Orphaned Protostars

TL;DR

This paper investigates the origin and dynamics of distant protostellar companions, termed orphans, through N-body simulations, revealing their formation, ejection mechanisms, and potential for observational identification.

Contribution

It introduces the concept of orphans as ejected protostars, demonstrating their prevalence and characteristics through simulations of unstable triple systems in dense cloud cores.

Findings

Half of all triple systems disintegrate during the protostellar stage.

Orphans can travel up to 0.2 pc during the protostellar phase.

Bound orphans are associated with close embedded binaries.

Abstract

We explore the origin of a population of distant companions (~1000 - 5000 AU) to Class I protostellar sources recently found by Connelley and co-workers, who noted that the companion fraction diminished as the sources evolved. Here we present N-body simulations of unstable triple systems embedded in dense cloud cores. Many companions are ejected into unbound orbits and quickly escape, but others are ejected with insufficient momentum to climb out of the potential well of the cloud core and associated binary. These loosely bound companions reach distances of many thousands of AU before falling back and eventually being ejected into escapes as the cloud cores gradually disappear. We use the term orphans to denote protostellar objects that are dynamically ejected from their placental cloud cores, either escaping or for a time being tenuously bound at large separations. Half of all triple systems are found to disintegrate during the protostellar stage, so if multiple systems are a frequent outcome of the collapse of a cloud core, then orphans should be common. Bound orphans are associated with embedded close protostellar binaries, but escaping orphans can travel as far as ~0.2 pc during the protostellar phase. The steep climb out of a potential well ensures that orphans are not kinematically distinct from young stars born with a less violent pre-history. The identification of orphans outside their heavily extincted cloud cores will allow the detailed study of protostars high up on their Hayashi tracks at near-infrared and in some cases even at optical wavelengths.