Different Modes of Star Formation: Gravitational Collapse of Magnetically Subcritical Cloud

TL;DR

This study uses 3D non-ideal MHD simulations to explore star formation in magnetically subcritical clouds, revealing a slower collapse process, low angular momentum, and different outflow characteristics compared to supercritical clouds.

Contribution

It provides the first detailed simulation-based analysis of star formation in magnetically subcritical clouds, highlighting key differences from supercritical cases.

Findings

Collapse takes > 5-10 freefall times due to magnetic flux removal.

No large-scale low-velocity outflow occurs during collapse.

A weak high-velocity jet forms near the protostar, but the circumstellar disc remains small.

Abstract

Star formation in magnetically subcritical clouds is investigated using a three-dimensional non-ideal magneto-hydrodynamics simulation. Since rapid cloud collapse is suppressed until the magnetic flux is sufficiently removed from the initially magnetically subcritical cloud by ambipolar diffusion, it takes > 5-10t_ff to form a protostar, where t_ff is the freefall timescale of the initial cloud. The angular momentum of the star forming cloud is efficiently transferred to the interstellar medium before the rapid collapse begins, and the collapsing cloud has a very low angular momentum. Unlike the magnetically supercritical case, no large-scale low-velocity outflow appears in such a collapsing cloud due to the short lifetime of the first core. Following protostar formation, a very weak high-velocity jet, which has a small momentum and might disappear at a later time, is driven near the protostar, while the circumstellar disc does not grow during the early mass accretion phase. The results show that the star formation process in magnetically subcritical clouds is qualitatively different from that in magnetically supercritical clouds.