Interstellar MHD Turbulence and Star Formation

Abstract

This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: i) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; ii) the nature of the clumps produced by thermal instability, noting that, contrary to classical ideas, they in general accrete mass from their environment; iii) the density-magnetic field correlation (or lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; v) the formation of cold, dense clouds aided by thermal instability; vi) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, and vii) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and diperses them while they collapse.

43 pages. Invited chapter for the book "Magnetic Fields in Diffuse Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as per referee's recommendations

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Cited by in corpus (13)

• Molecular Cloud Evolution V. Cloud Destruction by Stellar Feedback
• Gravity, Magnetic Field, and Turbulence: Relative Importance and Impact on Fragmentation in the Infrared Dark Cloud G34.43+00.24
• Formation of Molecular Clouds and Global Conditions for Star Formation
• The Galactic Faraday depth sky revisited
• Energy budget of forming clumps in numerical simulations of collapsing clouds
• Structure and Expansion Law of HII Regions in structured Molecular Clouds
• Supernova-regulated ISM -- V. Space- and time-correlations
• As a matter of tension -- kinetic energy spectra in MHD turbulence
• Topological signatures of interstellar magnetic fields - I. Betti numbers and persistence diagrams
• The role of turbulence, magnetic fields and feedback for star formation
• The influence of magnetic field on the CNM mass fraction and its alignment with density structures
• Magnetic Suppression of Turbulence and the Star Formation Activity of Molecular Clouds
• Cosmic Radioactivity and Galactic Chemical Evolution