Late-time tails in the Kerr spacetime

Outside a black hole, perturbation fields die off in time as 1/ t n . For spherical holes n = 2ℓ + 3 where ℓ is the multipole index. In the nonspherical Kerr spacetime there is no coordinate-independent meaning of 'multipole', and a common sense viewpoint is to set ℓ to the lowest radiatiable index, although theoretical studies have led to very different claims. Numerical results, to date, have been controversial. Here we show that expansion for small Kerr spin parameter a leads to very definite numerical results confirming previous theoretical predictions.