Detectable only by the effects of its gravitational pull, dark matter is an invisible material that scientists think makes up more than 80 percent of the mass in the universe. (See "Dark Matter Detected for First Time.")

Chakrabarti, of the University of California, Berkeley, devised a technique similar to that used 160 years ago to predict the existence of Neptune, which was given away by the wobbles its gravity induced in Uranus's orbit.

Based on gravitational perturbations of gases on the fringes of our Milky Way galaxy, Chakrabarti came to her conclusion that there's a heretofore unknown dwarf galaxy about 260,000 light-years away. (Related: "Huge Black Hole Found in Dwarf Galaxy.")

With an estimated mass equal to only one percent the