Outflow momentum flux correlation with envelope mass (left) and with bolometric luminosity (right). The black filled and open circles are the low-mass Class I and Class 0 sources from Bontemps et al. (1996). The light blue circles are the massive protostars from our sample. In the left panel, the black dashed line is the observational linear relation found by Bontemps et al. (1996), showing that it also holds for the massive individual protostars. On the right, we show the evolutionary tracks corresponding to those of Fig. 1.