Gyromagnetic factor of rotating disks of electrically charged dust in   general relativity
  We calculated the dimensionless gyromagnetic ratio ("$g$-factor") of self-gravitating, uniformly rotating disks of dust with a constant specific charge $\epsilon$. These disk solutions to the Einstein-Maxwell equations depend on $\epsilon$ and a "relativity parameter" $\gamma$ ($0<\gamma\le 1$) up to a scaling parameter. Accordingly, the $g$-factor is a function $g=g(\gamma,\epsilon)$. The Newtonian limit is characterized by $\gamma \ll 1$, whereas $\gamma\to 1$ leads to a black-hole limit. The $g$-factor, for all $\epsilon$, approaches the values $g=1$ as $\gamma\to 0$ and $g=2$ as $\gamma\to 1$. 
Yu-Chun Pynn, Rodrigo Panosso Macedo, Martin Breithaupt, Stefan   Palenta, Reinhard Meinel
gr-qc hep-th