Vera, Mistress of Dark Matter

(with apologies to "Elvira, Mistress of the Dark")

 

Yesternight a distant star

Failed to flicker from afar

It flickered not again tonight

I’m thinking, maybe things aren’t right.  (rkw)

 

     Yes, well, black holes are like that—absorbing stars and leaving only gravity behind. Dark matter is their direct descendant. It’s all around us. It fills most of the space in space. We know almost nothing about it. That’s the bad news.

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     We like to believe that planets, stars, and galaxies dominate our universe. It is logical for us to accept this. It is also, alas, not true. Everything we can see, and all that is too tiny to see, makes up only 0.5 percent of all matter. The rest is dark matter (and dark energy). You can’t see it. You can’t even feel it. It’s difficult to describe it. It’s almost impossible to even imagine it.

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     Yet Vera Rubin did. She even measured dark matter to prove it was there. So if you can’t see it, how did she do it? She measured its gravity—something else you can’t see. Everything that has mass has gravity. And the pull of gravity is directly proportional to mass. Vera measured the rotation of stars around the centers of spiral galaxies and found that their speed is much faster than their masses should allow, so an unknown and invisible mass, with its gravitational force, is spinning them in orbit. This is dark matter.

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     The vastness of space is almost entirely unseeable stuff. This is very irritating. We dangle on the remote end of a distant limb of the small spiral galaxy we call the Milky Way. This sweeping arm is held in check by matter that, as far as we know, has mass without substance—no particles, no interaction with normal matter, no reaction to anything, unseen because it doesn’t emit light.

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     So if this makes up most of the universe, then most of the universe is just forever missing from view. And we know nothing about it. This ignorance is embarrassing. We should be able to understand what we’re measuring.

“In a spiral galaxy,” Vera told us, “the ratio of dark-to-light matter is about a factor of ten.” Then she said, “That’s probably a good number for the ratio of our ignorance-to-knowledge. We’re out of kindergarten, but only in about third grade.”

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     That’s the good news.

 

Ron Wetherington