After a hit, a black hole rings like a bell. But instead of sound, it emits gravitational waves whose frequency rapidly decays: these are called quasinormal modes. From such a 'ring,' you can infer the hole's mass, spin, and other properties.
The authors took a black hole with quantum corrections (an addition that shows up at very small scales) and placed it in a universe with a cosmological constant — the very thing that makes space expand or contract. Using two numerical methods, they computed how the ring's spectrum changes. It turned out that the extra quantum parameter noticeably shifts the frequencies but doesn't make the system unstable. All perturbations decay, turning into towers of quasinormal oscillations.
Interestingly, the effect of quantum corrections is stronger for small black holes. For large ones, comparable to those born in mergers, the deviations are small, but they can still be searched for. It's like listening to a bell: if you slightly change the shape of the metal, the sound becomes different, but the bell doesn't crack. Same here — quantum corrections change the hole's 'voice' but don't break it.
Quasinormal modes of a black hole were first computed for a simple case back in the 1970s, but their direct observation remains a challenging task for gravitational-wave observatories even today.
In the movie 'Interstellar,' the visualization of the black hole Gargantua relied on real calculations, but quasinormal modes don't sound there: they could only be 'heard' with detectors.