Monica Valluri uses numerical calculations and simulations to probe observed galactic phenomena in order to understand the physical processes that produce them. Her current focus areas are dark objects whose presence we learn about via their gravitational effects on stars: supermassive black holes and dark matter halos. She has been working to develop sophisticated tools to use the motions stars close to the centers of galaxies to measure the masses of their supermassive black holes and to understand how these black holes affect the properties of their host galaxies. She has also been working on using the motions of millions of ancient stars in the Milky Way's halo to determine the properties of dark matter and compare the properties with those from large simulations of the universe.