Baryonic Tully-Fisher relation ($M_b\propto v_f^4$)

An empirical scaling between a disk galaxy's total baryonic mass and its characteristic flat rotation speed. The ideal isolated deep-MOND limit predicts $v_f^4=G{M}_b{a}_0$. Observational tests must specify the speed estimator, distances, gas masses and stellar mass-to-light ratios; the empirical relation alone does not determine a unique theory of gravity.