Turbulence in the interstellar medium

Abstract. Turbulence is ubiquitous in the insterstellar medium and plays a major role in several processes such as the formation of dense structures and stars, the stability of molecular clouds, the amplification of magnetic fields, and the re-acceleration and diffusion of cosmic rays. Despite its importance, interstellar turbulence, like turbulence in general, is far from being fully understood. In this review we present the basics of turbulence physics, focusing on the statistics of its structure and energy cascade. We explore the physics of compressible and incompressible turbulent flows, as well as magnetised cases. The most relevant observational techniques that provide quantitative insights into interstellar turbulence are also presented. We also discuss the main difficulties in developing a three-dimensional view of interstellar turbulence from these observations. Finally, we briefly present what the main sources of turbulence in the interstellar medium could be.

Download Full-text

Turbulent structure and star formation in a stratified, supernova-driven, interstellar medium

Proceedings of the International Astronomical Union ◽

10.1017/s174392130700172x ◽

2006 ◽

Vol 2 (S237) ◽

pp. 358-362

Author(s):

M. K. Ryan Joung ◽

Mordecai-Mark Mac Low

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Adaptive Mesh Refinement ◽

Formation Rate ◽

Three Dimensional ◽

Adaptive Mesh ◽

Mass Function ◽

Initial Mass Function ◽

Interstellar Turbulence ◽

Self Gravity

AbstractWe report on a study of interstellar turbulence driven by both correlated and isolated supernova explosions. We use three-dimensional hydrodynamic models of a vertically stratified interstellar medium run with the adaptive mesh refinement code Flash at a maximum resolution of 2 pc, with a grid size of 0.5 × 0.5 × 10 kpc. Cold dense clouds form even in the absence of self-gravity due to the collective action of thermal instability and supersonic turbulence. Studying these clouds, we show that it can be misleading to predict physical properties such as the star formation rate or the stellar initial mass function using numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. The amount of mass available for collapse depends on scale, suggesting a simple translation from the density PDF to the stellar IMF may be questionable. Even though the supernova-driven turbulence does produce compressed clouds, it also opposes global collapse. The net effect of supernova-driven turbulence is to inhibit star formation globally by decreasing the amount of mass unstable to gravitational collapse.

Download Full-text

IMAGINE: a comprehensive view of the interstellar medium, Galactic magnetic fields and cosmic rays

Journal of Cosmology and Astroparticle Physics ◽

10.1088/1475-7516/2018/08/049 ◽

2018 ◽

Vol 2018 (08) ◽

pp. 049-049 ◽

Cited By ~ 25

Author(s):

François Boulanger ◽

Torsten Enßlin ◽

Andrew Fletcher ◽

Philipp Girichides ◽

Stefan Hackstein ◽

...

Keyword(s):

Cosmic Rays ◽

Magnetic Fields ◽

Interstellar Medium ◽

Galactic Magnetic Fields ◽

Comprehensive View

Download Full-text

CO and the Multiphase ISM

Symposium - International Astronomical Union ◽

10.1017/s0074180900234025 ◽

1997 ◽

Vol 170 ◽

pp. 25-32

Author(s):

Christopher F. Mckee

Keyword(s):

Mach Number ◽

Magnetic Fields ◽

Interstellar Medium ◽

Molecular Clouds ◽

Molecular Gas ◽

Wave Pressure ◽

Multiphase Structure ◽

Co Observations

CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.

Download Full-text

On the stability of parallel flows with parallel magnetic fields

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1966.0175 ◽

1966 ◽

Vol 293 (1434) ◽

pp. 342-358 ◽

Cited By ~ 31

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Three Dimensional ◽

Two Dimensional ◽

Parallel Magnetic Field ◽

Parallel Flows ◽

The Mean ◽

The Stability ◽

The Magnetic Field ◽

Parallel Magnetic Fields

The first part of the paper is a physical discussion of the way in which a magnetic field affects the stability of a fluid in motion. Particular emphasis is given to how the magnetic field affects the interaction of the disturbance with the mean motion. The second part is an analysis of the stability of plane parallel flows of fluids with finite viscosity and conductivity under the action of uniform parallel magnetic fields. We show that, in general, three-dimensional disturbances are the most unstable, thus disagreeing with the conclusion of Michael (1953) and Stuart (1954). We show how results obtained for two-dimensional disturbances can be used to calculate the most unstable three-dimensional disturbances and thence we prove that a parallel magnetic field can never completely stabilize a parallel flow.

Download Full-text

Signatures of turbulence in the dense interstellar medium

Symposium - International Astronomical Union ◽

10.1017/s0074180900239466 ◽

1991 ◽

Vol 147 ◽

pp. 119-136

Author(s):

E. Falgarone ◽

T.G. Phillips

Keyword(s):

Interstellar Medium ◽

Turbulent Flows ◽

Fractal Geometry ◽

Molecular Clouds ◽

Large Range ◽

Line Profiles ◽

Physical Processes ◽

Molecular Line ◽

Scale Size ◽

Excitation Conditions

We present an ensemble of recent observational results on molecular clouds which, taken separately, could all be understood by invoking various unrelated physical processes, but taken all together form a coherent ensemble stressing the imprints of turbulence in the physics of the cold interstellar medium. These results are first, the existence of wings in the molecular line profiles, which can be interpreted on statistical grounds as the signature of the intermittency of the velocity field in turbulent flows, second the fractal geometry of the cloud edges, with properties reminiscent of those of various surfaces studied in turbulent laboratory flows, and third, the fact that the dense gas fills only a very small fraction of the space. The last points are supported by CO multitransition observations of a few fields in nearby molecular clouds. They show that the excitation conditions are the same for the gas emitting in the linewings and in the linecores and are also remarkably uniform over a large range (factor 10) of column densities. An attractive interpretation of the molecular line data is that most of the 12CO(J=2—1) and (J=3—2) emissions arise in cold (Tk ≥ 10K) and dense (nH2 ∼ 104cm—3 or more) structures distributed on a fractal set with no characteristic scale size greater than about 1000 AU.

Download Full-text

Fermi LAT study of cosmic-rays and the interstellar medium in nearby molecular clouds

10.1063/1.4792564 ◽

2013 ◽

Author(s):

Katsuhiro Hayashi ◽

Tsunefumi Mizuno ◽

Fermi-LAT Collaboration

Keyword(s):

Cosmic Rays ◽

Interstellar Medium ◽

Molecular Clouds

Download Full-text

Numerical Investigation of the Three-Dimensional Flow Structure About a Revolving Wing

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2012-72388 ◽

2012 ◽

Cited By ~ 2

Author(s):

Daniel J. Garmann ◽

Miguel R. Visbal ◽

Paul D. Orkwis

Keyword(s):

Turbulent Flows ◽

Numerical Study ◽

Three Dimensional ◽

Leading Edge ◽

Reynolds Numbers ◽

Vortex System ◽

Aerodynamic Loads ◽

Eddy Simulation ◽

Data Reduction Technique ◽

The Stability

A numerical study is conducted to examine the vortex structure about a revolving wing in quiescent flow employing a high-fidelity, implicit large eddy simulation (ILES) technique found to be effective in simulating flows that exhibit interspersed regions of laminar, transitional, and turbulent flows. The revolving wing configuration consists of a single, aspect ratio one rectangular plate extended out a distance of 0.5 chords from the origin. Shortly after the onset of the motion, the rotating wing generates a stable and coherent vortex system across the leading edge and wing root that remains throughout the motion. The aerodynamic loads are also analyzed and found to remain mostly constant during the maneuver. Transitional effects on the vortex system are investigated over a range of Reynolds numbers (3,000 < Re < 15,000). It is found that higher Reynolds numbers promote more breakdown of the leading edge and root vortices, but do not alter the stability of the vortex system. The aerodynamic loads also show little sensitivity to Reynolds number with the higher Reynolds numbers producing only moderately higher forces. Comparisons with recent experimental PIV measurements using a PIV-like data reduction technique applied to the computational solution show very favorable agreement with the mid-span velocity and vorticity contours.

Download Full-text

MHD turbulence-Star Formation Connection: from pc to kpc scales

Proceedings of the International Astronomical Union ◽

10.1017/s174392131100723x ◽

2010 ◽

Vol 6 (S274) ◽

pp. 333-339 ◽

Cited By ~ 1

Author(s):

E. M. de Gouveia Dal Pino ◽

R. Santos-Lima ◽

A. Lazarian ◽

M. R. M. Leão ◽

D. Falceta-Gonçalves ◽

...

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Flux ◽

Numerical Simulations ◽

Magnetic Reconnection ◽

Turbulent Flows ◽

Molecular Clouds ◽

Three Dimensional ◽

Mhd Turbulence ◽

Star Forming

AbstractThe transport of magnetic flux to outside of collapsing molecular clouds is a required step to allow the formation of stars. Although ambipolar diffusion is often regarded as a key mechanism for that, it has been recently argued that it may not be efficient enough. In this review, we discuss the role that MHD turbulence plays in the transport of magnetic flux in star forming flows. In particular, based on recent advances in the theory of fast magnetic reconnection in turbulent flows, we will show results of three-dimensional numerical simulations that indicate that the diffusion of magnetic field induced by turbulent reconnection can be a very efficient mechanism, especially in the early stages of cloud collapse and star formation. To conclude, we will also briefly discuss the turbulence-star formation connection and feedback in different astrophysical environments: from galactic to cluster of galaxy scales.

Download Full-text

Three-dimensional MHD simulations of molecular cloud fragmentation regulated by gravity, ambipolar diffusion, and turbulence

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309030245 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 115-116

Author(s):

Takahiro Kudoh ◽

Shantanu Basu

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Time Scale ◽

Molecular Cloud ◽

Molecular Clouds ◽

Three Dimensional ◽

Core Formation ◽

Mhd Simulations ◽

Dimensional Simulation

AbstractWe find that the star formation is accelerated by the supersonic turbulence in the magnetically dominated (subcritical) clouds. We employ a fully three-dimensional simulation to study the role of magnetic fields and ion-neutral friction in regulating gravitationally driven fragmentation of molecular clouds. The time-scale of collapsing core formation in subcritical clouds is a few ×107 years when starting with small subsonic perturbations. However, it is shortened to approximately several ×106 years by the supersonic flows in the clouds. We confirm that higher-spacial resolution simulations also show the same result.

Download Full-text