Exact Three Dimensional Black Holes in String Theory

A black hole solution to three dimensional general relativity with a negative cosmological constant has recently been found. We show that a slight modification of this solution yields an exact solution to string theory. This black hole is equivalent (under duality) to the previously discussed three dimensional black string solution. Since the black string is asymptotically flat and the black hole is asymptotically anti-de Sitter, this suggests that strings are not affected by a negative cosmological constant in three dimensions.