Research Interests

My research is focused on theoretical astrophysics, in particular the dynamics of a wide range of astrophysical systems, including planetary rings, comets, planetary systems, galactic nuclei, galaxies, and clusters of galaxies. With Goldreich I studied many of the major dynamical processes in planetary rings and successfully predicted the existence of satellite-driven density waves in Saturn's rings and shepherd satellites that maintained the sharp-edged narrow rings of Uranus. I predicted the existence of the Kuiper belt outside Neptune as the source of Jupiter-family comets and showed that the production of new comets is predominantly determined by the influence of the Galactic tide on the Oort comet cloud. Much of my current research concerns the structure and properties of the dark matter that dominates the mass of galaxies. I am also a member of a collaboration that has used the Hubble Space Telescope to find strong evidence of massive black holes in the centers of many nearby galaxies.

Membership Type


Election Year


Primary Section

Section 12: Astronomy

Secondary Section

Section 13: Physics