On the Role of Disks in the Formation of Stellar Systems: A Numerical Parameter Study of Rapid Accretion

TL;DR

This study uses 3D numerical simulations to explore how rapid accretion influences disk stability and star system multiplicity, revealing key thresholds for fragmentation and binary formation.

Contribution

It introduces a parameter study linking disk behavior and multiplicity to accretion rates and gravitational instabilities, providing predictive insights.

Findings

Fragmentation occurs only at accretion rates several times higher than the isothermal limit.

Disk-to-star accretion rate scales with infall rate and is driven by gravitational torques.

Disks exceeding ~50% of total system mass tend to fragment and form binaries.

Abstract

We study rapidly accreting, gravitationally unstable disks with a series of global, three dimensional, numerical experiments using the code ORION. In this paper we conduct a numerical parameter study focused on protostellar disks, and show that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the disk's accretion rate to its sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infall rate, and governed by gravitational torques generated by low-m spiral modes. We also confirm the existence of a maximum stable disk mass: disks that exceed ~50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.