Massive string states as extreme black holes

We consider the Schwarz-Sen spectrum of elementary electrically charged massive NR = 12 states of the four-dimensional heterotic string and show the maximum spin 1 supermultiplets to correspond to extreme black hole solutions. The NL = 1 states and NL > 1 states (with vanishing left-moving internal momentum) admit a single scalar-Maxwell description with parameters a = √3 or a = 1, respectively. The corresponding solitonic magnetically charged spectrum conjectured by Schwarz and Sen on the basis of S-duality is also described by extreme black holes.