Mass-Angular-Momentum Inequality for Black Ring Spacetimes

The inequality m3≥27π/4|J2||J1-J2| relating total mass and angular momenta is established for (possibly dynamical) spacetimes admitting black holes of ring (S1×S2) topology. This inequality is shown to be sharp in the sense that it is saturated precisely for the extreme Pomeransky-Sen'kov black ring solutions. The physical significance of this inequality and its relation to new evidence of black ring instability, as well as the standard picture of gravitational collapse, are discussed.