Singly-spinning Myers-Perry black holes in d ≥ 6 spacetime dimensions are unstable for sufficiently large angular momentum. We numerically construct (in d = 6 and d = 7) two new stationary branches of lumpy (rippled) black hole solutions which bifurcate from the onset of this ultraspinning instability. We give evidence that one of these branches connects through a topology-changing merger to black ring solutions which we also construct numerically. The other branch approaches a solution with large curvature invariants. We are also able to compare the d = 7 ring solutions with results from finite-size corrections to the blackfold approach, finding excellent agreement.
JHEP07(2014)045Introduction. As expressed by John Wheeler's statement, "Black holes have no hair" [1], black holes (BHs) in four spacetime dimensions are remarkably simple objects. The topology, rigidity, uniqueness, and no-hair theorems ensure that Kerr BHs are the only stationary, vacuum, and asymptotically flat solutions to general relativity, and that they are uniquely specified by their mass M and angular momentum J [2]. Because Kerr BHs are also linear mode stable [3], any stellar object undergoing gravitational collapse towards a BH is expected to settle to the Kerr solution.Yet, the uniqueness of the Kerr BH may seem surprising given the close connection between gravity and fluids. According to the membrane paradigm [4], external observers will find that BH horizons behave like fluid membranes, endowed with a viscosity, conductivity, temperature, entropy, etc. Moreover, in certain circumstances there are formal mappings between solutions of general relativity and solutions of Navier-Stokes [5,6]. Fluids, however, lack strong uniqueness theorems and admit a rich structure of solutions. Indeed, rotational instabilities appear in fluid droplets and non-spherical solutions develop [7]. In particular, a ring configuration is preferred for high spin. Therefore, it may be natural to suspect that BHs behave like fluid droplets and have a greater diversity of solutions. This is the emerging picture in d > 4 spacetime dimensions.In higher dimensions, gravity becomes weaker as it spreads out over extra dimensions. Horizons are therefore more flexible, creating new gravitational phenomena with no fourdimensional counterparts. For example, in d ≥ 5 black strings exist and suffer from the Gregory-Laflamme instability [8]. This instability leads to a fractal-like array of spherical BHs and cosmic censorship violation [9,10]. This behaviour is similar to the RayleighPlateau instability, where a fluid jet breaks into an array of spherical droplets [11].In addition, there are black rings with horizon topology S 1 × S d−3 . These have been constructed in closed analytic form in d = 5 [12] and numerically in d = 6 [13]. (The list of other BH horizon topologies that are allowed in d > 4 were discussed in [14]). In any d ≥ 5, black rings can be found perturbatively using the blackfold approach if the S 1 radius is much larger than the S d−3 radius [15]...