Gary T. Horowitz

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.

A black hole spun up almost to its limit is like an athlete balancing on the edge of a record. The most interesting action isn't inside the hole itself, but in the thinnest film of spacetime at its horizon. It's there that tiny corrections to Einstein's gravity can suddenly swell to gigantic proportions.