Transport-driven super-Jeans fragmentation in dynamical star-forming regions

Abstract

The Jeans criterion is one cornerstone in our understanding of gravitational fragmentation. A critical limitation of the Jeans criterion is that the background density is assumed to be a constant, which is often not true in dynamic conditions such as star-forming regions. For example, during the formation phase of the high-density gas filaments in a molecular cloud, a density increase rate ρ implies a mass accumulation time of tacc = ρ/ρ = −ρ(∇ · (ρv))−1. The system is non-stationary when the mass accumulation time becomes comparable to the free-fall time (Formula Presented). We study fragmentation in non-stationary settings, and find that accretion can significantly increase in the characteristic mass of gravitational fragmentation (λJeans, aac = λJeans(1 + tff/tacc)1/3, mJeans, acc = mJeans(1 + tff/tacc)). In massive star-forming regions, this mechanism of transport-driven super-Jeans fragmentation can contribute to the formation of massive stars by causing order-of-magnitude increases in the mass of the fragments.