From large-scale to protostellar disk fragmentation into close binary stars

TL;DR

This paper uses advanced numerical simulations to study how large-scale cloud core fragmentation and small-scale disk fragmentation lead to the formation of close binary stars, providing insights into early star formation processes.

Contribution

It presents the first direct numerical calculations down to 0.1 AU scales showing the combined effects of large-scale and small-scale fragmentation in star formation.

Findings

Large-scale cloud core fragmentation produces multiple protostars.

Circumstellar disks undergo eccentric ($m=1$) fragmentation to form close binaries.

Simulated ALMA images reveal disk structures and fragmentation processes.

Abstract

Recent observations of young stellar systems with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA) are helping to cement the idea that close companion stars form via fragmentation of a gravitationally unstable disk around a protostar early in the star formation process. As the disk grows in mass, it eventually becomes gravitationally unstable and fragments, forming one or more new protostars in orbit with the first at mean separations of 100 astronomical units (AU) or even less. Here we report direct numerical calculations down to scales as small as $\sim 0.1$ AU, using a consistent Smoothed Particle Hydrodynamics (SPH) code, that show the large-scale fragmentation of a cloud core into two protostars accompanied by small-scale fragmentation of their circumstellar disks. Our results demonstrate the two dominant mechanisms of star formation, where the disk forming around a protostar, which in turn results from the large-scale fragmentation of the cloud core, undergoes eccentric ($m=1$) fragmentation to produce a close binary. We generate two-dimensional emission maps and simulated ALMA 1.3 mm continuum images of the structure and fragmentation of the disks that can help explain the dynamical processes occurring within collapsing cloud cores.