探索频道 Cosmos 宇宙的边疆06
Among the many glowing clouds of interstellar gas is one called the Orion Nebula, only 1500 light years from Earth.
These three bright stars are seen by earthlings as the belt in the familiar constellation of Orion, the Hunter.
The nebula appears from Earth as a patch of light, the middle star in Orion's sword. But it is not a star, it is another thing entirely, a cloud that veils one of nature's secret places.
This is a stellar nursery, a place where stars are born. They condense by gravity from gas and dust until their temperatures become so high that they begin to shine. Such clouds mark the births of stars as others bear witness to their deaths.
And after stars condense in the hidden interiors of interstellar clouds, what happens to them? The Pleiades are a loose cluster of young stars only 50 million years old. These fledgling stars are just being let out into the galaxy. Still surrounded by wisps of nebulosity, the gas and dust from which they formed.
There are clouds that hang like inkblots between the stars. They are made of fine rocky dust, organic matter and ice. Inside, a few stars begin to turn on, nearby worlds of ice evaporate and form long comet-like tails driven back by the stellar winds.
Black clouds, light years across, drift between the stars. They are filled with organic molecules. The building blocks of life are everywhere. They are easily made. On how many worlds have such complex molecules assembled themselves into patterns we would call "alive"?
Most stars belong to systems of two or three or many suns, bound together by gravity. Each system is isolated from its neighbors by the light years. We are approaching a single ordinary yellow dwarf star surrounded by a system of nine planets, dozens ……
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