Yesterday was the first day of the winter meeting of the American Astronomical Society. True to tradition, several news stories about astronomy research were released. The three main stories were: The North Star's closest companion was imaged by the Hubble Space Telescope, yet more evidence that black holes exist, and explaining the "warping" in the disk of the Milky Way.
Personally, I find the last of these the most interesting (though this is my opinion only). The Milky Way galaxy is flat, like a frisbee, or a vinyl record (or a CD for those of you younger than me). But the Milky Way is not completely flat -- one side of the disk (record) is pulled up, and the other pulled down. It's not unlike a vinyl record left too close to the fireplace or out in the sun.
The cause of this warp was uncertain. The most likely cause of the warp is gravity, but the known galaxies closest to the Milky Way, the Large and Small Magellenic Clouds, are not massive enough to cause the warp. In other words, their gravitational pull is not strong enough to bend the Milky Way.
Astronomers from the University of California, Berkeley used computer models to figure out how the gravity of the Magellenic Clouds can be enhanced by the Milky Way's own dark matter halo. This invisible stuff surrounding the Milky Way may actually be 90% of the mass of the galaxy! There is plenty of matter there to be able to bend the Milky Way's disk. And, not only does the dark matter cause the Milky Way's disk to bend, but it actually starts the disk "flapping", as the disk flaps up and down.