Turbulent Dynamics of Star Formation in Molecular Clouds

Molecular clouds are vast reservoirs of cold gas in which stars form through a complex interplay of supersonic turbulence, self-gravity, magnetic fields and stellar feedback. Turbulent motions within these clouds generate a network of shocks and filaments that concentrate gas into dense cores. At low densities, turbulence maintains a roughly log-normal distribution of gas, whereas gravity at higher densities drives a power-law tail in the density probability distribution. The balance between compressive and solenoidal turbulent modes, the virial parameter of gas clumps and the efficiency of energy dissipation all set the pace of collapse and regulate the star formation efficiency per free-fall time. Observational programmes and numerical simulations now converge on a picture in which the cloud structure, from sub-parsec cores to tens of parsecs scales, is shaped by a cascade of turbulent energy and modified by radiation, jets and winds from young stars. Understanding this cascade is central to predicting star formation rates in our Galaxy and beyond, and underpins models of galaxy evolution and feedback in different environments.

Research from Nature Portfolio

Laboratory experiments have created boundary-free, supersonic plasma turbulence by colliding high-velocity laser-driven jets. The statistical properties of the density and velocity power spectra measured in these experiments agree with those inferred from observations of nearby molecular clouds, demonstrating a transition from Kolmogorov-like turbulence at low Mach number to Burgers-like turbulence at high Mach number. This result provides a terrestrial benchmark for numerical models of interstellar turbulence and confirms that compressible, high-Mach flows are a key driver of density fluctuations in star-forming regions.

Turbulent Dynamics of Star Formation in Molecular Clouds publication trend

The graph below shows the total number of articles in turbulent dynamics of star formation in molecular clouds across all publications each year (not limited to Nature Index journals).

Technical terms

Supersonic turbulence: Turbulent motion with velocities exceeding the local sound speed, characteristic of molecular clouds.

Mach number: Ratio of flow velocity to the local sound speed, indicating the degree of compressibility of the gas.

Density probability distribution function: Statistical distribution of gas densities within a cloud, often log-normal at low densities and showing a power-law tail at high densities.

Log-normal distribution: A distribution that is Gaussian in logarithmic space, arising from multiplicative random processes such as isothermal turbulence.

Power-law tail: High-density extension of a distribution following a ρ⁻ᵅ dependence, tracing regions undergoing gravitational collapse.

Virial parameter: Dimensionless ratio of kinetic to gravitational energy in a gas structure, indicating its stability against collapse.

Free-fall time: The characteristic timescale for a self-gravitating region to collapse in the absence of opposing forces.

References

1. Understanding star formation in molecular clouds. Astronomy & Astrophysics (2022).
2. Supersonic plasma turbulence in the laboratory. Nature Communications (2019).
3. Stellar feedback in the star formation–gas density relation: Comparison between simulations and observations. Astronomy & Astrophysics (2024).
4. What Sets the Star Formation Rate of Molecular Clouds? The Density Distribution as a Fingerprint of Compression and Expansion Rates. The Astrophysical Journal (2023).
5. The Anatomy of the Column Density Probability Distribution Function (N-PDF). The Astrophysical Journal (2018).