Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Molecular Cloud

  • William M. Irvine
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_1010-6


A molecular cloud is a concentration of interstellar gas and dust in which the gas phase is primarily molecular, with the dominant constituent being molecular hydrogen (H2). It is in molecular clouds that new stars and planetary systems are born. Because molecular hydrogen lacks pure rotational transitions, molecular clouds are normally traced by radio astronomers by observing the millimeter-wavelength transitions of the next most abundant constituent, carbon monoxide (CO). There are in addition more than 150 other molecular species that have been detected in molecular clouds, most of these species being organic (see Molecules in Space). Although molecular clouds occupy only a small fraction of the volume of the Milky Way and other galaxies, they contain a significant fraction of the total gas mass. The largest such clouds are called giant molecular clouds, or GMCs, and can contain more than a million times the mass of the Sun. For a comprehensive description of the Interstel...


Carbon Monoxide Molecular Species Star Formation Significant Fraction Molecular Hydrogen 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
This is a preview of subscription content, log in to check access.

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Department of AstronomyUniversity of Massachusetts, Lederle Graduate Research Tower B 619EAmherstUSA