Two different “chirps“ of gravitational waves produced by black holes

The best-fit models of LIGO’s gravitational-wave signals are converted into sounds. The first sound is from modeled gravitational waves detected by LIGO on Dec. 26, 2015, when two black holes merged. This is then compared to the first-ever gravitational waves detected by LIGO on Sept. 14, 2015, when two higher-mass black holes merged. This sequence is repeated. The pitch of both signals is then increased, allowing them to be heard more easily, and this sequence is also repeated.