The curious black blob in the center of the nebula is a "Bok globule" -- a cloud of cold gas, molecules and cosmic dust. Astronomers believe Bok globules like the one in NGC 1999 may be a stellar nursery. "This globule probably has the mass to form one or two stars," said Keith Noll, an astronomer at the Space Telescope Science Institute in Maryland.

The globule, centered in front of NGC 1999, appears dark because of its extremely high density. "In the same way that a terrestrial cloud blocks out the view of anything behind it, Bok globules appear dark because they have enough dust in them to block out the light from any objects behind them," said C. Robert ODell, space physics and astronomy professor at Rice University.

NGC 1999 lies 1,500 light-years from Earth. It was first discovered some two centuries ago by Sir William Herschel and his sister Caroline. The image was collected just weeks after NASA astronauts repaired the Hubble in December 1999.