Spinning Black Binaries in de Sitter Space

We numerically construct stationary, rotating black binaries in general relativity with a positive cosmological constant. We consider identical black holes with either aligned or anti-aligned spins. Both cases have less entropy than the corresponding single Kerr-Schwarzschild-de Sitter black hole with the same total angular momentum and cosmological horizon entropy. Our solutions establish continuous nonuniqueness in general relativity without matter. They also provide initial data for the spinning binary merger problem (when orbital angular momentum is added).