A more successful feedback model was first presented by Andrew King at the University of Leicester in 2003. In King's model, feedback occurs through momentum transfer, rather than energy transfer as in the case of Silk & Rees's model. A "momentum-driven flow" is one in which the gas cooling time is so short that essentially all the energy in the flow is in the form of bulk motion. In such a flow, most of the energy released by the black hole is lost to radiation, and only a few percent is left to affect the gas mechanically. King's model predicts a slope of α = 4 for the M – σ relation, and the normalization is exactly correct; it is roughly a factor c / σ ≈ 10 times larger than in Silk & Rees's relation.