● This molecular cloud is one of the coldest places and isolated from the Universe.

This Molecular Cloud is known as Barnard 68 Nebula in the constellation Ophiuchus, is located 500 light years from Earth, is composed of molecular gas and dust absorbing the light of the stars in the background. This molecular cloud is one of the coldest places and isolated from the Universe.

Where did All the Stars go?

What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars.

American astronomer Edward Emerson Barnard added this nebula to his catalog of dark nebulae in 1919. He published his catalog in 1927, at which stage it included some 350 objects. Because of its opacity, its interior is extremely cold, its temperature being about 16 K (−257 °C). Its mass is about twice that of the Sun and it measures about half a light-year across.

The dingy surroundings help make the interiors of molecular clouds one of the coldest places in the universe isolated. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured here above.

Despite being opaque at visible-light wavelengths, use of the Very Large Telescope at Cerro Paranal has revealed the presence of about 3,700 blocked background Milky Way stars, some 1,000 of which are visible at infrared wavelengths. Careful measurements of the degree of obscuration resulted in a finely sampled and accurate mapping of the dust distribution inside the cloud.

Observations obtained with Herschel Space Observatory were able to constrain the distribution of the dust component and its temperature even more. Having a dark cloud in the solar neighborhood greatly facilitates observation and measurement. If not disrupted by external forces, the stability of dust clouds is a fine balance between outward pressure caused by the heat or pressure of the cloud's contents, and inward gravitational forces generated by the same particles.

This causes the cloud to wobble or oscillate in a manner not unlike that of a large soap bubble or a water-filled balloon which is jiggled. In order for the cloud to become a star, gravity must gain the upper hand long enough to cause the collapse of the cloud and reach a temperature and density where fusion can be sustained. When this happens, the much smaller size of the star's envelope signals a new balance between greatly increased gravity and radiation pressure.

The cloud's mass is about twice that of the Sun, and it measures about half a light-year across. Barnard 68's well-defined edges and other features show that it is on the verge of gravitational collapse within the next 100,000 years or so, and is on its way to becoming a star.

Observation data.

Right ascension17h 22m 38.2s
Declination−23° 49′ 34″ 
Distance500 ly 

Constellation        Ophiuchus

Physical characteristics.

Radius0.25 ly 
DesignationsBarnard 68, LDN 57

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