  In this letter we present the result of a spin-dependent groundstate-energy
calculation for fermionic boundstates in the spacetime around a rotating
blackhole. Using a slow rotation approximation and a minimax variational
approach we find boundstate energies of 0 to 5 percent of the fermions
flatspace restmass. The groundstate displays a spin-dependent splitting with an
energy difference of about 10 percent of the binding energy. For a dilute gas
of primordial mini blackholes with gravitationally bound electrons spin-flip
transitions could possibly give rise to observable signatures in the observed
soft X-ray spectrum for sources at cosmological distances.
