Book contents
- Frontmatter
- Contents
- Preface
- Turbulence in the Interstellar Medium: a Retrospective Review
- Mechanism of Formation of Atmospheric Turbulence Relevant for Optical Astronomy
- Properties of Atomic Gas in Spiral Galaxies
- Turbulence in the Ionized Gas in Spiral Galaxies
- Probing Interstellar Turbulence in the Warm Ionized Medium using Emission Lines
- The Spectrum & Galactic Distribution of MicroTurbulence in Diffuse Ionized Gas
- Small Scale Structure and Turbulence in the Interstellar Medium
- What is the Reynolds Number of the Reynolds' Layer?
- Photoionized Gas in the Galactic Halo
- Turbulent Heating of the Diffuse Ionized Gas
- Cosmic Rays in Interstellar Turbulence
- Turbulence in Line-Driven Stellar Winds
- An Introduction to Compressible MHD Turbulence
- Turbulence in Atomic Hydrogen
- Supershells in Spiral Galaxies
- The Size Distribution of Superbubbles in the Interstellar Medium
- Large-Scale Motions in the ISM of Elliptical and Spiral Galaxies
- Vortical Motions Driven by Supernova Explosions
- The Intermittent Dissipation of Turbulence: is it Observed in the Interstellar Medium?
- Chemistry in Turbulent Flows
- Supersonic Turbulence in Giant Extragalactic HII Regions
- Turbulence in HII regions: New results
- Hypersonic Turbulence of H2O Masers
- Water Masers Tracing Alfvenic Turbulence and Magnetic Fields in W51 M and W49 N
- Turbulence in the Ursa Major cirrus cloud
- The Collisions of HVCs with a Magnetized Gaseous Disk
- The Initial Stellar Mass Function as a Statistical Sample of Turbulent Cloud Structure
- The Structure of Molecular Clouds: are they Fractal?
- Diagnosing Properties of Turbulent Flows from Spectral Line Observations of the Molecular Interstellar Medium
- Centroid Velocity Increments as a Probe of the Turbulent Velocity Field in Interstellar Molecular Clouds
- High-Resolution C18O Mapping Observations of Heiles' Cloud 2 – Statistical Properties of the Line Width –
- Observations of Magnetic Fields in Dense Interstellar Clouds: Implications for MHD Turbulence and Cloud Evolution
- The Density PDFs of Supersonic Random Flows
- Turbulence as an Organizing Agent in the ISM
- Turbulence and Magnetic Reconnection in the Interstellar Medium
- The Evolution of Self-Gravitating, Magnetized, Turbulent Clouds: Numerical Experiments
- Super–Alfvénic Turbulent Fragmentation in Molecular Clouds
- Decay Timescales of MHD Turbulence in Molecular Clouds
- Numerical Magnetohydrodynamic Studies of Turbulence and Star Formation
- Direct Numerical Simulations of Compressible Magnetohydrodynamical Turbulence
- Fragmentation in Molecular Clouds: The Formation of a Stellar Cluster
- Accretion Disk Turbulence
- List of participants
The Structure of Molecular Clouds: are they Fractal?
Published online by Cambridge University Press: 04 August 2010
- Frontmatter
- Contents
- Preface
- Turbulence in the Interstellar Medium: a Retrospective Review
- Mechanism of Formation of Atmospheric Turbulence Relevant for Optical Astronomy
- Properties of Atomic Gas in Spiral Galaxies
- Turbulence in the Ionized Gas in Spiral Galaxies
- Probing Interstellar Turbulence in the Warm Ionized Medium using Emission Lines
- The Spectrum & Galactic Distribution of MicroTurbulence in Diffuse Ionized Gas
- Small Scale Structure and Turbulence in the Interstellar Medium
- What is the Reynolds Number of the Reynolds' Layer?
- Photoionized Gas in the Galactic Halo
- Turbulent Heating of the Diffuse Ionized Gas
- Cosmic Rays in Interstellar Turbulence
- Turbulence in Line-Driven Stellar Winds
- An Introduction to Compressible MHD Turbulence
- Turbulence in Atomic Hydrogen
- Supershells in Spiral Galaxies
- The Size Distribution of Superbubbles in the Interstellar Medium
- Large-Scale Motions in the ISM of Elliptical and Spiral Galaxies
- Vortical Motions Driven by Supernova Explosions
- The Intermittent Dissipation of Turbulence: is it Observed in the Interstellar Medium?
- Chemistry in Turbulent Flows
- Supersonic Turbulence in Giant Extragalactic HII Regions
- Turbulence in HII regions: New results
- Hypersonic Turbulence of H2O Masers
- Water Masers Tracing Alfvenic Turbulence and Magnetic Fields in W51 M and W49 N
- Turbulence in the Ursa Major cirrus cloud
- The Collisions of HVCs with a Magnetized Gaseous Disk
- The Initial Stellar Mass Function as a Statistical Sample of Turbulent Cloud Structure
- The Structure of Molecular Clouds: are they Fractal?
- Diagnosing Properties of Turbulent Flows from Spectral Line Observations of the Molecular Interstellar Medium
- Centroid Velocity Increments as a Probe of the Turbulent Velocity Field in Interstellar Molecular Clouds
- High-Resolution C18O Mapping Observations of Heiles' Cloud 2 – Statistical Properties of the Line Width –
- Observations of Magnetic Fields in Dense Interstellar Clouds: Implications for MHD Turbulence and Cloud Evolution
- The Density PDFs of Supersonic Random Flows
- Turbulence as an Organizing Agent in the ISM
- Turbulence and Magnetic Reconnection in the Interstellar Medium
- The Evolution of Self-Gravitating, Magnetized, Turbulent Clouds: Numerical Experiments
- Super–Alfvénic Turbulent Fragmentation in Molecular Clouds
- Decay Timescales of MHD Turbulence in Molecular Clouds
- Numerical Magnetohydrodynamic Studies of Turbulence and Star Formation
- Direct Numerical Simulations of Compressible Magnetohydrodynamical Turbulence
- Fragmentation in Molecular Clouds: The Formation of a Stellar Cluster
- Accretion Disk Turbulence
- List of participants
Summary
Molecular clouds are observed to be highly structured and fragmented but also follow simple power law relationships between, for example, their size and linewidth as first described by Larson. This self-similarity has led to a fractal description of cloud structure, but in recent years there have been a number of observations that indicate the existence of characteristic scales in molecular cloud cores and clusters of young stars. I present some observations of molecular clouds from large (1-10 pc) to small (0.1 pc) scales, and discuss whether a fractal description of cloud structure is universally appropriate.
Introduction
The density and velocity structure within a molecular cloud is a remnant of its formation environment and the starting point for the creation of stars. It determines how deeply radiation can propagate through the cloud, and is a critical parameter for understanding the evolution of the ISM. How is it best described?
Beginning with Larson (1981), correlations between cloud properties such as linewidth and size have been fit by power laws. Since a power law does not have a characteristic scale, the implication is that clouds are scale-free and self-similar. This has led to statements in the literature that clouds are best described as fractals (e.g. Falgarone, Phillips, & Walker 1991; Elmegreen 1997). On the other hand, other recent studies (Larson 1995; Simon 1997; Goodman et al. 1998; Blitz & Williams 1997) suggest that there are characteristic size and velocity scales in star-forming regions.
- Type
- Chapter
- Information
- Interstellar Turbulence , pp. 190 - 197Publisher: Cambridge University PressPrint publication year: 1999
- 6
- Cited by