Harvesting Energy from a Black Hole

Our biggest challenge won’t be fusion power

The ergosphere is a bizarre region just outside of the event horizon of a black hole. Specifically, a rotating black hole. It’s the energetic and looming arena before the point of no return. The faster a black hole spins, the larger the volume of its ergosphere. And because we wouldn’t be crossing the famed event horizon, we could someday curiously probe the ergosphere by entering it and coming back out. But it’s a strange and forceful place. No person — or thing — entering this region could be stationary. Instead they’d be dragged along by the powerful rotation of the black hole, a promising form of kinetic energy that we could extract and use to our advantage. The energy wouldn’t be endless, per se, because at some point the black hole would stop spinning and evaporate away. But to us with lifespans of mere decades it would seem like an endless source of power.

The galaxy NGC 1365 has an ambitious supermassive black hole at its center. It spins at 84% the speed of light, twirling and twisting the fabric of spacetime at an incomprehensible rate. As astonishing as this rate of spin might sound, it’s not rare for black holes to spin at near lightspeed. They’re born from cosmic giants — rich, enormous glowing stars that would make our own sun seem quite dainty in comparison. These giant…