Kerr black holes
Kerr black holes are, in theory, the space-time region outside of a black hole. Kerr black holes were first proposed in 1963, and for nearly 60 were not mathematically proven to have stability. In other words, an inevitably perturbance to a Kerr black hole.
Relying on proof by contradiction, on May 30 three researchers posted online a 912-page paper a mathematical analysis to show "that slowly rotating Kerr black holes are indeed stable."