molecular clouds

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Related to molecular clouds: molecular gas

molecular clouds

Cool dense regions of interstellar matter within which atoms tend to be combined into molecules. The clouds are composed principally of molecular hydrogen (H2 ), with between 300 and 2000 molecules/cm3. There is also a small admixture of cosmic dust comprising about 1% of the mass, with gas temperatures between 10 and 20 K. Hydrogen molecules do not usually emit at radio and infrared wavelengths, and molecular clouds were discovered only in the mid-1970s in surveys of radio emission from carbon monoxide, CO, which is 10 000 times less common than hydrogen molecules in the clouds. The 2.6-and 1.33-mm CO lines are still the prime means of mapping and investigating the clouds. A wide variety of molecules, in addition to H2 and CO, have been found in the clouds (see molecular-line radio astronomy); more than 80 types have been detected in the largest clouds, such as Sagittarius B2.

Several dense core regions, with about 105 hydrogen molecules/cm3 and mass about 102 to 103 solar masses, may be found within one molecular cloud. In giant molecular clouds, these dense cores contain infrared sources, H II regions, maser sources, and the peak CO temperatures, which suggest that these regions are sites of massive star formation. There are also smaller clouds, containing about 500 solar masses of molecular hydrogen, throughout which low-mass stars are forming and which may be relatively isolated, as in the Taurus–Auriga star-forming region.

References in periodicals archive ?
A project involving JPL and Caltech scientists, among others, to study the process by which stars form out of giant molecular clouds of gas within our galaxy.
Infrared space also provides information about much colder objects, such as smaller stars too dim to be detected by their visible light, extra solar planets and giant molecular clouds.
Objective: New stars form within large turbulent complexes harboring several thousands of solar masses of cold gas: the molecular clouds.
Chapters show how energetic particles first organized into atoms, then molecular clouds (the star factories), then protoplanetary disks and eventually the diverse residents of our planetary neighborhood including asteroids, Pluto and its plutino neighbors.
Hot molecular clouds around new-born stars are called "Hot Cores" and have temperature of -- 160 degrees Celsius, 100 degrees hotter than normal molecular clouds.
Other topics include magnetic fields in molecular clouds, critical reactions in contemporary nuclear astrophysics, adaptive optics for astronomy, observational evidence of active galactic nuclei feedback, and thermonuclear burst oscillations.
Stars begin their lives in dense clouds of cool hydrogen gas known as molecular clouds.
The chapters are grouped into nine major topics: molecular clouds, star formation, outflows, young stars and clusters, and circumstellar disks, among others.
In a more likely scenario, less dense giant molecular clouds may have enabled charged particles to enter Earth's atmosphere, leading to destruction of much of the planet's protective ozone layer.
Large lasers and Z-pinch generators in laboratories are recreating conditions relevant to astrophysical phenomena of the universe such as supernovae, black holes, molecular clouds like the Eagle Nebula, and the creation of new planets.
Objective: Stars like our Sun and planets like our Earth form in dense regions within interstellar molecular clouds, called pre-stellar cores (PSCs).
22 ( ANI ): A new paper describes the observation-based relationships of the structure and supersonic internal motions of molecular clouds where stars form.

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