“…The analysis of the stability of black hole outer regions, having passed decades ago the test of modal linear stability, has had, after a long period of little activity, a remarkable progress in the last few years. An incomplete list of recent advances related to the stability of the Schwarschild and Kerr black holes follow: (i) for Λ ≥ 0 Schwarzschild black holes the nonmodal linear stability was established in [24,25]; (ii) in the Λ = 0 case, the decay in time of generic linear perturbations of the Schwarzschild black hole, leaving a "slowly" rotating Kerr black hole was proved in [17]; (iii) the conditional stability of the Λ < 0 Schwarzschild black hole, and the breaking of the even/odd symmetry mediated by the Chandrasekhar operators (93) and (94) was studied in [6]; (iv) the non-linear stability of the Schwarzschild de Sitter black hole was proved in [32]; (v) a preprint is now available with a proof of the non-linear stability of the Λ = 0 Schwarzschild black hole [18]; (vi) pointwise decay estimates for solutions of the linearized Einstein's equations on the outer region of a Kerr black hole were obtained in [1]; (vii) the role of hidden symmetries (see the review [28]) in type D spacetimes, and the reconstruction of (gravitational, Maxwell and spinor) perturbation fields from "Debye potentials" (first introduced in [37,47]), was studied in depth and made clear in the series of papers [2][3][4][5].…”