Bok globules


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Bok globules

(bok) Small dark cool (10 K) clouds of gas and dust seen as near-circular objects against a background of stars or of an H II region; they are named after the American astronomer Bart J. Bok. They are believed to represent a late phase in the contraction of some dense cores when the material has become sufficiently dense to be opaque at optical wavelengths. The main sites for star formation are now known to be giant molecular clouds, but Bok globules give rise to some of the Galaxy's lower-mass stars. Most globules have diameters between 0.2 and 0.6 parsecs, and absorb between one and five magnitudes of light. Their mass varies from 20 to 200 solar masses. IRAS and other infrared telescopes have located protostars within some Bok globules; bipolar outflows from these produce Herbig–Haro objects seen at the globule's edge.
References in periodicals archive ?
It cannot come from the Einstein's mass-energy equivalence, considering the low gas temperature within the Bok globules.
The problem of correctly defining the source of the gravitational power heating the Bok globules remained unsolved in absence of a theory of the gravitational interaction able to specify the rate at which the gravitational waves hit the particles.
2] molecules of the Bok globules, quick calculations can be made recognising that Eq.
The observed Bok globules denounced an inner hot core.
4] metres within the observed Bok globules (R = 2 x [10.
The most important event in the life of Bok globules is the ignition of the nuclear reactions which takes place when the inner core attains a temperature of the order of [10.
Bok globules and small molecular clouds: Deep IRAS Photometry and CO Spectroscopy.
As a result," Hester explains, "the lifetimes of the EGGs subjected to photo-evaporation are fairly short as compared with most objects normally referred to as Bok globules.
The other difference," he says, "is that while Bok globules are seen throughout the volume of the nebula, these smaller globules are only seen along the very edge because they don't survive for long once uncovered.
Close examination of the newly completed Palomar Observatory Sky Survey revealed more than 17,000 Bok globules, as these objects came to be known.
It was Fred Hoyle's 1957 science fiction tale, The Black Cloud, that really catapulted Bok globules into the public's awareness.