Enormous nebulas condense to form enormous stars. Then the stars explode.
When gaseous nebulas condense to form a region's early, enormous stars, the stars, in turn, shape the gas. Blasting it with light, they shift and split the gas's shapes and structures, casting some of it far into space.
Then, they explode.
The star-forming region Simeis 188, pictured above, has yet to lose some of its massive stars, and color filtering makes its different types of nebulas visible. Hydrogen, its electrons stripped by the light of young stars, glows red in emission nebulas; dust, scattered by the same light, seems blue; and other dust, dark and murky, subsumes light in absorption nebulas. After the dust from the young star's explosion boils away, and the nebulas's gas is blown away -- a process that takes many millions of years -- an open stellar cluster remains.
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