Peter H. Jumper, Robert T. Fisher
The formation of brown dwarfs (BDs) poses a key challenge to star formation theory. The observed dearth of nearby ($\leq 5$ AU) brown dwarf companions to solar-mass stars, known as the brown dwarf desert, as well as the tendency for low-mass binary systems to be more tightly-bound than stellar binaries, have been cited as evidence for distinct formation mechanisms for brown dwarfs and stars. In this paper, we explore the implications of the minimal hypothesis that brown dwarfs in binary systems originate via the same fundamental fragmentation mechanism as stars, within isolated, turbulent giant molecular cloud cores. We demonstrate analytically that the scaling of specific angular momentum with turbulent core mass naturally gives rise to the brown dwarf desert, as well as wide brown-dwarf binary systems. Further, we demonstrate analytically that the turbulent core fragmentation model also naturally predicts that very low-mass (VLM) binary and BD/BD systems are more tightly-bound than stellar systems. In addition, in order to capture the stochastic variation intrinsic to turbulence, we generate $10^4$ model turbulent cores with synthetic turbulent velocity fields to show that the turbulent fragmentation model accommodates a small fraction of binary brown dwarfs with wide separations, similar to observations. Consequently, because the turbulent core fragmentation model can accommodate the brown dwarf desert as well as hard low-mass binaries, we suggest that these binary properties are not strong evidence for separate formation mechanisms for brown dwarfs. Indeed, the picture which emerges from the turbulent fragmentation model is that a single fragmentation mechanism largely shapes both stellar and brown dwarf binary distributions during formation.
View original:
http://arxiv.org/abs/1206.1045
No comments:
Post a Comment