A black hole is like a whirlpool in the ocean: anything that falls in disappears forever. But if the whirlpool spins and carries a slight electric charge, and invisible axion particles (dark matter candidates) are buzzing around it, its surface stops being smooth. It becomes covered with ripples so powerful that any boat approaching it would be torn apart before being pulled under.
The authors of the study showed that for almost any values of the axion mass and its interaction with ordinary matter, the event horizon — the boundary beyond which you cannot see — becomes singular. This means the curvature of spacetime there is infinite, and Einstein's familiar equations lose their meaning. Previously, it was thought that this happens only at the center of a hole, but axions bring the catastrophe to the surface if the hole rotates and carries at least a tiny electric charge.
The effect is amplified for nearly extreme black holes — those that spin at the limit of what is possible. Here, even a weak influence of axions generates anomalously large tidal forces. Any object, be it a star or a cloud of gas, would be stretched and squeezed with monstrous force, like a piece of taffy being pulled in opposite directions. This discovery connects two worlds: the quantum physics of particles and the gravity of massive bodies, and offers hope of detecting axions through their destructive effect on matter around black holes.
Tidal forces near a nearly extreme black hole could be so strong that they would tear atoms apart long before the horizon, even if the hole itself is the size of the Solar System.
In Peter Watts's novel Blindsight, the crew encounters unpredictable anomalies near a black hole — axion ripples could explain their nature.