 Horowitz investigates gravitational phenomena, such as black holes, in string theory.In the 1990s, he worked with, among others, Andrew Strominger and Joseph Polchinski showing that string theory provides a description of the quantum microstates of certain black holes (following earlier work of Strominger and Cumrun Vafa ).In 1985 Horowitz published an influential paper with Philip Candelas, Andrew Strominger and Edward Witten on the compactification of superstrings in Calabi-Yau spaces.