Formation of multiple low mass stars, brown dwarfs and planemos via gravitational collapse

TL;DR

This paper uses numerical simulations to explore how very low-mass stars, brown dwarfs, and planet-mass objects form through gravitational collapse and fragmentation of molecular cores, producing diverse binary systems with properties similar to observations.

Contribution

It presents a new simulation scheme that reproduces observed binary properties of VLMS, BDs, and planemos, including wide binaries and realistic mass ratio distributions.

Findings

Formation of wide VLMS and BD binaries up to 441 AU.

Mass ratio distribution between 0.31 and 0.74.

Moderate core rotation leads to planemo formation.

Abstract

The origin of very low-mass stars (VLMS) and brown dwarfs (BDs) is still an unresolved topic of star formation. We here present numerical simulations of the formation of VLMS, BDs, and planet mass objects (planemos) resulting from the gravitational collapse and fragmentation of solar mass molecular cores with varying rotation rates and initial density perturbations. Our simulations yield various types of binary systems including the combinations VLMS-VLMS, BD-BD, planemo-planemo, VLMS-BD, VLMS-planemos, BD-planemo. Our scheme successfully addresses the formation of wide VLMS and BD binaries with semi-major axis up to 441 AU and produces a spectrum of mass ratios closer to the observed mass ratio distribution (q > 0.5). Molecular cores with moderate values of the ratio of kinetic to gravitational potential energy (0.16 <= beta <= 0.21) produce planemos. Solar mass cores with rotational parameters beta outside of this range yield either VLMS/BDs or a combination of both. With regard to the mass ratios we find that for both types of binary systems the mass ratio distribution varies in the range 0.31 <= q <= 0.74. We note that in the presence of radiative feedback, the length scale of fragmentation would increase by approximately two orders of magnitude, implying that the formation of binaries may be efficient for wide orbits, while being suppressed for short-orbit systems.