Jeremiah Paul Ostriker is a distinguished astrophysicist at Princeton University. From 1971 to 1995, Ostriker was a professor at Princeton, and served as Provost there from 1995 to 2001. From 2001 to 2003, he was appointed as Plumian Professorship of Astronomy and Experimental Philosophy at Cambridge. He has since returned to Princeton.
Ostriker has been very influential in advancing the theory that most of the mass in the universe is not visible at all, but consists of dark matter. His research has also focused on the interstellar medium.
Source: Wikipedia http://en.wikipedia.org/wiki/Jeremiah_P._Ostriker