If mature black holes had personalities, they would be extremely introverted. They don’t let anything out – not light, not particles, and certainly not music.
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Hawking radiation is a fascinating exception to this rule, but for astrophysical black holes, it is a tiny effect.
But before they settle down, during their brief but wild youth, newly formed black holes ring out a strange, pure music. It would be beautiful to experience, and soon we will be able to do it.
When a new black hole is formed, say by collapse of a star or by fusion of other objects such as neutron stars or smaller black holes, the material that produced it gets swallowed up. Once that material passes beyond the newly formed event horizon, no trace of it remains perceptible.
The baby black hole itself, as a distortion of space-time, quickly settles into a stable shape, sculpted by its own gravity. The same force that makes stars and planets very nearly into round balls – or, if they’re spinning, smooth ellipsoids – works even more powerfully to mould black holes.
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Precisely because they swallow all signs of their origin and squash any outer lumpiness, black holes reach a level of mathematical perfection that is unique among macroscopic objects. Given only a black hole’s mass and angular momentum, the equations of general relativity predict with utter precision the distortion of space-time it embodies.
