  We study special points in the moduli space of vacua at which supersymmetric
electric solutions of the heterotic string theory become massless. We
concentrate on configurations for which supersymmetric non-renormalization
theorem is valid. Those are ten-dimensional supersymmetric string waves and
generalized fundamental strings with SO(8) holonomy group. From these we find
the four dimensional spherically symmetric configurations which saturate the
BPS bound, in particular near the points of the vanishing ADM mass. The
non-trivial massless supersymmetric states in this class exist only in the
presence of non-Abelian vector fields.We also find a new class of
supersymmetric massive solutions, closely related to the massless ones. A
distinctive property of all these objects, either massless or massive, is the
existence of gravitational repulsion. They reflect all particles with
nonvanishing mass and/or angular momentum, and therefore they can be called
white holes (repulsons), in contrast to black holes which tend to absorb
particles of all kinds. If such objects can exist, we will have the first
realization of the universal gravitational force which repels all particles
with the strength proportional to their mass and therefore can be associated
with antigravity.
