Massless String Theory Black Holes as Black Diholes and Quadruholes

Massless black holes can be understood as bound states of a (positive-mass) extreme $a=\sqrt{3}$ black hole and a singular object with opposite (i.e., negative) mass with vanishing Arnowitt-Deser-Misner (total) mass but nonvanishing gravitational field. Supersymmetric balance of forces is crucial for the existence of this kind of bound states and explains why the system does not move at the speed of light. We also explain how supersymmetry allows for negative mass as long as it is never isolated but in bound states of total non-negative mass.