Black holes are well, black, you can't see them with your naked eye. However, if you have two black holes orbitting each other, they release "gravitational waves". You also can't see these with your eyes but we've built detectors to find these gravitational waves. In the following blogpost, Enn and Palis will show you how to simulate a binary black hole and what the emitted waves look like. Then they will show you how given the data in the detectors what the properties of the black holes are and what these properties tell us about nature.