title: Gibbons–Hawking ansatz
text: # Gibbons–Hawking ansatz
  
  In mathematics, the Gibbons–Hawking ansatz is a method of constructing gravitational instantons introduced by Gary Gibbons and Stephen Hawking (1978, 1979). It gives examples of hyperkähler manifolds in dimension 4 that are invariant under a circle action.
  
  