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Understanding the evolution of our galaxy

My name is Sukanya Chakrabarti. I'm a UC President's Fellow in the astronomy department at UC Berkeley.

My research focuses primarily on performing computer simulations to understand the dynamical evolution of galaxies. We analyzed perturbations, or disturbances, in the gas disk of our own galaxy, the Milky Way. 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. 

So, I did a set of computer simulations off a Milky Way light galaxy that's tightly interacting with dark sub halos or dim dwarf galaxies and I varied the masses, the distance of closest approach and the orbits of these satellites to see what produced the best fit to the observed disturbances.  Now, we don't know a lot about dark matter, but we do know that it is massive. So, it can exert a gravitational effect on other bodies and by analyzing the tidal gravitational effect that it produces on other bodies, we can begin to characterize these dark objects.

This is, for instance, similar to say, dropping pebbles in a pond and looking at the disturbances the pebbles cause in the pond. If you understood the physics well enough, even if you never saw the pebble fall in and all you could see were the resulting ripples or disturbances in the water, from the analysis of those disturbances, you could characterize how massive the pebble had to be to produce the observed disturbances. 

This type of work is in essence very similar to the discovery of Neptune by analysis of the disturbances in the orbits of Uranus in the 1840s by Le Verrier. This is the first example of the discovery of an essentially dark object by its gravitational effect on another body.