Chapter

# Jet Driven Turbulence?

• ##### Ralf S. Klessen
DOI: 10.1007/978-3-642-00576-3_50

ABSTRACT Molecular clouds, the birth sites of stars, are permeated by supersonic gas motions. Here, we summarize our results from numerical
simulations on individual jets interacting with their ambient medium. These single jet simulations show that the volume filling
factor of supersonic turbulence excited by jets is very low. In general, supersonic motions, if driven at small scales, do
not propagate far from their source and are damped quickly. Therefore, it is unlikely that the supersonic motions observed
in molecular clouds are maintained by jets launched from protostellar objects. Our preliminary results from three dimensional
simulations of collapsing cloud cores with a self-consistent description of mechanical feedback around protostellar objects
point towards the same results.

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##### Article: Turbulent Flow-Driven Molecular Cloud Formation: A Solution to the Post-T Tauri Problem?
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ABSTRACT: We suggest that molecular clouds can be formed on short time scales by compressions from large scale streams in the interstellar medium (ISM). In particular, we argue that the Taurus-Auriga complex, with filaments of 10-20 pc $\times$ 2-5 pc, most have been formed by H I flows in $\lesssim 3$Myr, explaining the absence of post-T Tauri stars in the region with ages $\gtrsim 3$ Myr. Observations in the 21 cm line of the H I `halos' around the Taurus molecular gas show many features (broad asymmetric profiles, velocity shifts of H I relative to $^{12}$CO) predicted by our MHD numerical simulations, in which large-scale H I streams collide to produce dense filamentary structures. This rapid evolution is possible because the H I flows producing and disrupting the cloud have much higher velocities (5-10 kms) than present in the molecular gas resulting from the colliding flows. The simulations suggest that such flows can occur from the global ISM turbulence without requiring a single triggering event such as a SN explosion. Comment: 26 pages, 12 ps figures. Apj accepted
The Astrophysical Journal 07/1999; · 6.73 Impact Factor
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##### Article: A study of high velocity molecular outflows with an up-to-date sample
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ABSTRACT: A statistical study of the properties of molecular outflows is performed based on an up-to-date sample. 391 outflows were identified in published articles or preprints before February 28, 2003. The parameters of position, morphology, mass, energy, outflow dynamics and central source luminosity are presented for each outflow source. Outflow lobe polarity is known for all the sources, and 84% are found to be bipolar. The sources are divided into low mass and high mass groups according to either the available bolometric luminosity of the central source or the outflow mass.Energetic mass ejection may be a common aspect of the formation of high mass as well as low mass stars. Outflow masses are correlated strongly with bolometric luminosity of the center sources, which was obtained for the first time. There are also correlations between the central source luminosity and the parameters of mechanical luminosity and the thrust or force necessary to drive the outflow. The results show that flow mass, momentum and energy depend on the nature of the central source. Despite their similarity, there are differences between the high mass and low mass outflows on collimation, flow masses, mass-dynamical time relation and associated objects such as HH objects and water masers.Sources with characteristics of collapse or infall comprise 12% of the entire outflow sample. The spatial distribution of the outflow sources in the Galaxy is presented and the local occurrence rate is compared with the stellar birth rate. Comment: 16 pages, 9 figures
Astronomy and Astrophysics 10/2004; · 5.08 Impact Factor
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##### Article: Dissipation in Compressible Magnetohydrodynamic Turbulence
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ABSTRACT: We report results of a three-dimensional, high resolution (up to 5123) numerical investigation of supersonic compressible magnetohydrodynamic turbulence. We consider both forced and decaying turbulence. The model parameters are appropriate to conditions found in Galactic molecular clouds. We find that the dissipation time of turbulence is of the order of the flow crossing time or smaller, even in the presence of strong magnetic fields. About half of the dissipation occurs in shocks. Weak magnetic fields are amplified and tangled by the turbulence, while strong fields remain well ordered.
The Astrophysical Journal 01/2009; 508(1):L99. · 6.73 Impact Factor