Dancing with the stars: Stirring up extraordinary turbulence in Galactic center clouds

TL;DR

This paper investigates whether stellar interactions, especially stellar winds, can explain the high turbulence in Galactic center molecular clouds, finding winds are a plausible driver while dynamical friction is not.

Contribution

It demonstrates that stellar winds from crossing stars can account for the turbulence levels and scaling in CMZ clouds, a novel explanation for their extraordinary turbulence.

Findings

Stellar winds can explain turbulence levels and scaling in CMZ clouds.

Dynamical friction is ineffective in driving turbulence in these clouds.

The mechanism's effectiveness diminishes beyond the CMZ extent.

Abstract

Molecular clouds in the central molecular zone (CMZ) have been observed to feature turbulent line widths that are significantly higher, and scale with cloud size more steeply, than in the rest of the Milky Way. In the same Galactic region, the stellar density is also much higher than in the rest of the Milky Way, and the vertical stellar velocity dispersion is large, meaning that even young stars are likely to cross the entire vertical extent of the CMZ within their lifetimes. Here, we investigate whether interactions of CMZ molecular clouds with crossing stars can account for the extraordinary properties of observed turbulence in this part of the Galaxy. We calculated the rate of energy deposition by stars crossing CMZ clouds due to (a) stellar winds and (b) dynamical friction, and compared it to the rate of turbulence decay. We calculated the predicted scaling of turbulence line width with cloud size in each case. We find that energy deposition by stellar winds of crossing massive stars can account for both the level and the scaling of CMZ cloud turbulence with cloud size. We also find that the mechanism stops being effective at a Galactocentric distance comparable to the CMZ extent. On the other hand, we find that dynamical friction by crossing stars does not constitute a significant driver of turbulence for CMZ clouds.