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

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.

12 pages, 8 figures, Accepted for publication in ApJ

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• Implementing Primordial Binaries in Simulations of Star Cluster Formation with a Hybrid MHD and Direct N-Body Method
• Relativistic dust accretion onto a scale--dependent polytropic black hole
• The role of magnetic fields in the formation of multiple massive stars
• The McDonald Accelerating Stars Survey (MASS): Architecture of the Ancient Five-Planet Host System Kepler-444
• Radiative non-isothermal Bondi accretion onto a massive black hole
• Numerical Methods for Simulating Star Formation