EL RRUN RRUN: THE FUTURE IS DARK...DARK MATTER OF SPACE, THAT IS

By Elizabeth Wason
U of Michigan LSA Magazine

EVERY YEAR, MARIO Mateo brings a trash can lid to Chile and looks at the stars.

At least, the object looks like the round metal lid of a trash can. But it’s a bit stranger than that. The big metal disc – about the size of a snow sled – has been studded with a constellation of holes drilled through the surface.

Red, blue, maroon, and teal doodles use tangled lines to connect some of the holes, circle several, and label others with cryptic names and reference numbers. People at the airport might take one look at his gear and mistake Mateo for something other than a tenured professor – given his old T-shirt, beat-up sneakers, bushy white mustache that matches the tufts of hair orbiting his head, and unique luggage – but one of those leaky metal lids hangs on the wall of his office in LSA’s Department of Astronomy.

The “plug plates,” Mateo calls them, have drastically increased the number of stars he can view and measure through a telescope: an unprecedented 256 celestial objects at a time. He and his grad students precisely map the pinpoints of light they want to observe in the Chilean sky, then drill holes at those points on the disc. Braids of fiber optic cables pierce the back of the plate, where Mateo plugs each of the holes with its own wire by hand.

With the help of a telescope, the fiber optics collect light from each target star glinting through the atmosphere. Over repeated observations, Mateo learns things about the stars he sees – their chemistry, temperature, size, and motion. He gets a sense of how each star moves through space, and how quickly.

After tracking thousands of stars over the years, Mateo has seen for himself what some scientists have puzzled over for a while: That something weird is going on. Stars at the outer edge of small galaxies orbit the galactic center much faster than they should.

Galaxies, too, orbit each other, and Mateo finds that distant galaxies also spin more quickly than expected around our own galaxy, the Milky Way. Imagine spinning a yo-yo around your head so fast that the toy snaps off its string and flings away. Peripheral stars move so fast that they actually should detach from their home galaxy like wild projectiles.

But they don’t. As early as the 1930s, astronomers came to assume that some mysterious thing must grip celestial objects in their outer orbits, keeping stars from busting loose. They gave the hypothetical thing a name: dark matter.