Discovery of an expanding molecular bubble in Orion BN/KL

TL;DR

This paper reports the discovery of an expanding, spherical molecular bubble in Orion BN/KL, likely caused by the disintegration of a massive stellar system 500 years ago, differing from typical stellar outflows.

Contribution

It presents the first identification of a spherical, expanding molecular bubble in Orion BN/KL, revealing a new type of outflow phenomenon associated with stellar system disintegration.

Findings

Identified a 500-1000 year old expanding molecular bubble

The bubble's center aligns with a disintegrated stellar system

The bubble's characteristics differ from known stellar outflows

Abstract

During their infancy, stars are well known to expel matter violently in the form of well-defined, collimated outflows. A fairly unique exception is found in the Orion BN/KL star-forming region where a poorly collimated and somewhat disordered outflow composed of numerous elongated ``finger-like'' structures was discovered more than 30 years ago. In this letter, we report the discovery in the same region of an even more atypical outflow phenomenon. Using $^{13}$CO(2-1) line observations made with the Submillimeter Array (SMA), we have identified there a 500 to 1,000 years old, expanding, roughly spherically symmetric bubble whose characteristics are entirely different from those of known outflows associated with young stellar objects. The center of the bubble coincides with the initial position of a now defunct massive multiple stellar system suspected to have disintegrated 500 years ago, and with the center of symmetry of the system of molecular fingers surrounding the Kleinmann-Low nebula. We hypothesize that the bubble is made up of gas and dust that used to be part of the circumstellar material associated with the decayed multiple system. The Orion hot core, recently proposed to be the result of the impact of a shock wave onto a massive dense core, is located toward the south-east quadrant of the bubble. The supersonic expansion of the bubble, and/or the impact of some low-velocity filaments provide a natural explanation for its origin.