Final spin of a coalescing black-hole binary: An effective-one-body approach

We update the analytical estimate of the final spin of a coalescing black-hole binary derived within the effective-one-body (EOB) approach. We consider unequal-mass nonspinning black-hole binaries. It is found that a more complete account of relevant physical effects (higher post-Newtonian accuracy, ringdown losses) allows the analytical EOB estimate to ``converge towards'' the recently obtained numerical results within 2%. This agreement illustrates the ability of the EOB approach to capture the essential physics of coalescing black-hole binaries. Our analytical approach allows one to estimate the final spin of the black hole formed by coalescing binaries in a mass range =m₁m₂/ (m₁+m₂) ^2<0. 16 which is not presently covered by numerical simulations.