The “chirp” signal sweeps smoothly across specific frequency range: usually 125 kHz, 250 kHz or 500 kHz wide. How long the sweep takes to complete is determined by the “spreading factor” (SF).

The two events were a bit different, so it's not surprising that their gravitational-wave signals differ as well. For example, the Dec. 25 sonic signal is quite a bit longer and more drawn-out.

The discovery of gravitational waves in 2015 – already postulated by Einstein one hundred years ago – led to the 2017 Nobel Prize in Physics and initiated the dawn of gravitational-wave astronomy.

They are mysterious, exciting and inescapable – black holes are some of the most exotic objects in the Universe. With gravitational-wave detectors, it is possible to detect the chirp sound that ...