High Accretion Rate during Class 0 Phase due to External Trigger

Recent observations indicate that some class 0 sources have orders of magnitude higher accretion rates than those of class I. We investigated the conditions for the high accretion rates of some class 0 sources by numerical calculations, modelling an external trigger. For no external trigger, we find that the maximum value of the accretion rate is determined by the ratio $\alpha$ of the gravitational energy to the thermal one within a flat inner region of the cloud core. The accretion rate reaches $\sim 10^{-4} M_{\sun} yr^{-1}$ if the cloud core has $\alpha > 2$. For an external trigger we find that the maximum value of the accretion rate is proportional to the momentum given to the cloud core. The accretion rate reaches $> 10^{-4} M_{\sun} yr^{-1}$ with a momentum of $\sim 0.1 M_{\sun} km s^{-1}$ when the initial central density of the cloud core is $\sim 10^{-18} g cm^{-3}$. A comparison between recent observational results for prestellar cores and our no triggered collapse model indicates that the flat inner regions of typical prestellar cores are not large enough to cause accretion rates of $\sim 10^{-4} M_{\sun} yr^{-1}$. Our results show that the triggered collapse of the cloud core is more preferable for the origin of the high accretion rates of class 0 sources than no triggered collapse.