Narrator:       This is Science Today. Researchers at the University of California, Berkeley are using computer simulations to understand the evolution of galaxies. Sukanya Chakrabarti is a University of California President's Fellow in the astronomy department.

Chakrabarti: We analyzed disturbances in the gas disk of our galaxy, the Milky Way. It's very unlikely that this is the response of an isolated galaxy. So, our hypothesis was that these disturbances that we see in the gas disk of our galaxy on the outskirts of the gas disk of our galaxy are due to an external perturber, such as a dark satellite of the Milky Way.

Narrator:       In a computer simulation, Chakrabarti was able to determine the mass of the satellite and how close it would have to get to produce the observed disturbances.

Chakrabarti: This is, for instance, similar to dropping pebbles in a pond and looking at the disturbances the pebbles cause in the pond.

Narrator:       For Science Today, I'm Larissa Branin.