Chaos in the orbits of merging black holes is much more common than we thought, and it leaves a distinct flat signature in gravitational waves.
April 24, 2026
Original Paper
Astrophysically Realistic Secondary Spins Trigger Chaos in Schwarzschild Spacetime and Discernible Gravitational Wave Signatures
arXiv · 2604.20533
The Takeaway
Realistic secondary spins in black hole inspirals trigger chaotic orbital paths that produce a discernible flat frequency spectrum. Most models assume that black hole mergers follow a predictable, smooth spiral unless the spin is extremely high. This new study shows that even normal spins are enough to throw the system into chaos, changing the signal we receive on Earth. This chaos isn't just noise, it's a specific pattern that carries information about the black hole history. Recognizing these chaotic signatures will allow astronomers to more accurately measure the properties of black holes across the universe.
From the abstract
Chaos in extreme-mass-ratio inspirals is often thought to require unrealistically large secondary spins, making its astrophysical relevance uncertain. However, we find that chaos persists across the astrophysically realistic spin range for a spinning secondary orbiting a Schwarzschild black hole. This nonintegrable dynamics leaves clear signatures in the emitted gravitational waves. Nearby regular and chaotic trajectories can remain similar in the time domain and retain broadly aligned dominant