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Monday, 6 March, 2000, 15:27 GMT
A silhouette in space
A "Bok' globule" blocks light from a distant star
By BBC News Online science editor Dr David Whitehouse

The Hubble Space Telescope (HST) snapped this picture of NGC 1999, a gas cloud in the constellation of Orion. It was taken just a few weeks after astronauts repaired HST in December last year.

NGC 1999 is an example of a reflection nebula which shines only because the light from an embedded star illuminates it.

NGC 1999 lies close to the famous Orion Nebula, about 1,500 light-years from Earth and a region where new stars are being formed. It is illuminated by a bright, recently-formed star, visible in the Hubble photo just to the left of centre.

Astronomers catalogue this star as V380 Orionis, and its white colour is due to its high surface temperature of about 10,000 deg C, nearly twice that of our own Sun. Its mass is estimated to be 3.5 times that of the Sun. The star is so young that it is still surrounded by a cloud of material left over from its formation - the NGC 1999 reflection nebula.

Bok globules

The picture shows a remarkable jet-black cloud near its centre. This is an example of a so-called "Bok globule," named after the late University of Arizona astronomer Bart Bok.

It is a cold cloud of gas, molecules, and cosmic dust, so dense it blocks all of the light behind it. In the Hubble image, the globule is seen silhouetted against the reflection nebula illuminated by V380 Orionis.

Astronomers believe that new stars may be forming inside Bok globules, through the contraction of the dust and molecular gas under their own gravity.

NGC 1999 was discovered some two centuries ago by Sir William Herschel and his sister Caroline, and was catalogued later in the 19th century as object 1999 in the New General Catalogue.

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