Turmoil in Orion: The Nearest Massive Protostar

TL;DR

This paper reviews theories of massive star formation, discusses the Orion KL region's features, and evaluates the evidence supporting the Turbulent Core Model as a framework for understanding the formation of massive protostars like source "I".

Contribution

It provides an analysis of the Orion KL region, supporting the Turbulent Core Model as a plausible explanation for massive star formation in this area.

Findings

Source "I" likely hosts a massive protostar consistent with the TCM.

The binary system involving Theta^1C and BN explains their observed motions.

Source "n" shows signs of bipolar outflow activity.

Abstract

I discuss different theories of massive star formation: formation from massive cores, competitive Bondi-Hoyle accretion, and protostellar collisions. I summarize basic features of the Turbulent Core Model (TCM). I then introduce the Orion Kleinmann-Low (KL) region, embedded in the Orion Nebula Cluster (ONC) and one of the nearest regions of massive star formation. The KL region contains three principal radio sources, known as "I", "n" and "BN". BN is known to be a runaway star, almost certainly set in motion by dynamical ejection within the ONC from a multiple system of massive stars, that would leave behind a recoiling, hard, massive, probably eccentric binary. I review the debate about whether this binary is Theta^1C, the most massive star in the ONC, or source "I", and argue that it is most likely to be Theta^1C, since this is now known be a recoiling, hard, massive, eccentric binary, with properties that satisfy the energy and momentum constraints implied by BN's motion. Source "n" is a relatively low-mass protostar with extended radio emission suggestive of a bipolar outflow. Source "I", located near the center of the main gas concentration in the region, the Orion Hot Core, is the likely location of a massive protostar that is powering the KL region, and I discuss how its basic properties are consistent with predictions from the TCM. In this scenario, the radio emission from source "I" is the base of a bipolar outflow that is ionized by the massive protostar and should be elongated along the axis of the outflow.