Three quantum-inspired cores leave opposite fingerprints on the ringing of black holes
Every black hole hides a question at its center. Einstein's theory predicts that whatever falls in is crushed into a singularity, a point of infinite density where the theory itself breaks down. Most physicists expect quantum gravity to replace that point with something finite. But the center lies hidden behind the horizon. How could we ever learn what is there?
Black holes harbor questions at their core, with quantum gravity seeking to replace singularities with finite structures. When a black hole merges, it emits gravitational waves in specific tones called quasinormal modes. These tones depend on the black hole's center, which can be altered by quantum gravity theories. Batic, Scardigli, and the author computed these tones for three black holes shaped by quantum gravity ideas.
They found that weaker gravity at short distances results in higher and longer-ringing black holes, while stronger gravity leads to lower and shorter-ringing ones. The main gravitational tone of the Hayward black hole, for example, rings 9.5% higher and fades 22.1% more slowly than an Einstein black hole of the same mass, meaning its ringing lasts 28% longer.
This pattern holds for other quantum gravity theories as well. While the hidden center of a black hole remains inaccessible, its ringing provides clues about the hidden structure, offering a way to learn about the nature of quantum gravity.
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