Exploring the dark Universe: Dark matter

>>MORDECAI-MARK MAC LOW: My name is Mordecai-Mark Mac Low and my position is Curator of Astrophysics. Dark matter was first identified and even named by a character named Fritz Zwicky who worked at Caltech— famous not only for his excellent astronomy, but also for his scatalogical language. He would rarely say anything that could be quoted in polite company. Nevertheless, he made several extremely important discoveries, one of which was that if you look at galaxies in clusters, they orbit around each other. From the speed of the orbit, you can measure the mass of the cluster. So, that's what Zwicky did. So, he adds up the mass of all the galaxies in the cluster and compares it to the mass that he's derived from the velocities. And it's not even close. So, he says, "There must be some sort of dark material—dark not emitting light, like the stars are— that is making up all this missing mass. When this was first published, everybody said, "Okay we don't really understand galaxies in distant clusters anyway," and the result was largely ignored for 40 years. Vera Rubin and her collaborators in the 1970s found that even if you look at individual galaxies, they still move too fast. And that was even harder to explain and brought people's attention back to this old question of why do galaxies in clusters move so fast? What we know now about dark matter is that it isn't any sort of ordinary matter. It's not planets. It's not stars. It's not puppies. It's not black holes, even. It turns out to be something that doesn't absorb light, nor emit it. The other thing we know about dark matter is that it controls where ordinary matter piles up and forms galaxies, stars, planets, us. So we are here in the Milky Way galaxy because there's a huge halo of dark matter that has so much mass that it drew in the gas to form the galaxy in the first place. The speculation— very mathematically grounded speculation— among physicists is that the dark matter particle is the first representative of a whole new class of particles called supersymmetric particles. If the dark matter particle has the properties predicted, that will open up essentially a whole new field of physics that will help us to understand the properties of the stuff that we're made of, as well, and why our universe and everything in it behaves the way does. And that's dark matter. [MUSIC PLAYS]