Its Dark Out Here

As we discussed in Chapter 21, dark matter accounts for a great deal of the mass of a galaxy—up to 10 times more than the mass of the galaxy's visible matter— visible at any wavelength. The shocking conclusion that this observation leads us to is that 90 percent of the universe is dark matter—that is, matter that is invisible in the most profound sense, in that it neither produces nor reflects any electromagnetic radiation of any sort at any wavelength.

You can think of it as an embarrassing truth, or as an exciting unanswered question. The fact remains: We're not quite sure what 90 percent of the matter in the universe is made of.

Telescopes Mastery

Telescopes Mastery

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