Waves on the surface of the Orion molecular cloud

TL;DR

This paper reports the discovery of wave-like Kelvin-Helmholtz instabilities on the surface of the Orion molecular cloud, providing evidence of hydrodynamical processes influencing star-forming regions.

Contribution

It presents the first observational evidence of Kelvin-Helmholtz instabilities on a molecular cloud surface, linking stellar feedback to cloud morphology.

Findings

Detection of wave-like structures on the Orion cloud surface

Identification of Kelvin-Helmholtz instability as the cause

Implication of stellar feedback in cloud dynamics

Abstract

Massive stars influence their parental molecular cloud, and it has long been suspected that the development of hydrodynamical instabilities can compress or fragment the cloud. Identifying such instabilities has proved difficult. It has been suggested that elongated structures (such as the `pillars of creation') and other shapes arise because of instabilities, but alternative explanations are available. One key signature of an instability is a wave-like structure in the gas, which has hitherto not been seen. Here we report the presence of `waves' at the surface of the Orion molecular cloud near where massive stars are forming. The waves seem to be a Kelvin-Helmholtz instability that arises during the expansion of the nebula as gas heated and ionized by massive stars is blown over pre-existing molecular gas.