  As a further test of the conjectured equivalence of string states and
extremal black holes, we compute the dipole moments of black holes with
arbitrary spin and superspin in D=4,N=4 supergravity coupled to 22 vector
multiplets and compare them with the dipole moments of states in the heterotic
string on $T^6$ or the Type IIA string on $K3 \times T^2$. Starting from a
purely bosonic black hole with Kerr angular momentum L, the superpartners are
generated by acting with fermion zero modes, thus filling out the complete
supermultiplet. $L$ is then identified with the superspin. On the heterotic
side, elementary states belong only to short to long multiplets, but Type IIA
elementary states can belong to intermediate multiplets as well. We find that
the black hole gyromagnetic ratios are in perfect agreement with the string
states not only for the BPS states belonging to short multiplets but also for
those belonging to intermediate multiplets. In fact, these intermediate
multiplets provide a stronger test of the black-hole/string-state equivalence
because the gyromagnetic ratios are not determined by supersymmetry alone, in
contrast to those of the short multiplets. We even find agreement between the
non-supersymmetric (but still extremal) black holes and non-BPS string states
belonging to long supermultiplets. In addition to magnetic dipole moments we
also find electric dipole moments even for purely electrically charged black
holes. The electric dipole moments of the corresponding string states have not
yet been calculated directly but are consistent with heterotic/Type IIA
duality.
