Molecular Clouds and Star Formation in the Milky Way
Summary
Molecular clouds constitute the principal reservoirs of cold, dense gas in the Milky Way, with masses ranging from tens to millions of solar masses. Predominantly composed of molecular hydrogen, they are traced by emission from carbon monoxide isotopologues (12CO, 13CO, C18O), which reveal complex internal structures shaped by turbulence, magnetic fields and self-gravity. Observations at multiple wavelengths expose a hierarchy of filaments and clumps, within which local condensations collapse to form protostars. Filamentary networks appear to channel material towards dense hubs, establishing the initial conditions for star formation across scales. The efficiency of this process depends on the interplay between turbulent support, gravitational instability and feedback from young stellar objects, such as winds, outflows and radiation pressure. Spiral-arm dynamics and large-scale shocks further influence cloud formation and life cycles, organising molecular gas into giant molecular cloud complexes along the Galaxy’s spiral pattern. Advances in radio and submillimetre instrumentation, combined with astrometric surveys, have transformed our three-dimensional view of the interstellar medium, linking cloud properties to Galactic structure. These developments have far-reaching implications for understanding star cluster formation, the initial mass function and the chemical evolution of our Galaxy.
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Molecular Clouds and Star Formation in the Milky Way publication trend
The graph below shows the total number of articles in molecular clouds and star formation in the milky way across all publications each year (not limited to Nature Index journals).
Technical terms
Molecular cloud: A cold, dense aggregate of interstellar gas and dust, primarily hydrogen molecules, serving as the birthplaces of stars and star clusters.
Giant molecular cloud: A massive complex of molecular clouds with masses exceeding 10^5 solar masses, spanning tens of parsecs and hosting sites of clustered star formation.
CO isotopologue: A variant of carbon monoxide molecule (for example 12CO, 13CO, C18O) used as a tracer of molecular hydrogen owing to its rotational line emission.
Filament: An elongated, thread-like structure of dense molecular gas, often observed in networks, which can fragment to form prestellar cores along its length.
Protostellar outflow: A bipolar ejection of gas from a young forming star, driven by accretion processes and magnetic fields, which injects momentum into the surrounding cloud.
References
- On the Flux–Intensity Relation of Molecular Clouds. The Astrophysical Journal Letters (2024).
- Distributions and Physical Properties of Molecular Clouds in the Third Galactic Quadrant: l = [219.°75, 229.°75] and b = [−5.°25, 5.°25]. The Astrophysical Journal Supplement Series (2023).
- The Multilayer Nature of Molecular Gas toward the Cygnus Region. The Astronomical Journal (2024).
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