Astronomers suggested long ago that a smaller pair of passerby galaxies, the Large and Small Magellanic Clouds, were bending the Milky Way through a tidal pull, much like the moon raises tides on Earth. But those two small galaxies do not weigh enough to have that kind of pull, so astronomers ruled them out as a reason.

The Milky Way's warping is a well-known phenomenon, says astronomer Robert Lupton of Princeton University. He is part of the Sloan Digital Sky Survey effort, an astronomical atlas of galaxies. His team found another lump in our galaxy, the remains of another dwarf galaxy. But those lumpy remains are much farther out. --- Contributing: Jess Zielinski