First-Ever Recording Of Black Hole Recoil Captured During Merger – And You Can Listen To It

Back in 2019, researchers observed a collision between two black holes of wildly different masses. New analysis has revealed that the collision produced a massive recoil, sending the newly formed black hole moving so fast that it is no longer bound by the gravity of the globular cluster where it was born.

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The event was named GW190412, and it involved a black hole eight times the mass of our Sun smacking into another black hole 30 times the mass of the Sun, 3.6 times heavier than the first. The collision took place 2.4 billion light-years away, and it sent the resulting black hole flying at about 50 kilometers (31 miles) per second.

What's special about this event is the fact that the masses were so wildly different that researchers were able to measure the “high-order modes” of the collision, which allowed the team to measure the recoil, the orbital angular momentum, and the separation of the two black holes in the couple of seconds before the merger.

“Black-hole mergers can be understood as a superposition of different signals, just like the music of an orchestra consistent with the combination of music played by many different instruments. However, this orchestra is special: audiences located in different positions around it will record different combinations of instruments, which allows them to understand where exactly they are around it,” lead author Professor Juan Calderon-Bustillo, from the Instituto Galegode Físicade Altas Enerxías, said in a statement.

The music analogy is especially apt because the asymmetry of the system actually produced two measurable harmonics that have frequencies that are a 1.5 factor apart: that's a perfect fifth! Translated to frequencies we could play and hear, if the main frequency of the waves was a C on a piano, the overtone would be the next higher G – a perfect fifth, and incidentally, the jump in the opening two notes of Elvis Presley singing Can't Help Falling In Love.

The chirp of the event has been recreated with computers in frequencies we can hear, although it's not as good as Elvis. In a less rock-and-roll way, researchers had developed a new method to work out the properties ahead of this discovery. Once they finally got observations with those high-order modes, they were able to finally deploy it and learn about this event in much more detail.

“This is one of the few phenomena in astrophysics where we’re not just detecting something—we’re reconstructing the full 3D motion of an object that’s billions of light-years away, using only ripples in spacetime. It’s a remarkable demonstration of what gravitational waves can do,” co-author Dr Koustav Chandra, a postdoctoral researcher at Penn State, added.

In the 10 years since the first detection of gravitational waves, the way we study and understand them has wildly changed – and many more changes are coming.

The study is published in the journal Nature Astronomy.