The biggest ingredient to the Milky Way is just stars, about 200 billion solar masses of them, which probably means something like a trillion stars or so, considering that most stars have less mass than the sun. About 5-10 percent of the total mass of the Milky Way is in gas and dust spread out either in individual clouds, or in a thin 'interstellar medium'. What you see with your eye at night is the faint glow of billions of distant stars added together. There is also a 'dark matter' component that might include something like 100 billion solar masses of 'something'. Astronomers don't know what it is, it might be black holes, dwarf stars or something else entirely.
Copyright 1997 Dr. Sten Odenwald
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