint (Sarrato-Alós et al.) directly confronts the methodological mismatch that has long inflated the cusp-core problem. Instead of comparing simulation slopes at fixed physical radii chosen for numerical convenience against observationally derived slopes at different radii, the authors restrict all comparisons to radii where stellar kinematics reliably constrain the potential. This single protocol change, applied across stellar masses from 10^3 to 10^11 solar masses, reveals a shared mass-dependent trend: cuspy profiles at the lowest masses transitioning to cores above 10^6 solar masses.

Context from the broader literature shows why this matters. Earlier claims of persistent tension often rested on NFW fits to data that the new work shows are statistically disfavored once core-formation physics is included. The increased scatter among satellites relative to centrals aligns with expected tidal effects, a nuance missed when samples mix field and satellite galaxies. Willman 1 remains the sole clear outlier, suggesting either extreme tidal stripping or systematic bias in its mass modeling.

The analysis implies that galaxy-formation feedback, rather than exotic dark-matter physics, is sufficient to explain the observed diversity once apples-to-apples comparisons are enforced. Future wide-field spectroscopic surveys that increase the number of tracers per satellite will test whether the remaining scatter shrinks as predicted.