While often depicted as perfect spheres, spinning black holes’ event horizons can flatten slightly at the poles due to centrifugal forces. This distortion affects nearby orbiting matter and light paths.
It matters because horizon shape influences accretion disk physics and gravitational lensing.
It also impacts simulations of mergers and waveforms of gravitational waves.
Spinning black holes can become slightly oblate instead of perfectly round.
[ESA, esa.int]