Protostar Mass Due to Infall and Dispersal

TL;DR

This paper models how protostar mass results from infall and dispersal processes, revealing conditions that lead to low-mass or high-mass stars and connecting core mass distributions to the initial mass function.

Contribution

It introduces a model linking protostar mass to infall and dispersal dynamics, explaining the origin of the IMF peak and mass ratios in star formation.

Findings

Protostar mass approaches a time-independent value under high contrast and short dispersal.

Massive star formation occurs with lower density contrast and longer dispersal times.

Protostar and core mass ratios are consistent with the IMF shape.

Abstract

The mass of a protostar is calculated from the infall and dispersal of an isothermal sphere in a uniform background. For high contrast between peak and background densities and for short dispersal time t_d, the accretion is "self-limiting": gas beyond the core is dispersed before it accretes, and the protostar mass approaches a time-independent value of low mass. For lower density contrast and longer dispersal time, the accretion "runs away": gas accretes from beyond the core, and the protostar mass approaches massive star values. The final protostar mass is approximately the initial gas mass whose free-fall time equals t_d. This mass matches the peak of the IMF for gas temperature 10 K, peak and background densities 10^6 and 10^3 cm^-3, and for t_d comparable to the core free-fall time t_core. The accretion luminosity exceeds 1 L-Sun for 0.1 Myr, as in the "Class 0" phase. For t_d/t_core=0.4-0.8 and temperature 7-50 K, self-limiting protostar masses are 0.08-5 M-Sun. These protostar and core masses have ratio 0.4 +- 0.2, as expected if the core mass distribution and the IMF have the same shape.