So here’s the gist: As a pair of black holes orbit one another (the “Inspiral” part), some of the energy is lost as gravitational waves. (Gravitational waves - ripples in spacetime; akin to concentric rings a raindrop makes in a puddle, but trippier). As they approach one another, their orbital speed increases (think of a figure skater spinning faster as his/her arms are brought inward). The frequency of the gravitational waves increase. Finally - when the two black holes collide - BOOM. A spike in the frequency of gravitational waves - an elevation in pitch - that can be detected by instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory). LIGO can catch these ultra low frequency gravitational waves, but our ears cannot. But it’s not enough to build a detector to expand upon humans’ senses. Scientists want to “hear” the gravitational waves for themselves.
As I said, these frequencies are very low. In fact the more massive the black holes, the slower the orbit, the lower the frequency of gravitational waves, and the harder to detect. Dr. Bartos and his team are attempting to making the necessary alterations to gravitational wave data to make it more audible to the human ear, as well as determining what size of orbiting black holes generate frequencies within this range.
I’m looking forward to Inspiral’s first big hit. For now, I encourage you to play Black Hole Hunter to see if you can hear the moment two black holes collide. I couldn’t get past level 3.