# Black hole ringdown and quasinormal modes

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The first detection of gravitational waves came with an unexpected windfall: a clear signal from the merger of two black holes into a final, spinning black hole. General Relativity predicts that following merger, the final black hole relaxes by emitting radiation in a characteristic spectrum of decaying modes. I will discuss these quasinormal modes'' and what can be learned from them, as well as the black hole ringdown observed in GW150914. I will also explore the exotic side of ringdown, including the modes of nearly extremal black holes, and a tool for understanding the ringdown of black holes which differ from the standard Kerr solution.