We present measurements of the mean dense core lifetimes in numerical simulations of magnetically supercritical , turbulent , isothermal molecular clouds ( MCs ) , in order to compare with observational determinations .
The mean “ prestellar ” lifetimes are given as a function of the mean density within the cores , which in turn is determined by the density threshold n _ { thr } used to define them .
The mean lifetimes are consistent with observationally reported values , ranging from a few to several free-fall times .
We also present estimates of the fraction of cores in the “ prestellar ” , “ stellar ” , and “ failed ” stages as a function of n _ { thr } .
Failed cores are defined as those that do not manage to collapse , but rather re-disperse back into the environment .
Due to resolution limitations , the number ratios are measured indirectly in the simulations , as either lifetime ratios ( for the prestellar cores ) , or as time-weighted mass ratios ( for the failed cores ) .
Our approach contains one free parameter , the lifetime of a protostellar object \tau _ { yso } ( Class 0 + Class I stages ) , which is outside the realm of the simulations .
Assuming a value \tau _ { \mathrm { yso } } = 0.46 Myr , we obtain number ratios of starless to stellar cores ranging from 4–5 at n _ { thr } = 1.5 \times 10 ^ { 4 } { ~ { } cm } ^ { -3 } to \sim 1 at n _ { thr } = 1.2 \times 10 ^ { 5 } { ~ { } cm } ^ { -3 } , again in good agreement with observational determinations .
We also find that the failed cores are generally difficult to detect , although the mass in these cores is comparable to that in stellar cores at n _ { thr } = 1.5 \times 10 ^ { 4 } { ~ { } cm } ^ { -3 } .
At n _ { thr } = 1.2 \times 10 ^ { 5 } { ~ { } cm } ^ { -3 } the mass in failed cores is negligible , in agreement with recent observational suggestions that at the latter densities the cores are in general gravitationally dominated .
We conclude by noting that the timescale for core contraction and collapse is virtually the same in the subcritical , ambipolar diffusion-mediated model of star formation , in the model of star formation in turbulent supercritical clouds , and in a model intermediate between the previous two , suggesting a convergence of the models at least at the level of the core lifetimes , for currently accepted values of the clouds ’ magnetic criticality .