Estimated lifetime as a function of number density (n_n). The green filled squares are obtained from our model for a normalized neutral–ion collision time . The blue filled triangles show the corresponding data points for the population of 446 candidate prestellar cores identified with Herschel in the Aquila cloud (Könyves et al. 2015). Earlier data from Ward-Thompson et al. (2007) are shown by the red circles for better comparison. The black dashed line shows the dynamical time (Z₀/c_s), i.e., the free-fall time, of our model.