Scientists talk a lot about dark matter. It sounds exciting, but what does it do for us?
"If the dark matter wasn't there, the galaxy should fly apart," Case Western Reserve University physics professor Glenn Starkman said.
Starkman chases dark matter for a living. Scientists started thinking about dark matter in the middle of the last century, when they looked at galaxies and saw something wasn't quite right.
"Really the galaxy should be spinning much, much more slowly in order for it to not fly apart," Starkman said.
The things inside galaxies have mass, so they cause gravity just like the Earth. Gravity keeps us on Earth, and gravity has to told the galaxies together as they spin. But that's the problem.
"It's like going to the amusement park and seeing one of those swing rides swinging around. And if you looked and saw that the chairs were held on by shoelaces, you wouldn't be very happy. You wouldn't get on," Starkman said. "What you'd like to see is nice strong chains. Well, the galaxy seems to be held together by shoelaces, and we're trying to find those nice strong chains."
Scientists think those "nice strong chains" come in the form of dark matter - stuff we can't see that causes the gravity that keeps the galaxies from flying apart. But it's a pretty tough job to see the unseeable.