molecular clouds

molecular clouds
NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration · Public domain · source
Name	Molecular cloud
Type	Interstellar cloud
Distance	Varied
Mass	10–10^6 M☉
Radius	1–100 pc
Composition	H2, CO, He, dust, complex molecules

molecular clouds Molecular clouds are dense, cold concentrations of interstellar gas and dust that serve as primary sites of star and planet formation. Found in the Milky Way and other galaxies such as Andromeda Galaxy, Triangulum Galaxy, and the Large Magellanic Cloud, they range from small Bok globules to giant molecular clouds associated with spiral arms like the Orion Arm. Observations by missions and facilities including James Clerk Maxwell Telescope, Atacama Large Millimeter/submillimeter Array, Spitzer Space Telescope, and Hubble Space Telescope have revealed complex structure, kinematics, and chemistry.

Overview

Molecular clouds appear in diverse galactic environments such as the Galactic Center, Perseus Arm, and dwarf galaxies surveyed by the Sloan Digital Sky Survey; catalogues compiled by teams at institutions like the Max Planck Institute for Astronomy and the Harvard–Smithsonian Center for Astrophysics classify clouds by mass and size. Giant molecular clouds (GMCs) such as those associated with the Orion Nebula or the Taurus Molecular Cloud contain stellar clusters and are linked to large-scale dynamics driven by spiral density waves studied alongside the Milky Way Project and simulations from groups at the Institute for Advanced Study. Smaller structures, Bok globules catalogued by observers like Bart Bok, are compact and often isolated, producing low-mass stars studied in surveys by the Two Micron All Sky Survey and follow-up at facilities like Keck Observatory.

Physical Properties

Densities, temperatures, and velocity dispersions in molecular clouds are measured across scales using instruments such as Very Large Array and Green Bank Telescope; typical cold cores reach 10–100 K and densities of 10^3–10^6 cm^-3. Mass spectra follow power laws identified in surveys from the James Clerk Maxwell Telescope Gould Belt Survey and analyses at the European Southern Observatory, with virial analyses referencing work from researchers at Princeton University and University of Cambridge. Internal turbulence and magnetic support are investigated through polarization studies with the Planck mission and Zeeman splitting observations associated with teams at the National Radio Astronomy Observatory; magnetic field strengths often compare to predictions from magnetohydrodynamic simulations produced by groups at the Max Planck Institute for Astrophysics.

Formation and Evolution

Cloud assembly is tied to large-scale processes like spiral arm shocks described in models by researchers at the Kavli Institute for Theoretical Physics and triggered compression from events such as supernova remnants studied in relation to remnants like Cassiopeia A and feedback from OB associations catalogued in the Hipparcos Catalogue. Convergence of atomic flows, thermal instability, and magnetorotational effects addressed in studies from Caltech and the University of Chicago lead to molecule-rich, gravitationally bound regions. Evolution proceeds through fragmentation, competitive accretion, and feedback from protostellar outflows observed in projects at the National Aeronautics and Space Administration and theoretical work at the Princeton Plasma Physics Laboratory; dispersal mechanisms include photoionization from massive stars seen in regions like the Carina Nebula and mechanical clearing by clusters such as those in NGC 3603.

Chemistry and Molecular Content

Molecular clouds host chemistry ranging from simple diatomic species to complex organic molecules detected by instruments on the Rosetta mission and in surveys from the IRAM 30m Telescope and Nobeyama Radio Observatory. Carbon monoxide (CO) isotopologues are principal tracers used in mapping campaigns by the CfA Millimeter-Wave Group and the FUGIN survey, while abundant species like H2 (inferred indirectly), NH3, HCN, and CS are studied in targeted observations at the Effelsberg Radio Telescope and the Submillimeter Array. Complex organic molecules such as methanol and formamide identified in hot cores near regions like Sgr B2 inform astrochemical networks developed by research teams at the Leiden Observatory and NASA Jet Propulsion Laboratory.

Star Formation within Molecular Clouds

Star formation occurs in dense cores and clumps inside molecular clouds, with initial mass functions characterized in clusters like the Pleiades and embedded regions such as Orion Nebula Cluster; surveys by the Herschel Space Observatory and the Spitzer Space Telescope quantify protostellar lifetimes and accretion rates. Massive star formation linked to ultra-compact H II regions catalogued by the RMS survey and triggered modes near expanding bubbles identified in the GLIMPSE survey illustrate feedback-regulated modes analyzed by teams at Cambridge University and Yale University. Binary and multiple star outcomes studied in clusters like NGC 1333 inform population synthesis models developed at the University of California, Berkeley.

Observational Techniques and Surveys

Mapping and spectroscopy exploit rotational transitions observable with facilities such as ALMA, NOEMA, and the Submillimeter Array; surveys like the Galactic Ring Survey, the BU-FCRAO Galactic Ring Survey, and the COHRS project have produced large-scale CO maps. Infrared extinction and emission techniques using data from the WISE mission and the Two Micron All Sky Survey reveal embedded structure, while polarization surveys by the Planck mission and follow-up with the SOFIA observatory probe magnetic geometry. High-resolution studies combining VLBI from the European VLBI Network with maser observations trace kinematics in star-forming cores and calibrate distances via parallax measurements coordinated by groups at the Bar and Spiral Structure Legacy Survey.

Category:Interstellar medium