What is dark matter and why do astronomers think that it comprises most of the mass in our Galaxy?

or:What is dark matter and why do astronomers think that it comprises most of the mass in our Galaxy?or:Wikipedia said, \"Dark matter is a hypothetic

or:What is dark matter and why do astronomers think that it comprises most of the mass in our Galaxy?

or:Wikipedia said, \"Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe.\" So, since dark matter accounts for most of the matter in the universe, it'd not surprising that anyone will think that dark matter comprises most of the mass in our galaxy.

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