A new solution to Einstein's equations hides a topological surprise

Gravitational instantons are solutions to Einstein's equations in imaginary time, relevant to quantum gravity and topology. A new two-parameter example has been identified from the Euclidean double Kerr-NUT family — only the third in an infinite sequence whose existence was proven abstractly years ago. Unlike every previously known Ricci-flat instanton, this one is not Hermitian, making it the first concrete example of a whole new geometrical class.